Hydrocodone-Chlorpheniramne Er (hydrocodone polistirex/chlorpheniramine polistirex)

Dosage of chlorpheniramine and dexchlorpheniramine should be individualized according to the patient's response and tolerance. Dosage of dexchlorpheniramine maleate is approximately 50% that of chlorpheniramine maleate.

Hydrocodone bitartrate and hydrocodone polistirex are administered orally.

When the extended-release oral suspension containing hydrocodone polistirex and chlorpheniramine polistirex (e.g., Tussionex(R) Pennkinetic(R)) is used, patients and caregivers should be strongly advised to use an accurate, calibrated dosing device to measure doses of the suspension. Use of a household teaspoon as a measuring device could result in overdosage. The extended-release oral suspension should not be diluted with other liquids or mixed with other drugs, since this may alter resin binding, thereby altering the rate of hydrocodone absorption and possibly resulting in toxicity. The extended-release oral suspension should not be given more frequently than every 12 hours; if cough is not controlled, the clinician should be contacted. The extended-release oral suspension should be shaken well before each use.

Chlorpheniramine maleate and dexchlorpheniramine maleate are administered orally.

Concomitant use of opiate agonists and benzodiazepines or other CNS depressants (e.g., anxiolytics, sedatives, hypnotics, tranquilizers, muscle relaxants, general anesthetics, antipsychotics, other opiate agonists, alcohol) may result in profound sedation, respiratory depression, coma, and death. Opiate agonist antitussives should be avoided in patients taking benzodiazepines, other CNS depressants, or alcohol. Concurrent use of anticholinergic agents with hydrocodone may produce paralytic ileus. Concomitant use of opiate agonists with serotonergic drugs can cause serotonin syndrome. (See Drug Interactions in the Opiate Agonists General Statement 28:08.08.)

Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

Opioid Analgesics/Opioid Antagonists

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Naltrexone, nalmefene, and samidorphan are opioid antagonists and thus inhibit the effects of opioid analgesics.(1-3)

CLINICAL EFFECTS: Concurrent administration or the administration of naltrexone within 7-10 days of opioids may induce acute abstinence syndrome or exacerbate a pre-existing subclinical abstinence syndrome.(1,4) Patients taking naltrexone may not experience beneficial effects of opioid-containing medications.(4) Samidorphan can precipitate opioid withdrawal in patients who are dependent on opioids. In patients who use opioids, delay initiation of samidorphan for a minimum of 7 days after last use of short-acting opioids and 14 days after last use of long-acting opioids.(3) Concurrent use of nalmefene tablets with opioid agonists may prevent the beneficial effects of the opioid.(2)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of naltrexone states that the administration of naltrexone concurrently with opioids or to patients dependent on opioids is contraindicated.(1,4) Patients previously dependent on short-acting opioids should be opioid-free for a minimum of seven to ten days before beginning naltrexone therapy. Patients previously on buprenorphine or methadone may be vulnerable to withdrawal symptoms for as long as 2 weeks.(1,4) The manufacturer of naltrexone states that the naloxone challenge test, described in the naltrexone prescribing information, can be administered to determine if patients are opioid free.(1) The manufacturer of samidorphan states the concurrent use of samidorphan in patients using opioids or undergoing acute opioid withdrawal is contraindicated. Prior to initiating samidorphan, there should be at least a 7-day opioid free interval from the last use of short-acting opioids, and at least a 14-day opioid free interval from the last use of long-acting opioids.(3) The UK manufacturer of nalmefene tablets (for reduction of alcohol consumption) states the concurrent use of opioid analgesics is contraindicated.(2) Suspend the use of nalmefene tablets for 7 days prior to the anticipated use of opioids (e.g., elective surgery).(2)

DISCUSSION: A double-blind, randomized, placebo-control study evaluated pain relief and side effects of 35 opioid-naive patients undergoing cesarean section. All patients received spinal anesthesia (bupivacaine and morphine) and were randomized to also receive placebo, naltrexone 3 mg, or naltrexone 6 mg. Patients treated with naltrexone experienced shorter duration of pain relief (not statistically significant), however incidence of opioid-induced side effects was reduced. Patients in the naltrexone 6 mg group had lower rates of pruritus, vomiting, and somnolence (all statistically significant) compared to the placebo group.(5) In a double-blind, randomized, placebo-control trial ten recreational opioid users were studied to determine the effects of hydromorphone (4 mg and 16 mg), tramadol (87.5 mg, 175 mg, and 350 mg), and placebo after pretreatment with naltrexone (50 mg) or placebo. Results show that lower doses of hydromorphone and tramadol acted similar to placebo. Hydromorphone 16 mg alone caused euphoria and miosis which were blocked by naltrexone. Tramadol 350 mg produced a lower magnitude of euphoria and miosis compared to hydromorphone. Naltrexone partially diminished the euphoria caused by tramadol, while it enhanced some of the unpleasant monoaminergic effects (flushing, malaise, vomiting).(6) A case report describes a 28 year-old ex-heroin addict who was stable on methadone 100 mg daily and simultaneously stopped using heroin and began drinking alcohol. He was admitted to the hospital for alcohol detoxification and, by mistake, was given naltrexone 100 mg instead of methadone 100 mg. The patient experienced withdrawal symptoms including chills, agitation, muscle and abdominal pain, generalized piloerection, and dilated pupils. Treatment of withdrawal was titrated to treat symptoms and required administration 78 mg of parenteral hydromorphone, after which the patient experienced relief for the following six hours.(8) Intentional administration of an opioid antagonist, naloxone, with opioid analgesics has been performed with close monitoring to lower required opioid dose by inducing withdrawal. Three case reports describe patients who had improved pain relief on significantly reduced doses of opioid analgesics.(8) In a double-blind controlled trial, 267 trauma patients were randomized to receive 0.05 mg/kg intravenous morphine either alone or in combination with 5 mg naltrexone oral suspension. Evaluated endpoints include reduction of pain and incidence of side effects. Results indicate that ultra-low dose naltrexone does not alter opioid requirements for pain control, but does lower incidence of nausea [2 (1.16%) vs 16 (11.6%), p<0.001].(9)

Selected Antihistamines/Selected Maois

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: MAOIs prolong and intensify the effects of antihistamines.(1-6)

CLINICAL EFFECTS: Concurrent use of antihistamines and a MAOI may result in severe hypotension.(1-6)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Concurrent use of antihistamines and a MAOI is contraindicated.(1-6)

DISCUSSION: MAOIs may prolong and intensify the effects of antihistamines, resulting in severe hypotension.(1-6) A case report describes a patient having cyproheptadine added to their phenelzine therapy in an attempt to relieve the patients anorgasmia. The patient began to suddenly experience visual hallucination after taking the cyproheptadine for two months. Once the medication was terminated, the hallucinations stopped occurring within 48 hours.(7) Methylene blue, when administered intravenously, has been shown to reach sufficient concentrations to be a potent inhibitor of MAO-A.(8,9)

Selected Opioids/Mifepristone

SEVERITY LEVEL: 1-Contraindicated Drug Combination: This drug combination is contraindicated and generally should not be dispensed or administered to the same patient.

MECHANISM OF ACTION: Mifepristone is an inhibitor of CYP3A4 and may increase levels and effects of drugs metabolized by this enzyme, including alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil.(1)

CLINICAL EFFECTS: Alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil are particularly susceptible to significant toxicity, including profound sedation, respiratory depression, coma, and/or death.(1,2)

PREDISPOSING FACTORS: Due to the need for continuous therapy and mifepristone's long half-life of 85 hours(1) which leads to accumulation, patients with endogenous Cushing's syndrome may be at an increased risk for toxicity.

PATIENT MANAGEMENT: The US manufacturer of mifepristone for hypercortisolism due to endogenous Cushing's syndrome states use with CYP3A4 substrates with a narrow therapeutic range, including alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil, is contraindicated.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(3) If concomitant use is unavoidable, monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(4)

DISCUSSION: Administration of mifepristone 1200 mg daily for 10 days followed by a single dose of simvastatin 80 mg led to an increase of simvastatin and simvastatin acid (active metabolite) area-under-curve (AUC) of 10.4-fold and 15.7-fold, respectively.(1) Mifepristone is a time- and concentration-dependent CYP3A4 inhibitor. Single dose mifepristone 200 mg may have a lower risk of inhibiting the metabolism of CYP3A4 substrates, including selected opioids.

Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

Agents That Affect Iodide/Radioactive Iodide

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Many compounds can affect iodide protein binding and alter iodide pharmacokinetics and pharmacodynamics.(1)

CLINICAL EFFECTS: Compounds that affect iodide pharmacokinetics and pharmacodynamics may impact the effectiveness of radioactive iodide.(1)

PREDISPOSING FACTORS: Compounds that affect iodide pharmacokinetics and pharmacodynamics are expected to have the most impact during therapy using radioactive iodide. Diagnostic procedures would be expected to be impacted less.

PATIENT MANAGEMENT: Discuss the use of agents that affect iodide pharmacokinetics and pharmacodynamics with the patient's oncologist.(1) Because indocyanine green contains sodium iodide, the iodine-binding capacity of thyroid tissue may be reduced for at least one week following administration. Do not perform radioactive iodine uptake studies for at least one week following administration of indocyanine green.(2) The manufacturer of iopamidol states administration may interfere with thyroid uptake of radioactive iodine and decrease therapeutic and diagnostic efficacy. Avoid thyroid therapy or testing for up to 6 weeks post administration of iopamidol.(3)

DISCUSSION: Many agents interact with radioactive iodine. The average duration of effect is: anticoagulants - 1 week antihistamines - 1 week anti-thyroid drugs, e.g: carbimazole, methimazole, propylthiouracil - 3-5 days corticosteroids - 1 week iodide-containing medications, e.g: amiodarone - 1-6 months expectorants - 2 weeks Lugol solution - 3 weeks saturated solution of potassium iodine - 3 weeks vitamins - 10-14 days iodide-containing X-ray contrast agents - up to 1 year lithium - 4 weeks phenylbutazone - 1-2 weeks sulfonamides - 1 week thyroid hormones (natural or synthetic), e.g.: thyroxine - 4 weeks tri-iodothyronine - 2 weeks tolbutamide - 1 week topical iodide - 1-9 months (1)

Agents That Affect Iodide/Sodium Iodide I 131

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Many compounds can affect iodide protein binding and alter iodide pharmacokinetics and pharmacodynamics.(1,2)

CLINICAL EFFECTS: Compounds that affect iodide pharmacokinetics and pharmacodynamics may impact the effectiveness of radioactive iodide.(1,2)

PREDISPOSING FACTORS: Compounds that affect iodide pharmacokinetics and pharmacodynamics are expected to have the most impact during therapy using radioactive iodide. Diagnostic procedures would be expected to be impacted less.

PATIENT MANAGEMENT: Discuss the use of agents that affect iodide pharmacokinetics and pharmacodynamics with the patient's oncologist.(1,2) Because indocyanine green contains sodium iodide, the iodine-binding capacity of thyroid tissue may be reduced for at least one week following administration. Do not perform radioactive iodine uptake studies for at least one week following administration of indocyanine green.(3) The manufacturer of iopamidol states administration may interfere with thyroid uptake of radioactive iodine and decrease therapeutic and diagnostic efficacy. Avoid thyroid therapy or testing for up to 6 weeks post administration of iopamidol.(4)

DISCUSSION: Many agents interact with radioactive iodine. The average duration of effect is: anticoagulants - 1 week antihistamines - 1 week anti-thyroid drugs, e.g: carbimazole, methimazole, propylthiouracil - 3-5 days corticosteroids - 1 week iodide-containing medications, e.g: amiodarone - 1-6 months expectorants - 2 weeks Lugol solution - 3 weeks saturated solution of potassium iodine - 3 weeks vitamins - 10-14 days iodide-containing X-ray contrast agents - up to 1 year lithium - 4 weeks phenylbutazone - 1-2 weeks sulfonamides - 1 week thyroid hormones (natural or synthetic), e.g.: thyroxine - 4 weeks tri-iodothyronine - 2 weeks tolbutamide - 1 week topical iodide - 1-9 months (1,2)

Agents That May Cause Respiratory Depression/Sodium Oxybate

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Oxybate by itself may be associated with severe somnolence or respiratory depression. Concurrent use with other CNS depressants may further increase the risk for respiratory depression or loss of consciousness.(1-3)

CLINICAL EFFECTS: Concurrent use of sodium oxybate and sedative hypnotics or alcohol may further increase the risk for profound sedation, respiratory depression, coma, and/or death.(1,2) Fatalities have been reported.(3)

PREDISPOSING FACTORS: Based upon FDA evaluation of deaths in patients taking sodium oxybate, risk factors may include: use of multiple drugs which depress the CNS, more rapid than recommended oxybate dose titration, exceeding the maximum recommended oxybate dose, and prescribing for unapproved uses such as fibromyalgia, insomnia or migraine. Note that in oxybate clinical trials for narcolepsy 78% - 85% of patients were also receiving concomitant CNS stimulants.(1-3)

PATIENT MANAGEMENT: Avoid use of concomitant opioids, benzodiazepines, sedating antidepressants, sedating antipsychotics, general anesthetics, or muscle relaxants, particularly when predisposing risk factors are present. If combination use is required, dose reduction or discontinuation of one or more CNS depressants should be considered. If short term use of an opioid or general anesthetic is required, consider interruption of sodium oxybate treatment.(1,2) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(4) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(5)

DISCUSSION: The FDA evaluated sodium oxybate postmarket fatal adverse event reports from the FDA Adverse Event Reporting System(AERS)and from the manufacturer. Although report documentation was not always optimal or complete, useful information was obtained. Factors which may have contributed to fatal outcome: concomitant use of one or more drugs which depress the CNS, more rapid than recommended oxybate dose titration, exceeding the maximum recommended oxybate dose, and prescribing for unapproved uses such as fibromyalgia, insomnia or migraine. Many deaths occurred in patients with serious psychiatric disorders such as depression and substance abuse. Other concomitant diseases may have also contributed to respiratory and CNS depressant effects of oxybate.(3)

Anticholinergics/Clozapine

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Clozapine has potent anticholinergic properties and inhibits serotonin receptors, including 5-HT3.(1-4) Both of these properties may cause inhibition of gastrointestinal (GI) smooth muscle contraction, resulting in decreased peristalsis.(3,4) These effects may be compounded by concurrent use of anticholinergic agents.(1-6)

CLINICAL EFFECTS: Concurrent use of clozapine with other anticholinergic agents may increase the risk of constipation (common) and serious bowel complications (uncommon), including complete bowel obstruction, fecal impaction, paralytic ileus and intestinal ischemia or infarction.(1-6)

PREDISPOSING FACTORS: The risk for serious bowel complications is higher with increasing age, higher frequency of constipation, and in patients on higher doses of clozapine or multiple anticholinergic agents.(1,5)

PATIENT MANAGEMENT: Avoid the use of other anticholinergic agents with clozapine.(1-6) If concurrent use is necessary, evaluate the patient's bowel function regularly. Monitor for symptoms of constipation and GI hypomotility, including having bowel movements less than three times weekly or less than usual, difficulty having a bowel movement or passing gas, nausea, vomiting, and abdominal pain or distention.(2) Consider a prophylactic laxative in those with a history of constipation or bowel obstruction.(2) Review patient medication list for other anticholinergic agents. When possible, decrease the dosage or number of prescribed anticholinergic agents, particularly in the elderly. Counsel the patient about the importance of maintaining adequate hydration. Encourage regular exercise and eating a high-fiber diet.(2)

DISCUSSION: In a prospective cohort study of 26,720 schizophrenic patients in the Danish Central Psychiatric Research Registry, the odds ratio (OR) for ileus was 1.99 with clozapine and 1.48 with anticholinergics. The OR for fatal ileus was 6.73 with clozapine and 5.88 with anticholinergics. Use of anticholinergics with 1st generation antipsychotics (FGA) increased the risk of ileus compare to FGA alone, but this analysis was not done with clozapine.(5) A retrospective cohort study of 24,970 schizophrenic patients from the Taiwanese National Health Insurance Research Database found that the hazard ratio (HR) for clozapine-induced constipation increased from 1.64 when clozapine is used alone, to 2.15 when used concomitantly with anticholinergics. However, there was no significant difference in the HR for ileus when clozapine is used with and without anticholinergics (1.95 and 2.02, respectively).(6) In the French Pharmacovigilance Database, 7 of 38 cases of antipsychotic-associated ischemic colitis or intestinal necrosis involved clozapine, and 5 of these cases involved use of concomitant anticholinergic agents. Three patients died, one of whom was on concomitant anticholinergics.(3) In a case series, 4 of 9 cases of fatal clozapine-associated GI dysfunction involved concurrent anticholinergic agents.(4)

Anticholinergics/Glucagon (DIAGNOSTIC)

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Glucagon and anticholinergic agents may have additive effects on inhibition of gastrointestinal motility.(1)

CLINICAL EFFECTS: Concurrent use of glucagon with anticholinergic agents may increase the risk of gastrointestinal hypomotility, including constipation and bowel complications.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Concurrent use of glucagon as a diagnotic aid is not recommended with the use of anticholinergic agents.(1) If concurrent use is necessary, evaluate the patient's bowel function. Monitor for symptoms of constipation and gastrointestinal hypomotility.

DISCUSSION: Both glucagon and anticholinergic agents may have additive effects on inhibition of gastrointestinal motility and increase the risk of gastrointestinal adverse effects.(1)

Anticholinergics/Solid Oral Potassium Capsules

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Concentrated potassium may damage the lining of the GI tract. Anticholinergics delay gastric emptying, resulting in the potassium product remaining in the gastrointestinal tract for a longer period of time.(1-16))

CLINICAL EFFECTS: Use of solid oral dosage forms of potassium in patients treated with anticholinergics may result in gastrointestinal erosions, ulcers, stenosis and bleeding.(1-16)

PREDISPOSING FACTORS: Diseases or conditions which may increase risk for GI damage include: preexisting dysphagia, strictures, cardiomegaly, diabetic gastroparesis, elderly status, or insufficient oral intake to allow dilution of potassium.(1-10,21) Other drugs which may add to risk for GI damage include: nonsteroidal anti-inflammatory drugs (NSAIDs), bisphosphonates, or tetracyclines.(21)

PATIENT MANAGEMENT: Regulatory agency and manufacturer recommendations regarding this interaction: - In the US, all solid oral dosage forms (including tablets and extended release capsules) of potassium are contraindicated in patients receiving anticholinergics at sufficient dosages to result in systemic effects.(2-8) Patients receiving such anticholinergic therapy should use a liquid form of potassium chloride.(2) - In Canada, solid oral potassium is contraindicated in any patient with a cause for arrest or delay in tablet/capsule passage through the gastrointestinal tract and the manufacturers recommend caution with concurrent anticholinergic medications.(1,9-10) Evaluate each patient for predisposing factors which may increase risk for GI damage. In patients with multiple risk factors for harm, consider use of liquid potassium supplements, if tolerated. For patients receiving concomitant therapy, assure any potassium dose form is taken after meals with a large glass of water or other fluid. To decrease potassium concentration in the GI tract, limit each dose to 20 meq; if more than 20 meq daily is required, give in divided doses.(2) If concurrent therapy is warranted, monitor patients receiving concurrent therapy for signs of blood loss, including decreased hemoglobin, hematocrit, fecal occult blood, and/or decreased blood pressure and promptly evaluate patients with any symptoms. Patients should be instructed to immediately report any difficulty swallowing, abdominal pain, distention, severe vomiting, or gastrointestinal bleeding. Instruct patients to report any signs and symptoms of bleeding, such as unusual bleeding from the gums or nose; unusual bruising; red or black, tarry stools; red, pink or dark brown urine; acute abdominal or joint pain and/or swelling.

DISCUSSION: In clinical trials, there was a higher incidence of gastric and duodenal lesions in patients receiving a high dose of a wax-matrix controlled-release formulation with a concurrent anticholinergic agent. The lesions were asymptomatic and not accompanied by bleeding, as shown by a lack of positive Hemoccult tests.(1-17) Several studies suggest that the incidence of gastric and duodenal lesions may be less with the microencapsulated formulation of potassium chloride.(14-17)

Anticholinergics/Solid Oral Potassium Tablets

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Concentrated potassium may damage the lining of the GI tract. Anticholinergics delay gastric emptying, resulting in the potassium product remaining in the gastrointestinal tract for a longer period of time.(1-16)

CLINICAL EFFECTS: Use of solid oral dosage forms of potassium in patients treated with anticholinergics may result in gastrointestinal erosions, ulcers, stenosis and bleeding.(1-16)

PREDISPOSING FACTORS: Diseases or conditions which may increase risk for GI damage include: preexisting dysphagia, strictures, cardiomegaly, diabetic gastroparesis, elderly status, or insufficient oral intake to allow dilution of potassium.(1-10,21) Other drugs which may add to risk for GI damage include: nonsteroidal anti-inflammatory drugs (NSAIDs), bisphosphonates, or tetracyclines.(21)

PATIENT MANAGEMENT: Regulatory agency and manufacturer recommendations regarding this interaction: - In the US, all solid oral dosage forms (including tablets and extended release capsules) of potassium are contraindicated in patients receiving anticholinergics at sufficient dosages to result in systemic effects.(2-8) Patients receiving such anticholinergic therapy should use a liquid form of potassium chloride.(2) - In Canada, solid oral potassium is contraindicated in any patient with a cause for arrest or delay in tablet/capsule passage through the gastrointestinal tract and the manufacturers recommend caution with concurrent anticholinergic medications.(1,9-10) Evaluate each patient for predisposing factors which may increase risk for GI damage. In patients with multiple risk factors for harm, consider use of liquid potassium supplements, if tolerated. For patients receiving concomitant therapy, assure any potassium dose form is taken after meals with a large glass of water or other fluid. To decrease potassium concentration in the GI tract, limit each dose to 20 meq; if more than 20 meq daily is required, give in divided doses.(2) If concurrent therapy is warranted, monitor patients receiving concurrent therapy for signs of blood loss, including decreased hemoglobin, hematocrit, fecal occult blood, and/or decreased blood pressure and promptly evaluate patients with any symptoms. Patients should be instructed to immediately report any difficulty swallowing, abdominal pain, distention, severe vomiting, or gastrointestinal bleeding. Instruct patients to report any signs and symptoms of bleeding, such as unusual bleeding from the gums or nose; unusual bruising; red or black, tarry stools; red, pink or dark brown urine; acute abdominal or joint pain and/or swelling.

DISCUSSION: In clinical trials, there was a higher incidence of gastric and duodenal lesions in patients receiving a high dose of a wax-matrix controlled-release formulation with a concurrent anticholinergic agent. Some lesions were asymptomatic and not accompanied by bleeding, as shown by a lack of positive Hemoccult tests.(1-17) Several studies suggest that the incidence of gastric and duodenal lesions may be less with the microencapsulated formulation of potassium chloride.(14-17)

Anticholinergics; Opioids/Eluxadoline

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Eluxadoline is a mixed mu-opioid and kappa-opioid agonist and delta-opioid antagonist and may alter or slow down gastrointestinal transit.(1)

CLINICAL EFFECTS: Constipation related adverse events that sometimes required hospitalization have been reported, including the development of intestinal obstruction, intestinal perforation, and fecal impaction.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid use with other drugs that may cause constipation. If concurrent use is necessary, evaluate the patient's bowel function regularly. Monitor for symptoms of constipation and GI hypomotility, including having bowel movements less than three times weekly or less than usual, difficulty having a bowel movement or passing gas, nausea, vomiting, and abdominal pain or distention.(1) Instruct patients to stop eluxadoline and immediately contact their healthcare provider if they experience severe constipation. Loperamide may be used occasionally for acute management of severe diarrhea, but must be discontinued if constipation develops.(1)

DISCUSSION: In phase 3 clinical trials, constipation was the most commonly reported adverse reaction (8%). Approximately 50% of constipation events occurred within the first 2 weeks of treatment while the majority occurred within the first 3 months of therapy. Rates of severe constipation were less than 1% in patients receiving eluxadoline doses of 75 mg and 100 mg.(1)

Opioids (COUGH & COLD)/Gabapentinoids

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Opioid-induced reduction in GI motility may increase the absorption of gabapentin and pregabalin.(1) Gabapentin and pregabalin may reverse opioid-induced tolerance of respiratory depression.(2) Concurrent use may result in profound sedation, respiratory depression, coma, and/or death.(3)

CLINICAL EFFECTS: Concurrent use of opioids may result in elevated levels of and toxicity from gabapentin and pregabalin, including profound sedation, respiratory depression, coma, and/or death.(1-7)

PREDISPOSING FACTORS: Patients who are elderly, are taking other CNS depressants, have decreased renal function, and/or have conditions that reduce lung function (e.g. Chronic Obstructive Pulmonary Disease [COPD]) may be at a higher risk of this interaction.

PATIENT MANAGEMENT: Avoid prescribing opioid-including cough medications for patients taking CNS depressants.(8) If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. If starting a gabapentinoid with an opioid analgesic, prescribe a lower initial dose of the gabapentinoid than indicated in the absence of an opioid and titrate based upon clinical response. If an opioid analgesic is indicated in a patient already taking a gabapentinoid, prescribe a lower dose of the opioid and titrate based upon clinical response.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(9) Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(9)

DISCUSSION: In a study in 12 healthy males, administration of a single dose of morphine (60 mg sustained release) increased the area-under-curve (AUC) of a single dose of gabapentin (600 mg) by 44%.(1,3,4) There were no affects on the pharmacokinetics of morphine.(1,3,4) The combination of gabapentin plus morphine increased pain tolerance over the combination of morphine plus placebo. Side effects were not significantly different between morphine plus placebo and morphine plus gabapentin.(1) A retrospective, case-control study of opioid users in Ontario, Canada between August 1, 1997 and December 31, 2013 who died of an opioid-related cause matched cases to up to 4 controls who also used opioids. Use of gabapentin in the 120 days prior to death resulted in a significant increase in odds of opioid-related death (OR 1.99, CI=1.61-2.47, p<0.001), compared to opioid use alone. Use of moderate dose (900 mg to 1,799 mg daily) or high dose (>= 1,800 mg daily) gabapentin increased the odds of opioid-related death 60% compared to opioid use without gabapentin. Review of gabapentin prescriptions from calendar year 2013 found that 46% of gabapentin users received at least 1 opioid prescription.(3) Among 49 case reports submitted to FDA over a 5 year period (2012-2017), 12 people died from respiratory depression with gabapentinoids. Two randomized, double-blind, placebo-controlled clinical trials in healthy people, three observational studies, and several studies in animals were reviewed. A trial showed that using pregabalin alone and using it with an opioid pain reliever can depress breathing function. Three observational studies showed a relationship between gabapentinoids given before surgery and respiratory depression occurring after surgery. Several animal studies also showed that pregabalin plus opioids can depress respiratory function.(7) A retrospective cohort study evaluated the risk of mortality among Medicare beneficiaries aged 65 and older who were taking gabapentin with or without concurrent use of opioids. All-cause mortality in gabapentin users compared to duloxetine users was 12.16 per 1,000 person years vs. 9.94 per 1,000 person years, respectively. Adjusted for covariates, the risk of all-cause mortality among gabapentin users on high-dose opioids was more than double the control group (hazard ratio (HR) 2.03, CI=1.19-3.46).(10)

Opioids (COUGH AND COLD)/Antipsychotics; Phenothiazines

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Concurrent use of opioids and antipsychotics, including phenothiazine derivatives, may result in additive CNS depression.(1)

CLINICAL EFFECTS: Concurrent use of opioids and other CNS depressants, such as antipsychotics, including phenothiazine derivatives, may result in profound sedation, respiratory depression, coma, and/or death.(1)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Avoid prescribing opioid-including cough medications for patients taking CNS depressants such as antipsychotics, including phenothiazine derivatives.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(2) If concurrent use is necessary, monitor patients for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(3)

DISCUSSION: A nested case-control study looked at the relationship between antipsychotic use and risk of acute respiratory failure. Current use of antipsychotics was associated with a 2.33-fold increase in risk of respiratory failure compared to no use of antipsychotics. The risk was also significantly increased in patients with recent use of antipsychotics (within the past 15-30 days, OR = 1.79) and recent past use (within 31-90 days OR = 1.41). The risk increased with higher doses and longer duration of use.(4) Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(5) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(6) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(7) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(8) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(9) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(10)

Opioids (COUGH AND COLD)/Benzodiazepines

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Concurrent use of opioids and benzodiazepines may result in additive CNS depression.(1)

CLINICAL EFFECTS: Concurrent use of opioids and other CNS depressants, such as benzodiazepines, may result in profound sedation, respiratory depression, coma, and/or death.(1)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Avoid prescribing opioid-including cough medications for patients taking CNS depressants such as benzodiazepines.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(2) If concurrent use is necessary, monitor patients for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(3)

DISCUSSION: Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(4) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(5) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(6) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(7) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(8) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(9) A study of 315,428 privately insured patients who filled at least one prescription for an opioid from 2001 to 2013 were enrolled in a retrospective study. Concurrent use of a benzodiazepine was recorded as having at least one day of overlap in a given calendar year. Baseline characteristics among opioid users with concurrent use of a benzodiazepine were older (44.5 v. 42.4, p<0.001), less likely to be men (35% v. 43%, p<0.001), and had a higher prevalence rate of every comorbidity examined (p<0.001). The proportion of opioid users with concurrent benzodiazepine use nearly doubled from 9% in 2001 to 17% in 2013. The primary outcome was an emergency room visit or inpatient admission for opioid overdose within a calendar year. Among all opioid users, the annual adjusted incidence for the primary outcome was 1.16% without concurrent benzodiazepine use compared to 2.42% with concurrent benzodiazepine use (OR 2.14; 95% CI 2.05-2.24; p<0.001). Intermittent opioid users (1.45% v. 1.02%; OR 1.42; 95% CI 1.33-1.51; p<0.001) and chronic opioid users (5.36% v. 3.13%; OR 1.81; 95% CI 1.67-1.96; p<0.001) also experienced a higher adjusted incidence of the primary outcome with concurrent benzodiazepine use compared to without concurrent benzodiazepine use, respectively.(10) In a nested case-control study of adults with a new opioid dispensing between 2010-2018, patients with concurrent use of an opioid with a benzodiazepine were significantly more likely to have opioid-related overdose compared to patients receiving opioids, benzodiazepines, or neither (OR 9.28; 95% CI 7.87, 10.93). Longer concurrent use of 1-7, 8-30, and 31-90 days was associated with 4.6, 12.1, and 26.7-fold higher likelihood of opioid-related overdose (p<0.01). Patients with overlapping prescriptions during previous 0-30, 31-60, and 61-90 days were 13.2, 6.0, and 3.2-times more likely to experience an overdose (p<0.01).(11)

Opioids (COUGH AND COLD)/Muscle Relaxants

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Concurrent use of opioids and muscle relaxants may result in additive CNS depression.(1)

CLINICAL EFFECTS: Concurrent use of opioids and other CNS depressants, such as muscle relaxants, may result in profound sedation, respiratory depression, coma, and/or death.(1)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Avoid prescribing opioid-including cough medications for patients taking CNS depressants such as muscle relaxants.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(2) If concurrent use is necessary, monitor patients for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(3)

DISCUSSION: Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(4) A retrospective cohort study compared the risk of opioid overdose associated with concomitant use of opioids and skeletal muscle relaxants versus opioid use alone. The study examined two types of opioid users (naive opioid use and prevalent opioid use) with and without exposure to skeletal muscle relaxants. The adjusted hazard ratios (HR) were 1.09 and 1.26 in the naive and prevalent opioid user cohorts, respectively, generating a combined estimate of 1.21. The risk increased with treatment duration (less than or equal to 14 days: 0.91; 15-60 days: 1.37; and greater than 60 days: 1.80) and for the use of baclofen and carisoprodol (HR 1.83 and 1.84, respectively). Elevated risk was associated with concomitant users with daily opioid dose greater than 50 mg and benzodiazepine use (HR 1.50 and 1.39, respectively).(5) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(6) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(7) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(8) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(9) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(10)

Opioids (COUGH AND COLD)/Sleep Drugs

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Concurrent use of opioids and sleep drugs or tranquilizers may result in additive CNS depression and sleep-related disorders.(1)

CLINICAL EFFECTS: Concurrent use of opioids and other CNS depressants, such as sleep drugs or tranquilizers, may result in profound sedation, respiratory depression, coma, and/or death.(1) Concurrent use of opioids with eszopiclone, zaleplon, or zolpidem may increase the risk of sleep-related disorders including central sleep apnea and sleep-related hypoxemia, and complex sleep behaviors like sleepwalking, sleep driving, and other activities while not fully awake. Rarely, serious injuries or death have resulted from complex sleep behaviors.(2)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Avoid prescribing opioid-including cough medications for patients taking CNS depressants such as sleep drugs or tranquilizers.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(3) If concurrent use is necessary, monitor patients for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Eszopiclone, zaleplon, and zolpidem are contraindicated in patients who have had a previous episode of complex sleep behavior.(2) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(4)

DISCUSSION: Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(5) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(6) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(7) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(8) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(9) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(10) As of April 2019, the FDA had identified 66 cases of complex sleep behaviors with eszopiclone, zaleplon, or zolpidem, of which 20 cases resulted in death and the remainder resulted in serious injuries. It was not reported how many of the cases involved concomitant use of other CNS depressants.(2)

Selected Opioids (COUGH AND COLD)/Metaxalone

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Concurrent use of opioids and muscle relaxants may result in additive CNS depression.(1)

CLINICAL EFFECTS: Concurrent use of opioids and other CNS depressants, such as muscle relaxants, may result in profound sedation, respiratory depression, coma, and/or death.(1)

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Avoid prescribing opioid-including cough medications for patients taking CNS depressants such as muscle relaxants.(1) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(2) If concurrent use is necessary, monitor patients for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness.(1) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(3)

DISCUSSION: Between 2002 and 2014, the number of patients receiving an opioid analgesic increased 8%, from 75 million to 81 million patients, and the number of patients receiving a benzodiazepine increased 31%, from 23 million to 30 million patients. During this time, the proportion of patients receiving concurrent therapy increased 31%, from 23 million to 30 million patients.(4) A retrospective cohort study compared the risk of opioid overdose associated with concomitant use of opioids and skeletal muscle relaxants versus opioid use alone. The study examined two types of opioid users (naive opioid use and prevalent opioid use) with and without exposure to skeletal muscle relaxants. The adjusted hazard ratios (HR) were 1.09 and 1.26 in the naive and prevalent opioid user cohorts, respectively, generating a combined estimate of 1.21. The risk increased with treatment duration (less than or equal to 14 days: 0.91; 15-60 days: 1.37; and greater than 60 days: 1.80) and for the use of baclofen and carisoprodol (HR 1.83 and 1.84, respectively). Elevated risk was associated with concomitant users with daily opioid dose greater than 50 mg and benzodiazepine use (HR 1.50 and 1.39, respectively).(5) From 2004 to 2011, the rate of nonmedical use-related emergency room visits involving both opioids and benzodiazepines increased from 11 to 34.2 per 100,000 and drug overdose deaths involving both opioids and benzodiazepines increased from 0.6 to 1.7 per 100,000. The proportion of prescription opioid analgesic deaths which also involved benzodiazepines increased from 18% to 31% during this time.(6) A prospective observational cohort study in North Carolina found that the rates of overdose death among patients co-dispensed opioid analgesics and benzodiazepines were 10 times higher than patients receiving opioid analgesics alone.(7) A case-cohort study of VA data from 2004-2009 found that the risk of death from overdose increased with concomitant opioid analgesics and benzodiazepines. Compared to patients with no history of benzodiazepines, patients with a history of benzodiazepine use (hazard ratio [HR] = 2.33) and patients with a current benzodiazepine prescription (HR=3.86) had an increased risk of fatal overdose.(8) A study found that opioid analgesics contributed to 77% of deaths in which benzodiazepines were determined to be a cause of death and that benzodiazepines contributed to 30% of deaths in which opioid analgesics were determined to be a cause of death. This study also found that other CNS depressants (including barbiturates, antipsychotic and neuroleptic drugs, antiepileptic and antiparkinsonian drugs, anesthetics, autonomic nervous system drugs, and muscle relaxants) were contributory to death in many cases where opioid analgesics were also implicated.(9) A study found that alcohol was involved in 18.5% of opioid analgesic abuse-related ED visits and 22.1 percent of opioid analgesic-related deaths.(10)

Selected Opioids/Ceritinib; Crizotinib

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: Ceritinib(1) and crizotinib(2) inhibit CYP3A4, and thus may inhibit the metabolism of agents processed by this isoenzyme, including alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil.

CLINICAL EFFECTS: Concurrent use of ceritinib(1) or crizotinib(2) with alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, or sufentanil may lead to elevated drug levels and increased side effects of the opioid, including profound sedation, respiratory depression, coma, and/or death.(1-3)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid coadministration of sensitive or narrow therapeutic window CYP3A4 substrates such as alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, or sufentanil with ceritinib and crizotinib. If concomitant use is unavoidable, dosage adjustments of the opioid should be considered when initiating or discontinuing ceritinib(1) or crizotinib.(2) Patients maintained on ceritinib or crizotinib may need lower initial doses of opioid medications. Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(5) Monitor patients receiving concurrent therapy for adverse affects, including unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(6)

DISCUSSION: In a study, ceritinib (750 mg daily for 3 weeks) increased the area-under-curve (AUC) and maximum concentration (Cmax) of midazolam (a CYP3A4 substrate) by 5.4-fold and 1.8-fold, respectively, compared to midazolam alone.(1) Crizotinib (250 mg twice daily for 28 days) increased the AUC of oral midazolam by 3.7-fold.(2) Thus, ceritinib(1) and crizotinib(2) are expected to increase levels of opioids metabolized by CYP3A4.

Selected Opioids/Selected Cyp3a4 Inhibitors

SEVERITY LEVEL: 2-Severe Interaction: Action is required to reduce the risk of severe adverse interaction.

MECHANISM OF ACTION: CYP3A4 inhibitors may inhibit the metabolism of alfentanil,(1,2) benzhydrocodone,(3) fentanyl,(1,2) hydrocodone,(4) oxycodone,(5) and sufentanil.(6) Benzhydrocodone is a prodrug of hydrocodone.(3)

CLINICAL EFFECTS: The concurrent administration of a CYP3A4 inhibitor may result in elevated levels of and toxicity from alfentanil,(1,2) benzhydrocodone,(3) fentanyl,(1,2) hydrocodone,(4) oxycodone,(5) and sufentanil,(6) including profound sedation, respiratory depression, coma, and/or death.

PREDISPOSING FACTORS: Heat.

PATIENT MANAGEMENT: Monitor patients receiving potent or moderate CYP3A4 inhibitors for an extended period of time. Dosage adjustments should be made if warranted. The manufacturer of itraconazole states that concomitant administration of fentanyl is not recommended during and 2 weeks after itraconazole treatment.(7) Avoid exposing the fentanyl patch application site and surrounding area to direct external heat sources as there have been reports of overdose and death as a result of exposure to heat. The manufacturer of sufentanil sublingual tablets states that if concomitant use with CYP3A4 inhibitors is necessary, consider use of an alternate agent that allows dose adjustment.(6) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(8) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(9)

DISCUSSION: A nested-case control study of patients who were prescribed fentanyl patches, hydromorphone, or oxycodone and were hospitalized for opioid toxicity found that, among 70 cases and 120 control patients, CYP3A4-inhibiting macrolides (erythromycin and clarithromycin) were associated with a higher risk of opioid toxicity (aOR 3.80, 95% CI: 1.36-11.56 with fentanyl; aOR 3.38, 95% CI: 1.28-8.97 with hydromorphone; aOR 3.11, 95% CI: 1.05-9.51 with oxycodone).(10) In a randomized, placebo-controlled trial in 20 healthy subjects, clarithromycin (500 mg twice daily) increased the area-under-curve (AUC) of a single oral dose of oxycodone (10 mg) by 2-fold and 2.3-fold in young and elderly subjects, respectively.(11) In a controlled cross-over study in 6 subjects, 7 days of pretreatment with erythromycin decreased the clearance of alfentanil by 25%. Alfentanil half-life increased by 56%.(12) Erythromycin has been shown to inhibit fentanyl metabolism in vitro.(13) In a randomized, double-blind, placebo-controlled crossover study in 9 subjects, single doses of intravenous fluconazole (400 mg) and oral fluconazole (400 mg) decreased the clearance of a single dose of alfentanil (20 mcg/kg) by 58% and 55%, respectively. Alfentanil half-life almost doubled after both intravenous and oral fluconazole. Both intravenous and oral fluconazole increased subjective effects of alfentanil and increased alfentanil-induced respiratory depression.(14) In a cross-over study, pretreatment with itraconazole (200 mg daily for 4 days) had no effect on a single dose of intravenous fentanyl (3 mcg/kg).(15) In a cross-over study in 12 healthy subjects, itraconazole (200 mg daily for 5 days) increased the AUC and Cmax of a single oral dose of oxycodone (10 mg) by 144% and 45%, respectively. The AUC of noroxycodone decreased 49% and the AUC of oxymorphone increased 359% with concurrent itraconazole and oral oxycodone. Itraconazole increased the AUC of a single intravenous dose of oxycodone (0.1 mg/kg) by 51%.(16) In a randomized cross-over study in 12 healthy subjects, ketoconazole increased the AUC of oxycodone by 2-fold to 3-fold and also increased oxycodone-related nausea, drowsiness, and pruritus.(17) In a randomized cross-over study in 10 healthy subjects, ketoconazole increased the AUC of oxymorphone by 3-fold following a single dose of oxycodone (0.2 mg/kg). Increased side effects were also noted.(18,19) Ketoconazole has been shown to inhibit the metabolism of alfentanil,(20) fentanyl,(13) and oxycodone(21) in vitro. In a study of 11 subjects, ritonavir reduced the clearance of fentanyl 67% and increased the AUC 174%. Eight subjects reported nausea during the study.(22) In a randomized cross-over study in 16 healthy subjects, ritonavir (300 mg twice daily for 4 days) and lopinavir/ritonavir (400/100 mg twice daily for 4 days) increased the AUC of a single dose of oxycodone (10 mg) by 3.0-fold and 2.6-fold, respectively. Oxycodone half-life increased 55% and 58%, respectively, with concurrent ritonavir or lopinavir/ritonavir. Both regimens also increased self-reported oxycodone effects.(23) The Australian manufacturer of ritonavir states that the AUC of fentanyl may be potentially increased 3-fold with concurrent ritonavir.(24) In a randomized cross-over study in 11 healthy subjects, telithromycin (800 mg daily for 4 days) increased the AUC of a single dose of oxycodone (10 mg immediate-release) by 80%. The AUC of noroxycodone was decreased by 46%. There was a modest increase in the pharmacodynamic effects of oxycodone.(25) In a randomized cross-over study in 10 healthy subjects, troleandomycin increased the AUC of alfentanil by 135%.(26) In a randomized cross-over study in 12 healthy subjects, troleandomycin increased the AUC of a single dose of fentanyl (oral transmucosal, 10 mcg/kg) by 76%.(27) Troleandomycin has been shown to inhibit alfentanil(19) and fentanyl(28) metabolism in vitro. In a randomized, cross-over study in 12 healthy subjects, concurrent use of voriconazole and alfentanil increased the AUC of alfentanil 6-fold and decreased its clearance by 85%.(25,29) In a randomized, cross-over study in 12 healthy subjects, voriconazole (400 mg twice daily, Day 1; 200 mg twice daily, Day 2) and fluconazole (400 mg daily, Day 1; 200 mg daily, Day 2) decreased the clearance of a single dose of intravenous fentanyl (5 mcg/kg) by 23% and 16%, respectively.(30) In a randomized cross-over study in 12 healthy subjects, pretreatment with voriconazole for 4 days increased the AUC, Cmax, and half-life of a single dose of oxycodone (10 mg) by 3.6-fold, 1.7-fold, 2.0-fold, respectively.(31) There are case reports of interactions between alfentanil and erythromycin,(32) fentanyl and clarithromycin,(33) fentanyl and fluconazole,(34) fentanyl and itraconazole,(35) and oxycodone and voriconazole.(36) In the case report with fentanyl and fluconazole, the patient died of respiratory depression.(34) A study in healthy subjects shown that the application of heat over the fentanyl patch system increased mean overall fentanyl exposure by 120% and average maximum fentanyl level by 61%.(2) In a single dose study of sufentanil sublingual tablet 15 mcg with a strong CYP3A4 inhibitor, ketoconazole, resulted in 77% and 19% greater AUC and Cmax values of sufentanil, respectively, compared to its administration alone.(6) Strong CYP3A4 inhibitors that have been documented to interact with alfentanil, benzhydrocodone, fentanyl, hydrocodone, and/or oxycodone or would be expected to interact with these agents include: boceprevir, clarithromycin, cobicistat, elvitegravir, ensitrelvir, grapefruit, idelalisib, indinavir, itraconazole, josamycin, ketoconazole, lonafarnib, lopinavir, mibefradil, nefazodone, nelfinavir, nirmatrelvir, paritaprevir, posaconazole, relacorilant, ribociclib, saquinavir, telaprevir, telithromycin, tipranavir, troleandomycin, tucatinib, voriconazole.(37) Moderate CYP3A4 inhibitors that have been documented to interact with alfentanil, benzhydrocodone, fentanyl, hydrocodone, and/or oxycodone include: erythromycin and fluconazole.(37)

Moderate Interaction: Assess the risk to the patient and take action as needed.

Agents With Hyponatremia Risk/Desmopressin

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Carbamazepine, chlorpromazine, lamotrigine, NSAIDs, opioids, SSRIs, thiazide diuretics, and/or tricyclic antidepressants increase the risk of hyponatremia.(1-3)

CLINICAL EFFECTS: Concurrent use may increase the risk of hyponatremia with desmopressin.(1-3)

PREDISPOSING FACTORS: Predisposing factors for hyponatremia include: polydipsia, renal impairment (eGFR < 50 ml/min/1.73m2), illnesses that can cause fluid/electrolyte imbalances, age >=65, medications that cause water retention and/or increase the risk of hyponatremia (glucocorticoids, loop diuretics).

PATIENT MANAGEMENT: The concurrent use of agents with a risk of hyponatremia with desmopressin may increase the risk of hyponatremia. If concurrent use is deemed medically necessary, make sure serum sodium levels are normal before beginning therapy and consider using the desmopressin nasal 0.83 mcg dose. Consider measuring serum sodium levels more frequently than the recommended intervals of: within 7 days of concurrent therapy initiation, one month after concurrent therapy initiation and periodically during treatment. Counsel patients to report symptoms of hyponatremia, which may include: headache, nausea/vomiting, feeling restless, fatigue, drowsiness, dizziness, muscle cramps, changes in mental state (confusion, decreased awareness/alertness), seizures, coma, and trouble breathing. Counsel patients to limit the amount of fluids they drink in the evening and night-time and to stop taking desmopressin if they develop a stomach/intestinal virus with nausea/vomiting or any nose problems (blockage, stuffy/runny nose, drainage).(1)

DISCUSSION: In clinical trials of desmopressin for the treatment of nocturia, 4 of 5 patients who developed severe hyponatremia (serum sodium <= 125 mmol/L) were taking systemic or inhaled glucocorticoids. Three of these patients were also taking NSAIDs and one was receiving a thiazide diuretic.(2) Drugs associated with hyponatremia may increase the risk, including loop diuretics, carbamazepine, chlorpromazine, glucocorticoids, lamotrigine, NSAIDs, opioids, SSRIs, thiazide diuretics, and/or tricyclic antidepressants.(1,3-4)

Anticholinergics/Topiramate

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Topiramate can cause decreased sweating and elevated body temperature. Agents with anticholinergic activity can predispose patients to heat-related disorders.(1-2)

CLINICAL EFFECTS: Concurrent use of topiramate with agents with anticholinergic activity may increase the incidence of oligohidrosis and hyperthermia, especially in pediatric or adolescent patients.(1-2) Overheating and dehydration can lead to brain damage and death.

PREDISPOSING FACTORS: Pediatric and adolescent patients and patients with dehydration may be more likely to experience heat-related disorders.(1)

PATIENT MANAGEMENT: The manufacturer of topiramate states that caution should be used when topiramate is prescribed with other medicinal products that predispose to heat-related disorders, such as agents with anticholinergic activity (e.g. clomipramine, hydroxyzine, diphenhydramine, haloperidol, imipramine, and oxybutynin) concurrently with zonisamide.(1) Monitor for signs and symptoms of heat stroke: skin feels very hot with little or no sweating, confusion, muscle cramps, rapid heartbeat, or rapid breathing. Monitor for signs and symptoms of dehydration: dry mouth, urinating less than usual, dark-colored urine, dry skin, feeling tired, dizziness, or irritability. If signs or symptoms of dehydration, oligohidrosis, or elevated body temperature occur, discontinuation of zonisamide should be considered.

DISCUSSION: Case reports of decreased sweating and elevated temperature have been reported, especially in pediatric patients. Some cases resulted in heat stroke that required hospital treatment.(1) A 64-year old woman developed non-exertional hyperthemia while taking multiple psychiatric medications with topiramate.(2)

Anticholinergics/Zonisamide

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Zonisamide can cause decreased sweating and elevated body temperature. Agents with anticholinergic activity can predispose patients to heat-related disorders.(1-2)

CLINICAL EFFECTS: Concurrent use of zonisamide with agents with anticholinergic activity may increase the incidence of oligohidrosis and hyperthermia, especially in pediatric or adolescent patients.(1-2) Overheating and dehydration can lead to brain damage and death.

PREDISPOSING FACTORS: Pediatric and adolescent patients and patients with dehydration may be more likely to experience heat-related disorders.(1)

PATIENT MANAGEMENT: The UK and US manufacturers of zonisamide state that caution should be used in adults when zonisamide is prescribed with other medicinal products that predispose to heat-related disorders, such as agents with anticholinergic activity.(1-2) Pediatric and adolescent patients must not take anticholinergic agents (e.g. clomipramine, hydroxyzine, diphenhydramine, haloperidol, imipramine, and oxybutynin) concurrently with zonisamide.(1) Monitor for signs and symptoms of heat stroke: skin feels very hot with little or no sweating, confusion, muscle cramps, rapid heartbeat, or rapid breathing. Monitor for signs and symptoms of dehydration: dry mouth, urinating less than usual, dark-colored urine, dry skin, feeling tired, dizziness, or irritability. If signs or symptoms of dehydration, oligohidrosis, or elevated body temperature occur, discontinuation of zonisamide should be considered.

DISCUSSION: Case reports of decreased sweating and elevated temperature have been reported, especially in pediatric patients. Some cases resulted in heat stroke that required hospital treatment and resulted in death.(1)

Opioids (COUGH & COLD)/Selected Stimulants

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Opioids and stimulants exhibit opposing effects on the CNS.

CLINICAL EFFECTS: Opposing CNS effects of opioids and stimulants may compromise the effectiveness of both agents and mask opioid overdose symptoms such as drowsiness and inability to focus.

PREDISPOSING FACTORS: Concurrent use of alcohol or other CNS depressants may increase the risk of adverse effects.

PATIENT MANAGEMENT: Limit prescribing opioid analgesics with CNS stimulants such as amphetamines to patients for whom alternatives are ineffective, not tolerated, or would be otherwise inadequate to provide sufficient management of pain. If concurrent use is necessary, limit the dosages and duration of each drug to the minimum possible while achieving the desired clinical effect. Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(1) Monitor patients receiving concurrent therapy for signs of substance abuse. Monitor patients receiving concurrent therapy for unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing opioid reversal agents (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).

DISCUSSION: A total of 70,237 persons died from drug overdoses in the United States in 2017; approximately two thirds of these deaths involved an opioid.(2). The CDC analyzed 2016-2017 changes in age-adjusted death rates involving cocaine and psychostimulants by demographic characteristics, urbanization levels, U.S. Census region, 34 states, and the District of Columbia (DC). The CDC also examined trends in age-adjusted cocaine-involved and psychostimulant-involved death rates from 2003 to 2017 overall, as well as with and without co-involvement of opioids. Among all 2017 drug overdose deaths, 13,942 (19.8%) involved cocaine, and 10,333 (14.7%) involved psychostimulants. Death rates increased from 2016 to 2017 for both drug categories across demographic characteristics, urbanization levels, Census regions, and states. In 2017, opioids were involved in 72.7% and 50.4% of cocaine-involved and psychostimulant-involved overdoses, respectively, and the data suggest that increases in cocaine-involved overdose deaths from 2012 to 2017 were driven primarily by synthetic opioids.(3) There was opioid co-involvement in 72.7 percent of cocaine and 50.4 percent of stimulant-involved overdose deaths. This was largely driven by synthetic opioids such as fentanyl. However, stimulant-involved overdose without opioid co-involvement is also increasing.(2)

Opioids/Buprenorphine; Pentazocine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Buprenorphine is a partial agonist at mu-opiate receptors, exhibiting a ceiling effect at which higher doses produce no further effect. Pentazocine is a mixed agonist-antagonist at opiate receptors.(1) Full mu-opioid agonists (e.g., morphine, methadone) continue to have increased effects at higher doses without ceiling effects.(2)

CLINICAL EFFECTS: Concurrent use of buprenorphine or pentazocine with other opioids in opioid dependent patients may result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia and decreased opioid side effects.

PREDISPOSING FACTORS: Patients dependent on opioids or who take higher dosages of opioids may be more likely to experience withdrawal symptoms with concurrent use.

PATIENT MANAGEMENT: Use buprenorphine and pentazocine with caution in patients maintained or dependent on other opioids and monitor for signs of withdrawal. In other patients, also monitor for changes in analgesic effects. The manufacturer of Sublocade states buprenorphine may precipitate opioid withdrawal in patients who are currently physically dependent on full opioid agonists. The risk of withdrawal may be increased if buprenorphine is given less than 6 hours after short-acting opioids (such as heroin, morphine) and less than 24 hours after long-acting opioids (such as methadone).(3)

DISCUSSION: Concurrent use of buprenorphine with other opioids in opioid dependent patients could result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia, decreased opioid side effects, and/or renarcotization.(2) In clinical trials, administration of buprenorphine injection produced withdrawal symptoms in patients maintained on methadone (30 mg daily) when administered 2 hours post-methadone,(4) but not when administered 20 hours post-methadone.(5) In another study, sublingual buprenorphine produced withdrawal symptoms in patients maintained on methadone. Symptoms were more pronounced in patients maintained on 60 mg daily doses than in patients maintained on 30 mg daily doses.(6) In a study of 10 patients maintained on methadone (100 mg daily), only three were able to tolerate escalating sublingual doses of buprenorphine/naloxone up to 32/8 mg. Split doses produced less withdrawal symptoms than full doses.(7) In a case report, a heroin-user maintained in a buprenorphine-maintenance program began stockpiling his buprenorphine instead of ingesting it and began using heroin. He then decided to re-initiate treatment on his own and ingested between 80 and 88 mg of buprenorphine over a two day period and experienced extreme withdrawal symptoms, despite restarting heroin during these symptoms. Methadone relieved his withdrawal symptoms.(8)

Opioids/Butorphanol

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Butorphanol antagonize mu-opiate receptors. Other opioids agonize mu-opiate receptors.(1)

CLINICAL EFFECTS: Concurrent use of butorphanol with other opioids in opioid dependent patients may result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia and decreased opioid side effects.

PREDISPOSING FACTORS: Patients dependent on opioids may be more likely to experience withdrawal symptoms with concurrent use. Patients using higher doses of opioids may also be at a higher risk.

PATIENT MANAGEMENT: Use butorphanol with caution in patients maintained or dependent on other opioids and monitor for signs of withdrawal. In other patients, also monitor for changes in analgesic effects.

DISCUSSION: Because butorphanol antagonizes mu-opiate receptors and other opioids agonize mu-opiate receptors, concurrent use of buprenorphine with other opioids in opioid dependent patients may result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia and decreased opioid side effects.(1) In a study in patients maintained on methadone, butorphanol produced withdrawal symptoms comparable to naloxone.(2) In a case report, the use of remifentanil for conscious sedation in a patient maintained on butorphanol produced severe withdrawal symptoms.(3)

Opioids/Nalbuphine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Nalbuphine(1) antagonizes mu-opiate receptors. Other opioids agonize mu-opiate receptors.

CLINICAL EFFECTS: Concurrent use of nalbuphine with other opioids in opioid dependent patients may result in withdrawal symptoms. Concurrent use in other patients may result in additive or decreased analgesia, decreased opioid side effects, and/or renarcotization.

PREDISPOSING FACTORS: Patients dependent on opioids may be more likely to experience withdrawal symptoms with concurrent use. In opioid naive patients, higher doses of nalbuphine may result in decreased analgesic effects.

PATIENT MANAGEMENT: Use nalbuphine with caution in patients maintained or dependent on other opioids and monitor for signs of withdrawal. In other patients, also monitor for changes in analgesic effects. If nalbuphine is used to reverse opioid anesthesia, monitor patients for renarcotization.

DISCUSSION: Nalbuphine has been successfully used as an adjunct to morphine without decreasing analgesic effects.(2,3) However, other studies reported increased morphine requirements in patients who had initially received nalbuphine.(4,5) Nalbuphine has been used to reverse fentanyl anesthesia;(8-13) however, patients often required additional pain medication(5-7) and some studies reported renarcotization after the effects of nalbuphine wore off.(9,10) Nalbuphine has also been used to prevent epidural fentanyl,(13) morphine(14-16), and hydromorphone induced pruritus;(17-18) however, one study reported shortening of the duration of analgesia(16) and another reported increased PCA demands.(17) In methadone-dependent subjects, administration of nalbuphine produced withdrawal symptoms similar to naloxone.(19,20) Administration of nalbuphine to patients maintained on controlled-release morphine resulted in withdrawal symptoms.(20,21)

Selected Opioid Analgesics/Cimetidine

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: The metabolism of selected opioid analgesics may be inhibited by cimetidine.(1-15) At doses of 800-2400 mg daily, cimetidine is a moderate inhibitor of CYP3A4 and a weak inhibitor of CYP1A2, CYP2C19, CYP2C9, and CYP2D6.(16) Benzhydrocodone is a prodrug of hydrocodone.(12)

CLINICAL EFFECTS: The effect of selected opioid analgesics may be increased including profound sedation, respiratory depression, coma, and/or death. Opioid analgesics have been associated with histamine release and is dependent on dose, route of administration, and rate of administration. Histamine release can cause arteriole dilation and contribute to a profound decrease in systemic blood pressure. The cardiovascular effects of histamine release occurring with the opioid analgesics may be decreased by giving cimetidine concurrently.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Cimetidine use at higher doses of 200-400 mg four times daily would have an increased risk of inhibiting the metabolism of opioid analgesics. Lower doses and over-the-counter doses of cimetidine would be expected to have a diminished effect. Consider using alternative H2 antagonists when long-term concurrent therapy with opioid analgesics is indicated. The manufacturer of sufentanil sublingual tablets states that if concomitant use with CYP3A4 inhibitors is necessary, consider use of an alternate agent that allows dose adjustment.(15) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(17) Monitor the patient for increased adverse effects of the opioid analgesic including respiratory and central nervous system depression, unusual dizziness or lightheadedness, extreme sleepiness, slowed or difficult breathing, or unresponsiveness. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(18)

DISCUSSION: Severe respiratory depression has been reported with the concurrent administration of opioid analgesics and cimetidine. Systemic levels of opioid analgesics metabolized by CYP3A4 may be increased during concurrent use with cimetidine, a CYP3A4 inhibitor.(1-15) In a study of 6 healthy subjects, the effects of ketoconazole (a strong CYP3A4 inhibitor) 400 mg daily for 3 days on alfentanil were studied. The maximum concentration (Cmax) and area-under-curve (AUC) of alfentanil were increased with both sequential and simultaneous dosing of alfentanil with concurrent ketoconazole.(19) In a study of 16 healthy subjects, the effects of ketoconazole 300 mg twice daily for 2 days on fentanyl 5 mcg/kg single dose were examined. Fentanyl AUC was increased by 133% and clearance was reduced to 78%. The metabolism of fentanyl to norfentanyl by CYP3A4 was delayed and partial metabolic clearance decreased by 18% with concurrent ketoconazole.(20) In vitro results of the effects of ketoconazole on hydrocodone confirmed CYP3A4 is responsible for the metabolism of hydrocodone to norhydrocodone.(21) A review discussed the metabolism of hydrocodone by CYP2D6 to O-demethylated hydromorphone and by CYP3A4 to N-demethylated norhydrocodone. CYP3A4 activity is reported as higher in women resulting in higher fractions of the norhydrocodone metabolite in women than in men.(22) A case report of a 46 year old hemodialysis patient was on routine therapy with phenytoin 100 mg three times daily and cimetidine 300 mg three times daily. Four days after starting cimetidine, morphine 15 mg IM every 4 hours was initiated for pain. After the sixth dose of morphine, the patient was apneic with a respiratory rate of 3 breaths/minute and had a grand mal seizure. The patient responded to naloxone 0.4 mg IV single dose with improvement in respiratory rate to 12 breaths/minute. Cimetidine was stopped and phenytoin decreased to 100 mg twice daily with improvement after 80 hours from initial episode. A month later the patient required surgery and was given cimetidine 150 mg twice daily followed by Pantopon 15 mg IM every 3-6 hours postoperatively for pain. The patient again became apneic, confused, and developed muscle twitching which responded to naloxone 0.4 mg for 4 doses over the next 24 hours with complete recovery.(23) In a study of 8 healthy subjects, the effects of cimetidine on morphine were studied. Subjects were evaluated in three study periods: morphine 10 mg IM single dose; cimetidine 600 mg oral given one hour before morphine 10 mg IM single dose; and cimetidine 600 mg oral single dose. Morphine reduced resting ventilation and increased end-tidal CO2 with peak effects at 120 minutes and resolution at 12 hours. Morphine with cimetidine pretreatment had similar effects on resting ventilation and end-tidal CO2, however the recovery ratio from 120 to 720 minutes was significantly different than morphine alone (p<0.05).(24) In a study of 7 healthy subjects, the effects of cimetidine 300 mg oral four times daily for 4 days on morphine 10 mg IV single dose were evaluated. No significant differences were found in morphine concentrations at any time point from zero to ten hours after dose administration with and without cimetidine. Morphine elimination half-life (t1/2), systemic clearance, volume of distribution, and AUC with and without cimetidine had no statistical differences.(25) In a study of 40 patients undergoing elective coronary artery bypass graft surgery were randomized to receive either cimetidine 4 mg/kg, diphenhydramine 1 mg/kg, a combination of both cimetidine and diphenhydramine, or placebo, followed by morphine 1 mg/kg. Patients were randomized to one of four groups: 1. placebo plus morphine; 2. cimetidine plus morphine; 3. diphenhydramine plus morphine; or 4. cimetidine plus diphenhydramine plus morphine. Patients in group 1 had a 10-fold increase in plasma histamine levels within 2 minutes of morphine with a decrease in mean BP, diastolic BP, and systemic vascular resistance (SVR). Group 2 has similar effects with a peak change in SVR and plasma histamine rise within 2 minutes of morphine. The change in SVR was significant when compared to placebo but less than group 1. Group 3 patients had an increase in heart rate (HR) from diphenhydramine alone as well as peak effects within 2 minutes of morphine with decreases in BP and SVR but were less than morphine alone. Group 4 patients had a 7-fold increase in histamine with a significant increase in HR, diastolic BP, and BP. When group 4 is compared to group 1, patients had a decrease in SVR and diastolic BP that was significantly less despite comparable increases in plasma histamine.(26) In vitro testing of oxycodone and methadone, cimetidine caused a greater than 50% inhibition in all pathways: CYP2B6, CYP3A4, CYP2C18, and CYP2D6. Cimetidine was found to be a weak reversible inhibitor in vitro. Extrapolation of the data to in vivo inhibition is unlikely to produce significant inhibition unless concentrations exceed normal doses by 10-fold.(27) Two studies examined the effects of CYP2D6 and CYP3A4 on the metabolism of oxycodone as well as genetic polymorphism influences. After concurrent administration of oxycodone with ketoconazole, the Cmax of the metabolites noroxycodone and noroxymorphone were decreased by 80% from baseline.(28,29) A review discussed the metabolism of oxycodone by CYP3A4 to noroxycodone, the major metabolite with weak antinociceptive properties, and by CYP2D6 to the active minor metabolite oxymorphone.(30) In a study of 8 male subjects, effects of cimetidine 600 mg twice daily for seven days on pethidine 70 mg IV single dose was evaluated. Concurrent use with cimetidine was associated with a 22% decrease in clearance, 11% decrease in elimination rate, and a 13% decrease in volume of distribution of pethidine. Changes were also seen in norpethidine, the primary metabolite, with a 23% decrease in AUC and 29% decrease in Cmax.(31) Opioid analgesics linked to this monograph include: alfentanil, benzhydrocodone, dihydrocodeine, fentanyl, hydrocodone, meperidine, meptazinol, nalbuphine, oxycodone, oxymorphone, pentazocine, propoxyphene, and sufentanil.

Selected Opioids/Barbiturates; Phenobarbital; Primidone

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: There are two mechanisms involved in this interaction. Pharmacokinetic: alfentanil, benzhydrocodone, buprenorphine, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil are primarily metabolized by CYP3A4/5 and glucuronidation pathways.(1-8) Phenobarbital is an inducer of these pathways. Pharmacodynamic: both opioids and barbiturates are associated with respiratory depression; these effects may be additive.(1,3,9) Benzhydrocodone is a prodrug of hydrocodone.(2) Primidone is metabolized to phenobarbital.

CLINICAL EFFECTS: Short term or intermittent use of phenobarbital and opioids metabolized by CYP3A4 may be associated with respiratory suppression or other CNS depression. Continuous, longer term use of phenobarbital may result in decreased levels and effectiveness of the opioid. Induction of meperidine metabolism may result in an increase in levels of normeperidine, the toxic metabolite of meperidine, resulting in a higher risk of excitatory effects, including hallucinations, tremors, and seizures.(6,10)

PREDISPOSING FACTORS: Patients with a history of alcohol or sedative abuse may be at risk for relapse and overuse or abuse of prescribed phenobarbital.(1,3,5,11) Individuals with significant obstructive pulmonary disease, the elderly, and debilitated patients are at greater risk for respiratory depression from either agent.(1,3) Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: Patients on chronic therapy with phenobarbital who are newly starting opioids metabolized by CYP3A4 may need higher than usual doses of the opioid for analgesia or opioid maintenance.(1,3,12) Opioid-treated patients newly started on phenobarbital should be monitored initially for additive CNS sedation or respiratory depression, particularly when predisposing factors (e.g. COPD, sleep apnea, debilitation, elderly) are present. Continued use of phenobarbital leads to induction of the opioids' metabolism. The onset is gradual and may not peak for several weeks. Monitor patient for possible loss of efficacy or opioid withdrawal. If a patient has been maintained on concurrent treatment with an opioid metabolized by CYP3A4 and phenobarbital, and the phenobarbital is discontinued, opioid levels will gradually rise as induction effects diminish. Monitor for increased opioid effects and adjust the dose accordingly.(1,3,12) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(13) For patients receiving opioid maintenance treatment, it would be prudent to assure all controlled substance prescriptions are approved or written by the opioid provider. Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(14)

DISCUSSION: Alfentanil, benzhydrocodone, fentanyl, hydrocodone, meperidine, oxycodone, and sufentanil are metabolized by CYP3A4, and barbiturates, phenobarbital, and primidone would be expected to induce their metabolism.(1,2,4-6) Newer metabolites and minor metabolic pathways for buprenorphine have been recently described. Phenobarbital, an inducer of multiple enzyme pathways (e.g. CYP2B, CYP2C, CYP3A and UGT) could potentially lower systemic buprenorphine levels via major and minor pathways.(12)

Selected Opioids/Selected Moderate Cyp3a4 Inhibitors

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Inhibitors of CYP3A4 may inhibit the metabolism of alfentanil, benzhydrocodone, fentanyl,(1) hydrocodone, meperidine,(2) oxycodone,(3) and sufentanil.(4)

CLINICAL EFFECTS: The concurrent administration of a CYP3A4 inhibitor may result in elevated levels of and toxicity from alfentanil, benzhydrocodone, fentanyl,(1,5) hydrocodone, meperidine,(2) oxycodone(3) and sufentanil(4), including somnolence and potentially fatal respiratory depression.

PREDISPOSING FACTORS: Heat.

PATIENT MANAGEMENT: Monitor patients receiving moderate CYP3A4 inhibitors for an extended period of time. Dosage adjustments should be made if warranted. The manufacturer of sufentanil sublingual tablets states that if concomitant use with CYP3A4 inhibitors is necessary, consider use of an alternate agent that allows dose adjustment.(4) Respiratory depression can occur at any time during opioid therapy, especially during therapy initiation and following dosage increases. The risk of opioid-related overdose or overdose-related death is increased with higher opioid doses, and this risk persists over the course of therapy. Consider these risks when using concurrently with other agents that may cause CNS depression.(6) Discuss opioid reversal agents (e.g., naloxone, nalmefene) with all patients when prescribing or renewing an opioid analgesic or medicine to treat opioid use disorder (OUD). Consider prescribing an opioid reversal agent (e.g., naloxone, nalmefene) to patients prescribed medicines to treat OUD or opioid analgesics who are at increased risk of opioid overdose (such as those taking CNS depressants) and when a patient has household members/close contacts at risk for accidental overdose. Discuss the options for obtaining an opioid reversal agent (e.g., prescription, over-the-counter, or as part of a community-based program).(7) Avoid exposing the fentanyl patch application site and surrounding area to direct external heat sources as there have been reports of overdose and death as a result of exposure to heat.(1)

DISCUSSION: Fentanyl(1) and oxycodone(3) are metabolized by the CYP3A4 isoenzyme. Moderate and strong inhibitors of this isoenzyme are expected to increase fentanyl(1) and oxycodone(3) levels. In a single dose study of sufentanil sublingual tablet 15 mcg with a strong CYP3A4 inhibitor, ketoconazole, resulted in 77% and 19% greater AUC and Cmax values of sufentanil, respectively, compared to its administration alone.(4) In a randomized study in 30 patients, continuous diltiazem (1 mcg/kg/min) infusion had no effect on epidural fentanyl consumption when compared to placebo. There were no significant differences in Visual Analogue Scores (VAS), Verbal Rating Scores (VRS), or incidence of side effects, although there was a trend towards increased nausea with concurrent diltiazem.(5) In a randomized study of coronary artery bypass patients, concurrent diltiazem (60 mg orally 2 hours before induction of anesthesia then 0.1 mg/kg/hr infusion) increased the area-under-curve (AUC) and half-life of alfentanil by 40% and 50%, respectively, when compared to placebo. Patients who received diltiazem were extubated an average of 2.5 hours later than in patients who received placebo.(8) In a study in 13 patients, administration of a single dose of verapamil (75mcg/kg to 150mcg/kg) had no significant effects on the pharmacodynamic effects of a single dose of fentanyl; however, individual patients had modest decreases in blood pressure.(9) In a case report, concurrent diltiazem and fentanyl produced delirium.(10) A study in healthy subjects shown that the application of heat over the fentanyl patch system increased mean overall fentanyl exposure by 120% and average maximum fentanyl level by 61%.(1) Moderate inhibitors of CYP3A4 include: amprenavir, aprepitant, atazanavir, avacopan, berotralstat, clofazimine, conivaptan, darunavir, diltiazem, dronedarone, duvelisib, fedratinib, fosamprenavir, fosnetupitant, imatinib, isavuconazonium, lenacapavir, letermovir, netupitant, nilotinib, rilzabrutinib, schisandra, stiripentol, treosulfan, and verapamil.(11,12)

Selected Opioids/Selected Strong Cyp3a4 Inducers

SEVERITY LEVEL: 3-Moderate Interaction: Assess the risk to the patient and take action as needed.

MECHANISM OF ACTION: Strong inducers of CYP3A4 may induce the metabolism of alfentanil, benzhydrocodone, buprenorphine,(1) fentanyl, hydrocodone, meperidine,(2-4) morphine,(5) oxycodone, papaveretum, and sufentanil.(6)

CLINICAL EFFECTS: Concurrent use of a strong CYP3A4 inducer may result in decreased levels of alfentanil, benzhydrocodone, buprenorphine, fentanyl, hydrocodone, meperidine, morphine, oxycodone, papaveretum, and sufentanil, which may result in decreased effectiveness and may precipitate withdrawal symptoms.(1-6) Induction of meperidine metabolism may result in an increase in levels of normeperidine, the toxic metabolite of meperidine, resulting in a higher risk of excitatory effects, including hallucinations, tremors, and seizures.(2,3)

PREDISPOSING FACTORS: Induction effects may be more likely with regular use of the inducer for longer than 1-2 weeks.

PATIENT MANAGEMENT: Patients maintained on alfentanil, benzhydrocodone, buprenorphine, fentanyl, hydrocodone, meperidine, morphine, oxycodone, papaveretum, and sufentanil may require dosage adjustments if a strong CYP3A4 inducer is initiated or discontinued. The effects of the interaction may last for several weeks after the discontinuation of the inducer. Patients who transfer to Sublocade (extended release subcutaneous syringe buprenorphine) from transmucosal buprenorphine used concomitantly with CYP3A4 inducers should be monitored to ensure that the plasma buprenorphine level produced by Sublocade is adequate. If patients already on Sublocade require newly-initiated treatment with CYP3A4 inducer, the patient should be monitored for withdrawal. If the dose of Sublocade is not adequate in the absence of the concomitant medication, and the concomitant medication cannot be reduced or discontinued, the patient should be transitioned back to a formulation of buprenorphine that permits dose adjustment. If a patient has been stabilized on Sublocade with a CYP3A4 inducer and the concomitant medication is discontinued, the patient should be monitored for signs and symptoms of over-medication. Within 2 weeks of Sublocade administration, if the dose provided by Sublocade is excessive in the absence of the concomitant inducer, it may be necessary to remove the Sublocade and treat the patient with a formulation of buprenorphine that permits dose adjustments.(15) The manufacturer of sufentanil sublingual tablets states that if concomitant use with CYP3A4 inducers is necessary, consider use of an alternate agent that allows dose adjustment.(6)

DISCUSSION: In a study in 12 opoid-dependent patients, rifampin (600 mg daily) decreased the area-under-curve (AUC) of buprenorphine by 70%. Half of the subjects experienced withdrawal symptoms. When compared to historical values, there was no effect on rifampin levels.(1) In a study of four healthy volunteers, phenytoin increased meperidine clearance from 1017 +/- 225 ml/min (mean +/- SD) to 1280 +/- 130 ml/min and decreased half-life from 6.4 hours to 4.3 hours. Phenytoin also increased normeperidine AUC by 1.53-fold after IV meperidine and by 1.25-fold after oral meperidine.(3) In a study in 10 healthy subjects, pretreatment with rifampin (600 mg daily) for 13 days decreased the area-under-curve (AUC) and maximum concentration (Cmax) of a single dose of morphine by 28% and 41%, respectively. The AUCs of morphine-3-glucuronide and morphine-6-glucuronide were proportionally decreased as well. Following rifampin pretreatment, no analgesic effects of morphine were seen.(5) In a randomized controlled trial of 12 healthy participants St. John's wort decreased the oxycodone AUC by 50%, shortened the oxycodone elimination half-life, and decreased the self-reported drug effect of oxycodone compared to placebo.(7) In a study in 12 healthy subjects, pretreatment with rifampin had no effect on fentanyl Cmax or time to Cmax (Tmax) after administration of oral transmucosal fentanyl. However, fentanyl AUC decreased 62%.(8) In a study in 9 healthy subjects, rifampin increased the clearance of alfentanil by 169%. Alfentanil half-life decreased 61%.(9) In a study of patients undergoing craniotomy, higher fentanyl maintenance doses were required in patients receiving carbamazepine and phenytoin compared to control subjects not receiving enzyme-inducing agents.(10) There are case reports of decreased levels and effectiveness of oxycodone with concurrent phenytoin(11) and rifampin(12) and with concurrent fentanyl and rifampin.(13-14) Selected strong CYP3A4 inducers linked to this monograph include: apalutamide, carbamazepine, encorafenib, enzalutamide, fosphenytoin, ivosidenib, lumacaftor, mitotane, phenytoin, rifampin, rifapentine, and St. John's Wort.

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• Acute asthma attack
• Congenital long QT syndrome
• Paralytic ileus

• Alcohol intoxication
• Angle-closure glaucoma
• Benign prostatic hyperplasia
• Bladder outflow obstruction
• Chronic idiopathic constipation
• Chronic kidney disease stage 3A (moderate) GFR 45-59 ml/min
• Chronic kidney disease stage 3B (moderate) GFR 30-44 ml/min
• Chronic kidney disease stage 4 (severe) GFR 15-29 ml/min
• Chronic kidney disease stage 5 (failure) GFr<15 ml/min
• Coma
• Dehydration
• Disease of liver
• Drug abuse
• Exacerbation of chronic obstructive pulmonary disease
• Familial dysautonomia
• Gastrointestinal obstruction
• History of opioid overdose
• Hypercapnia
• Hypotension
• Inflammatory bowel disease
• Intracranial hypertension
• Morbid obesity
• Neoplasm of brain
• Respiratory depression
• Shock
• Sleep apnea
• Stenosing peptic ulcer
• Systemic mastocytosis
• Toxic psychosis
• Untreated hypothyroidism
• Urethral stricture
• Urinary retention

• Acute abdominal pain
• Acute pancreatitis
• Adrenocortical insufficiency
• Alcohol withdrawal delirium
• Biliary spasm
• Bradycardia
• Chronic obstructive pulmonary disease
• Constipation
• Cor pulmonale
• Debilitation
• Esophageal dysmotility
• Gallbladder disease
• Gastrointestinal tract surgery
• Hypertension
• Hyperthyroidism
• Primary adrenocortical insufficiency
• Seizure disorder

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Less Frequent

• Angioedema
• Atelectasis
• Bradycardia
• Bronchospastic pulmonary disease
• CNS depression
• Dyspnea
• Laryngeal edema
• Laryngismus
• Respiratory depression
• Tachycardia

Rare or Very Rare

• Accidental fall
• Adrenocortical insufficiency
• Allergic dermatitis
• Anaphylaxis
• Anaphylaxis
• Biliary spasm
• Blood dyscrasias
• Dehydration
• Depression
• Disorder of adrenal gland
• Drug dependence
• Extrasystoles
• Female hypogonadism
• Hallucinations
• Hallucinations
• Hearing loss
• Hemolytic anemia
• Hypersensitivity drug reaction
• Hypertension
• Hypokalemia
• Hypotension
• Ileus
• Increased cerebrospinal fluid pressure
• Involuntary muscle movement
• Ischemic colitis
• Male hypogonadism
• Muscle rigidity
• Pancreatitis
• Paralytic ileus
• Seizure disorder
• Seizure disorder
• Skin rash
• Sleep apnea
• Tinnitus
• Urticaria

More Frequent

• Anticholinergic toxicity
• Constipation
• Dizziness
• Dizziness
• Drowsy
• Drowsy
• General weakness
• Hypotension
• Malaise
• Nausea
• Sedation
• Syncope
• Thick bronchial secretions

Less Frequent

• Acute abdominal pain
• Acute cognitive impairment
• Anorexia
• Arthralgia
• Back pain
• Blurred vision
• Diplopia
• Dysphoric mood
• False sense of well-being
• Fatigue
• Flushing
• Gastroesophageal reflux disease
• Headache disorder
• Hyperhidrosis
• Lethargy
• Mood changes
• Muscle spasm
• Muscle weakness
• Myalgia
• Nervousness
• Night sweats
• Opioid dependence
• Orthostatic hypotension
• Peripheral edema
• Sedation
• Symptoms of anxiety
• Tremor
• Upper respiratory infection
• Ureteral spasm
• Urinary tract infection
• Visual changes
• Vomiting
• Xerostomia

Rare or Very Rare

• Abdominal distension
• Accidental fall
• Acute abdominal pain
• Acute cognitive impairment
• Agitation
• Androgen deficiency
• Anorexia
• Ataxia
• Ataxia
• Blurred vision
• Chest discomfort
• Chills
• Constipation
• Diarrhea
• Diplopia
• Dry nose
• Dry throat
• Dysgeusia
• Dysphagia
• Dyspnea
• Dysuria
• Elevated serum amylase
• Erectile dysfunction
• Euphoria
• Excitement
• Fatigue
• Gastrointestinal irritation
• Headache disorder
• Hyperhidrosis
• Infertility
• Insomnia
• Insomnia
• Irritability
• Libido changes
• Maculopapular rash
• Malaise
• Migraine
• Migraine
• Musculoskeletal pain
• Nausea
• Neck pain
• Nervousness
• Nightmares
• Nightmares
• Non-cardiac chest pain
• Opioid induced allodynia
• Opioid induced hyperalgesia
• Palpitations
• Palpitations
• Paresthesia
• Paresthesia
• Pruritus of skin
• Pruritus of skin
• Skin photosensitivity
• Skin rash
• Symptoms of anxiety
• Tachycardia
• Tinnitus
• Tremor
• Urinary retention
• Urticaria
• Vertigo
• Visual changes
• Vomiting
• Wheezing
• Xerostomia

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Safe use of hydrocodone during pregnancy has not been established; therefore, the drug should not be administered to pregnant women unless the possible benefits outweigh the potential risks.

Reproduction studies in animals using dexchlorpheniramine have not been performed to date, but reproduction studies in rabbits and rats using chlorpheniramine maleate dosages up to 50 and 85 times the usual human dosage, respectively, have not revealed evidence of harm to the fetus. Decreased postnatal survival in offspring of rats receiving 33 and 67 times the usual human dosage of chlorpheniramine maleate has been reported. There are no adequate and controlled studies to date using chlorpheniramine or dexchlorpheniramine in pregnant women, and the drugs should be used during the first 2 trimesters only when clearly needed. In one epidemiologic study, use of chlorpheniramine was not associated with an increased risk of teratogenic effects; however, only a limited number of pregnant women received the drug in this study. Because of the risk of severe reactions (e.g., seizures) to antihistamines in neonates, chlorpheniramine or dexchlorpheniramine should not be used during the third trimester.

It is not known whether hydrocodone is distributed into human milk. A decision should be made to discontinue nursing or the drug, taking into account the importance of the drug to the woman.

It is not known whether chlorpheniramine or dexchlorpheniramine is distributed into milk, but other antihistamines (e.g., diphenhydramine) have been detected in milk. Because of the potential for serious adverse reactions to antihistamines in nursing infants, a decision should be made whether to discontinue nursing or chlorpheniramine or dexchlorpheniramine, taking into account the importance of the drug to the woman.

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