Nifedipine Er (nifedipine)

No dosing information is available for this tab.

Nifedipine is administered orally as short-acting (conventional, immediate-release) capsules or as extended-release tablet formulations; the tablet formulations are commercially available as a gastrointestinal therapeutic system (GITS) or coat-core (CC) tablet.

Nifedipine has been administered sublingually+ or intrabuccally+ for rapid reduction of blood pressure; however, it is no longer acceptable to use short-acting (conventional, immediate-release capsules) nifedipine for this use.

Whenever extended-release tablets of nifedipine are dispensed, care should be taken to ensure that the extended-release dosage form has been prescribed.

The manufacturers recommend that dosage of nifedipine be decreased gradually with close clinical supervision when discontinuance of the drug is required.

Concomitant oral administration of 1,4-dihydropyridine-derivative calcium-channel blocking agents (e.g., nifedipine) with grapefruit juice usually should be avoided since potentially clinically important increases in bioavailability may result.

Metabolism of nifedipine is mediated by the cytochrome P-450 (CYP) microsomal enzyme system (principally the 3A isoenzyme) and concomitant use of nifedipine with inhibitors or inducers of CYP3A may be associated with altered nifedipine exposure resulting in favorable or unfavorable effects. In addition, in vitro and in vivo data indicate that nifedipine may inhibit metabolism of drugs that are substrates of CYP3A, thereby increasing exposure to other drugs. Nifedipine does not appear likely to affect the metabolism of CYP2D6 substrates.

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

Nifedipine/Selected Cyp3a4 Inducers

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: CYP3A4 inducers may induce the hepatic metabolism of nifedipine.(1)

CLINICAL EFFECTS: Concurrent use of an inducer of CYP3A4 may decrease levels and effectiveness of nifedipine.(1)

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

PATIENT MANAGEMENT: The concurrent use of strong CYP3A4 inducers with nifedipine is contraindicated.(1)

DISCUSSION: In a study in 12 healthy males, pretreatment with rifampin (600 mg daily for 14 days) decreased the maximum concentration (Cmax) and area-under-curve (AUC) of a single dose of nifedipine (20 mg) by 95% and 97%, respectively.(1) In a study of 6 healthy subjects, pretreatment with rifampin (600 mg daily for 7 days) increased the clearance of a single oral dose of nifedipine (20 mg) by 9.28-fold and decrease the nifedipine bioavailability by 87%. There were no significant effects on a single intravenous dose of nifedipine.(2) In a study in 6 healthy subjects, pretreatment with a single dose of rifampin (600 mg) 8 hours before a single oral dose of nifedipine decreased nifedipine bioavailability by 64.2%. Nifedipine half-life decreased by 60%. Nifedipine clearance increased by 1.89-fold.(3) There have been case reports of decreased effectiveness of nifedipine during concurrent rifampin therapy.(4-6) Enzalutamide is a strong inducer of CYP3A4.(7) Selected CYP3A4 inducers linked to this monograph include apalutamide, encorafenib, enzalutamide, ivosidenib, lumacaftor, mitotane, rifabutin, rifampin, and rifapentine.

Nifedipine/St. John's Wort

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: St. John's wort may induce the metabolism of nifedipine by CYP3A4.(1)

CLINICAL EFFECTS: The concurrent use of St. John's wort may result in decreased levels and clinical effects of nifedipine.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US manufacturer of nifedipine states that concurrent use of strong CYP3A4 inducers such as St. John's wort is contraindicated.(1)

DISCUSSION: Coadministration of phenytoin, another inducer of CYP3A4, with nifedipine (10 mg capsule and 60 mg extended-release tablet) decreased the area-under-curve (AUC) and maximum concentration (Cmax) of nifedipine by 70%.(1) In a study in 12 healthy males, pretreatment with rifampin (600 mg daily for 14 days), another inducers of CYP3A4, decreased the Cmax and AUC of a single dose of nifedipine (20 mg) by 95% and 97%, respectively.(1)

Nifedipine; Nimodipine; Nisoldipine/Slt Strong 3A4 Inducers

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: Concurrent use of barbiturates, carbamazepine, phenobarbital, phenytoin, or primidone may induce the CYP3A4 mediated metabolism of nifedipine,(1) and nimodipine,(2,3) and nisoldipine.(4) Nisoldipine is particularly susceptible to changes in CYP3A4 activity.(4,5)

CLINICAL EFFECTS: Concurrent use of barbiturates, carbamazepine, phenobarbital, phenytoin, or primidone may result in decreased levels and effectiveness of nifedipine(1), nimodipine or nisoldipine.(6)

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

PATIENT MANAGEMENT: Due to the risk for treatment failure, use an alternative agent if possible. The US manufacturer of nifedipine states that the concurrent use of strong CYP3A4 inducers such as carbamazepine, phenobarbital, phenytoin, or primidone is contraindicated because efficacy could be significantly reduced.(1) The UK manufacturer of nimodipine states that the concurrent use of carbamazepine, phenobarbital, phenytoin, or primidone is contraindicated.(2) The US manufacturer of nimodipine states that the concurrent use of strong CYP3A4 inducers should generally be avoided due to decreased nimodipine plasma concentrations and significantly reduced efficacy.(6) The US manufacturer of nisoldipine states it should generally not be coadministered with CYP3A4 inducers. Concurrent administration of phenytoin with nisoldipine (40 mg) decreased nisoldipine plasma concentrations below detectable levels.(7)

DISCUSSION: Coadministration of phenytoin with nifedipine (10 mg capsule and 60 mg extended-release tablet) decreased the area-under-curve (AUC) and maximum concentration (Cmax) of nifedipine by 70%.(1) A study examined nimodipine pharmacokinetics in three groups: normal drug-free controls (n=8), epileptic patients taking enzyme-inducing anticonvulsants (phenobarbital alone, n=4; phenobarbital with carbamazepine, n=2, carbamazepine with clobazam, n=1, and carbamazepine with phenytoin, n=1), and epileptic patients taking valproic acid (n=8). In patients taking enzyme-inducing anticonvulsants, nimodipine AUC, Cmax, and half-life (T1/2) were 86.2%, 89.2%, and 68.1%, respectively, lower than in controls. In patients taking valproic acid, nimodipine AUC was 54.5% higher than in control patients.(3) Concurrent administration of phenytoin with nisoldipine (40 mg) decreased nisoldipine plasma concentrations below detectable levels.(7) In a study comparing patients receiving chronic phenytoin therapy to healthy controls, phenytoin decreased the AUC of a single dose of nisoldipine by 89%.(8)

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

Agents That Affect Catecholamines/Iobenguane I 131

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

MECHANISM OF ACTION: Many compounds that reduce catecholamine uptake or that deplete catecholamine stores may interfere with iobenguane uptake into cells.(1)

CLINICAL EFFECTS: Compounds that reduce catecholamine uptake or that deplete catecholamine stores may impact the dosimetry calculations or effectiveness of iobenguane.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Discuss the use of agents that affect catecholamines. Discontinue drugs that reduce catecholamine uptake or deplete catecholamine stores for at least 5 half-lives before administration of either the dosimetry or a therapeutic dose of iobenguane. Do not administer these drugs until at least 7 days after each iobenguane dose.(1)

DISCUSSION: Many agents may reduce catecholamine uptake or deplete catecholamine stores.(1) Examples include: - CNS stimulants or amphetamines (e.g. cocaine, methylphenidate, dextroamphetamine) - norepinephrine and dopamine reuptake inhibitors (e.g. phentermine) - norepinephrine and serotonin reuptake inhibitors (e.g. tramadol) - monoamine oxidase inhibitors (e.g. phenelzine, linezolid) - central monoamine depleting drugs (e.g. reserpine) - non-select beta adrenergic blocking drugs (e.g. labetalol) - alpha agonists or alpha/beta agonists (e.g. pseudoephedrine, phenylephrine, ephedrine, phenylpropanolamine, naphazoline) - tricyclic antidepressants or norepinephrine reuptake inhibitors (e.g. amitriptyline, bupropion, duloxetine, mirtazapine, venlafaxine) - botanicals that may inhibit reuptake of norepinephrine, serotonin or dopamine (e.g. ephedra, ma huang, St. John's Wort, yohimbine) - calcium channel blockers

Calcium Channel Blockers/Dantrolene

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

MECHANISM OF ACTION: The exact mechanism is unknown. Dantrolene may decrease the release of calcium from the sarcoplasmic reticulum, resulting in additive or synergistic effects with calcium channel blockers.(1)

CLINICAL EFFECTS: Concurrent use of dantrolene and calcium channel blockers may result in cardiogenic shock.(2-4)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US, UK, and Australian manufacturers of dantrolene state that concurrent use with calcium channel blockers during the management of malignant hyperthermia crisis is not recommended.(2-4) The Australian and UK manufacturers of diltiazem state that concurrent use of dantrolene infusion with calcium channel blockers is contraindicated.(5-6)

DISCUSSION: Cardiogenic shock in patients treated simultaneously with verapamil and dantrolene is rare but has been reported.(2-4,7) Concurrent use of dantrolene and verapamil in swine has been reported to result in cardiogenic shock and hyperkalemia.(8) In dogs, the combination has been reported to cause hyperkalemia.(9) The combination of diltiazem and dantrolene has been reported to cause adverse cardiovascular effects in swine.(10) A study in swine showed no adverse effects from the combination of dantrolene and nifedipine(10) and one patient who experience cardiogenic shock with dantrolene and verapamil had no adverse effects with the combination of dantrolene and nifedipine;(7) however, the US manufacturer cannot endorse the safety of the combination.(2)

Selected Calcium Channel Blockers/Selected Macrolides

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

MECHANISM OF ACTION: Some macrolides may inhibit metabolism of calcium channel blockers.(1) In some patients, calcium channel blockers may inhibit the metabolism of the macrolide. Some macrolides have been associated with cardiac arrhythmias, including torsades de pointes.(2)

CLINICAL EFFECTS: In some patients, concurrent use may result in elevated levels of and effects from the calcium channel blockers, including hypotension,(2,3) shock,(2) and acute kidney failure.(3) In others, elevated levels of the macrolide may occur, which may increase the risk of sudden death from cardiac causes.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: If possible, avoid the concurrent use of calcium channel blockers with macrolides that inhibit CYP.(1,2) Depending on the infection, azithromycin may be an alternative in patients maintained on calcium channel blockers.(1) If concurrent use is required, monitor patients for and instruct them to report signs of hypotension, cardiac arrhythmias, or renal failure.

DISCUSSION: A retrospective review examined sudden cardiac death in Tennessee Medicaid patients. Erythromycin use increased the risk of sudden cardiac death by 1.79-fold. Concurrent use of erythromycin with a potent inhibitor of CYP3A4 (diltiazem, fluconazole, itraconazole, ketoconazole, troleandomycin, or verapamil) increased the risk of sudden cardiac death by 5.35-fold when compared to patients receiving no antibiotic therapy.(2) In a retrospective review of residents of Ontario, Canada aged 66 or older who were receiving calcium channel blockers, use of clarithromycin and erythromycin were associated with an increased risk of hospitalization for hypotension (odds ratio 3.7 and 5.8, respectively). There was no association between use of azithromycin and hospitalization for hypotension.(2) In a retrospective review of residents of Ontario, Canada aged 65 or older who were receiving calcium channel blockers, use of clarithromycin was associated with an increased risk of hospitalization with acute kidney injury when compared to use of azithromycin (0.44% of patients versus 0.22% - odds ratio 1.98). Risk was highest with the use of nifedipine (odds ratio 5.33). Use of clarithromycin was also associated with a higher risk of hospitalization with hypotension (0.12% of patients versus 0.07%, odds ratio 1.60) and all-cause mortality (1.02% of patients versus 0.59%, odds ratio 1.74).(3) In a cross-over study in 12 healthy male subjects, the administration of a single dose of felodipine (10 mg extended-release) after four doses of erythromycin (250 mg) resulted in an increase in felodipine area-under-curve (AUC), maximum concentration (Cmax), and half-life by 149%, 127%, and 61%, respectively. Concurrent administration increased dehydrofelodipine AUC, Cmax, and half-life by 92%, 56%, and 93%, respectively, when compared to felodipine administration alone. Concurrent administration of felodipine and erythromycin decreased felodipine M3 metabolite AUC and Cmax concentrations by 41% and 36%, respectively. The extent of the interaction was extremely variable between subjects.(4) In a case report, a 43 year-old female developed palpitations, flushing, ankle edema, and hypotension 2-4 days after the addition of erythromycin to felodipine therapy. Felodipine levels were found to be elevated.(5) In a case report, a 77 year-old male developed shock, heart block, and multi-organ failure two days after the addition of clarithromycin to nifedipine therapy.(6) In a case report, a 76 year-old female developed hypotension, bradycardia, shortness of breath, and weakness two days after the addition of telithromycin to verapamil therapy.(7)

Selected Inhibitors Of Cnt Or Ent/Cladribine

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

MECHANISM OF ACTION: Inhibitors of concentrative nucleoside transporters (CNT) or equilibrative nucleoside transporters (ENT) may increase the absorption of cladribine.(1-2)

CLINICAL EFFECTS: The concurrent administration of cladribine with an inhibitor of CNT or ENT may result in elevated levels of cladribine and signs of toxicity.(1-2)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of cladribine states concurrent use of CNT or ENT inhibitors should be avoided during the 4- to 5-day cladribine treatment.(1-2) Selection of an alternative concurrent medication with no or minimal transporter inhibiting proprieties should be considered. If this is not possible, dose reduction to the minimum mandatory dose of the CNT or ENT inhibitor, separation in timing of administration, and careful patient monitoring is recommended.(1-2) Monitor for signs of hematologic toxicity. Lymphocyte counts should be monitored.

DISCUSSION: Cladribine is a substrate of CNT and ENT. Inhibitors of these transporters are expected to increase cladribine levels.(1-2) Nucleoside inhibitors linked to this monograph include: cilostazol, dipyridamole, nifedipine, nimodipine, reserpine, and sulindac.(1-2)

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

Calcium Channel Blockers/Selected Hepatitis C Agents

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

MECHANISM OF ACTION: Boceprevir(1), ombitasvir-paritaprevir-ritonavir,(2) or telaprevir(3) may inhibit the metabolism of calcium channel blockers by CYP3A4.

CLINICAL EFFECTS: Concurrent use of boceprevir, ombitasvir-paritaprevir-ritonavir, or telaprevir may result in elevated levels of and toxicity from calcium channel blockers.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Monitor patients receiving concurrent therapy with either boceprevir, ombitasvir-paritaprevir-ritonavir, or telaprevir and amlodipine for increased calcium channel blocker effects. The dosage of the calcium channel blocker may need to be adjusted(1,3) or an alternative agent considered.(1,3) The US manufacturer of ombitasvir-paritaprevir-ritonavir states that when administered concomitantly with amlodipine the dose of amlodipine should be decreased by at least 50%. Monitor patients for edema and/or signs and symptoms of hypotension. If these events occur, consider further dose reduction of amlodipine or switching to an alternative calcium channel blocker.

DISCUSSION: In a study in 19 healthy subjects, telaprevir (750 mg every 8 hours for 7 days) increased the maximum concentration (Cmax) and area-under-curve (AUC) of a single dose of amlodipine (5mg) by 1.27-fold and 2.79-fold, respectively.(3,4) In an interaction study, 26 healthy subjects were given ombitasvir-paritaprevir-ritonavir and dasabuvir for 24 days. A single dose of amlodipine 5 mg was given on day 1 and 14 of therapy. Amlodipine AUC increased 2.1-fold and the half-life increased from 42 (+ or - 6.7) hours to 104 (+ or - 18) hours.(5)

Diltiazem; Nifedipine; Verapamil/Dronedarone

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

MECHANISM OF ACTION: Dronedarone my inhibit the metabolism of diltiazem, nifedipine, and verapamil by CYP3A4. Diltiazem and verapamil may inhibit the metabolism of dronedarone by CYP3A4. Calcium channel blockers may potentiate dronedarone conduction effects by depressing the sinus and AV nodes.(1)

CLINICAL EFFECTS: Concurrent use may result in elevated levels and effects of both dronedarone and the calcium channel blocker. Calcium channel blockers may also potentiate dronedarone's conduction effects.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Give low initial doses of the calcium channel blockers. The dosage of the calcium channel blocker should only be increased after ECG verification of good tolerability.(1)

DISCUSSION: Concurrent use of diltiazem and verapamil with dronedarone (exact dosages not stated) increased dronedarone exposure by 1.7-fold and 1.4-fold, respectively.(1) Concurrent use of dronedarone with diltiazem, nifedipine, or verapamil (exact dosages not stated) increased exposure of the calcium channel blocker by 1.4-fold to 1.5-fold.(1)

Selected Antihypertensive Agents/Selected Maois

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

MECHANISM OF ACTION: Both MAOIs and antihypertensive agents may increase the risk of postural hypotension.(1,2)

CLINICAL EFFECTS: Postural hypotension may occur with concurrent therapy of MAOIs and antihypertensive agents.(1,2)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The manufacturer of phenelzine states all patients should be followed closely for symptoms of postural hypotension. Hypotensive side effects have occurred in patients who have been hypertensive and normotensive, as well as hypotensive at initiation of phenelzine.(1) The manufacturer of tranylcypromine states hypotension has been observed most commonly but not exclusively in patients with pre-existing hypertension. Tranylcypromine doses greater than 30 mg daily have a major side effect of postural hypotension and can lead to syncope. Gradual dose titration is recommended to decrease risk of postural hypotension. Combined use with other agents known to cause hypotension have shown to have additive side effects and should be monitored closely.(2) Monitor the patient for signs and symptoms of postural hypotension including dizziness, lightheadedness, or weakness, especially upon standing. Monitor blood pressure as well as orthostatic vitals and adjust antihypertensive therapy, including decreasing the dose, dividing doses, or scheduling doses at bedtime, as needed to maintain goal blood pressure. If blood pressure remains hypotensive, consider decreasing the dose of phenelzine or tranylcypromine. In some cases, discontinuation of one or both agents may be necessary.(3) Normotensive patients on stable antihypertensive therapy who are started on either phenelzine or tranylcypromine may be at increased risk for hypotension. Hypertensive patients on stable phenelzine or tranylcypromine who require antihypertensive therapy would be at decreased risk for hypotension.

DISCUSSION: A review article describes the pharmacology of phenelzine and tranylcypromine as non-selective MAOIs which inhibit both type A and type B substrates. Orthostatic hypotension is described as the most common MAOI side effect and usually occurs between initiation and the first 3-4 weeks of therapy.(3) In a double-blind study, 71 patients were randomized to receive a 4-week trial of either tranylcypromine, amitriptyline, or the combination. The number of patients reporting dizziness at 4 weeks was not different between the three treatment groups (tranylcypromine 52.4%; amitriptyline 65%; combination 66.7%). Blood pressure (BP) assessment noted a significant drop in standing BP in the tranylcypromine group compared to baseline (systolic BP change = -10 mmHg; p<0.02 and diastolic BP change = -9 mmHg; p<0.02). Combination therapy also had a significant drop in standing BP compared to baseline (systolic BP change = -9 mmHg; p<0.02). Patients receiving amitriptyline had no significant change in BP from baseline at 4 weeks. All three groups had a trend toward increasing orthostatic hypotension in BP changes from lying to standing. The change in orthostatic hypotension was significant in the amitriptyline group with an average systolic BP orthostatic drop of -9 mmHg (p<0.05).(4) A randomized, double-blind study of 16 inpatients with major depressive disorder were treated with either phenelzine or tranylcypromine. Cardiovascular assessments were completed at baseline and after 6 weeks of treatment. After 6 weeks, 5/7 patients (71%) who received phenelzine had a decrease in standing systolic BP greater than 20 mmHg from baseline. Head-up tilt systolic and diastolic BP decreased from baseline in patients on phenelzine (98/61 mmHg v. 127/65 mmHg, respectively; systolic change p=0.02 and diastolic change p=0.02). After 6 weeks, 6/9 patients (67%) who received tranylcypromine had a decrease in standing systolic BP greater than 20 mmHg from baseline. Head-up tilt systolic and diastolic BP decreased from baseline in patients on tranylcypromine (113/71 mmHg v. 133/69 mmHg, respectively; systolic change p=0.09 and diastolic change p=0.07).(5) Selected MAOIs linked to this monograph include: phenelzine and tranylcypromine. Selected antihypertensive agents include: ACE inhibitors, alpha blockers, ARBs, beta blockers, calcium channel blockers, aprocitentan, clonidine, hydralazine, moxonidine, and sparsentan.

Selected Antihypertensives And Vasodilators/Apomorphine

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

MECHANISM OF ACTION: Apomorphine causes dose-dependent decreases in blood pressure. Concurrent use with antihypertensive agents may result in additive effects on blood pressure.(1)

CLINICAL EFFECTS: Concurrent use of antihypertensives and apomorphine may result in orthostatic hypotension with or without dizziness, nausea, or syncope.(1)

PREDISPOSING FACTORS: The risk of orthostatic hypotension may be increased during dose escalation of apomorphine and in patients with renal or hepatic impairment.(1)

PATIENT MANAGEMENT: Patients receiving concurrent therapy should be monitored for hypotension. Counsel patients about the risk of orthostatic hypotension.(1)

DISCUSSION: Healthy volunteers who took sublingual nitroglycerin (0.4 mg) concomitantly with apomorphine experienced a mean largest decrease in supine systolic blood pressure (SBP) of 9.7 mm Hg and in supine diastolic blood pressure (DBP) of 9.3 mm Hg, and a mean largest decrease in standing SBP and DBP of 14.3 mm Hg and 13.5 mm Hg, respectively. The maximum decrease in SBP and DBP was 65 mm Hg and 43 mm Hg, respectively. When apomorphine was taken alone, the mean largest decrease in supine SBP and DBP was 6.1 mm Hg and 7.3 mm Hg, respectively, and in standing SBP and DBP was 6.7 mm Hg and 8.4 mm Hg, respectively.(1)

Selected Antihypertensives/Tizanidine

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

MECHANISM OF ACTION: Tizanidine is an alpha-2 agonist. Concurrent use with antihypertensive agents may result in additive effects on blood pressure.(1)

CLINICAL EFFECTS: Concurrent use of antihypertensives and tizanidine may result in hypotension.(1)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Patients receiving concurrent therapy should be monitored for hypotension. The risk of hypotension may be decreased by careful titration of tizanidine dosages and monitoring for hypotension prior to dose advancement. Counsel patients about the risk of orthostatic hypotension.(1)

DISCUSSION: Severe hypotension has been reported following the addition of tizanidine to existing lisinopril therapy.(2-4)

Selected Calcium Channel Blockers/Cimetidine

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

MECHANISM OF ACTION: Cimetidine may decrease the metabolism of diltiazem, felodipine, isradipine, nicardipine, nifedipine, nisoldipine, and nitrendipine.

CLINICAL EFFECTS: The pharmacological effects of the calcium channel blocker may be increased.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Observe the patient for changes in clinical response to the calcium channel blocker when starting or stopping cimetidine. The dosage of the calcium channel blocker may need to be adjusted. Ideally, suggest an alternative H-2 antagonist such as famotidine, nizatidine, or ranitidine.

DISCUSSION: Significant effects have been observed during concurrent administration of nifedipine or felodipine with cimetidine. During combined administration of nifedipine and cimetidine in six healthy volunteers, the area-under-curve (AUC) of nifedipine was increased by 80% compared to nifedipine alone. Increased heart rate and a drop in mean arterial pressure 14 mmHg were also reported. Ranitidine showed only a nonsignificant 25% rise in peak plasma levels of nifedipine and no effects on blood pressure. Similar results were reported in another study where concurrent administration of felodipine and cimetidine resulted in an increase in felodipine AUC and maximum concentration (Cmax) by 50%. Concurrent administration of cimetidine has also been shown to increase the AUC and Cmax of diltiazem by 53% and 58%, respectively. The manufacturers of isradipine and nicardipine recommend carefully monitoring patients receiving concurrent therapy with cimetidine. The manufacturer of isradipine states that concurrent therapy with cimetidine has been shown to increase the AUC of isradipine by 50%. The manufacturer of nifedipine states that careful titration is necessary in patients receiving concurrent therapy. The manufacturers of felodipine and diltiazem state that dosage adjustments may be necessary in patients receiving concurrent therapy. Ranitidine has much less affinity for CYP metabolism than cimetidine and would therefore be expected to have less of an effect on calcium channel blocker metabolism. Studies have shown that nizatidine and famotidine do not inhibit CYP3A4 metabolism.

Selected Calcium Channel Blockers/Digoxin

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

MECHANISM OF ACTION: Calcium channel blockers may inhibit the renal clearance of digoxin through an unknown mechanism.

CLINICAL EFFECTS: Plasma digoxin concentrations may be elevated. In addition, the negative chronotropic effects of digoxin and bepridil are additive, resulting in a cumulative decrease in heart rate. Symptoms of digoxin toxicity can include anorexia, nausea, vomiting, headache, fatigue, malaise, drowsiness, generalized muscle weakness, disorientation, hallucinations, visual disturbances, and arrhythmias.

PREDISPOSING FACTORS: Low body weight, advanced age, impaired renal function, hypokalemia, hypercalcemia, and/or hypomagnesemia may increase the risk of digoxin toxicity.

PATIENT MANAGEMENT: If concurrent therapy is warranted, monitor serum digoxin levels and observe the patient for symptoms of digoxin toxicity. Upon adding a calcium channel blocker, digoxin should first be decreased in anticipation of interaction, then adjust the dosage accordingly. The dosage of digoxin may need to be decreased by 15-50% or the frequency of administration may be reduced.

DISCUSSION: The effect of bepridil on steady-state serum digoxin levels was studied in a randomized, double-blind investigation. Concurrent administration of bepridil and digoxin produced a 34% increase in serum digoxin levels compared to administration of digoxin alone. Concomitant administration of both drugs was associated with additive negative chronotropic effects. Information on the effects of diltiazem on digoxin concentrations are conflicting. Several studies have reported that concurrent use of digoxin and diltiazem led to an increased steady state digoxin level as well as an increased digoxin area-under-curve (AUC) and decreased renal clearance, and reduced volume of distribution. However, one of these studies reported no significant change in digoxin half-life, peak concentration (Cmax), time to Cmax (Tmax), or volume of distribution, and seven other studies reported no effect of diltiazem on serum digoxin concentrations or renal digoxin clearance. Concomitant isradipine administration significantly decreased (by 9%) the the digoxin volume of distribution and increased (by 25%) digoxin Cmax; however, the digoxin steady state serum concentration, AUC, and renal clearance were not affected. In patients with congestive heart failure on digoxin therapy, the addition of felodipine resulted in a significant increase in digoxin Cmax attained following oral administration. This increase was most notable in patients with high felodipine serum concentrations. Digoxin trough levels and six hour post-dose levels were unaffected; as were digoxin AUC measurements. There is one case report of an interaction between nifedipine and digoxin; however, a study in 28 patients found no effect of nifedipine on digoxin. A study in ten subjects showed that nisoldipine increased digoxin levels by 15%. Information on the effects of nicardipine on digoxin kinetics is conflicting. One study in twenty patients showed no effect of nicardipine on digoxin. One study in ten subjects showed a significant increase in digoxin levels: however, this was seen in only one subject. Concurrent nitrendipine has been shown to increase digoxin serum levels by 57% and digoxin AUC by 15%. Concurrent diltiazem has been shown to increase digoxin serum concentration by 20%. Concurrent nifedipine has been shown to increase digoxin serum concentration by 45%.

Selected Calcium Channel Blockers/Labetalol

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

MECHANISM OF ACTION: Both labetalol and calcium channel blockers have negative inotropic and chronotropic effects.

CLINICAL EFFECTS: Concurrent use of labetalol with calcium channel blockers may result in additive cardiovascular effects.

PREDISPOSING FACTORS: Preexisting left ventricular dysfunction and high doses of the beta-blocking agent may predispose patients to adverse responses to this drug combination. Other possible factors include parenteral administration and concurrent administration of other cardio-depressant drugs such as antiarrhythmics.

PATIENT MANAGEMENT: The concurrent use of labetalol and calcium channel blockers should be monitored closely for signs of increased cardio-depressant effects and hypotension. Adjust the dose of one or both medicines accordingly.

DISCUSSION: Concurrent use of labetalol with calcium channel blockers may result in additive cardiovascular effects. Coadministration of these classes of drugs may be effective in the treatment of angina pectoris and hypertension. Patients should be screened in order to determine who should receive this combination of agents.

Selected Calcium Channel Blockers/Nirmatrelvir-Ritonavir

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

MECHANISM OF ACTION: Nirmatrelvir-ritonavir may inhibit the metabolism of calcium channel blockers by CYP3A4.(1,2)

CLINICAL EFFECTS: Concurrent use of nirmatrelvir-ritonavir may result in elevated levels of and toxicity from calcium channel blockers.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Concurrent use of nirmatrelvir-ritonavir and selected calcium channel blockers should be approached with caution. Monitor patients receiving concurrent therapy with nirmatrelvir-ritonavir and either amlodipine, diltiazem, felodipine, nicardipine, nifedipine, or verapamil for increased calcium channel blocker effects. The dosage of the calcium channel blocker may need to be adjusted.(1,2) The Journal of American College of Cardiology recommends a 50% reduction in the dose amlodipine for 8 days with the initiation of nirmatrelvir-ritonavir. Close monitoring of blood pressure and dose reduction or temporary discontinuation of calcium channel blockers may be needed. Resume calcium channel blockers 3 days after the last dose of nirmatrelvir-ritonavir.(3)

DISCUSSION: Nirmatrelvir-ritonavir is a strong CYP3A4 inhibitor and may increase the levels of calcium channel blockers that are CYP3A4 substrates.(1,2) In a case report of a 80-year old female on verapamil, on day 2 of concurrent nirmatrelvir-ritonavir the patient presented to the hospital with symptomatic bradycardia (heart rate of 28 beats per minute and blood pressure of 58/35 mmHg) requiring hospitalization, medical management, and a temporary transvenous pacer.(4)

Selected Calcium Channel Blockers/Selected Beta-Blockers

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

MECHANISM OF ACTION: Synergistic pharmacologic activity.

CLINICAL EFFECTS: May see an increase in the therapeutic and toxic effects of both drugs. Concurrent use in patients with low heart rates may unmask sick sinus syndrome.

PREDISPOSING FACTORS: Preexisting left ventricular dysfunction and high doses of the beta-blocking agent may predispose patients to adverse responses to this drug combination. Other possible factors include parenteral administration and concurrent administration of other cardio-depressant drugs such as antiarrhythmics.

PATIENT MANAGEMENT: Monitor the patient for signs of increased cardio-depressant effects and hypotension. Adjust the dose accordingly.

DISCUSSION: Coadministration of these classes of drugs may be effective in the treatment of angina pectoris and hypertension. Patients should be screened in order to determine who should receive this combination of agents. The concurrent use of mibefradil and beta-blockers in patients with low heart rates may unmask underlying sick sinus syndrome. One or more of the drug pairs linked to this monograph have been included in a list of interactions that could be considered for classification as "non-interruptive" in EHR systems. This DDI subset was vetted by an expert panel commissioned by the U.S. Office of the National Coordinator (ONC) for Health Information Technology.

Selected Calcium Channel Blockers/Slt Strong Cyp3a4 Inhibit

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

MECHANISM OF ACTION: Strong CYP3A4 inhibitors may inhibit the first-pass and elimination metabolism of calcium channel blockers by CYP3A4.

CLINICAL EFFECTS: The concurrent use of strong CYP3A4 inhibitors with calcium channel blockers metabolized by CYP3A4 may result in elevated levels of the calcium channel blocker and risk of adverse effects, including hypotension and bradycardia.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The concurrent use of strong CYP3A4 inhibitors with calcium channel blockers should be approached with caution. When these agents are used concurrently, the dose of the calcium channel blocker may need to be adjusted or an alternative agent considered. Monitor patients for increased calcium channel blocker effects. If the strong CYP3A4 inhibitor is discontinued, the dose of the calcium channel blocker may need to be increased and patients should be observed for decreased effects.

DISCUSSION: A double-blind, randomized, two-phase crossover study in nine subjects examined the effects of itraconazole on felodipine. The half-life of felodipine increased by 71% during concurrent itraconazole. In seven of the nine subjects, the maximum concentration (Cmax) of felodipine when administered with placebo was lower than the 32-hour concentration of felodipine when administered with itraconazole. Concurrent use also resulted in significantly greater effects on both blood pressure and heart rate.(10,11) A randomized cross-over trial in seven subjects examined the effects of ketoconazole (200 mg daily for 4 days) on nisoldipine (5 mg daily). The concurrent use of ketoconazole increased the nisoldipine area-under-curve (AUC) and Cmax by 24-fold and 11-fold, respectively. Increases in the M9 nisoldipine metabolite were similar.(7) PKPB modeling of nifedipine and ritonavir noted a decreased systolic blood pressure > 40 mmHg.(8) There are several case reports of patients developing increased levels of calcium channel blockers and adverse effects with concurrent strong CYP3A4 inhibitors.(9-16) Strong CYP3A4 inhibitors include: adagrasib, ceritinib, cobicistat, ensitrelvir, grapefruit, idelalisib, indinavir, itraconazole, ketoconazole, levoketoconazole, lopinavir, mibefradil, mifepristone, nefazodone, nelfinavir, posaconazole, relacorilant, ribociclib, saquinavir, tipranavir, troleandomycin, tucatinib, and voriconazole.(17,18)

Selected Calcium Channel Blockers/Tacrolimus

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

MECHANISM OF ACTION: Some calcium channel blockers may inhibit the metabolism of tacrolimus by CYP3A4.(1-13)

CLINICAL EFFECTS: Concurrent use of calcium channel blockers may result in elevated levels of and side effects from tacrolimus, including nephrotoxicity, neurotoxicity, and prolongation of the QTc interval and life-threatening cardiac arrhythmias, including torsades de pointes.(1-13)

PREDISPOSING FACTORS: The risk of QT prolongation or torsade de pointes may be increased in patients with cardiovascular disease (e.g. heart failure, myocardial infarction, history of torsade de pointes, congenital long QT syndrome), hypokalemia, hypomagnesemia, hypocalcemia, bradycardia, female gender, or advanced age. Concurrent use of more than one drug known to cause QT prolongation or higher systemic concentrations of either QT prolonging drug are additional risk factors for torsade de pointes. Factors which may increase systemic drug concentrations include rapid infusion of an intravenous dose or impaired metabolism or elimination of the drug (e.g. coadministration with an agent which inhibits its metabolism or elimination, and/or renal/hepatic dysfunction).

PATIENT MANAGEMENT: Patients maintained on tacrolimus should be closely monitored if calcium channel blockers such as amlodipine, diltiazem, felodipine, nifedipine, or verapamil are initiated or discontinued. The dosage of tacrolimus may need to be adjusted or the calcium channel blocker may need to be discontinued. When concurrent therapy of selected calcium channel blockers and tacrolimus is warranted, consider obtaining serum calcium, magnesium, and potassium levels and monitoring ECG at baseline and at regular intervals. Correct any electrolyte abnormalities. Instruct patients to report any irregular heartbeat, dizziness, or fainting.

DISCUSSION: A study of 9 healthy volunteers who are CYP3A5 expressers found that concomitant tacrolimus and amlodipine resulted in increased tacrolimus AUC by 2.44-fold and 4.1-fold in a single-dose and a 7-day multi-dose study, respectively, compared to tacrolimus alone. No interaction was observed in CYP3A5 non-expressers.(2) However, a case report of a 4-year-old renal transplant patient who is a CYP3A5 non-expresser on tacrolimus and started on amlodipine described increased tacrolimus trough level and AUC from 3.7 to 12.2 ng/mL and 211 to 638 h/ng/mL, respectively.(3) A non-randomized study in 2 liver and 2 renal transplant recipients examined the effects of diltiazem on tacrolimus. In the 2 kidney recipients, concurrent diltiazem at a dosage of 20 mg daily increased tacrolimus AUC by 26% and by 67%. Diltiazem at a dosage of 180 mg increased tacrolimus AUC by 48% and by 177%. In the 2 liver recipients, no tacrolimus increases were seen until diltiazem dosage reached 60 mg daily. One subject received 120 mg of diltiazem daily and tacrolimus AUC was increased by 18%. The other subject received 180 mg diltiazem daily and tacrolimus AUC increased 22%.(4) There is one case report of elevated tacrolimus levels and toxicity in a liver transplant patient 3 days after the addition of diltiazem to his regimen.(5) There is one case report of elevated tacrolimus levels in a renal transplant patient.(6) In contrast, a retrospective review of renal transplant patients found no difference in tacrolimus-related side effects or tacrolimus exposure in patients treated with diltiazem versus those not treated with diltiazem.(7) There is one report of increased tacrolimus levels with concurrent felodipine in a renal transplant patient.(8) A retrospective review examined the effects of nifedipine on tacrolimus dosing requirements in renal transplant patients. In patients who received concurrent nifedipine (n=22), tacrolimus daily dosing requirements were 26%, 29%, and 38% lower at 3, 6, and 12 months post-transplant when compared to patients not taking nifedipine (n=28).(9) In a study of liver transplant patients, nifedipine improved kidney function as indicated by lowering of serum creatinine levels at 6 and 12 months.(10) In vitro studies in human tissue found that tacrolimus metabolism was inhibited by nifedipine and verapamil.(12,13)

Slt Calcium Channel Blockers/Atazanavir;Darunavir;Fosampren

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

MECHANISM OF ACTION: Atazanavir, darunavir, and fosamprenavir may inhibit the CYP3A4-mediated metabolism of calcium channel blockers.(1-5)

CLINICAL EFFECTS: Concurrent use of atazanavir, darunavir, or fosamprenavir may result in increased levels of calcium channel blockers. The combination of atazanavir with non-dihydropyridines may result in an additive effect on the PR interval.(1-2,6-7)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: The US Department of Health and Human Services HIV guidelines recommend that concurrent use of calcium channel blockers with protease inhibitors be monitored closely. The dose of the calcium channel blocker should be titrated to clinical response and adverse events.(5) Additional recommendations apply to patients on atazanavir. EKG monitoring is recommended for patients on concurrent therapy with calcium channel blockers. A dose reduction of diltiazem by 50% should be considered for patients starting atazanavir.(1,2,5)

DISCUSSION: In a study in 28 subjects, concurrent atazanavir (400 mg daily) with diltiazem (180 mg daily) increased the diltiazem area-under-curve (AUC) and maximum concentration (Cmax) by 225% and 98%, respectively.(1,2) Diltiazem minimum concentration (Cmin) increased by 242%. The Cmax, AUC, and Cmin of desacetyl-diltiazem increased by 272%, 265%, and 221%, respectively. There were no significant effects on atazanavir levels.(1)

*Hypersensitivity to nifedipine or any component of the formulation.

*Cardiogenic shock.

*Concomitant administration with strong cytochrome P-450 (CYP) inducers (e.g., rifampin).

• Cardiogenic shock
• Kock pouch
• Severe hypotension

• Acute coronary syndrome
• Acute myocardial infarction
• Chronic idiopathic constipation
• Gastrointestinal obstruction
• Hypotension
• Intestinal stenosis
• Myasthenia gravis
• Porphyria
• Severe aortic valve stenosis

• Chronic heart failure
• Disease of liver
• Gastrointestinal hypomotility
• Kidney disease with reduction in glomerular filtration rate (GFr)
• Peripheral edema
• Porphyria

The most common adverse effects reported with nifedipine in clinical studies were peripheral edema, dizziness/lightheadedness, flushing/heat sensation, headache, tremor, nervousness, mood changes, weakness, fatigue/asthenia, muscle cramps, nausea, heartburn, constipation, palpitation, dyspnea, cough, wheezing, nasal congestion, and sore throat.

Less Frequent

• Allergic dermatitis
• Hypotension
• Pulmonary edema

Rare or Very Rare

• Abnormal hepatic function tests
• Acute eruptions of skin
• Acute eruptions of skin
• Acute myocardial infarction
• Allergic dermatitis
• Anaphylaxis
• Anemia
• Angioedema
• Arthralgia
• Arthralgia
• Atrial fibrillation
• Bradycardia
• Bullous dermatitis
• Cellulitis
• Chronic heart failure
• Chronic heart failure
• Erythema multiforme
• Exfoliative dermatitis
• Gastrointestinal concretion
• Gastrointestinal obstruction
• Gastrointestinal ulcer
• Gingival hyperplasia
• Gingival hyperplasia
• Hepatitis
• Jaundice
• Kidney stone
• Leukopenia
• Maculopapular rash
• Progressive angina pectoris
• Purpura
• Purpura
• Severe hypotension
• Skin rash
• Skin rash
• Stevens-johnson syndrome
• Stevens-johnson syndrome
• Tachycardia
• Thrombocytopenic disorder
• Toxic epidermal necrolysis
• Toxic epidermal necrolysis
• Transient blindness

More Frequent

• Dizziness
• Flushing
• General weakness
• Headache disorder
• Headache disorder
• Nausea
• Peripheral edema
• Peripheral edema

Less Frequent

• Constipation
• Constipation
• Cough
• Cramps in legs
• Cramps in legs
• Diarrhea
• Dizziness
• Dyspnea
• Epistaxis
• Erectile dysfunction
• Erectile dysfunction
• Fatigue
• Fever
• Flushing
• General weakness
• Hyperhidrosis
• Increased urinary frequency
• Joint stiffness
• Mood changes
• Nausea
• Nervousness
• Palpitations
• Paresthesia
• Paresthesia
• Pruritus of skin
• Rhinitis
• Rhinitis
• Sleep disorder
• Urticaria

Rare or Very Rare

• Acute cognitive impairment
• Anticholinergic toxicity
• Anticholinergic toxicity
• Arthritis
• Breast engorgement
• Chills
• Depression
• Drowsy
• Dyspepsia
• Dysphagia
• Dysuria
• Eosinophilia
• Eructation
• Erythromelalgia
• Esophagitis
• Facial edema
• Flatulence
• Gout
• Gynecomastia
• Hyperglycemia
• Hypertonia
• Hypoesthesia
• Hypotension
• Increased urinary frequency
• Insomnia
• Insomnia
• Libido changes
• Lymphadenopathy
• Muscle weakness
• Myalgia
• Nocturia
• Palpitations
• Pharyngitis
• Phlebitis
• Phototoxicity
• Phototoxicity
• Polyuria
• Rales
• Stridor
• Symptoms of anxiety
• Syncope
• Telangiectasia
• Visual changes
• Visual changes
• Weight loss
• Xerostomia

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Although safety and efficacy remain to be fully established in pediatric patients younger than 18 years of age, some experts have recommended pediatric dosages for hypertension based on clinical experience.

There are no adequate and well-controlled studies using nifedipine in pregnant women, and the drug should be used during pregnancy only when the potential benefits justify the possible risks to the fetus.

Nifedipine has been shown to be teratogenic in rats and rabbits. Digital anomalies similar to those reported with phenytoin also have been reported in the offspring of animals receiving other dihydropyridines; these anomalies may occur secondary to compromised uterine blood flow. Nifedipine administration in rats, mice, rabbits, and monkeys also has been associated with a variety of other embryotoxic, placentotoxic, and fetotoxic effects, including stunted fetuses (rats, mice, and rabbits), rib deformities (mice), cleft palate (mice), small placentas and underdeveloped chorionic villi (monkeys), embryonic and fetal deaths (rats, mice, and rabbits), and prolonged pregnancy/decreased neonatal survival (rats; not evaluated in other species). The dosages (on a mg/kg basis) of nifedipine associated with teratogenic, embryotoxic, or fetotoxic effects in animals were higher (5-50 times) than the maximum recommended human dosage (120 mg daily); however, such dosages were within one order of magnitude of the maximum recommended human dosage. The dosages of nifedipine associated with placentotoxic effects in monkeys were equivalent to or lower than the maximum recommended human dosage on a mg/m2 basis.

From the clinical evidence available, a specific prenatal risk has not been identified. However, an increase in perinatal asphyxia, caesarean delivery, prematurity, and intrauterine growth retardation has been reported.

Monitor blood pressure carefully when administering nifedipine in combination with IV magnesium sulfate in pregnant women due to the possibility of an excessive fall in blood pressure, which could harm the mother and fetus.

Nifedipine is distributed into milk. In one lactating woman who received 10, 20, and 30 mg of the drug every 8 hours as conventional capsules, peak milk concentrations of nifedipine occurred within 1 hour after a dose and ranged from about 13-53 ng/mL; the drug generally was not detectable during the hour prior to a dose. Because of the potential for serious adverse reactions to nifedipine in nursing infants, a decision should be made whether to discontinue nursing or the drug, taking into account the importance of the drug to the woman.

Increased nifedipine exposure has been observed in pharmacokinetic studies in small numbers of geriatric patients; however, clinical experience generally has not revealed age-related differences in response or tolerance. The greater frequency of decreased hepatic, renal, and/or cardiac function and of concomitant disease and drug therapy observed in geriatric patients should be considered; initiate therapy at the low end of the dosage range and adjust dosage as necessary based on patient response.

Although a prolonged elimination half-life and an increase in peak plasma concentration and AUC have been observed in pharmacokinetic studies in small numbers of patients, clinical studies of nifedipine did not include sufficient numbers of patients 65 years of age and older to determine whether geriatric patients respond differently than younger adults. While other clinical experience generally has not revealed age-related differences in response or tolerance, drug dosage generally should be titrated carefully in geriatric patients, usually initiating therapy at the low end of the dosage range and adjusting dosage as necessary based on patient response. The greater frequency of decreased hepatic, renal, and/or cardiac function and of concomitant disease and drug therapy observed in geriatric patients also should be considered.

Following oral administration of coat-core (CC) extended-release nifedipine tablets in healthy geriatric individuals (older than 60 years of age), the mean peak plasma concentrations and average plasma concentrations of nifedipine were 36 and 70% higher, respectively, compared with those observed in younger adults.