B Complex-Vitamin C-Folic Acid (folic acid/vitamin B complex and vitamin C)

Dosage of folic acid injection (sodium folate) is expressed in terms of folic acid. In general, although patient response to folic acid therapy depends on the degree and nature of the deficiency, once proper corrective measures are undertaken, folate-deficient patients generally respond rapidly. During the first 24 hours of treatment, the patient experiences an improved sense of well-being, and within 48 hours, the bone marrow begins to become normoblastic. Reticulocytosis generally begins within 2-5 days following initiation of folic acid therapy.

Ascorbic acid is usually administered orally. When oral administration is not feasible or when malabsorption is suspected, the drug may be administered IM, IV, or subcutaneously. When given parenterally, utilization of the vitamin reportedly is best after IM administration and that is the preferred parenteral route.

Folic acid is usually administered orally. When oral administration is not feasible or when malabsorption is suspected, the drug may be administered by deep IM, subcutaneous, or IV injection. However, most patients with malabsorption are able to absorb oral folic acid.

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Concurrent administration of more than 200 mg of ascorbic acid per 30 mg of elemental iron increases absorption of iron from the GI tract; however, most individuals are able to absorb orally ingested iron adequately without concurrent administration of ascorbic acid.

Increased urinary excretion of ascorbic acid and decreased excretion of aspirin occur when the drugs are administered concurrently.

Salicylates inhibit uptake of ascorbic acid by leukocytes and platelets. As a result, leukocyte and plasma concentrations of ascorbic acid are decreased to concentrations slightly higher than those associated with tissue depletion of the vitamin; however, there is no evidence to date that salicylate therapy precipitates ascorbic acid deficiency. Although concomitant administration of ascorbic acid supplements in patients receiving salicylates increases plasma ascorbic acid concentrations, leukocyte ascorbic acid concentrations are not increased and tissue stores of the vitamin may not be increased. Therefore, routine administration of ascorbic acid supplements to patients receiving salicylates is not warranted; however, patients receiving high dosages of salicylates who exhibit any signs or symptoms of ascorbic acid deficiency should be evaluated for such a deficiency.

Ascorbic acid has reportedly decreased the anticoagulant effect of warfarin; however, other investigators have failed to show this effect. Concurrent administration of ascorbic acid and fluphenazine reportedly resulted in decreased fluphenazine plasma concentration. Acidification of the urine following administration of ascorbic acid may result in altered excretion of other drugs.

In folate-deficient patients, folic acid therapy may increase phenytoin metabolism, resulting in decreased phenytoin serum concentrations. Although this interaction is not usually clinically important, an increase in seizure frequency may occur in some patients.

It has been reported that concurrent administration of chloramphenicol and folic acid in folate-deficient patients may result in antagonism of the hematopoietic response to folic acid. Although the importance and mechanism of the interaction is unclear, the hematologic response to folic acid in patients receiving both drugs should be carefully monitored.

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

Pyridoxine/Altretamine

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: The mechanism by which pyridoxine adversely affects response duration while coadministering altretamine is not known at this time and requires further investigation.

CLINICAL EFFECTS: The coadministration of oral pyridoxine with chemotherapy regimens consisting of oral altretamine adversely affected response duration.(1,2)

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Although pyridoxine administration significantly reduces the neurotoxicity associated with altretamine, it should not be administered with altretamine due to its adverse effect on response duration.(1,2)

DISCUSSION: In a study, 248 patients with Stages III-IV ovarian epithelial cancer were randomized to one of four cisplatin and altretamine regimens. In each regimen, oral altretamine (200 mg/m2 daily) was administered on days 8-21. In addition, intravenous cisplatin was administered on day 1 (37.5 mg/m2, regimens A and B, or 75 mg/m2, regimens C and D). Oral pyridoxine (300 mg/m2 daily, days 1-21) was added to regimens B and D. While pyridoxine did decrease neurologic toxicity and had no effect on response, pyridoxine was found to adversely affect response duration in all patients. This effect was the greatest in previously untreated patients. In addition, pyridoxine had a slight negative effect on failure-free survival in previously untreated patients.(1)

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

Folic Acid/Fluorouracil & Fluorouracil Prodrugs

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

MECHANISM OF ACTION: Folic acid has been shown to enhance both the therapeutic and toxic effects of fluoropyrimidines, such as 5-fluorouracil (5-FU) and fluorouracil prodrugs.(1-3) Fluorouracil prodrugs include capecitabine and tegafur.

CLINICAL EFFECTS: Folic acid, when used concurrently with 5-FU or fluorouracil prodrugs, has been shown to increase side effects of 5-FU.(1-3)

PREDISPOSING FACTORS: Patients who are intermediate or poor dihydropyrimidine dehydrogenase (DPYD) metabolizers have diminished or no DPYD function. Since DPYD is the rate-limiting enzyme involved in fluoropyrimidine metabolism, these patients may be more susceptible to the effects of this interaction.(3)

PATIENT MANAGEMENT: Folic acid or folate analog-containing products should not be used concurrently with fluorouracil or fluorouracil prodrugs unless directed by the healthcare provider.(1-3) Fluorouracil prodrugs include capecitabine and tegafur.

DISCUSSION: Due to increased toxic effects, stomatitis and diarrhea are observed more commonly, may be more severe, and may occur for a prolonged duration when compared to therapy with 5-FU alone. It is postulated that the lower standard dose of 5-FU in the US versus other regions may be due to increased folic acid supplementation within the US food supply.(2) In a cohort study in 290 patients, the use of dietary supplements with folic acid during treatment compared to nonuse increased the risk of capecitabine toxicities (HR 1.81, 95%CI: 1.15,2.85). The detection of folic acid in plasma also increased the risk of capecitabine toxicities (HR 2.09, 95%CI: 1.24,3.52 and HR 2.31, 95%CI: 1.29,4.13 at diagnosis and during treatment, respectively).(4) In a cohort study of 9 patients, patients taking folate-containing supplements and higher serum folate levels had an increased risk of grade >=2 toxicity. The risk of grade >=2 toxicity increased by 9% for every increase in serum folate level by 10 nmol/L. Patients with grade >=2 toxicity had higher serum folate levels than patients with grade <= 1 toxicity (28 nmol/L [range, 13.2-45.4] vs. 20 nmol/L [range, 12.8-45.4]; p=0.001).(5) In two case reports, patients developed capecitabine toxicity while taking supplements containing folic acid 400-500 mcg.(6) In a case report, a woman developed grade 4 diarrhea, grade 3 vomiting, and grade 3 hand-foot syndrome 8 days after the addition of capecitabine (2500 mg/m2/day) to high-dose folic acid supplementation. She developed necrotic colitis and died, despite the discontinuation of folic acid and capecitabine.(7) There are two other reports of excessive fluorouracil toxicity in patients treated with folic acid.(8)

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

Folic Acid/Pafolacianine

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

MECHANISM OF ACTION: Folate, folic acid, and folate-containing supplements may reduce binding of pafolacianine to folate receptors expressed on ovarian cancer cells.

CLINICAL EFFECTS: Folate, folic acid, and folate-containing supplements could reduce the detection of malignant lesions with pafolacianine.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid administration of folate, folic acid, or folate-containing supplements within 48 hours before administration of pafolacianine.

DISCUSSION: Folate, folic acid, and folate-containing supplements may reduce binding of pafolacianine to folate receptors expressed on cancer cells, which could result in reduced detection of malignant lesions with pafolacianine.

Folic Acid; Pyrimethamine/Hydantoins

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

MECHANISM OF ACTION: Unknown, but probably involves altered metabolism of the hydantoin.

CLINICAL EFFECTS: May observe decreased effectiveness of hydantoin, resulting in loss of seizure control.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: If both drugs are administered, monitor both the hydantoin plasma levels as well as the seizure control of the patient. Adjust the dose of hydantoin accordingly.

DISCUSSION: The effects of an interaction are not expected to occur in the majority of patients. Discontinuation of folic acid has caused phenytoin levels to increase in patients who experienced a decrease in phenytoin levels when folic acid was started. Monitor these patients for hydantoin toxicity. Signs and symptoms of hydantoin toxicity include ataxia, nystagmus and involuntary movements.

Pyridoxine/Levodopa

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

MECHANISM OF ACTION: Pyridoxine increases levodopa metabolism, decreasing the amount of levodopa available to the central nervous system.

CLINICAL EFFECTS: The pharmacologic effects of levodopa may be decreased.

PREDISPOSING FACTORS: None determined.

PATIENT MANAGEMENT: Avoid pyridoxine in patients receiving levodopa alone; however, the interaction can be minimized by giving levodopa with a peripheral decarboxylase inhibitor (e.g. carbidopa, benserazide). Treatment with combination carbidopa-levodopa may contribute to reduced vitamin B6 levels. Higher doses of carbidopa-levodopa may increase the risk of vitamin B6 deficiency. Seizures associated with vitamin B6 deficiency have been reported in the postmarketing setting. In patients taking combination therapy with carbidopa/levodopa, evaluate vitamin B6 levels periodically while on treatment or if symptoms associated with vitamin B6 deficiency are identified. Supplement with vitamin B6 as necessary.

DISCUSSION: In patients with Parkinson's disease, as little as 10 mg of pyridoxine may reverse the clinical benefits as well as the adverse effects of levodopa. Coadministration of levodopa with either carbidopa or benserazide has minimized the effects of this interaction.

There is no enhanced messaging for this drug.

There are no contraindication contraindications for this drug.

There are no severe contraindications for this drug.

• No disease contraindications

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Rare or Very Rare

• Bronchospastic pulmonary disease
• Concentration difficulty

Rare or Very Rare

• Abdominal distension
• Acute cognitive impairment
• Anorexia
• Depression
• Dysgeusia
• Erythema
• Excitement
• Flatulence
• Irritability
• Malaise
• Nausea
• Pruritus of skin
• Skin rash
• Sleep disorder

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