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# Folic Acid ## Overview Folic acid (vitamin B9) is essential for DNA synthesis, repair, and methylation, as well as red blood cell formation. It is a water-soluble vitamin. ## Primary Indications * Treatment and prevention of folic acid deficiency anemia. * Prevention of neural tube defects (NTDs) in pregnancy. * Adjunct in certain hematologic conditions and as an antidote for folate antagonists. ## Adult Dosing * **Folic acid deficiency anemia:** 1 mg daily. Some sources recommend up to 5 mg daily in severe deficiency. * **Prevention of NTDs (pre-conception and during pregnancy):** 400 mcg (0.4 mg) daily. Women with a history of NTDs or on certain medications (e.g., anticonvulsants) may require higher doses (e.g., 4 mg daily) as per physician guidance. * **Megaloblastic anemia due to folate deficiency:** 1 mg to 5 mg daily. * **Adjunct therapy for methotrexate toxicity:** Dosing varies widely based on the methotrexate regimen and local protocol. ## Pediatric Dosing * **Folic acid deficiency anemia:** * 0 to 1 year: 50 mcg (0.05 mg) daily. * 1 to 12 years: 1 mg daily. * **Prevention of NTDs:** 400 mcg (0.4 mg) daily for women of childbearing potential. ## Dose Adjustments No specific dose adjustments are generally required for renal or hepatic impairment, though caution is advised in severe cases. ## Contraindications * Uncorrected vitamin B12 deficiency (folic acid can mask the hematologic signs of B12 deficiency, allowing neurological damage to progress). * Hypersensitivity to folic acid or any component of the formulation. ## Adverse Effects Generally well-tolerated. * **Gastrointestinal:** Nausea, bloating, abdominal distension, unpleasant taste. * **Hypersensitivity:** Rash, pruritus, bronchospasm, erythema, malaise. ## Key Drug Interactions * **Anticonvulsants (e.g., phenytoin, phenobarbital, primidone):** Folic acid may decrease serum levels of these drugs, potentially leading to loss of seizure control. * **Sulfasalazine:** May interfere with folate absorption. * **Methotrexate:** Folic acid is used as an antidote for methotrexate toxicity, but timing and dosing are critical. * **Trimethoprim:** Can inhibit dihydrofolate reductase, potentially increasing folate requirements. ## Monitoring * Monitor complete blood count (CBC) and peripheral blood smear to assess response to therapy. * In patients with suspected vitamin B12 deficiency, serum vitamin B12 levels should be assessed before initiating folic acid therapy. * Monitor for signs and symptoms of hypersensitivity reactions. ## Clinical Pearls * Folic acid is essential for preventing NTDs. All women of childbearing potential should receive adequate folic acid intake. * Do not use folic acid to treat undiagnosed megaloblastic anemia, as it may mask a vitamin B12 deficiency. * Oral administration is typically effective unless malabsorption is present. *** **Disclaimer:** This information is intended for clinical pharmacists and healthcare professionals. It is crucial to consult the most current official prescribing information and relevant clinical guidelines for comprehensive and up-to-date details before making any treatment decisions. Dosing and indications may vary based on specific patient factors, local protocols, and evolving medical knowledge.