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# Folic Acid ## Overview Folic acid (vitamin B9) is a water-soluble B vitamin essential for DNA synthesis, repair, and erythropoiesis. It is vital for rapid cell division and growth. ## Primary Indications * Folic acid deficiency (megaloblastic/macrocytic anemia). * Prevention of neural tube defects (NTDs) in pregnancy. * Prophylaxis in chronic hemolytic anemias or patients on dialysis. * Adjunct therapy with methotrexate (to reduce gastrointestinal and hematologic toxicity). ## Adult Dosing * **Deficiency:** 1 mg daily. Severe cases may require up to 5 mg daily. * **Maintenance (Chronic Hemolysis/Dialysis):** 1 mg daily. * **Pregnancy (Prevention of NTDs):** 0.4–0.8 mg daily. High-risk patients (history of NTD-affected pregnancy): 4 mg daily. * **Methotrexate Adjunct:** 1–5 mg daily (or 5–10 mg weekly following the methotrexate dose, depending on institutional protocols). ## Pediatric Dosing * **Deficiency:** * Infants: 0.1 mg daily. * Children/Adolescents: 0.5–1 mg daily. * **Maintenance:** 0.1–0.5 mg daily. * *Note: Ensure child-appropriate formulations are used to prevent overdose.* ## Dose Adjustments * **Renal Impairment:** No specific adjustment required; however, patients on hemodialysis require supplementation due to dialysis clearance. * **Hepatic Impairment:** No standard adjustment required. ## Contraindications * Hypersensitivity to folic acid. * Undiagnosed anemia (specifically pernicious anemia/B12 deficiency). Folic acid can correct hematologic indices while allowing irreversible neurological damage from B12 deficiency to progress. ## Adverse Effects * Rare at standard doses. * High doses (>15 mg/day) may cause GI disturbances (nausea, abdominal distension), unpleasant taste, sleep disturbances, or rash. ## Key Drug Interactions * **Methotrexate:** Folic acid may decrease the efficacy of methotrexate in oncology; timed dosing is critical in non-oncology indications. * **Anticonvulsants (Phenytoin, Carbamazepine, Valproate):** Folic acid may decrease serum levels of these agents, potentially reducing seizure control. * **Sulfonamides/Trimethoprim:** May interfere with folate metabolism. ## Monitoring * **Baseline:** CBC with indices (MCV), serum/RBC folate, and Vitamin B12 levels to rule out pernicious anemia. * **Follow-up:** Resolution of anemia, improvement in hemoglobin/hematocrit, and potential changes in seizure frequency if on anticonvulsants. ## Clinical Pearls * Always rule out Vitamin B12 deficiency before initiating high-dose folic acid therapy. * Folic acid is photosensitive; protect stored medication from light. * In the context of pregnancy, supplementation ideally begins at least one month before conception and continues through the first trimester. * Dosages exceeding 1 mg may require a prescription in some jurisdictions; verify local mandates. *** *Disclaimer: This information is for educational purposes. Dosing and therapeutic protocols vary by institution and clinical context. Always verify specific patient needs and drug information via current official prescribing labels (e.g., DailyMed) or institutional clinical decision support systems before prescribing or administering medication.*