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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 a synthetic form of folate used as a supplement or therapeutic agent for deficiency states and the prevention of neural tube defects. ## Primary Indications * Treatment of folate deficiency megaloblastic anemia. * Prevention of neural tube defects (NTDs) in pregnancy. * Prophylaxis in chronic hemolytic anemia or renal dialysis. * Reduction of side effects associated with methotrexate therapy. ## Adult Dosing * **Deficiency Treatment:** 1 mg daily. Higher doses (up to 5 mg/day) may be required for malabsorption syndromes. * **Pregnancy (NTD Prevention):** 400 mcg (0.4 mg) to 800 mcg (0.8 mg) daily. High-risk patients (previous NTD pregnancy) may require 4 mg daily. * **Methotrexate Supplementation:** 1 mg daily or 5 mg weekly (non-methotrexate day), per local protocol or prescriber preference. ## Pediatric Dosing * **Deficiency Treatment:** 0.5 to 1 mg daily for infants and children; neonates may require 0.1 mg daily. * **Maintenance:** 0.1 mg daily for infants; 0.3 mg daily for children 1–3 years; 0.4 mg daily for children 4+ years. * *Note: Dosing often follows specific institutional protocols based on underlying pathology.* ## Dose Adjustments * **Renal Impairment:** No specific adjustment required; however, patients on dialysis require supplementation due to clearance during the procedure. * **Hepatic Impairment:** No standard adjustment required. ## Contraindications * Hypersensitivity to folic acid. * **Warning:** Do not use as monotherapy in Vitamin B12 deficiency (pernicious anemia) as it may mask neurological progression while improving hematologic markers. ## Adverse Effects * Generally well-tolerated. * Rare: Allergic reactions (rash, pruritus, bronchospasm), gastrointestinal distress (nausea, abdominal bloating), or altered sleep patterns/irritability with very high doses. ## Key Drug Interactions * **Methotrexate:** Folic acid may decrease the efficacy of methotrexate in cancer treatment. * **Anticonvulsants (e.g., Phenytoin, Phenobarbital, Primidone):** Folic acid can decrease serum levels of these medications, potentially reducing seizure control. * **Sulfonamides/Trimethoprim:** May interfere with folate metabolism. ## Monitoring * Monitor hemoglobin/hematocrit and reticulocyte counts to evaluate efficacy in anemia treatment. * Monitor serum B12 levels if high-dose folic acid is used to ensure underlying B12 deficiency is not masked. ## Clinical Pearls * **Masking Effect:** Always rule out Vitamin B12 deficiency before initiating high-dose folic acid supplementation in patients with megaloblastic anemia. * **Stability:** Highly sensitive to light and heat; keep in a tightly closed, light-resistant container. * **Food Intake:** Bioavailability is high and it can be taken regardless of meals. *** *Disclaimer: This information is for educational purposes only. Always verify current prescribing information, institutional protocols, and patient-specific factors via reliable clinical resources (e.g., Lexicomp, Micromedex) before prescribing or administering medication.*