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# Folic Acid ## Overview Folic acid (vitamin B9) is a water-soluble B vitamin essential for DNA synthesis, repair, and erythropoiesis. Exogenous supplementation is necessary as the body has limited storage capacity. ## Primary Indications * Treatment and prophylaxis of folate-deficiency megaloblastic anemia. * Prevention of neural tube defects (NTDs) during pregnancy. * Reduction of hematologic/GI side effects associated with methotrexate therapy. ## Adult Dosing * **Megaloblastic Anemia (Deficiency):** Initial dose 1 mg daily; maintenance dose 0.4 mg per day. Severe deficiency may require up to 5 mg per day. * **Pregnancy (Prevention of NTDs):** 0.4 mg to 0.8 mg daily, starting at least 1 month before conception and continuing through the first trimester. High-risk patients (history of affected pregnancy) may require 4 mg daily. * **Methotrexate Supplementation:** 1 mg daily (avoid on the day of methotrexate dose) or 5 mg weekly to manage toxicity. ## Pediatric Dosing * **Megaloblastic Anemia:** * Infants: 0.1 mg daily. * Children/Adolescents: 0.4 mg daily (maintenance). * Refractory cases: Up to 1 mg daily. * **Maintenance (Chronic Hemolysis/Dialysis):** 0.1 to 0.4 mg daily (based on age/nutritional status). ## Dose Adjustments * **Renal/Hepatic Impairment:** No standard dose adjustment required; however, monitoring is suggested in maintenance dialysis patients. ## Contraindications * Hypersensitivity to the drug. * **Warning:** Do not use as monotherapy for pernicious anemia (Vitamin B12 deficiency) without adequate B12 supplementation, as folic acid can mask neurological progression of B12 deficiency. ## Adverse Effects * Generally well-tolerated. * Rare: Allergic reactions (rash, pruritus, bronchospasm), GI disturbances (nausea, abdominal distension), and bitter taste. ## Key Drug Interactions * **Methotrexate:** Folic acid may decrease the efficacy of methotrexate in oncologic doses. * **Anticonvulsants (Phenytoin, Carbamazepine, Valproate):** Folic acid may decrease serum concentrations of these agents, potentially increasing seizure risk. * **Sulfonamides/Pyrimethamine:** May interfere with folate absorption or metabolism. ## Monitoring * **Efficacy:** Hemoglobin, hematocrit, reticulocyte count, and MCV (resolution of macrocytosis). * **Safety:** Serum B12 levels if neurologic symptoms are present or if high-dose supplementation (≥1 mg) is required for long durations. ## Clinical Pearls * Folic acid is highly sensitive to heat and light; store in a dry, cool place. * Always rule out Vitamin B12 deficiency via serum B12 testing before initiating high-dose folic acid (≥1 mg) to avoid permanent neurological damage from masked B12 deficiency. * Many regional protocols vary regarding high-risk pregnancy dosing; follow local obstetric guidelines for titration. *** **Disclaimer:** This information is for educational purposes. Always verify current prescribing information, institutional protocols, and patient-specific factors before administration.