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# Folic Acid ## Overview Folic acid (vitamin B9) is a water-soluble B-vitamin essential for DNA synthesis, repair, and erythropoiesis. Supplemental folic acid is chemically stable and well-absorbed orally. ## Primary Indications * Prevention and treatment of folate deficiency anemia. * Prevention of neural tube defects (NTDs) in pregnancy. * Adjunct therapy with methotrexate (to reduce gastrointestinal and hematologic toxicity). ## Adult Dosing * **Folate Deficiency:** 1 mg daily. Maintenance: 0.4 mg/day. * **Pregnancy (Prevention of NTDs):** 0.4–0.8 mg daily, starting at least 1 month before conception and continuing through the first trimester. High-risk patients (history of NTD-affected pregnancy): 4-5 mg daily as directed by clinical protocol. * **Methotrexate Adjunct:** 1–5 mg daily (scheduled to avoid concurrent administration). ## Pediatric Dosing * **Maintenance (Deficiency):** * Infants: 0.1 mg daily. * Children 1–4 years: 0.3 mg daily. * Children >4 years: 0.4 mg daily. * **Treatment (Deficiency):** 0.5–1 mg daily. ## Dose Adjustments * **Renal/Hepatic:** No formal dose adjustments; folate is excreted renally, but clinical insufficiency in renal failure typically mimics deficiency patterns requiring standard replenishment. ## Contraindications * **Primary:** Hypersensitivity to folic acid or any component of the formulation. * **Warning:** Folic acid should never be used as monotherapy for megaloblastic anemia caused by B12 deficiency (pernicious anemia), as it may correct anemia while allowing irreversible neurological damage to progress. ## Adverse Effects * Generally well-tolerated. * Rare: Pruritus, rash, urticaria, flushing, or gastrointestinal distress (nausea, abdominal distension). ## Key Drug Interactions * **Methotrexate:** Folic acid may decrease the efficacy of methotrexate in cancer treatment. * **Anticonvulsants (Phenytoin, Carbamazepine, Valproic Acid):** Folic acid supplementation may decrease serum concentrations of these medications. * **Sulfonamides/Sulfasalazine:** May inhibit folate absorption or metabolism, requiring higher supplementation doses. ## Monitoring * **Hematologic:** Monitor CBC (Hgb, Hct, MCV, RDW) to assess therapeutic response. * **B12 Status:** Ensure vitamin B12 levels are adequate before initiating high-dose folic acid to prevent "masking" symptoms of occult B12 deficiency. ## Clinical Pearls * **Masking B12 Deficiency:** Large doses (>1 mg/day) may mask subacute combined degeneration of the spinal cord by improving anemia without addressing the underlying B12 deficiency. * **Administration:** May be taken with or without food. Bioavailability is generally excellent. * **Duration:** Therapy duration depends on the underlying etiology of the deficiency (e.g., malabsorption, medication-induced, or dietary). *** **Educational Disclaimer:** This information is for educational purposes only. Clinical protocols may vary by institution. Always verify specific dosing, safety guidelines, and metabolic status via the most current product labeling or institutional guidelines before prescribing or administering medication.