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# Folic Acid ## Overview Folic acid (vitamin B9) is a water-soluble B vitamin essential for DNA synthesis, repair, and erythropoiesis. Synthetic folic acid has higher bioavailability than naturally occurring food folates. ## Primary Indications * Treatment/prevention of folate-deficiency anemia. * Prevention of neural tube defects (NTDs) in pregnancy. * Reduction of hematologic/GI toxicity in patients on methotrexate therapy. * Adjunctive therapy in psychiatric disorders (e.g., major depressive disorder). ## Adult Dosing * **Folate-Deficiency Anemia:** 1 mg daily (range: 1–5 mg/day). * **Pregnancy (NTD Prevention):** 400–800 mcg daily, starting at least 1 month before conception and continuing through the first trimester. * **High-Risk Pregnancy (History of NTD):** 4–5 mg daily. * **Methotrexate Supplementation:** 1–5 mg daily (non-MTX days) or 5 mg once weekly to reduce toxicity. ## Pediatric Dosing * **Treatment of Deficiency:** 0.5–1 mg daily. * **Maintenance:** * Infants: 0.1 mg daily. * Children 1–10 years: 0.2–0.3 mg daily. * Children >11 years: 0.4 mg daily. * **Note:** Dosing varies by institutional protocol for specific conditions (e.g., malabsorption syndromes). ## Dose Adjustments * **Renal/Hepatic Impairment:** No standard dose reduction required. * **Dialysis:** Patients on hemodialysis may require higher doses (e.g., 1–5 mg daily) due to dialysate losses. ## Contraindications * Hypersensitivity to folic acid. * **Crucial:** Do not use as monotherapy in undiagnosed megaloblastic anemia (e.g., pernicious anemia/B12 deficiency); it may mask vitamin B12 deficiency symptoms while allowing neurological damage to progress. ## Adverse Effects Generally well-tolerated. Rare reports include: * GI: Nausea, abdominal distension, flatulence. * Dermatologic: Pruritus, rash, urticaria. * Neurologic: Altered sleep patterns, irritability (at very high doses). ## Key Drug Interactions * **Methotrexate:** Folic acid can reduce the therapeutic efficacy of methotrexate for rheumatoid arthritis or psoriasis; schedule appropriately. * **Anticonvulsants (Phenytoin, Carbamazepine, Valproate):** Folic acid may decrease serum concentrations of these medications, potentially increasing seizure risk. * **Sulfasalazine:** Inhibits intestinal absorption of folic acid. ## Monitoring * **Efficacy:** Hemoglobin, hematocrit, and mean corpuscular volume (MCV). * **Vitamin B12:** Always rule out B12 deficiency (serum B12, methylmalonic acid) prior to initiating high-dose folic acid. ## Clinical Pearls * Folic acid is highly stable; however, it is light-sensitive and should be stored in light-resistant containers. * Patients with MTHFR mutations may benefit from 5-methyltetrahydrofolate (L-methylfolate), though clinical evidence for superior outcomes over folic acid in general populations is debated. * In the presence of B12 deficiency, folic acid will correct the anemia but will **not** prevent or reverse the irreversible neurological deficits associated with B12 deficiency. *** **Disclaimer:** This information is for educational purposes only. Clinical protocols and safety information can change. Always verify current prescribing information, institutional guidelines, and patient-specific factors via an official drug database (e.g., Lexicomp, UpToDate) or the product package insert before prescribing or administering medication.