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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 * Folic acid deficiency (megaloblastic anemia). * Prevention of neural tube defects (NTDs) in pregnancy. * Prophylaxis in chronic hemolytic anemia or renal dialysis. * Adjunct to methotrexate therapy. ## Adult Dosing * **Deficiency:** 1 mg daily. Maintenance dose is 0.4 mg/day. * **Pregnancy (Prevention of NTDs):** 0.4 to 0.8 mg daily (start at least 1 month before conception and continue through first trimester). High-risk patients (history of NTD) may require 4 mg daily per specific protocols. * **Methotrexate Adjunct:** 1–5 mg daily (non-MTX days) to reduce toxicity. ## Pediatric Dosing * **Infants:** 0.1 mg/day. * **Children (1–3 years):** 0.15 mg/day. * **Children (4–8 years):** 0.2 mg/day. * **Children (9–13 years):** 0.3 mg/day. * **Adolescents (14+ years):** 0.4 mg/day. * *Note: Megaloblastic anemia treatment doses often range from 0.5 to 1 mg daily depending on the underlying cause and severity.* ## Dose Adjustments * **Renal/Hepatic Impairment:** No specific adjustment required; however, patients on chronic dialysis may require increased supplementation (e.g., 1 mg/day) due to dialytic loss. ## Contraindications * Hypersensitivity to folic acid. * **Warning:** Do not use as monotherapy in undiagnosed megaloblastic anemia (e.g., Vitamin B12 deficiency) as it may improve hematologic parameters while allowing neurological damage from B12 deficiency to progress. ## Adverse Effects * Rare. Potential for allergic reactions (rash, pruritus, bronchospasm). * High doses may cause gastrointestinal discomfort (nausea, flatulence) or altered sleep patterns. ## Key Drug Interactions * **Methotrexate:** Folic acid may decrease efficacy if administered concurrently; timing (non-MTX days) is critical. * **Anticonvulsants (Phenytoin, Carbamazepine, Valproate):** May reduce serum folate levels; supplementation may decrease anticonvulsant effectiveness. * **Sulfonamides/Trimethoprim:** May interfere with folate metabolism. ## Monitoring * Monitor hemoglobin, hematocrit, and RBC indices for correction of anemia. * In suspected deficiency, always assess B12 levels prior to initiation to prevent masked neurologic sequelae. * Serum folate levels may be monitored, but clinical response is often a better indicator. ## Clinical Pearls * Ensure that megaloblastic anemia is not secondary to vitamin B12 deficiency; if both are present, B12 replacement must be prioritized. * Folic acid is highly sensitive to light and oxidation. * Most "high dose" protocols (4 mg/day) for high-risk pregnancies are based on specific institutional or obstetric society guidelines (e.g., ACOG); verify local protocol. *** **Educational Disclaimer:** This information is for educational purposes only. Always consult current clinical decision support tools (e.g., Lexicomp, UpToDate) and local institutional guidelines to verify specific dosing, safety profiles, and therapeutic indications before prescribing or administering medication.