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# Folic Acid ## Overview Folic acid (vitamin B9) is a water-soluble B vitamin essential for DNA synthesis, erythropoiesis, and amino acid metabolism. Synthetic folic acid is more bioavailable than naturally occurring folates. ## Primary Indications * Treatment/prevention of folate deficiency (e.g., malabsorption, alcoholism, hemolytic anemia). * Prevention of neural tube defects (NTDs) in pregnancy. * Adjunct therapy with methotrexate (MTX) to reduce toxicity. ## Adult Dosing * **Folate Deficiency:** 1 mg daily; may increase to 5 mg if malabsorption is present. * **Pregnancy (Prevention of NTDs):** 0.4–0.8 mg daily starting at least one month before conception through the first trimester. High-risk patients (history of NTD or epilepsy) may require 4–5 mg daily (per clinical protocol). * **Methotrexate Adjunct:** 1–5 mg daily (or 5–10 mg weekly) based on provider preference to mitigate mucosal/gastrointestinal toxicity. ## Pediatric Dosing * **Deficiency (Treatment):** 0.5–1 mg daily. * **Deficiency (Maintenance):** * <1 year: 0.1 mg daily. * 1–3 years: 0.15 mg daily. * 4–8 years: 0.2 mg daily. * 9+ years: 0.4 mg daily. * **Methotrexate Adjunct:** 1 mg daily (or titrated dose) as determined by oncology/rheumatology protocols. ## Dose Adjustments * **Renal/Hepatic Impairment:** No formal adjustments required; however, monitor closely in end-stage renal disease. * **Malabsorption:** Doses up to 5 mg/day may be necessary. ## Contraindications * Hypersensitivity to folic acid or components. * **Crucial Rule:** Never administer as monotherapy in untreated pernicious anemia (B12 deficiency); it may resolve hematologic markers while allowing irreversible neurological damage to progress. ## Adverse Effects * Generally well-tolerated. * Rare: Allergic reactions (rash, pruritus, bronchospasm), nausea, abdominal distension, altered sleep, or irritability at very high doses. ## Key Drug Interactions * **Anticonvulsants (Phenytoin, Carbamazepine, Valproate):** Folic acid may decrease serum concentrations of these agents, potentially leading to breakthrough seizures. * **Methotrexate:** High doses of folic acid can interfere with the therapeutic efficacy of methotrexate when used for oncologic conditions. * **Sulfonamides/Pyrimethamine:** May antagonize the effects of folic acid. ## Monitoring * CBC and hematocrit/hemoglobin levels. * Serum folate and Vitamin B12 levels (prior to initiation to rule out B12 deficiency). * Signs of neurological changes if B12 deficiency is suspected. ## Clinical Pearls * Documentation of B12 levels is mandatory before starting high-dose folic acid to prevent masking Vitamin B12 deficiency. * Folic acid is highly susceptible to degradation by light and heat. * Ensure patients understand that "Folate" and "Folic Acid" are often used interchangeably, but folic acid is the pharmaceutical form required for therapeutic dosing. *** **Educational Disclaimer:** This information is for educational purposes only. Always verify dosages, contraindications, and drug interactions against current local institutional protocols and official prescribing information (package insert) before clinical application.