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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 required as it cannot be synthesized by the human body. ## Primary Indications * Treatment and prevention of folate-deficiency anemia. * Prevention of neural tube defects (NTDs) during pregnancy. * Prophylaxis in chronic hemolytic states (e.g., sickle cell anemia) or dialysis. * Adjunct therapy in methotrexate treatment. ## Adult Dosing * **Folate-deficiency anemia:** 1 mg daily; doses up to 5 mg daily may be required for malabsorption or refractory cases. * **Pregnancy (General population):** 0.4–0.8 mg daily, starting at least 1 month prior to conception through the first trimester. * **Pregnancy (High risk/Previous NTD-affected pregnancy):** 4 mg daily. * **Methotrexate adjunct:** 1–5 mg daily (non-treatment days) to reduce gastrointestinal and hematologic toxicity. ## Pediatric Dosing * **Maintenance:** 0.1–0.3 mg daily. * **Deficiency anemia:** 0.5–1 mg daily. * **Infants:** 0.1 mg daily. * *Note: Dosing should be individualized based on age, nutritional status, and underlying medical conditions.* ## Dose Adjustments * **Renal Impairment:** No specific adjustment required; however, folate is removed during hemodialysis, and replacement is commonly prescribed post-dialysis. * **Hepatic Impairment:** No specific adjustment required. ## Contraindications * Known hypersensitivity to folic acid. * **Critical:** Do not use as monotherapy for pernicious anemia (Vitamin B12 deficiency) or other megaloblastic anemias where B12 deficiency is not ruled out, as it may mask neurologic progression despite hematologic response. ## Adverse Effects * Generally well-tolerated. * Rare: Allergic reactions (rash, pruritus, erythema, bronchospasm). * Gastrointestinal: Nausea, abdominal distension, or flatulence (at high doses). ## Key Drug Interactions * **Methotrexate/Pemetrexed:** Folic acid may decrease the efficacy of these folate antagonists. * **Anticonvulsants (Phenytoin, Carbamazepine, Valproate):** May decrease serum concentrations due to increased metabolism. * **Sulfonamides:** May inhibit folate absorption. ## Monitoring * **Baseline:** Complete Blood Count (CBC) and, if indicated, serum Vitamin B12 levels. * **Response:** Monitor reticulocyte count (within 5–10 days) and hemoglobin/hematocrit (within 2–4 weeks) to assess response to therapy in anemia treatment. ## Clinical Pearls * Therapeutic response to anemia treatment is usually observed by an increase in reticulocytes within the first week. * Ensure that B12 deficiency is ruled out via serum B12 or methylmalonic acid testing before initiating high-dose folic acid to prevent irreversible neurological damage. * Folic acid is photosensitive; store in a cool, light-protected area. * Many protocols use 1 mg daily for empirical deficiency treatment, but always refer to local institutional guidelines for specific chronic disease management. *** **Disclaimer:** This information is for educational purposes only. Always verify dosing, contraindications, and drug interactions against current prescribing information, institutional protocols, and official package inserts before clinical application.