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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 prophylactic prevention of complications.
## Primary Indications
* Treatment of folate deficiency anemia.
* Prophylaxis of neural tube defects (NTDs) in pregnancy.
* Prevention of hematologic/GI side effects in patients taking methotrexate.
* Megaloblastic anemia due to sprue or nutritional deficiency.
## Adult Dosing
* **Folate Deficiency:** 1 mg daily. Severe cases may require up to 5 mg daily.
* **Pregnancy/Lactation (Prophylaxis):** 0.4–0.8 mg daily, starting at least 1 month before conception and throughout the first trimester.
* **High-risk Pregnancy (e.g., prior NTD):** 4 mg daily.
* **Methotrexate Supplementation:** 1–5 mg daily (non-MTX days) or 1–5 mg weekly, depending on local institutional protocol and methotrexate dosing schedule.
## Pediatric Dosing
* **Infants:** 0.1 mg/day.
* **Children (1–4 years):** 0.3 mg/day.
* **Children (4+ years) and Adolescents:** 0.4 mg/day (equivalent to adult RDA).
* **Deficiency Treatment:** 0.5–1 mg/day; higher doses may be used under specialist supervision.
## Dose Adjustments
* **Renal/Hepatic Impairment:** No standard dose adjustment required; however, monitoring of hematologic response is recommended in chronic disease.
## Contraindications
* Hypersensitivity to folic acid.
* **Warning:** Do not use as monotherapy for pernicious anemia (B12 deficiency) or other B12-deficiency anemias. Folic acid may mask the hematologic symptoms while allowing subacute combined degeneration of the spinal cord to progress.
## Adverse Effects
* Generally well-tolerated.
* Rare: Allergic reactions (rash, pruritus, dyspnea).
* High doses (>15 mg/day) may cause GI distress, irritability, or alteration in sleep patterns.
## Key Drug Interactions
* **Methotrexate:** Folic acid is an antagonist; concurrent use is intended to mitigate toxicity, but timing should be optimized (often avoided on the day of methotrexate administration).
* **Anticonvulsants (Phenytoin, Carbamazepine, Valproate):** May decrease phenytoin serum levels and be affected by chronic anticonvulsant therapy, necessitating increased folic acid intake.
* **Sulfonamides/Pyrimethamine:** May interfere with folate metabolism.
## Monitoring
* **Baseline:** Complete Blood Count (CBC) and serum B12 levels to rule out B12 deficiency.
* **Ongoing:** Hemoglobin, hematocrit, and red cell folate levels if indicated by clinical response.
## Clinical Pearls
* Neural tube defect reduction is most effective when supplementation is initiated prior to conception.
* Folic acid is remarkably safe with minimal toxicity even at high doses, as excess is renally excreted.
* Always confirm B12 status before starting high-dose folic acid to prevent neurological complications of untreated pernicious anemia.
* Dietary intake alone is often insufficient for pregnancy requirements or rapid cellular turnover states (e.g., hemolytic anemia).
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**Educational Disclaimer:** This information is for educational purposes only. Always verify drug dosages, contraindications, and drug interactions with the most current institutional protocols, prescribing leaflets, or clinical decision support software before administration.
