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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.
## Primary Indications
* Folate deficiency anemia.
* Prevention of neural tube defects (NTDs) in pregnancy.
* Prophylaxis during chronic hemolysis or dialysis.
* Adjuvant therapy with methotrexate to reduce hematologic and GI toxicity.
## Adult Dosing
* **Deficiency/Anemia:** 1 mg daily. Severe cases may require up to 5 mg daily.
* **Pregnancy (Prevention of NTDs):** 0.4–0.8 mg daily, starting at least 1 month before conception and through the first trimester. High-risk patients (e.g., history of NTD-affected pregnancy) may require 4–5 mg daily.
* **Methotrexate rescue:** 1–5 mg daily (or 5 mg weekly, depending on institutional protocol).
## Pediatric Dosing
* **Maintenance:** 0.1 mg daily (infants/toddlers); 0.3–0.4 mg daily (children 4–12 years).
* **Deficiency:** 0.5–1 mg daily.
* **Note:** Dosing varies widely based on clinical indication (e.g., hemolytic anemia vs. general supplement); consult age-specific growth charts and local institutional protocols.
## Dose Adjustments
* **Renal Impairment:** No specific adjustment required; however, patients on hemodialysis require daily supplementation to replace losses (typically 1 mg daily).
* **Hepatic Impairment:** No specific adjustment required.
## Contraindications
* Hypersensitivity to folic acid.
* Untreated Vitamin B12 deficiency (folic acid can mask the hematologic symptoms of B12 deficiency while allowing irreversible neurological damage to progress).
## Adverse Effects
* Generally well-tolerated.
* Rare: Allergic reactions (rash, pruritus, bronchospasm), GI upset, or bitter taste.
## Key Drug Interactions
* **Methotrexate:** Folic acid may decrease the efficacy of methotrexate in oncologic applications (does not significantly interfere with low-dose rheumatologic dosing).
* **Anticonvulsants (Phenytoin, Carbamazepine, Valproate):** Folic acid may decrease serum concentrations of these agents, potentially increasing seizure risk.
* **Sulfonamides:** May inhibit folate absorption.
## Monitoring
* **Efficacy:** Hemoglobin, hematocrit, and mean corpuscular volume (MCV).
* **Safety:** Monitor for neurological symptoms if correcting anemia without excluding Vitamin B12 deficiency.
## Clinical Pearls
* **The B12 Trap:** Never treat megaloblastic anemia with folic acid alone until Vitamin B12 deficiency is definitively ruled out.
* **Stability:** Highly sensitive to light and heat; store in a light-resistant container.
* **Absorption:** Bioavailability is high (near 100%) when taken orally.
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*Disclaimer: This information is for educational purposes only. Clinical guidelines and local protocols vary; always verify current prescribing information, contraindications, and dosing with institutional policies or official pharmaceutical package inserts before administration.*
