Folic Acid (Vitamin B9) is a synthetic, water-soluble B vitamin essential for DNA synthesis, repair, and methylation, as well as red blood cell formation. The 5mg strength is a pharmacological dose used for therapeutic purposes, distinct from lower-dose nutritional supplements. It is a critical cofactor in one-carbon metabolism, converting homocysteine to methionine.
Adult: Treatment of deficiency: 5mg once daily for 4 months or until hematological recovery is complete. Maintenance: 1-5mg daily depending on cause. Prophylaxis in high-risk (e.g., hemolytic anemia, dialysis): 1-5mg daily.
Note: Administer orally, preferably on an empty stomach (1 hour before or 2 hours after meals) for maximum absorption. Can be taken with food if GI upset occurs, though absorption is reduced. Tablet can be crushed if needed. Consistent daily timing is recommended.
Folic acid acts as a precursor to tetrahydrofolate (THF) and other derivatives, which serve as coenzymes in the transfer of single-carbon units. This is essential for: 1) The synthesis of purines and pyrimidines (thymidylate, purine bases), the building blocks of DNA and RNA. 2) The conversion of homocysteine to methionine, a reaction vital for methylation reactions and neurological health. 3) Amino acid interconversions (serine to glycine, histidine catabolism).
Pregnancy: Category A. Essential for preventing neural tube defects (NTDs). For women with a previous NTD pregnancy, a high dose of 4-5mg daily is recommended starting at least 1 month before conception and continuing through the first trimester. Routine prenatal supplementation is 400-800 mcg daily. 5mg is a therapeutic/preventive dose for high-risk pregnancies.
Driving: No known effects on driving ability.
| Phenytoin, Phenobarbital, Primidone | Anticonvulsant serum levels may be decreased. Folic acid efficacy may be reduced. Requires monitoring. | Moderate |
| Methotrexate, Pyrimethamine, Trimethoprim | These are folate antagonists. Folic acid can interfere with their therapeutic effect in certain conditions (e.g., cancer, toxoplasmosis). However, it is used to reduce their toxicity in other contexts. Use under strict medical supervision. | Major |
| Sulfasalazine | Impairs absorption and metabolism of folate, potentially increasing requirement. | Moderate |
| Oral Contraceptives | May increase folate requirement; long-term use can lower serum folate levels. | Minor |
| Zinc Supplements | High-dose folic acid may impair zinc absorption. Separate administration by 2-3 hours. | Minor |
Same composition (Folic Acid (5mg)), different brands: