Folic acid
VITAMIN B9
What it isVitamin B9 precursor for one-carbon metabolism; deficiency, methotrexate cover and periconceptional supplementation.
Why this onePericonceptional supplementation prevents neural tube defects, which is one of the clearest preventive interventions in medicine.
What limits itIt corrects the anemia of B12 deficiency while the neuropathy progresses — always check B12 before repleting folate alone.
FDA-approved for
- folate deficiency
- neural-tube-defect prevention
FDA label
Read the full label on DailyMed ↗
| FDA dosing | Population | Start | Target | Max |
|---|---|---|---|---|
| Megaloblastic anemia / folate deficiency — treatment | Adults | Up to 1 mg QD | Up to 1 mg QD | 1 mg QD (>1 mg QD adds no hematologic effect; resistant cases may require larger doses) |
| Megaloblastic anemia / folate deficiency — treatment | Children, any age | Up to 1 mg QD | Up to 1 mg QD | 1 mg QD (>1 mg QD adds no hematologic effect; resistant cases may require larger doses) |
| Maintenance after symptoms subside and blood picture normalizes | Adults | 0.4 mg QD | 0.4 mg QD | |
| Maintenance after symptoms subside and blood picture normalizes | Pregnant and lactating women | 0.8 mg QD | 0.8 mg QD | |
| Maintenance after symptoms subside and blood picture normalizes | Children ≥4 yr | 0.4 mg QD | 0.4 mg QD | |
| Maintenance after symptoms subside and blood picture normalizes | Children <4 yr | Up to 0.3 mg QD | Up to 0.3 mg QD | |
| Maintenance after symptoms subside and blood picture normalizes | Infants | 0.1 mg QD | 0.1 mg QD |
Renal Undefined
Hepatic Undefined
Daily doses >1 mg do not enhance the hematologic effect and the excess is excreted unchanged in urine; maintenance should never be less than 0.1 mg/day.
Instructions
- Oral administration is preferred; patients with malabsorption who cannot absorb food folates can still absorb oral folic acid.
- Parenteral administration is not advocated but may be necessary in some patients (e.g., those on parenteral or enteral alimentation).
- Do not use doses >0.1 mg unless vitamin B12 deficiency has been ruled out or is being adequately treated with cobalamin.
- Keep patients under close supervision and adjust the maintenance dose if relapse appears imminent.
- The maintenance dose may need to be increased in alcoholism, hemolytic anemia, anticonvulsant therapy, or chronic infection.
Cautions
- Doses >0.1 mg may correct the hematologic picture of vitamin B12 deficiency while neurologic damage progresses — rule out or adequately treat B12 deficiency with cobalamin first.
- Decreased serum vitamin B12 levels may occur with prolonged folic acid therapy.
- Allergic sensitization has been reported after both oral and parenteral administration.
Adverse reactions
- Allergic sensitization after oral or parenteral administration; rare allergic responses — erythema, rash, pruritus, general malaise, respiratory difficulty from bronchospasm; one report of anaphylaxis-like symptoms after injection
- GI (reported at 15 mg/day for 1 month): anorexia, nausea, abdominal distention, flatulence, bitter or bad taste
- CNS (reported at 15 mg/day): altered sleep patterns, difficulty concentrating, irritability, overactivity, excitement, mental depression, confusion, impaired judgment
- Decreased serum vitamin B12 with prolonged therapy
- Increased incidence of seizures reported in some epileptic patients receiving phenobarbital, primidone, or phenytoin (diphenylhydantoin) who were given oral folic acid (uncontrolled study)
- Decreased phenytoin (diphenylhydantoin) serum levels reported in folate-deficient patients on phenytoin treated with folic acid 5 mg or 15 mg daily
Pregnancy Pregnancy Category A — folic acid requirements are markedly increased in pregnancy and deficiency causes fetal damage; usually indicated for megaloblastic anemia of pregnancy, with no evidence of increased fetal abnormality risk.
Lactation No lactation section on the label; the dosing section specifies a 0.8 mg daily maintenance dose for lactating women.
NO BOXED WARNINGS
Principal riskMasks the anemia of B12 deficiency while neuropathy progresses
Cost, est. cash$5–$150/month
Generic entry1982
Classes and tags
Clinical profile
Legacy pregnancy categoryA
Defining liabilityUsually well tolerated at replacement doses; excessive dosing can cause agent-specific metabolic or organ toxicity.
Active metabolites
Mechanism of action: Folic acid ballicule
Open Folic acid in the interactive console ↗
Memory aids: mascots and interaction avatars
