folic acid
vitamin· Brands: Folvite, Folicet, FolacinIMPOSC
Mechanism of action
Folic acid is a water-soluble B vitamin that is converted to tetrahydrofolate, a coenzyme involved in one-carbon transfer reactions essential for nucleotide synthesis, amino acid metabolism, and cell division. It acts as a precursor to active folates required for DNA synthesis and repair.
Pharmacokinetics
Folic acid is well absorbed from the gastrointestinal tract, predominantly in the proximal small intestine. It is transported in plasma bound to proteins, taken up by tissues, and converted to its active forms. It is stored in the liver as polyglutamates. Excretion occurs via the kidneys and in bile. It crosses the placenta and is present in breast milk.
Indications & dosing
Treatment of megaloblastic anaemia due to folate deficiency
Continue until blood count is normal; a maintenance dose may be lower.
- adult · PO: 5 mg once daily · Continue until blood count is normal; a maintenance dose may be lower.
Prevention of neural tube defects in pregnancy
Start before conception and continue until week 12. For women with a previous affected pregnancy or on antiepileptics, use 5 mg daily.
- adult · PO: 0.4 mg once daily · Start before conception and continue until week 12. For women with a previous affected pregnancy or on antiepileptics, use 5 mg daily.
Treatment of folate deficiency in children
Dose depends on age and severity of deficiency.
- pediatric · PO: 1–5 mg once daily · Dose depends on age and severity of deficiency.
Contraindications & precautions
- Hypersensitivity to folic acid or any component of the formulation · Rarely reported.
- Untreated vitamin B12 deficiency · Folic acid may mask the haematological features of B12 deficiency, allowing neurological damage to progress. If B12 deficiency is present, concurrent B12 supplementation is required.
- Exclude vitamin B12 deficiency before prescribing folic acid for megaloblastic anaemia, to avoid masking pernicious anaemia.
- Use with caution in patients with malignant disease, as folic acid may stimulate tumour growth.
- Monitor for signs of hypersensitivity, particularly in patients with a history of allergic reactions.
- Folic acid may interact with methotrexate, phenytoin and other drugs; consult local formulary for specific guidance.
Adverse effects
- Gastrointestinal disturbance (nausea, bloating, flatulence)
- Skin rash and urticaria
- Hypersensitivity reactions including anaphylaxisserious
- Bronchospasmserious
Monitoring, pregnancy & toxicity
- Serum folic acid · Baseline and after 1 month of treatment
- Erythrocyte folic acid · Baseline and after 3 months of treatment
- Haemoglobin and mean corpuscular volume (MCV) · Before and during treatment of anaemia
- Reticulocyte count · 7-10 days after starting treatment
- Pregnancy: Folic acid is recommended for all women of childbearing age, ideally starting at least 1 month before conception and continuing through the first 12 weeks of pregnancy to prevent neural tube defects. The dose is 400 mcg (0.4 mg) daily for low-risk women and 5 mg daily for high-risk women (e.g., previous child affected by a neural tube defect, antiepileptic therapy, diabetes, obesity, or malabsorption). Continue supplementation throughout pregnancy for those with folate deficiency.
- Toxicity: High doses (generally >1 mg/day) can mask the haematological signs of vitamin B12 deficiency, allowing neurological damage to progress untreated. · Discontinue folic acid, assess vitamin B12 status (e.g., serum B12, methylmalonic acid, homocysteine), and treat the underlying deficiency.
- Toxicity: Uncommon adverse effects include nausea, abdominal cramps, flatulence, and skin rash. · Symptoms are usually mild and transient; reduce dose or discontinue if troublesome.
Clinical notes
Used to treat and prevent folate deficiency anaemia, including megaloblastic anaemia due to folate deficiency, and as prophylaxis in pregnancy to reduce the risk of neural tube defects. It is also used in chronic haemolytic anaemias and as an adjunct to high-dose methotrexate therapy. Doses vary; typical supplements are 400 micrograms daily in pregnancy and 5 mg daily for deficiency. Exclude vitamin B12 deficiency before treatment, as folic acid may mask it. Folic acid is safe in pregnancy and breastfeeding.
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BNF; local formulary