Vitamins and Haematinics Pregnancy: Harmful effects in the human foetus, mother or pregnancy have not been reported following ingestion of folic acid; folic acid deficiency in pregnancy may lead to foetal malformations. Excreted in breast milk with no adverse effects observed in breast-fed infants.

Folic Acid

Brand names: Lexpec

Folic acid is a synthetic form of vitamin B9 used in children to treat or prevent folate-deficiency anaemia and as supplementation alongside certain therapies such as methotrexate or in haemolytic states.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 5 mg

Route: oral

Frequency: once daily

Folate-deficient megaloblastic anaemia: 5 mg daily for 4 months; up to 15 mg daily may be necessary in malabsorption states. Drug-induced folate deficiency: 5 mg daily. Prophylaxis in chronic haemolytic states or renal dialysis: 5 mg every 1–7 days depending on diet and underlying disease. Prevention of recurrence of neural tube defects: 5 mg daily starting before conception and continuing throughout the first trimester. Paediatric (per SPC): over 1 year, as adult dose; up to 1 year, 500 micrograms/kg daily — verify paediatric dosing against a children's formulary.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to folic acid or any excipient
Patients with malignant disease, unless megaloblastic anaemia is due to folic acid deficiency

Side effects

Allergic reactions (erythema, rash, pruritus, urticaria, dyspnoea, anaphylactic reactions including shock) — rare
Abdominal distension
Flatulence
Anorexia
Nausea

Interactions

Sulfasalazine may reduce folic acid absorption
Cholestyramine may interfere with absorption (take folic acid 1 hour before or 4–6 hours after)
Trimethoprim or sulfonamides (alone or as co-trimoxazole) may reduce the effect of folic acid
Folate may reduce serum levels of anticonvulsants (phenytoin, phenobarbital, primidone)
Fluorouracil toxicity may occur — combination should be avoided
Antacids containing aluminium or magnesium may reduce absorption (separate by at least 2 hours)

Clinical monograph

How it works

After conversion to tetrahydrofolate, it acts as a cofactor in single-carbon transfer reactions essential for purine, pyrimidine and amino acid synthesis, supporting normal red cell production.

Prescribing in practice

Exclude or treat concurrent vitamin B12 deficiency before or alongside folic acid, as folate can correct the anaemia while allowing neurological damage from untreated B12 deficiency to progress.
When given with methotrexate it is taken on different days from the methotrexate dose, per the prescribed schedule.
Confirm the indication and paediatric dosing against a children's formulary, as regimens differ for deficiency, prophylaxis and haemolytic conditions.

Monitoring

Monitor the full blood count and haematological response, and review vitamin B12 status where megaloblastic anaemia is present.

Counselling the patient

Give the supplement regularly as prescribed.
If used with methotrexate, take folic acid only on the days advised and not on the methotrexate day.
Tell the clinician about diet and any other supplements the child takes.

Evidence & guidelines

Folic acid supplementation for folate deficiency and as methotrexate co-therapy is standard practice supported by the SPC and haematology guidance.

Reference: NICE PH11 (Folic Acid Supplementation); Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways