Vitamins and Haematinics Pregnancy: Folic acid deficiency during pregnancy may lead to foetal malformations, and imbalance in folate-requiring trophoblast cells may lead to placental detachment. Very high doses have caused foetal abnormalities in rats; however, harmful effects in the human foetus, mother or pregnancy have not been reported following ingestion of folic acid. Folic acid is 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: Folate-deficient megaloblastic anaemia: 5 mg daily for 4 months

Route: Oral (tablets)

Frequency: Once daily

Max: Up to 15 mg daily may be necessary for malabsorption states

Other adult regimens in the same SPC — prophylaxis in chronic haemolytic states or in renal dialysis: 5 mg every 1 to 7 days depending on diet and underlying disease. Drug-induced folate deficiency: 5 mg daily. Prevention of recurrence of neural tube defects: 5 mg daily starting before conception and continuing throughout the first trimester of pregnancy. PAEDIATRIC (this page's focus): over 1 year — as the adult dose; up to 1 year — 500 micrograms/kg daily (see paedDose). Folic acid must not be given for pernicious anaemia or undiagnosed megaloblastic anaemia without sufficient vitamin B12, as folic acid alone will not prevent and may precipitate subacute combined degeneration of the spinal cord — a full clinical diagnosis should be made before starting treatment. Folate should not be routinely used in patients receiving coronary stents, and caution is needed in patients who may have folate-dependent tumours. The tablets contain lactose — not for patients with rare hereditary galactose intolerance, Lapp lactase deficiency or glucose-galactose malabsorption. Source: eMC SPC for Folic Acid 5 mg Tablets (§4.2).

Paediatric dose

Dose: 500 micrograms/kg

Route: Oral

Frequency: Once daily

Max: Not stated in this SPC for the paediatric population

UK SPC §4.2, Paediatric population: 'Over 1 year: As adult dose. Up to 1 year: 500 µg/kg daily.' The 500 micrograms/kg once-daily dose therefore applies to infants up to 1 year of age; children over 1 year receive the adult dose (5 mg daily for the indications listed above). The fetched SPC is for a 5 mg tablet, which is not a suitable formulation for infants — an oral liquid will be needed. Verify against a children's formulary.

Dose adjustments

Renal

No renal dose adjustment is stated. The SPC lists prophylaxis in renal dialysis as 5 mg every 1 to 7 days depending on diet and underlying disease, and notes that folic acid is removed by haemodialysis (§4.4).

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

Patient weight (kg)

Verify in a children's formulary

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Patients with malignant disease, unless megaloblastic anaemia due to folic acid deficiency

Side effects

May worsen the symptoms of co-existing vitamin B12 deficiency — should never be used to treat anaemia without full investigation of the cause
Allergic reactions (rare): erythema, rash, pruritus, urticaria, dyspnoea
Anaphylactic reactions including shock (rare)
Abdominal distension and flatulence
Anorexia and nausea

Interactions

Sulfasalazine — may reduce absorption of folic acid
Cholestyramine — may interfere with folic acid absorption; on prolonged cholestyramine therapy take folic acid 1 hour before or 4 to 6 hours after cholestyramine
Trimethoprim or sulfonamides, alone or as co-trimoxazole — may reduce the effect of folic acid, which may be serious in megaloblastic anaemia
Anticonvulsants (phenytoin, phenobarbital, primidone) — serum levels may be reduced by folate administration; monitor carefully and adjust the anticonvulsant dose as necessary
Fluorouracil — fluorouracil toxicity may occur in patients taking folic acid; this combination should be avoided
Antacids containing aluminium or magnesium, and edible clay — may reduce folic acid absorption; take antacids at least two hours after folic acid
Zinc — folic acid may reduce intestinal absorption of zinc (of particular importance in pregnancy)
Antibiotics — may interfere with the microbiological assay for serum and erythrocyte folic acid and cause falsely low results

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