1Folate Biochemistry & Active Forms
Folic acid (pteroylglutamic acid) is the synthetic, fully oxidised form of water-soluble Vitamin B9 used in pharmacological preparations and dietary fortification. Naturally occurring folates in foodstuffs exist as unstable polyglutamated tetrahydrofolates (THF).
Synthetic folic acid undergoes a two-step reduction by dihydrofolate reductase (DHFR) in enterocytes and the liver to form active tetrahydrofolate (THF), which subsequently enters one-carbon metabolism. Active THF derivatives donate methyl, methylene, and formyl groups indispensable for de novo purine synthesis, dUMP-to-dTMP pyrimidine conversion, and homocysteine-to-methionine remethylation.
2Pregnancy & Neural Tube Defect (NTD) Prevention
Human neural tube closure completes between post-conception days 21 and 28 (equivalent to 5–6 weeks of gestational age dated from the last menstrual period). Because this critical embryological window transpires before many women recognize pregnancy, periconceptional supplementation beginning prior to conception is essential.
| Risk Stratification | Clinical Criteria | Target Dose | Timing & Duration |
|---|---|---|---|
| Standard / Low Risk | All women planning conception; no personal or family history of NTD | 400–500 mcg/day | 1 month pre-conception through 12 completed weeks of gestation |
| High Risk | Prior pregnancy affected by anencephaly/spina bifida, maternal epilepsy on valproate/carbamazepine, pre-gestational diabetes, maternal BMI >30 kg/m² | 5 mg/day (Folvite 5mg) | 3 months pre-conception through 12 completed weeks of gestation |
3Megaloblastic Anaemia: The Dangers of Monotherapy
Both Vitamin B12 (cobalamin) and folate deficiencies result in identical haematological phenotypes characterized by macrocytic anaemia (MCV >100 fL), hypersegmented neutrophils, and bone marrow megaloblastosis.
4Methotrexate Protocols: Folic Acid vs Folinic Acid
| Clinical Setting | Prescribed Agent | Dosage & Administration Schedule | Pharmacological Rationale |
|---|---|---|---|
| Low-Dose MTX (RA / Psoriasis) | Folic acid | 5 mg orally once weekly, taken 24–48 hours after the MTX dose | Reduces mucosal ulceration, nausea, and transaminitis without diminishing antirheumatic efficacy. Never take on the same day as MTX. |
| High-Dose MTX (Oncology) | Folinic acid (Leucovorin) | 15 mg IV/IM/oral every 6 hours × 8 doses, starting 24h after MTX infusion | High-dose MTX competitively binds and shuts down DHFR. Folinic acid (5-formyl-THF) completely bypasses DHFR, delivering direct functional cofactors to rescue bone marrow and gastrointestinal epithelium. |
5Paediatric Folate Regimens
In paediatric practice, therapeutic repletion for documented folate-deficiency anaemia is dosed at 0.1 mg/kg/day orally (up to a maximum of 5 mg/day) for 3 to 4 months. In chronic haemolytic conditions such as beta-thalassaemia major and sickle cell disease, high erythrocyte turnover accelerates folate consumption; regular daily or weekly prophylaxis (1–5 mg/day depending on age and weight) is indicated to avoid aplastic and megaloblastic crises.