Also: oral liquid, injection
Mechanism
Reduced to tetrahydrofolate, the carrier of one-carbon units for purine, thymidine and methionine synthesis: without it, dividing cells cannot make DNA.
Indications
- Folate deficiency anemia
- Pregnancy and preconception, to prevent neural tube defects
- Alongside methotrexate
- Chronic hemolysis, where demand is high
Formulations
Dosing concepts
Preconception
Started before conception, because the neural tube closes in the first weeks, often before pregnancy is recognised. Higher doses are used with previous affected pregnancy, diabetes, obesity, or antiseizure medication.
With methotrexate
Taken on days other than the methotrexate day, to reduce mucositis and gastrointestinal effects without abolishing efficacy.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- Near complete
- Half-life
- Body stores last months, unlike B12's years
- Elimination
- renal: Excess excreted in urine
Adverse effects
- Generally very well toleratedcommon
- Masking of B12 deficiencyseriousThe important harm: it corrects the megaloblastic anemia while neurological damage continues unchecked.
Contraindications & precautions
Contraindications
- Untreated B12 deficiency
- Undiagnosed megaloblastic anemia
Precautions
- Always check B12 status first
Interactions
No curated interaction entries yet for this agent.
Monitoring
B12 level BEFORE starting
The single most important rule for this vitamin
Hemoglobin and mean cell volume
Response
Counselling points
- If you could become pregnant, this is taken before conception, not after a positive test.
- If you take methotrexate, take this on the days you are told and not on your methotrexate day.
- Daily, with or without food.
Clinical pearls
- The sequencing rule, B12 before folate, is one of the few pieces of vitamin prescribing that carries real neurological consequences for getting it wrong.
- Antiseizure medications, particularly the enzyme inducers, increase folate requirements and neural tube risk, which is why preconception doses are higher in epilepsy.
References & review
- Folic acid product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.