Section 18 · Monograph
Cyanocobalamin
Reviewed Nov 2026FDA label
Vitamin B12Vitamin
- Forms
- Inj: 1000mcg/mL | Tab: 100-5000mcg
- Dose
- B12 deficiency with neurologic involvement: 1000mcg IM daily x1 week, weekly x4 weeks, then monthly; oral high-dose option for maintenance
- MOA
- Cofactor for methionine synthase and methylmalonyl-CoA mutase
Indications
- Vitamin B12 deficiency including pernicious anemia and neurologic manifestations (subacute combined degeneration, neuropathy)FDA-labeled
Mechanism of Action
- Cofactor for methionine synthase and methylmalonyl-CoA mutase; essential for myelin synthesis and DNA synthesis
Full Dosing
Adult / usual
- B12 deficiency with neurologic involvement: 1000mcg IM daily for 1 week, then weekly for 4 weeks, then monthly (lifelong in pernicious anemia)
- High-dose oral therapy (1000-2000mcg daily) is acceptable for maintenance when absorption is adequate
Contraindications
- Hypersensitivity to cobalt or cobalamin
- Early Leber's disease (hereditary optic nerve atrophy)
Drug Interactions
- Metformin, PPIs and H2 blockers and colchicine reduce absorption
- Nitrous oxide inactivates vitamin B12
- Chloramphenicol may antagonize the response
Adverse Effects
- Injection-site pain
- Hypokalemia early in treatment of severe megaloblastic anemia
- Rare hypersensitivity
Monitoring Parameters
- CBC, B12 level with methylmalonic acid or homocysteine
- Potassium early in severe deficiency
- Neurologic recovery
Pregnancy & Lactation
- Safe; requirements are increased in pregnancy
- Compatible with breastfeeding