Vitamin B12 (cobalamin) deficiency
B12 deficiency in vegetarians and vegans without supplementation, patients with pernicious anaemia (anti-intrinsic factor antibodies), after gastric or ileal resection, with prolonged metformin or PPI therapy. Untreated, leads to megaloblastic anaemia and subacute combined degeneration of the spinal cord.
ICD-10 E53.83 drugs
Also known as: B12 deficiency, Pernicious anaemia, Cobalamin deficiency
Drugs used for this condition
- AHydroxocobalaminFirst line · Vitamin B12 (European form of choice) and cyanide poisoning antidoteHydroxocobalamin is the European form of choice for treating confirmed vitamin B12 deficiency in patients with pernicious anaemia, after gastric or ileal resection, and in vegetarians and vegans with confirmed deficiency. NICE 2024 and BSH 2014 recommend induction 1000 μg IM three times weekly for 2 weeks then maintenance 1000 μg every 2–3 months for life. Advantage over cyanocobalamin: fewer injections due to longer half-life. With neurological symptoms (subacute combined degeneration), induction may be extended until neurological recovery or plateau.
- AMethylcobalaminFirst line · Active coenzyme form of vitamin B12Methylcobalamin is one of the forms for treating confirmed vitamin B12 deficiency in patients with pernicious anaemia, after gastric or ileal resection, in vegetarians and vegans without supplementation, and during long-term metformin or PPI therapy. NICE 2024 and BSH 2014 regard hydroxocobalamin (the European form of choice) and cyanocobalamin as equivalent; methylcobalamin is considered an option for oral replacement. In severe deficiency with neurological symptoms, parenteral hydroxocobalamin is started first and oral methylcobalamin used for maintenance.
- AVitamin B12 (cobalamin)First line · Water-soluble B-vitamin; cofactor of methionine synthase and methylmalonyl-CoA mutaseVitamin B12 is the cornerstone of treatment for confirmed deficiency. AEMPS and FDA approve oral 1000–2000 mcg/day and intramuscular 1000 mcg on a schedule: daily for 1–2 weeks, then weekly until normalisation, then maintenance. The oral route works even with reduced absorption – a fraction is absorbed by passive diffusion. NIH ODS 2024 and British Society for Haematology 2021 accept high-dose oral therapy as equivalent to injections in most patients. Monitoring: serum B12, methylmalonic acid and homocysteine at 3 months.
How to read tiers A–F
Evidence tiers belong to the drug-indication pair, not to the drug as a whole: the same substance can be A for one condition and F for another.
- AStrong evidence – first or second line in international guidelines
- BRecommended in selected cases
- CStudy data contradict each other
- DBenefit not proven, no documented harm
- FDocumented harm, or risk without benefit