Antianaemic (vitamin B12)
Cyanocobalamin is the synthetic form of vitamin B12, essential for blood cell formation and nervous system function. It is used to treat pernicious anaemia and other vitamin B12 deficiencies due to malabsorption, usually by intramuscular injection. Oral supplementation may be needed in vegetarian/vegan diets.
Also known as: cobalamina, vitamina B12, vitamin B12, Cytacon
Long-term omeprazole may reduce absorption of dietary vitamin B12, but rarely affects supplemental cyanocobalamin.
Proton pump inhibitors such as omeprazole reduce the gastric acid secretion needed to release protein-bound vitamin B12 from food, so long-term use can reduce dietary B12 absorption and, in rare cases, lead to vitamin B12 deficiency. Supplemental cyanocobalamin at pharmacological doses is absorbed by passive diffusion, independent of intrinsic factor and pH, so oral supplementation maintains efficacy. In patients on chronic omeprazole with risk factors (elderly, vegetarian diet, atrophic gastritis), consider monitoring B12 and supplementing if needed.
Long-term omeprazole may reduce absorption of dietary vitamin B12, but rarely affects supplemental cyanocobalamin.
PPI-induced prolonged hypochlorhydria reduces release of food-bound B12.
Monitor blood count and B12 levels in elderly or malnourished patients.
Macrocytic anaemia or persistent neuropathic symptoms.
With long-term PPI use, monitor B12 levels in at-risk patients.
DailyMed (FDA) — approved Cyanocobalamin label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=3bb870d8-128d-75ea-e063-6394a90a707b ; approved Omeprazole label: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=6ea9a6f3-b756-4cdf-b3db-f666a2c17d66 — additional reference: Prontuário Terapêutico do INFARMED (11th ed., 2012)
Chronic alcoholism may reduce absorption of dietary vitamin B12, but it little affects oral cyanocobalamin at therapeutic doses.
In patients with alcoholism, monitor B12 levels and consider higher doses if needed.
EMC-UK (MHRA) — approved Cyanocobalamin SmPC: https://www.medicines.org.uk/emc/product/5716/smpc
Cyanocobalamin is contraindicated in Leber's disease because of the risk of worsening optic atrophy.
Do not use cyanocobalamin in Leber's disease; consider hydroxocobalamin if needed.
EMC-UK (MHRA) — approved Cyanocobalamin SmPC: https://www.medicines.org.uk/emc/product/5716/smpc
Cyanocobalamin can be used in pregnancy when B12 deficiency justifies it.
Use at the usual therapeutic doses; untreated deficiency is harmful to the fetus.
Excreted into breast milk; compatible with breastfeeding.
No specific additional contraception.
EMC-UK (MHRA) — approved Cyanocobalamin SmPC: https://www.medicines.org.uk/emc/product/5716/smpc
Clinical and educational support tool. The information does not replace a medical prescription or the opinion of a qualified healthcare professional.
Vitamin B12 (cobalamin) essential for haematopoiesis, nucleoprotein and myelin synthesis; the cyano form is the most widely used, with haematopoietic activity identical to hydroxocobalamin. The parenteral route is rapid and reliable; oral absorption depends on intrinsic factor.
Essential cofactor for methionine synthase (conversion of homocysteine to methionine, with tetrahydrofolate regeneration) and for methylmalonyl-CoA mutase (odd-chain fatty acid catabolism) — deficiency causes megaloblastic anaemia and subacute combined degeneration of the spinal cord.
Oral absorption depends on intrinsic factor and calcium in the terminal ileum (cubilin receptor pathway); ~1% is absorbed by simple diffusion (only relevant with very high doses); IM/SC absorption is rapid (plasma peak <1 h); plasma transport via transcobalamins I and II.
In the free (unbound) form, it is rapidly excreted in urine: 50-98% of an injected 100-1000 mcg dose appears in urine within 48 h (most within the first 8 h); most of the retained dose is stored in the liver.
Free cobalamin has a short plasma half-life until hepatic uptake (transcobalamin II-bound vitamin has a half-life of 60-90 min); the hepatic reserve extends the clinical effect for months; the half-life of stored vitamin is ~6 days until tissue utilisation.
Medicines from the same therapeutic group (ATC classification) or the same pharmacological class.
