[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Antianaemia agents (iron, folic acid, vitamin B12)](https://durgical.com/en/pharmacology/classes/antianaemia-agents/) › Cyanocobalamin [Pharmacology](https://durgical.com/en/pharmacology/) · [Antianaemia agents (iron, folic acid, vitamin B12)](https://durgical.com/en/pharmacology/classes/antianaemia-agents/) # Cyanocobalamin The common form of vitamin B12 used to treat and prevent B12 deficiency, including pernicious anaemia, by injection, nasal or oral route. Updated 2026-11-01 - Class: [Antianaemia agents (iron, folic acid, vitamin B12)](https://durgical.com/en/pharmacology/classes/antianaemia-agents/) - Target: Gastric intrinsic factor (absorption) and the B12-dependent enzymes - ATC code: B03BA01 Also called: vitamin B12 ◆**Gastric intrinsic factor (absorption) and the B12-dependent enzymes**Cyanocobalamin ⓘ The figure shows human intrinsic factor holding cobalamin, the complex the ileum absorbs; in pernicious anaemia this factor is missing, so oral B12 is unreliable. **Target in 3D:** Gastric intrinsic factor (absorption) and the B12-dependent enzymes. PDB structure 2PMV (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/2PMV) · Drag to rotate · pinch to zoom ## Mechanism of action Cyanocobalamin is converted in the body to the two active coenzymes. Methylcobalamin lets methionine synthase regenerate tetrahydrofolate, so DNA synthesis resumes; adenosylcobalamin lets methylmalonyl-CoA mutase work, which matters for myelin. Dietary B12 needs gastric intrinsic factor to be absorbed in the ileum. - Cobalamin is delivered to cells bound to transcobalamin - Methylcobalamin lets methionine synthase recycle folate - Adenosylcobalamin turns methylmalonyl-CoA into succinyl-CoA - DNA synthesis and myelin recover ## Pharmacokinetics **Absorption** Orally, needs intrinsic factor (ileum); injected intramuscularly or deep subcutaneously **Distribution** Stored in the liver **Elimination** Much of an injected dose appears in urine, more so if given intravenously ## Indications - Pernicious anaemia (lifelong parenteral treatment) [Pernicious anaemia →](https://durgical.com/en/conditions/pernicious-anaemia/) - Megaloblastic anaemia from B12 deficiency: gastrectomy, ileal disease, strict vegan diet [Megaloblastic anaemia (B12 or folate deficiency) →](https://durgical.com/en/conditions/megaloblastic-anaemia/) ## Adverse effects ### Common - Diarrhoea - Itching, rash - Feeling of swelling of the whole body ### Serious (rare, important) - Hypokalaemia and sudden death when severe megaloblastic anaemia is treated intensively - Pulmonary oedema and heart failure early in treatment - Anaphylaxis (rare) ## Contraindications - Hypersensitivity to cobalamins - Early Leber's hereditary optic neuropathy (rapid optic atrophy reported) ## Key interactions **Folic acid alone** Can correct the anaemia of B12 deficiency while nerve damage progresses; it is not a substitute **Marrow-suppressing drugs (e.g. chloramphenicol)** Blunt the response to vitamin B12 ## What is monitored - Reticulocyte count (rises within days if the diagnosis is right), haemoglobin and MCV - Potassium and platelets early in treatment of severe megaloblastic anaemia - Neurological symptoms over time ## Administration and safety - Intramuscular or deep subcutaneous injection; the intravenous route is avoided because most is lost in urine - Nasal and oral forms are used for maintenance in selected patients ## Nursing care - Check potassium in the first days of treating severe anaemia - Explain that pernicious anaemia needs treatment for life - Ask about numbness, unsteady gait and memory problems over time ## Pregnancy and breastfeeding B12 needs rise in pregnancy and breastfeeding; deficiency, common with strict vegan diets, also affects the breast-fed infant. ## Memory aid B12 = «Blood and Brain»: it fixes both; folate fixes only the blood. ## Test yourself Think of the answer, then tap the question to see it. ## Why is oral B12 unreliable in pernicious anaemia? Intrinsic factor, needed for ileal absorption, is missing. ## Which electrolyte can fall dangerously early in treatment? Potassium. ## Which two enzymes need vitamin B12? Methionine synthase and methylmalonyl-CoA mutase. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/cyanocobalamin/) ## Related drugs - [Hydroxocobalamin](https://durgical.com/en/pharmacology/hydroxocobalamin/) - [Folic acid](https://durgical.com/en/pharmacology/folic-acid/) ## Related conditions - [Pernicious anaemia](https://durgical.com/en/conditions/pernicious-anaemia/) - [Megaloblastic anaemia (B12 or folate deficiency)](https://durgical.com/en/conditions/megaloblastic-anaemia/) [← Back to the class: Antianaemia agents (iron, folic acid, vitamin B12)](https://durgical.com/en/pharmacology/classes/antianaemia-agents/) Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given. Sources: [DailyMed - CYANOCOBALAMIN injection, solution](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=92f08572-cfd9-4a99-bb49-937ab94eeb62) (DailyMed (U.S. National Library of Medicine), 2026); [Cyanocobalamin Injection: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a605007.html) (MedlinePlus (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 45 (McGraw Hill, 2023); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=B03BA01) (WHO Collaborating Centre for Drug Statistics Methodology, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/cyanocobalamin/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/cyanocobalamin/