Cyanocobalamin

Cyanocobalamin is a synthetic form of vitamin B12, a water‑soluble vitamin essential for DNA synthesis, red blood cell formation, and neurological function. It features a cobalt center with a cyanide ligand and is one of several cobalamin forms used in supplements and medicines.

Cyanocobalamin is widely used because it is chemically stable and inexpensive to manufacture. Other naturally occurring and therapeutic forms include hydroxocobalamin, methylcobalamin, and adenosylcobalamin. After administration, cyanocobalamin is converted in the body to the active coenzymes methylcobalamin and adenosylcobalamin, which participate in important biological reactions.

In the body, vitamin B12 acts as a cofactor for methionine synthase and for methylmalonyl‑CoA mutase. These reactions support DNA synthesis and the metabolism of certain fatty acids and amino acids. Absorption occurs in the ileum and requires intrinsic factor, a stomach‑secreted protein; at high oral doses, a portion can be absorbed by passive diffusion without intrinsic factor. Plasma transport is mainly via transcobalamin II, and excess B12 is stored in the liver with a long half‑life.

Medical uses include treatment and prevention of vitamin B12 deficiency, pernicious anemia, and malabsorption syndromes, as well as in people with strict vegan or other dietary restrictions. It can be given by intramuscular or subcutaneous injection, or orally when absorption is adequate; high‑dose oral therapy can be effective due to passive uptake.

Safety is generally good for most patients. Allergic reactions are rare. High‑dose therapy may precipitate hypokalemia during rapid erythropoiesis; it can also mask symptoms of folate deficiency. Cyanocobalamin is contraindicated in certain conditions, and supplementation should be tailored to individual needs.