Hydroxycobalamin

Hydroxycobalamin is a water-soluble form of vitamin B12 in which cobalt is coordinated to a hydroxyl ligand within the corrin ring. It is one of the natural vitamers of cobalamin and can be converted by the body into the other active coenzyme forms, methylcobalamin and adenosylcobalamin, that participate in essential metabolic reactions such as methionine synthesis and odd-chain fatty acid metabolism. Hydroxycobalamin is produced by certain bacteria and is available as a parenteral medication for deficiency treatment and as an antidote for cyanide poisoning.

In cyanide poisoning, hydroxycobalamin acts as a cyanide scavenger by binding cyanide ions to form cyanocobalamin, which is excreted in the urine. This mechanism is harnessed in emergency medicine with preparations such as Cyanokit, intended for intravenous use. The usual adult regimen involves a dose of several grams given IV (commonly 5 g), with additional dosing considered if exposure persists or clinical response is inadequate; dosing in children is weight-based.

For deficiency treatment, hydroxycobalamin is administered by intramuscular or intravenous injection, typically in high-dose regimens to restore cobalamin levels and treat conditions such as pernicious anemia or other malabsorption-related deficiencies. It is generally well tolerated; common adverse effects are injection-site reactions and flushing. A characteristic effect of pharmacologic hydroxycobalamin preparations is temporary reddish discoloration of the skin and urine.

Hydroxycobalamin is one of four major forms of cobalamin in nature (the others being cyanocobalamin, methylcobalamin, and adenosylcobalamin) and is widely used in clinical practice due to its safety profile and cyanide-scavenging capacity.