Pharmacology. Hydroxocobalamin and cyanocobalamin are analogs of vitamin B12 that have been used for the treatment of pernicious anemia. Hydroxocobalamin was approved as an antidote for human cyanide poisoning in France in 1996 and is now available in the United States. Hydroxocobalamin rapidly exchanges its hydroxyl group with free cyanide to produce nontoxic, stable cyanocobalamin. When administered to patients with cyanide poisoning, it rapidly improves the heart rate and systolic blood pressure and decreases acidemia. In humans, outcome is best when hydroxocobalamin is administered before cardiopulmonary arrest occurs. Animal studies suggest enhanced antidotal efficacy if thiosulfate (See Thiosulfate, Sodium) is given in addition to hydroxocobalamin therapy, but the drugs are not compatible in the same IV line. In normal individuals given 5- and 10-g doses, the plasma half-life values of hydroxocobalamin average 26 and 31 hours, respectively. Oral absorption is extremely poor; intranasal absorption occurs with very small doses.

Indications

1. 
   

   Treatment of acute cyanide poisoning or patients suspected to be at high risk for cyanide poisoning (eg, smoke inhalation victims; see VII. Formulations below).

   
   
2. 
   

   Prophylaxis against cyanide poisoning during nitroprusside infusion has been proposed.

Contraindications. Use caution when managing patients with known hypersensitivity to hydroxocobalamin or cyanocobalamin, and consider alternative treatments.

Adverse effects

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