Hydroxocobalamin is a strong red chromophore with absorption maxima at 274 nm and 351 nm and no absorption above 600 nm. No other clinical adverse effects are noted and allergic reactions are rare. In healthy adult smokers, 5 g of IV hydroxocobalamin is associated with a transient reddish discoloration of the skin, mucous membranes and urine and a mean elevation in systolic blood pressure of 14%, with a concomitant 16% decrease in heart rate. Based on the limited efficacy data available, as well as the more widely documented safety data, hydroxocobalamin is a safe and effective first-line antidote for cyanide toxicity and has been demonstrated to be efficacious in patients with cyanide poisoning with whole blood cyanide levels up to 150 μmol/L. In cases of ingestion of cyanide with suicidal intent (where blood cyanide levels may be >150 μmol/L or plasma lactate concentrations >20 μmol/L), the usual dose of 5–10 g may be insufficient.
At higher blood cyanide concentrations, there is little further rise in plasma cyanocobalamin and it is suggested that the rate-limiting step in the formation of cyanocobalamin is the availability of antidote, not the absence of cyanide ions. The amount of cyanocobalamin formed after a dose of 5 g hydroxocobalamin correlates linearly until a blood cyanide level of 40 μmol/L is reached. As the half-life of cyanide in smoke inhalation victims is calculated to be between 1.2 and 3.0 hours, it is suggested that hydroxocobalamin can be satisfactorily used as single-dose therapy. The half-life of hydroxocobalamin in cyanide-exposed patients is 26.2 hours. Hydroxocobalamin and cyanocobalamin are excreted by the kidney. In Australian it is approved for use under the Special Access Scheme. Antidotal doses of hydroxocobalamin are approximately 5000 times the physiological dose.
It complexes with cyanide, on a mole-for-mole ratio, to form cyanocobalamin. It is the cyanide antidote most widely used in Europe. Peter Cameron MBBS MD FACEM, in Textbook of Adult Emergency Medicine, 2020 Specific cyanide antidotes ( Table 25.13.1) Hydroxocobalamin (Cyanokit)Ī systematic review of cyanide poisoning management for the Australian Resuscitation Council has recommended this as the initial antidote for the management of adults with suspected severe cyanide poisoning.
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