How effective is hydroxocobalamin in treating cyanide toxicity?

Updated: May 30, 2020
  • Author: Inna Leybell, MD; Chief Editor: Michael A Miller, MD  more...
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Hydroxocobalamin, which is considered the drug of choice in continental Europe and Australia, is approved by the US Food and Drug Administration (FDA) for treating known or suspected cyanide poisoning. [32, 33] Coadministration of sodium thiosulfate (through a separate line or sequentially) has been suggested to have a synergistic effect on detoxification.

Hydroxocobalamin combines with cyanide to form cyanocobalamin (vitamin B-12), which is renally cleared. [34] Alternatively, cyanocobalamin may dissociate from cyanide at a slow enough rate to allow for cyanide detoxification by the mitochondrial enzyme rhodanese.

A review by Hall et al notes that hydroxocobalamin has not been associated with clinically significant toxicity in antidotal doses compared with other cyanide antidotes. Hydroxocobalamin has a rapid onset of action, neutralizes cyanide without interfering with cellular oxygen use, is conducive to prehospital use due to its tolerability and safety profiles, and is safe for use in patients with smoke inhalation. [35]

Adverse effects of hydroxocobalamin administration include transient hypertension (a benefit in hypotensive patients), reddish brown skin, mucous membrane and urine discoloration, and rare anaphylaxis and anaphylactoid reactions. Because of its bright red color, it also interferes with co-oximetry (about a 5% increase in carboxyhemoglobin levels) and blood chemistry testing (bilirubin, creatinine kinase and possibly liver enzymes, creatinine, phosphorus, glucose, magnesium, and iron levels). [36] It can also interfere with hemodialysis. [37]

Certain medications should not be administered simultaneously or through the same line as hydroxocobalamin. These include diazepam, dopamine, dobutamine, and sodium thiosulfate.

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