What is the pathophysiology of cyanide toxicity?

Updated: May 30, 2020
  • Author: Inna Leybell, MD; Chief Editor: Michael A Miller, MD  more...
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Cyanide exposure most often occurs via inhalation or ingestion, but liquid cyanide can be absorbed through the skin or eyes. Once absorbed, cyanide enters the blood stream and is distributed rapidly to all organs and tissues in the body. [15]

Inside cells, cyanide attaches itself to ubiquitous metalloenzymes, rendering them inactive. Its principal toxicity results from inactivation of cytochrome oxidase (at cytochrome a3), thus uncoupling mitochondrial oxidative phosphorylation and inhibiting cellular respiration, even in the presence of adequate oxygen stores. Cellular metabolism shifts from aerobic to anaerobic, with the consequent production of lactic acid. Consequently, the tissues with the highest oxygen requirements (brain and heart) are the most profoundly affected by acute cyanide poisoning.

The LCt50 (the concentration-time product capable of killing 50% of the exposed group) for hydrogen cyanide is 2500-5000 mg/min/m3. Vapor exposures in high concentrations (at or above the LCt50) typically can cause death in 6-8 minutes. [4] The lethal oral doses of HCN and cyanide salts are estimated to be 50 mg and 100-200 mg, respectively. For skin exposures, the LD50 (the dose capable of killing 50% of the exposed group) is estimated to be 100 mg/kg.

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