How effective are sodium nitrite and sodium thiosulfate in treating cyanide toxicity?

Updated: May 30, 2020
  • Author: Inna Leybell, MD; Chief Editor: Michael A Miller, MD  more...
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Answer

Sodium nitrite and sodium thiosulfate are often used in combination and are currently considered second-line therapy after hydroxocobalamin. Sodium nitrite is rapidly effective but can cause life-threatening toxicity, whereas sodium thiosulfate has a somewhat delayed effect but is far safer.

Sodium nitrite induces methemoglobin in red blood cells, which combines with cyanide, thus releasing cytochrome oxidase enzyme. Sodium thiosulfate donates a sulfur atom necessary for the transformation of cyanide to thiocyanate by rhodanese, thus increasing the activity of the endogenous detoxification system. The thiocyanate is then renally excreted.

Sodium nitrite should not be used in patients with smoke inhalation unless their carboxyhemoglobin concentration is very low (< 10%). The induction of methemoglobinemia by sodium nitrite compounds the effect of any existing carboxyhemoglobinemia, significantly reduces the oxygen-carrying capacity of blood. In addition, vasodilation from sodium nitrite may result in significant hypotension and cardiovascular collapse. [29]

Appropriate dosing of sodium nitrite has not been established in children. Consequently, these patients are at increased risk for excessive methemoglobinemia, hypotension, or both.


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