What is cyanide toxicity?

Updated: May 30, 2020
  • Author: Inna Leybell, MD; Chief Editor: Michael A Miller, MD  more...
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Cyanide toxicity is generally considered to be a rare form of poisoning. However, cyanide exposure occurs relatively frequently in patients with smoke inhalation from residential or industrial fires. [1] In addition, intensive treatment with sodium nitroprusside or long-term consumption of cyanide-containing foods is a possible source of cyanide poisoning.

Depending on its form, cyanide may cause toxicity through inhalation, ingestion, dermal absorption, or parenteral administration. Clinical manifestations vary widely, depending on the dose and route of exposure, and may range from minor upper airway irritation to cardiovascular collapse and death within minutes. (See Presentation.) In severe cases, rapid, aggressive therapy consisting of supportive care and antidote administration can be lifesaving. (See Treatment and Medication.)

Cyanide exists in gaseous, liquid, and solid forms. Hydrogen cyanide (HCN, also known as prussic acid) is a volatile liquid that boils at 25.6° C (78.1° F). Potassium and sodium cyanide salts are water soluble, whereas mercury, copper, gold, and silver cyanide salts are poorly water soluble.

In addition, a number of cyanide-containing compounds, known as cyanogens, may release cyanide during metabolism. These include, but are not limited to, cyanogen chloride and cyanogen bromide (gases with potent pulmonary irritant effects), nitriles (R-CN), and the vasodilator nitroprusside sodium, which may produce iatrogenic cyanide poisoning during prolonged or high-dose intravenous (IV) therapy (>10 mcg/kg/min). (See Etiology.)

Industry widely uses nitriles as solvents and in the manufacturing of plastics. Nitriles may release HCN during burning or when metabolized after absorption by the skin or gastrointestinal tract. A number of synthesized and natural compounds produce HCN when burned. These combustion gases likely contribute to the morbidity and mortality from smoke inhalation. Finally, long-term consumption of cyanide-containing foods, such as cassava root or apricot seeds, [3] may lead to cyanide poisoning.

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