Specific cyanide antidotes

Dicobalt edetate is the treatment of choice for proven cyanide poisoning, but should not be used when the diagnosis is uncertain as in the absence of cyanide, there may be serious side-effects.

Other options include:

• thiosulphate:
  • sodium salt combines with cyanide under the action of hepatic rhodanase enzyme
  • triggers an osmotic diuresis
  • not very effective when used alone because it penetrates cell membranes more slowly than cyanide
    
    
• nitrites:
  • provide a rapid way of inactivating cyanide by converting a portion of the body's haemoglobin to methaemoglobin - methaemoglobin contains ferric rather than ferrous iron
  • 40% of the body haemoglobin may be converted without serious effects. This represents about 300 g haemoglobin which, theoretically, should chelate 500 mg of cyanide ion
  • inhalation of amyl nitrite is poorly tolerated since only low levels of circulating methaemoglobin are produced before the induction of profound hypotension
    
    
• oxygen - this has a synergistic antidotal action when used in combination with sodium thiosulphate and sodium nitrite.
  
  
• hydroxocobalamin:
  • chelates to form cyanocobalamin
  • complex is excreted renally
  • high concentrations are required and effect is limited