Therapy with nitrites is not innocuous, since methemoglobin cannot transport oxygen in the blood. Once bound with the cyanide, the methemoglobin becomes cyanmethemoglobin ( Anon, 1998). Cyanide is more strongly drawn to methemoglobin than to the cytochrome oxidase of cells, effectively pulling the cyanide off the cells and onto the methemoglobin ( Berlin, 1970 Baskin and Brewer, 1997).

This antidote converts a portion of the hemoglobin’s iron from ferrous iron to ferric iron, converting the hemoglobin into methemoglobin. For example, in overdoses of phenytoin or salicylates, the capacity of the liver to metabolize the drugs is usually exceeded, and elimination changes from first-order (constant half-life) to zero-order (variable half-life) kinetics.The US standard cyanide antidote kit uses a small inhaled dose of amyl nitrite followed by IV sodium nitrite and sodium thiosulfate ( Anon, 1998 Rotenberg, 2003a). The clearance of drugs may be different at toxic concentrations than at therapeutic concentrations. In some cases, renal elimination of weak acids can be accelerated by urinary alkalinization, whereas renal elimination of some weak bases can be accelerated by urinary acidification.

Drugs with low volumes of distribution, including lithium, phenytoin, and salicylates, are more readily removed by dialysis and diuresis procedures.

For example, drugs with large apparent volumes of distribution, such as antidepressants and antimalarials, are not amenable to dialysis procedures for drug removal. Knowledge of a toxin's absorption, distribution, and elimination permits assessment of the value of procedures designed to remove it from the skin or gastrointestinal tract. This term denotes the disposition of poisons in the body (ie, their pharmacokinetics).

Cyanide antidote kit