Cyanides: Agents of Death

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They act quickly, and it takes only a small amount to kill. The average fatal dose is only 50 or 60 mg of gaseous hydrogen cyanide or of a solid salt containing the cyanide ion.
Cyanide blocks the oxidation of glucose inside the cell by forming a stable complex with iron (III) ions in oxidative enzymes called cytochrome oxidases. These enzymes normally act by providing electrons for the reduction of oxygen in the cell. Cyanide blocks this action and brings an abrupt end to cellular respiration, causing death in minutes.
Any antidote for cyanide poisoning must be administered quickly. Providing 100% oxygen to support respiration can sometimes help. Sodium nitrite is often given intravenously to oxidize iron atoms in the enzymes back to the active Fe3+ form. Sodium thiosulfate is then used if time permits. The thiosulfate ion transfers a sulfur atom to the cyanide ion, converting it to the relatively innocuous thiocyanate ion.

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