Pharmacokinetics of cyanide in poisoning of dogs, and the effect of 4-dimethylaminophenol or thiosulfate.

Cyanide in blood, plasma, and urine of dogs after administration of K14CN was determined with the isotope dilution technique. The addition of large amounts of inactive KCN as soon as possible to a sample to be analyzed inhibited the decrease of the original cyanide concentration. After administration of several lethal doses of cyanide into the stomach or by slow intravenous infusion a concentration of about 40 micron cyanide in plasma was found at the moment of respiratory arrest. Since 60% of the cyanide in plasma was bound to proteins the concentration of free cyanide which stopped respiration was about 16 micron. Quick formation of ferrihemoglobin by i.v. injection of 4-dimethylaminophenol after plasma cyanide had risen to or above 40 micron decreased the cyanide concentration in plasma and restored respiration, while cyanide was accumulated in red cells by formation of ferrihemoglobin cyanide. Equilibrium constants calculated for the reaction between ferrihemoglobin and cyanide in vivo indicated that the reaction approached equilibrium in a few minutes. Up to 60% of the radioactive cyanide absorbed was found as non-cyanide radioactivity in the urine.