METABOLISM OF SODIUM NITROPRUSSIDE AND CYANIDE IN THE DOG

Blood cyanide (HCN) and thiocyanate (SCN) concentrations weremeasured at intervals in anaesthetized dogs given bolus dosesof sodium nitroprusside (SNP) 1 mg kg^–1 or potassium cyanide1.07 mg kg^–1and in animals infused with SNP 1.5 mg kg^–1for1 h. Cyanide appeared rapidly in the red cells to give peakconcentrations which accounted for more than 90% of the totalblood HCN. A delay between the peak plasma and red cell HCNconcentrations confirmed that some of the SNP was degraded inthe plasma. Comparison of HCN and SCN concentrations with thosemeasured previously in patients receiving an infusion of SNPsuggests that the degradation of SNP and detoxication of HCNmay be more rapid in the dog. The various pathways of HCN detoxicationare discussed in relation to the reduced formation of SCN indogs receiving SNP compared with those receiving KCN. ^*Present addresses: Department of Anaesthesia, Royal Infirmary,Bristol BS2 8HW.Present addresses: Department of Medicine, Charing Cross Hospital,London W6 8RF.