THIOCYANATE FORMATION IN CYANIDE POISONING AS AFFECTED BY METHYLENE BLUE AND SODIUM NITRITE

¹ From the Laboratory of Pharmacology, The University of Michigan Medical School, Ann Arbor

The changes in the serum concentration and urinary excretion of thiocyanate, after sublethal doses of cyanide, were compared in dogs and rabbits, untreated, treated with sodium nitrite and treated with methylene blue.

The average normal serum thiocyanate concentration was 111 gamma per cent (SCN) in dogs and 42 gamma per cent in rabbits. The average normal daily excretion was 0.6 mgm. (SCN) in both animals.

The administration of cyanide resulted in a greater and more rapid increase and a more rapid fall in the serum thiocyanate concentration of the rabbit than of the dog.

Sodium nitrite caused a definite initial depression of the increase in serum thiocyanate concentration after cyanide, in keeping with the hypothesis that at least a part of the cyanide would be held as cyanmethemoglobin and would thus be unavailable for thiocyanate formation. This effect was more marked in dogs than in rabbits. A part of this action of sodium nitrite was explained by a destructive effect on thiocyanate itself.

Methylene blue produced a stimulation of thiocyanate formation in the rabbit and a questionable depression of this process in the dog.

Possible causes for the differences in results in the two animals are discussed.

The recovery of cyanide as urinary thiocyanate was rapid in the rabbit and slow in the dog, agreeing with the respective rapid and slow falls in serum thiocyanate concentrations in the two animals. The degree of recovery was very low in the dog in comparison with that in the rabbit which was partly explained by the slow excretion of thiocyanate in the former animal and the consequent difficulties in complete recovery.

The importance of thiocyanate formation as a detoxication process in the dog is discussed.