STUDIES UPON THE PERSISTENCE OF ACTION OF DIGITALIS AND DIGITALIS BODIES

¹ From the Department of Pharmacology, Medical College of Virginia, Richmond, Virginia

Digitalis bodies have been assayed by slow continuous intravenous injections into pigeons, and the results compared, in several instances, to similar values derived from experiments upon cats employing the method of Hatcher and Brody. Pigeons are approximately 25 per cent more tolerant to digitalis and its derivatives than cats. Against ouabain and strophanthin pigeons appear to have about twice as much tolerance as cats.

When digitalis preparations are administered by vein to pigeons in amounts of 75 per cent of the acute average m.l.d. many fatalities occur, some only after several days. In the case of digitoxin all animals die after the injection of 75 per cent of the average acute m.l.d. These results indicate the importance of the time factor in the various biological assay methods for standardizing digitalis.

Various lots of Verodigen and strophanthin show a remarkable constancy in acute toxicity; the reverse being true for digitoxin.

Persistence of action of various digitalis substances in pigeons was established by injecting 75 per cent (40 per cent in the case of digitoxin) of the average m.l.d. of the preparation and then, by determining at various intervals the amount of the same preparation necessary to produce death. Tinctures were found to vary in their persistence of effect; three showing no persistence of effect after five days, one, however, evidencing persistence for a period of over ten days. Ouabain showed a continuance of effect for five days; Verodigen up to about two weeks; strophanthin about three weeks; and digitoxin even longer.

The persistence of effect of digitalis bodies, as well as their acute toxicity, should be taken into consideration in the intelligent clinical usage of these substances.