SPECIFICITY RELATIONSHIPS BETWEEN TYPES OF ARSENICALS AND TYPES OF TRYPANOSOMES

¹ From the Department of Pharmacology of the University of Wisconsin, Madison

Several organic arsenicals were found to be effective in curing Trypanosoma lewisi infection in the rat, but were ineffective on infections caused by Trypanosoma equiperdum. Members of another group of organic arsenicals were found to be effective in curing T. equiperdum infections in the rat but were inactive in T. lewisi infections. Those compounds effecting cures on the T. lewisi infections possessed aliphatic side-chains which were acidic in nature, while those compounds curing the T. equiperdum infections possessed side-chains of a basic nature. Specificity of drug type to types of trypanosomes appears to be clearly indicated.

The trivalent arsenicals were more effective curative agents than the pentavalent arsonic acid derivatives on the T. lewisi infections. A shift in the aliphatic side-chain from the ortho position to the para position with respect to the arsenic radical produced a marked increase in therapeutic efficiency. A curative arsenical was found to be more highly bound to parasites "in vitro" than was a non-curative arsenical. "In vitro" binding power, therefore, appears to bear a definite relationship to "in vivo" curing capacity.