Antitrypanosomal activity of trivalent antimonials in vitro and its significance

The SbIII preparations available for clinical use were compared in vitro for their concentration/time/effect curves on Trypanosoma venezuelense (T. evansi), measuring decrease of motility and of parasite numbers. With these two criteria leading to similar relative results, the drugs are classified into a rapidly acting group, led by sodium emetic (AST), followed by its dimethylcysteine chelate (NAP) and Anthiomaline, and a less and more slowly acting one: Triostam, Astiban and Stibophen. The relative activity of these drugs in vitro is parallel to that encountered against Schistosoma mansoni, attributed to a similar pattern of intracellular absorption. In vivo effectiveness may depend on bioavailability of Sb in the host and the direct action on the parasite, reflected by its in vitro activity. The interplay of these two factors leads to a different in vitro/in vivo activity relationship of the antimonials even in the same host (mouse) and to its variation in other host species.