Trypanocidal resistance in Trypanosoma evansi in vitro: effects of verapamil, cyproheptidine, desipramine and chlorpromazine alone and in combination with trypanocides.

A study was conducted in vitro to assess the ability of calcium antagonists to reverse trypanocidal resistance in Trypanosoma evansi. Susceptibility patterns of sensitive and resistant parasites were evaluated against calcium antagonists of several chemical classes (verapamil, cyproheptidine, desipramine and chlopromazine), alone and in combination with suramin, diminazene aceturate or melarsen oxide cyteamine. The putative resistance modulators were intrinsically antitrypanosomal, but were unable to reverse resistance to any of the trypanocides tested. It was thus concluded that resistance to these trypanocides in T. evansi may differ from drug resistance mechanisms occurring in cancer cells, malaria or in South American trypanosomosis, where calcium antagonists have successfully reversed resistance.