An in vitro model for investigation of chemotherapeutic agents in leishmaniasis.

Clinically achievable concentrations of the three major antileishmanial drugs in use--pentavalent antimony, pentamidine, and amphotericin B--eliminated 90%--100% of the mammalian forms (amastigotes) of Leishmania tropica and Leishmania donovani from in vitro infected human monocyte-derived macrophages. This is apparently the first report of in vitro susceptibility of Leishmania to pentavalent antimony or to pentamidine. The insensitivity of insect forms (promastigotes) multiplying in cell-free media to thee drugs suggests that amastigotes are more sensitive than promastigotes to these antileishmanial agents. Alternatively, macrophages may concentrate or metabolize the drugs to increase their toxicity. In contrast, amphotericin B was toxic to both amastigotes and promastigotes. The sensitivities of Leishmania within human monocyte-derived macrophages in vitro to clinically achievable concentration of antileishmanial agents suggests that this model may be useful for investigation of mechanisms of sensitivity and resistance of antimicrobial agents against Leishmania.