Chemotherapeutic activity of rifampicin on leishmanial amastigotes and promastigotes in vitro.

Rifampicin reduced the in vitro growth of Leishmania tropica major promastigotes and amastigotes: 100 micrograms/ml reducing the growth of amastigotes on Day 2 and 250 to 500 micrograms/ml reducing the growth of promastigotes on Day 1. A distinct effect of solvents was noted. Methanol, dimethylsulfoxide and Tween 80 appeared to increase drug effectiveness. Pretreatment of L. tropica major promastigotes with 200 micrograms/ml rifampicin for 3 days had no effect on either macrophage engulfment of the treated promastigotes or their transformation into amastigotes. Intracellular amastigotes treated for only 3 days recovered and 8-day treatment with 100 micrograms/ml rifampicin was insufficient to totally eliminate the amastigotes. The promastigotes of different strains of Leishmania showed different sensitivities to rifampicin, L. aethiopica being more sensitive than L. donovani, L. tropica minor and L. tropica major.