Sensitivity to Glucantime of Leishmania viannia isolated from patients prior to treatment.

In vitro sensitivity to pentavalent antimony (SbV) as meglumine antimoniate (Glucantime) of Leishmania of the Viannia subgenus isolated prior to treatment from patients with uncomplicated cutaneous leishmaniasis was evaluated for intracellular amastigotes in the U-937 human monocytic cell line and log phase promastigotes. The 50% effective dose (ED50) of pharmaceutical and additive-free formulations of Glucantime were determined based on the kinetics of the response of Leishmania Viannia to SbV in vitro. ED50 to SbV was inversely related to time of exposure to drug. The potency of the additive-free formulation of Glucantime was significantly greater than that of the pharmaceutical formulation, irrespective of the parasite form. In vitro sensitivity to SbV ranged from < 5.3 micrograms/ml to > 170.0 micrograms/ml. Under the conditions used, 11 (39%) of 28 strains were sensitive to clinically achievable serum concentrations of SbV. No correlation was observed between the total amount of SbV required for healing of lesions and the in vitro response to the pharmaceutical formulation of Glucantime. In contrast, a significant correlation (P = 0.001) was observed between clinical response and the in vitro sensitivity of promastigotes to the additive-free formulation of Glucantime. The greater potency of the additive-free formulation of Glucantime, the correlation of in vitro sensitivity of promastigotes to this formulation and the clinical response to treatment, and the effect of time of exposure to SbV demonstrate the importance of assay conditions on the outcome and interpretation of in vitro evaluation of drug sensitivity.