In vitro interactions between sitamaquine and amphotericin B, sodium stibogluconate, miltefosine, paromomycin and pentamidine against Leishmania donovani

Objectives: To evaluate in vitro interactions between sitamaquine and the current antileishmanial drugs amphotericin B, sodium stibogluconate, miltefosine, paromomycin and pentamidine against intracellular Leishmania donovani amastigotes in peritoneal mouse macrophages. A second objective was to evaluate the susceptibility of antimony-resistant L. donovani isolates to sitamaquine. Methods: Mouse peritoneal macrophages were infected with L. donovani amastigotes. Drug susceptibility was assessed in a standard 5 day assay and drug interactions with a modified fixed ratio isobologram method. Fractional inhibitory concentrations (FICs), sum FICs (Sigma FICs) and an overall mean Sigma FIC were calculated for each combination. The nature of interaction was classified on the basis of the mean Sigma FIC as follows: synergy as mean Sigma FIC <= 0.5, indifference as mean Sigma FIC between > 0.5 and <= 4 and antagonism as mean Sigma FIC > 4. Results: Interactions between sitamaquine and amphotericin B, sodium stibogluconate, paromomycin and miltefosine were classified as indifferent at the 50% and 90% effective concentration (EC(50) and EC(90), respectively) levels. The sitamaquine/pentamidine combination was synergistic, with overall mean Sigma FICs from 0.5 to 0.6 at the EC(50) level and from 0.3 to 0.7 at the EC(90) level. Sitamaquine displayed in vitro activity against L. donovani isolates resistant to sodium stibogluconate. Conclusions: This study expands the preclinical data on drug combinations and provides the basis for further studies as antileishmanial chemotherapy is moving towards multidrug treatment regimens.