We have incorporated several inhibitors of sterol biosynthesis into long-circulating polyethyleneglycol-polylactide (PEG-PLA) nanospheres in order to improve the bioavailability of these poorly soluble compounds. Mice infected with CL and Y strains of Trypanosoma cruzi and treated for 30 consecutive days with DO870-loaded nanospheres at doses of 3 mg/kg/day, by the intravenous route, showed a significant cure rate (60-90%) for both strains. The activity was dose dependent and significant activity was observed for doses > or = 0.75 mg/kg/day. No cure was observed in mice treated with unloaded nanoparticles. Ketoconazole and itraconazole failed to induce cure against the Y strain even in the entrapped form.