Therapy of visceral leishmaniasis due to Leishmania infantum: experimental assessment of efficacy of AmBisome.

The tolerance and efficacy of amphotericin B (AmB) deoxycholate (Fungizone) were compared with those of liposomal AmB (AmBisome) in a murine model of visceral leishmaniasis induced by Leishmania infantum. Control groups consisted of untreated mice and mice treated with a pentavalent antimonial (Glucantime). BALB/c mice were infected intravenously on day 0 with 10(7) promastigotes of L. infantum and then treated from day 7 to 17 (early treatment group) or from day 60 to 70 (delayed treatment group). The pentavalent antimonial was administered daily by intraperitoneal injection, whereas AmB formulations were administered intravenously on alternate days. On days 20, 60, and 120 (early treatment group) and on days 72 and 125 (delayed treatment group), parasite burdens in the liver, spleen, and lungs were determined by subculturings using a microtitration method. A dose range study showed that administration of AmBisome at the well-tolerated doses of 5 or 50 mg/kg of body weight completely eradicated the parasites from the tissues. At 0.8 mg/kg, AmBisome proved more efficacious than AmB deoxycholate administered at the same dose. We also compared the levels of AmB deoxycholate and AmBisome in plasma and tissue. Mice treated with AmBisome had levels of AmB in tissue much higher than did AmB deoxycholate-treated mice with persistent detectable levels 14 weeks after treatment. These results seem to account for the remarkable efficacy of the liposomal formulation of AmB in the treatment of visceral leishmaniasis due to L. infantum.