In Vitro Efficacy and Toxicity Assessment of an Amphotericin B Gel for the Treatment of Cutaneous Leishmaniasis

<b>Background/Objectives</b>: Leishmaniasis is a neglected tropical disease caused by a protozoan parasite of <i>Leishmania</i>. This study aimed to evaluate the in vitro efficacy and toxicity of a previously developed amphotericin gel as a possible treatment for cutaneous leishmaniasis. <b>Methods</b>: First, quality control of the AmB-gel was carried out, including microbiological stability. The permeated and retained drug was tested on healthy and lacerated human skin. Tolerance to the AmB-gel was tested in vitro using HaCaT, RAW 264.7, and J774 cell lines and by an irritation test (HET-CAM). Promastigotes and amastigotes of various <i>Leishmania</i> species were tested, and the microscopic morphology of promastigotes exposed to the formulation was analyzed. Computational analysis was performed on the drug, polymer, and ergosterol in the promastigote. <b>Results</b>: The AmB-gel presented appropriate characteristics for topical use, including no microbial contamination after storage. The amount of drug retained on the intact and injured skin was 1180.00 ± 13.54 µg/g/cm² and 750.18 ± 5.43 µg/g/cm², respectively. The AmB-gel did not cause significant signs of toxicity. The IC₅₀ of the AmB-gel for promastigotes was less than 1 µg/mL for the four species examined, i.e., <i>Leishmania infantum</i>, <i>Leishmania tropica</i>, <i>Leishmania major</i>, and <i>Leishmania braziliensis</i>, and less than 2 µg/mL for amastigotes of <i>Leishmania infantum</i> and <i>Leishmania tropica</i>. The AmB-gel caused notable effects on the surface of promastigotes. Computational analysis revealed primarily hydrophobic and van der Waals interactions between AmB and Pluronic^® F127 and ergosterol. <b>Conclusions</b>: Based on the drug retention content and IC₅₀ values observed for both parasite stages, the AmB-gel may be a promising candidate for in vivo studies in patients with cutaneous leishmaniasis.