Amphotericin B-Loaded Bigel: Characterization and in vivo Antileishmanial Evaluation in BALB/c Mice Infected with Leishmania amazonensis.

American Tegumentary Leishmaniasis (ATL) is a zoonotic disease characterized by polymorphic cutaneous and mucosal manifestations, caused by protozoa of the genus Leishmania and transmitted through the bite of sandflies. Current treatment relies on pharmacotherapy with drugs such as amphotericin B (AmB), which is limited by adverse effects. Novel topical formulations of AmB, including bigels, have been investigated as alternatives for ATL therapy, aiming to achieve local efficacy with reduced toxicity and lower cost. This study sought to develop and characterize an AmB loaded-bigel for topical application and to evaluate its in vivo antileishmanial activity. The formulations were characterized by organoleptic analysis, pH, stability, oil retention capacity, swelling, spreadability, and texture profile. In vitro drug release and skin permeation were assessed using Franz diffusion cells and murine skin, while the ocular irritation potential was evaluated through the HET-CAM assay. In vivo efficacy was tested in BALB/c mice infected with Leishmania amazonensis, monitoring lesion progression and parasite burden. Treatment with the AmB loaded-bigel resulted in a 74.1% reduction in parasite load. Overall, the bigel demonstrated favorable physicochemical properties, stability, spreadability, and controlled release of AmB. The in vivo findings highlight its promising antileishmanial activity and support the potential of AmB-loaded bigels as a therapeutic alternative for ATL.