Efficacy of Diterpene Polyalthic Acid Combined with Amphotericin B against In Vitro.

Leishmaniasis, a neglected disease caused by spp. including , urgently requires new treatments. Polyalthic acid (PA), a natural diterpene from spp., has previously demonstrated significant antiparasitic potential. This study evaluated the leishmanicidal effects of polyalthic acid (PA), alone and with amphotericin B (AmpB), on promastigote and amastigote forms. PA showed significant activity against promastigotes, with 50% effective concentration (EC) values of 2.01 μM at 24 h and an EC of 3.22 μM against amastigotes after 48 h. The PA and AmpB combination exhibited a synergistic effect on both forms without inducing cytotoxicity or hemolysis. Morphological changes in promastigotes, including vacuole formation and cell rounding, were more pronounced with the combination. These findings suggest that PA and AmpB together could form a promising new treatment strategy against infections, offering enhanced efficacy without added toxicity.