Development and evaluation of madecassoside-loaded microemulsion for enhanced topical drug delivery

Abstract

Madecassoside, a major triterpenoid glycoside from Centella asiatica, has potential value for dermatological applications; however, its poor stratum corneum permeability is due to high hydrophilicity and large molecular size. This work focused on designing a microemulsion carrier to enhance the topical delivery of madecassoside. Formulation regions were first screened using pseudo-ternary phase diagrams, followed by preparation of madecassoside-loaded systems with different oil phases, surfactant HLB values, cosurfactant compositions, and drug loadings. The resulting formulations were characterized for droplet size, PDI, viscosity, rat-skin permeation, skin retention, CAM irritation response, and physical stability. All prepared systems were clear and homogeneous, with droplet sizes between 28.00 ± 0.44 and 60.10 ± 0.61 nm and PDI values not exceeding 0.27 ± 0.02. Further optimization identified M10, containing IPM, Brij 30/Brij 35, Transcutol HP, and 2% madecassoside, as the most suitable formulation. M10 produced a high 24 h cumulative permeation amount of 406.28 ± 180.73 μg/cm2, corresponding to an approximately 43.2-fold increase compared with the 2% madecassoside control solution (9.41 ± 2.08 μg/cm2). In the HET-CAM assay, M10 showed an irritation score lower than the 1% SLS reference group. The formulation also remained clear after centrifugation, freeze–thaw cycling, and 30 days of storage, with no marked changes in droplet size, PDI, or viscosity. These results suggest that microemulsions are a promising strategy for enhancing topical madecassoside delivery.