This study aimed to investigate the performance of the eutectic mixture of menthol and camphor (1:1, w/w) in nanoemulsion formulation for enhanced transdermal penetration of water-insoluble glabridin. Glabridin solubility in different media was determined by a shaking bottle method. The pseudoternary phase diagrams of the oil phase (drug-loaded eutectic mixture or IPM), the surfactant (Tween 80:glycerol = 2:1, w/w), and water were constructed using the aqueous titration method. The obtained glabridin nanoemulsions were characterized and compared on their particle sizes, in vitro and in vivo penetration performance on rat skin, and storage stability. The nanoemulsion formulation was optimized as 0.25% glabridin, 5% oil phase, 10% Tween 80, 5% glycerol, and 79.75% water. The obtained nanoemulsions showed a mean droplet size of nearly 100 nm for different oil phases. And the stability of both formulations was similar after storage for 3 months. In vitro skin permeation study showed that the nanoemulsion formulation with eutectic mixture exhibited higher skin permeability (28.26 μg/cm2) than that with IPM (9.94 μg/cm2) or the drug solution formulation (3.82 μg/cm2), which was further confirmed by in vivo skin permeation tests on the rat skin and human skin. The eutectic mixture is a preferable solvent for glabridin, and its nanoemulsion can be used as an excellent nanocarrier for enhanced transdermal delivery of glabridin.
Keywords: Eutectic mixture; Glabridin; Nanoemulsions; Skin penetration; Storage stability.