Effect and mechanism of penetration enhancement of organic base and alcohol on glycyrrhetinic acid in vitro.

The aim of the present study was to explore the effects of organic bases and alcohols on the percutaneous absorption of Glycyrrhetinic acid (GA). GA is a metabolite of Glycyrrhizic acid (GL), a major active ingredient of Glycyrrhizae (Gancao) Radices. Skin penetration parameters of GA were obtained via in vitro penetration experiments using intact and stripped mice back skin. Non-aqueous solvent comprising isopropyl myristate (IPM) and alcohols (ethanol, butanol, octanol and dodecanol) loaded with organic base (triethanolamine or triethylamine) were applied to improve the penetration of GA. In order to further confirm the mechanism by which the organic bases enhanced the penetration of GA, conductivity measurement, (1)H NMR spectroscopy and FT-IR analysis were used to observe the formation of ion pair between GA and organic base. The formation of ion pair increased the solubility of GA in the stratum corneum (SC) and its partition into the viable skin, and therefore enhanced the penetration of GA in skin.