Effect of HPβCD on solubility and transdermal delivery of capsaicin through rat skin

We evaluated the ability of hydroxypropyl-p-cyclodextrin (HP beta CD) to influence the percutaneous absorption of capsaicin (CP) through isolated rat skin. Phase solubility analysis and phase distribution studies suggested the potential of HP beta CD as a solubilizer and permeation enhancer for CP. In vitro permeation studies showed the trend that, the penetration flux (J(s)) of CP increased with the increasing concentration of HP beta CD from 0 to 2.20% (w/v), and then decreased dramatically when the concentration of HP beta CD kept on increasing up to 15% (w/v). 2.20% (w/v) of HP beta CD provided both just adequate solubilization and preferred Js for the permeation of CP (0.075%, w/v). Similar change patterns of the permeation parameters were also observed in the hydrogels, but the J(s) of CP was reduced significantly along with the increasing concentration of Carbopol U21. Histological analysis showed an invasive action of HP beta CD on the stratum corneum (SC) of rat skin, which could only reduce the lag time (T-L) but could not increase the J(s) of CP. On the other hand, the complexation of HP beta CD with CP could attenuate this invasive action. It is inferred that excess of HP beta CD could not only disturb the percutaneous absorption of CP but also disrupt the structure of SC. (C) 2008 Elsevier B.V. All rights reserved.