Nanoencapsulation as a way to control the release and to increase the photostability of clobetasol propionate: influence of the nanostructured system.

The aim of this study was to prepare and to evaluate the physicochemical and in vitro drug release characteristics of different nanostructured systems containing clobetasol propionate (CP): CP-loaded polymeric nanoparticles (nanocapsules and nanospheres) and CP-loaded nanoemulsion. Physicochemical characteristics of the formulations were monitored up to 9 months after preparation by means of drug content, encapsulation efficiency, mean size, polydispersity index, pH, and zeta potential. In vitro drug release studies were carried out using the dialysis bag method. Photostability of CP-loaded nanoparticles was evaluated by their exposition to UVA radiation. All formulations presented nanometric mean size (140-220 nm), polydispersity index below 0.25, neutral pH values, negative zeta potential and encapsulation efficiency close to 100%. All these parameters, except pH, remained unchangeable up to 9 months of storage at room temperature for CP-loaded nanocapsules. On the other hand, CP-loaded nanospheres and nanoemulsion showed an increase in their mean size, as well as in polydispersity index under storage (after 3 and 6 months, respectively). In vitro drug release studies showed a controlled release of CP from nanoparticles (nanocapsules > nanospheres > nanoemulsion) with a low burst release. Photostability of CP under UVA radiation was improved by its incorporation into nanoparticles (nanocapsules > nanoemulsions > nanospheres).