Physicochemical characterization and release mechanism of a novel prednisone biodegradable microsphere formulation

ABSTRACTThe aim of this work was the characterization of a new formulation of prednisone long‐term controlled release biodegradable microspheres. Poly(DL‐lactide‐co‐glycolide) (PLGA) polymers were used for MS preparation. A S/O/W solvent evaporation method was employed for prednisone entrapment. The system was characterized by using UV spectrophotometry, particle sizing, scanning electron microscopy, differential scanning calorimetry, X rays diffractometry, and microRaman spectroscopy. The release mechanism was studied by fitting Weibull, Peppas, Higuchi, and zero order kinetic models. The microspheres (MS) showed a good encapsulation efficiency and morphology, a suitable size and long‐term release profile. Burst release was seen to depend on crystalline prednisone distributing close to the MS surface, and no particular prednisone‐polymer interaction occurred. Weibull and Peppas were the best fitting models. Prednisone was released from PLGA MS following a Fickian diffusion and case II transport for higher molecular weight (MW) polymers, and a more complex mechanism involving solubilization, diffusion, and erosion, for low MW PLGA. Fully characterized PLGA MS may represent a good tool for a long‐term delivery of prednisone in low‐dose regimen treatments. © 2007 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:303–317, 2008