Preparation and in vitro evaluation of chitosan microspheres containing prednisolone: comparison of simple and conjugate microspheres

The purpose of the present study was to obtain a novel microparticulate formulation of prednisolone, which was adequate for the treatment of inflammatory bowel disease (IBD). The formulations prepared were evaluated in vitro. Two types of chitosan microspheres containing prednisolone, named Ch-Pred and Ch-SP-MS, were prepared by an emulsification-solvent evaporation method using a chitosan-prednisolone mixture and a chitosan-succinyl-prednisolone conjugate (Ch-SP), respectively. Ch-Pred and Ch-SP-MS were obtained in almost spherical shape. Ch-Pred showed a relatively high drug content of 13.2% (w/w), but the particle size was distributed from 10 to 45 µm, and a large initial burst release of approximately 60% was observed. On the other hand, although Ch-SP-MS exhibited a fairly low drug content of 3.5% (w/w), their particle size ranged from several hundred nanometers to 20 µm, with the mean diameter of 5 µm, and a gradual drug release profile was achieved. These characteristics on particle size and in vitro release suggested that Ch-SP-MS should have good potential as a microparticulate system for the treatment of IBD.