In vitro evaluation of sustained release of risperidone-loaded microspheres fabricated from different viscosity of PLGA polymers

The aim of this study was to fabricate different risperidone (RIS)-loaded poly(lactic-co-glycolic acid) microspheres (PLGA MS) with various viscosity of PLGA polymers and investigate the RIS release profiles. Risperidone-loaded PLGA MS were fabricated via an oil/water-type emulsion solvent evaporation method, using ethyl acetate and benzil alcohol as the dispersed solvents. The PLGA (75:25) with the viscosity of 0.82, 0.93, and 1.10dL/g was used in the fabrication. The morphology and the degradation of the RIS-PLGA MS were investigated with a scanning electron microscope. The distribution states of RIS in the PLGA MS were studied with differential scanning calorimetry. The residual of ethyl acetate and benzil alcohol in the resulting MS was monitored with gas chromatography. The in vitro release profiles of RIS from PLGA MS were also studied. Scanning electron microscope photographs illustrated that the obtained PLGA MS were monodisperse spheres with an average diameter of 100m. Gas chromatography results suggested that no residual ethyl acetate was left in the final RIS-PLGA MS, and the residue amount of benzil alcohol was about 1%. In vitro drug release profiles from the microsphere showed a substantially sigmoidal pattern of negligible initial burst up to 24hours and minimal release (time lag) for 14days. After the lag phase, slow release took a place up to 30days, and then rapid release occurred sharply for about 2weeks. The RIS release reached equilibrium around day 50. All release profiles showed the similar trend, and no significant difference was observed among these release profiles (P>.05). This phenomenon indicated that RIS-loaded PLGA MS with the viscosity of 0.82 to 0.93dL/g showed the optimal release behavior. However, no obvious differences were found among the MS obtained from the viscosity of 0.82 to 1.10dL/g. These studies provided basis for the quality control in the industrial production of PLGA MS.