Preparation and evaluation of risperidone slow-release injectable microspheres using chitosan

The aim of this study was preparation and evaluation of parenteral chitosan microspheres for sustained release of risperidone. Risperidone, a second-generation antipsychotic, is an effective in the treatment of schizophrenia and has a low incidence of adverse effect. Sustained release microsphere due to ascertain levels of drug in plasma, reduced toxicity and improving the efficacy of the drug. This study is done to consider the effect of four independent variables including, the drug to polymer ratio, TPP concentration, stirring speed and stirring time on the four dependent variables including, encapsulation efficiency, drug loading, particle size and the extent of initial burst in vitro release. In this study chitosan microspheres containing risperidone carried out by double emulsification/ solvent evaporation with two-step solidification process. The microspheres have been analyzed for their shape, size and surface characteristics. Interactions inside microspheres were investigated by differential scanning calorimetry and FTIR. In the following encapsulation efficiency, drug loading and burst release was investigated. The optimized formulation showed a narrow size distribution with an average of 115 ± 2 µm. The SEM image showed that microsphere was round in shape and discrete. The DSC analysis indicated the conversion of drug from crystalline state to molecular state in the optimized lyophilized formulation. FTIR analysis showed no changes in the chemical structure of risperidone in formulation. The in vitro release profile exhibited 92.3% drug release over 21 days in the sink condition.