Studies on in vitro release behaviour of indomethacin-loaded polystyrene microparticles

Indomethacin-loaded polystyrene microparticles were prepared by emulsion-solvent evaporation method from an aqueous system. The effect of different parameters like concentration of aqueous phase emulsion stabilizer, volume of the organic disperse phase and initial drug loading on drug content and release of drug were investigated. Keeping the drug-polymer ratio constant, variation in the concentration of emulsion stabilizer and volume of the organic disperse phase did not produce any significant change either in the actual drug content or in the drug release. The initial drug loading, however, greatly influenced the drug release which, as revealed by different analyses, was due to the presence of drug in different physical forms in the microparticles. Physical characterization using thin layer chromatography and infrared spectroscopy apparently revealed the absence of drug degradation and sizeable interaction between the drug and the polymer. Regardless of lack of interaction, thermodynamic properties such as solubility of the drug in the polymer and fraction of the drug present in crystalline form were determined by using differential scanning calorimetry and was further substantiated with scanning electron micrography and X-ray diffraction analysis.