PLA microparticles for the prolonged release of nimesulide: effect of preparative variables

Microparticles of nimesulide based on biodegradable and biocompatible polyl actic acid (PLA) were prepared using an emulsion solvent evaporation method . In order to investigate both the drug loading and drug release processes, several factors were modified in the microparticle preparation such as the drug/polymer ratio, the molecular weight of the polymer, the stirring rate and the amount of emulsifying agent (Pluronic F-68). All the nimesulide us ed in the process was practically incorporated in the microparticles reachi ng high drug loading. Over a drug/polymer ratio of 0.1 (w/w), nimesulide cr ystals were discerned in the microparticles by scanning electron microscopy . The degree of crystallinity of the drug in microparticles rose in lille w ith the drug/polymer ratio, as shown by both differential scanning calorime try and X-ray diffraction analysis. The release of nimesulide from micropar ticles was affected from all the preparative factors investigated and princ ipally by the drug/polymer ratio.