Eudragit RS and RL (acrylic resins) microcapsules as pH insensitive and sustained release preparations of ketoprofen

Microencapsulation of ketoprofen using Eudragit RS and RL (acrylic resins) was investigated based on the dispersion system of ketoprofen-containing acetone in liquid paraffin. Aluminium tristearate was used as an additive for the preparation of microcapsules. Good reproducibility was observed in the microencapsulation and the resulting microcapsules were uniform, free-flowing particles. The phase diagram of ketoprofen-Eudragit RS or RL-aluminium tristearate indicated that it is only in a very limited region that spherical microcapsules ranging from 250 to 1000 microns in diameter could be prepared. Instrumental analysis using an energy dispersive-type X-ray microanalyser and a scanning electron microscope showed that aluminium tristearate was localized near the surface of the microcapsules. From these results, it was presumed that aluminium tristearate reduces the phase tension between Eudragit microcapsules and liquid paraffin. The dissolution patterns of ketoprofen from Eudragit RS and RL microcapsules were independent of the pH of the dissolution medium, and the dissolution rates were considerably lower than those from ketoprofen powders.