82EUDRAGIT RS 100 PLACEBO MICROSPHERES IN DIFFERENT MEDIA. (1) STUDYING THE MORPHOLOGY; SURFACE AND INTERNAL MICROSPHERES STRUCTUREEudragit RS 100 placebo microspheres were prepared in different pH media using solvent evaporation technique. The organic phase was 100 dicloromethane containing 10 gm Eudragit RS100 added dropwise to the aqueous phase. The aqueous phases were distilled water, 0.1N HCL, hydrochloric acid solution pH 4 and freshly prepared sodium hydroxide solution pH 7.4 and pH 9.8. Either gelatin or PVP was used as an antiaggregating agent. In case of using PVP as an antiaggregating agent in distilled water as an aqueous phase, microspheres were formed with fragments of the polymer which depend on the concentration of PVP used. PVP at different concentrations were also used in O.l N HCl or phosphate buffer pH 7.4 as an aqueous phase where microspheres were not formed; only big aggregating particles. The surface of the microspheres was porous and depend the concentration of PVP used. On using gelatin at different concentrations in distilled water as an aqueou s phase, microspheres were formed with various filaments which increased with increasing gelatin concentrations. However Eudragit RS100 placebo microspheres in O.l N HC1 were formed on using gelatin at different concentrations. The microspheres size depends on the concentration of gelatin used. Also, on using phosphate buffer pH 7.4 co ntaining 2% gelatin as an aqueous phase, there was round pressed shape particles. The placebo Eudragit RS100 microspheres had porous surface structure. The microspheres prepared in the presence of PVP showed empty internal structure, while spheres prepared in the presence of gelatin had spongy like structure. The empty internal structure on using PVP as an antiaggregating agent may be due the solubility of PVP in the organic solvent which may enhance the diffusion and then evaporation of the organic solvent . At the same time the insolubility of gelatin in the organic solvent retard the diffusion and evaporation of the organic solvent whic h may be given the chance for formation of spongy internal microsphere structure.Omer.Mady@gmx.atResearch512015Placebo microspheres,Eudragit RS100, pH media,Antiaggregating agent,Gelatin,PVPMady O,Korsatko W,Zain Eldin EPharmaceutical Technology Department, Faculty of Pharmacy, Tanta University, Egypt,Institute für Pharmazeutische Chemie, Karl Franzens, Universität, Graz, Austria,Pharmaceutical Technology Department, Faculty of Pharmacy, Tanta University, Egypt