Release of diltiazem from Eudragit microparticles prepared by spray-drying

Microparticles containing diltiazem hydrochloride were prepared by the spray-drying technique using acrylate-methacrylate copolymers, Eudragit RS and Eudragit RL, as coating materials. The choice of solvent used during spray-drying determined the structure of the resultant microparticles. Spray-drying using dichloromethane as the solvent resulted in microspheres where the drug was distributed in the coating polymer matrix, whereas using toluene gave microcapsules with the drug coated by the polymer. The particle size distribution for both microspheres and microcapsules was narrow, with mean particle size below 10 mu m. DTA-analysis showed that the drug was amorphous in the microspheres but crystalline in the microcapsules. The release pattern of diltiazem hydrochloride was affected by microparticle structure, whether the structure was matrix (microspheres) or reservoir (microcapsules). The results indicate that spray-drying is a method that can be used to prepare microparticles from the Eudragit acrylic resins RL and RS with a narrow particle size distribution. It is concluded that drug release rate can be controlled by choice of polymer type and production conditions during spray-drying.