Purpose. We report on the development of a novel controlled-release gastric retention system, which consists of a matrix tablet, coated with a permeable membrane. When immersed in simulated gastric fluid, the tablet expands. The tablet remains expanded for eighteen to twenty hours, during which time the drug is released. The tablet then either disintegrates into fragments or loses its integrity.

Methods. Tablets containing a soluble drug (chlorpheniramine maleate, i.e., CPM) and a poorly soluble drug (riboflavin 5′ phosphate, i.e., R5′P) were compressed. They were coated with a permeable and elastic polymer (Eudragit®). Dissolution profiles of these tablets were studied. The changes in the pH, viscosity, and deformation characteristics as a function of time were measured.

Results. Carbopol® provided a firm structure to the swollen tablet. Polyvinyl pyrrolidone XL (PVP XL) contributed to the swelling of the tablet. Carbonates provided the initial alkaline micro-environment for Carbopol® to gel and conferred buoyancy to the tablet. Coating provided the support needed for the core to remain intact during drug release and, at the same time, it allowed drug release due to its permeable nature. During release, the gelling properties of Carbopol® lessened, resulting in a decrease in the firmness of the core. This was evident from the decrease in the viscosity of the core. The energy required at 50% strain also decreased as the drug release progressed.

Conclusions. When this tablet is ingested, the chances of its elimination through the pylorus should be greatly reduced due to tablet's expansion, and due to its disintegration or loss in integrity it should then be expelled out of the stomach at the end of the drug release.