pH- and flow-rate-independent release of drug from uncoated slow-release tablets

Slow-release tablets were prepared using a polyvinyl chloride--polyethylene matrix and sodium salicylate as a model drug. The in vitro release of salicylate was described adequately by a previously published equation. The release rate constant was independent of the pH of the dissolution fluid and the flow rate of the fluid past the tablet. Accordingly, the procedures used to test the in vitro drug release from this type of matrix tablet are not as critical as for conventional tablets. It may therefore be postulated that the in vivo performance of the tablet may be less subject to variations in the physiological parameters of the GI tract.