Mathematical model for in vitro drug release from controlled release dosage forms applied to propoxyphene hydrochloride pellets.

The in vitro release of drugs from controlled-release dosage forms has been studied in terms of a diffusion model. The model has been applied to a pellet formulation containing propoxyphene hydrochloride. It is demonstrated that the model may be used to predict the drug release profile adequately, when the pellet size is changed and when the thickness of the coating is varied. The size distribution of pellets in an experiment may be too broad to justify a simulation with just one average pellet size. Therefore, the results for pellets of the same size are generalized to any size distribution of pellets in an experiment. This is only trivial if sink condition exists in the extraction medium, since under that condition, the release from each pellet type is independent of the releases from other pellet types. In that case, the total release may therefore be found as the sum of the individual releases. In the general case considered here, the releases are coupled.