Effect of intragranular porosity on compression behaviour of and drug release from reservoir pellets

In this study, reservoir pellets were prepared and their compression behaviour as well as the importance of their porosity for compression-induced changes in drug release was investigated. Pellets of three different porosities, consisting of microcrystalline cellulose and salicylic acid, were prepared by extrusion–spheronisation and spray-coated with ethyl cellulose (ethanol solution). Lubricated reservoir pellets were compressed and retrieved by deaggregation of the tablets. The retrieved pellets were analysed regarding porosity, thickness, surface area, shape and drug release. It was found that the coating did not significantly affect their compression behaviour. Compaction of pellets of high original porosity considerably affected densification and degree of deformation, whereas the effect on drug release was minor. For low porosity pellets the influence of compaction on drug release was appreciable, but only slight regarding densification and degree of deformation. In conclusion, the porosity of pellets is a potential factor that the formulator can use to optimize drug release and one that can affect the robustness of a formulation during manufacture. Moreover, the coating may be able to adapt to the densification and deformation of the pellets.