A model to predict drug release from a single-layer osmotic controlled-release tablet

A single-layer osmotic controlled-release tablet, also referred to as an extrudable core system (ECS) tablet, has been modelled to predict the drug release rate as function of various parameters related to the excipients and the active pharmaceutical ingredient, the geometry of the tablet and the coating thickness. The analysis leads to a better understanding of the drug release process resulting in a mathematical tool for design of new formulations. The model accounts for all the main events occurring during the drug release process from a tablet coated with a semi-permeable membrane, namely, the solvent influx driven by the difference in osmotic pressure across the coating, dispersion of core components (drug, polymer and osmogen), swelling of the tablet due to solvent accumulation, build-up of hydrostatic pressure inside the tablet, tensile stress acting on the coating, the extrusion of the dispersed core components and dissolution of drug particles outside the tablet in the bulk. We also derive the condition for successful entrainment of drug particles based on the viscosity of the hydrated phase and other parameters of the system. The model was validated by comparing the predictions with drug release data for two drugs of varying solubility. The agreement between the predicted release and the measurements confirmed the suitability of the model in describing the drug release process in the osmotic controlled-release tablet.