A new model describing the swelling and drug release kinetics from hydroxypropyl methylcellulose tablets

A novel mathematical model for the water transport into and drug release fr om hydroxypropyl methylcellulose (HPMC) tablets is presented. Fick's second law of diffusion is used to describe the mass transfer processes in the th ree-component system drug/polymer/ water. Numerical solutions of the respec tive set of partial differential equations are provided, considering axial and radial diffusion within cylindrical tablets. It is shown that the diffu sion coefficients strongly depend on the water concentration (parameters qu antifying this dependence have been determined). Swelling of the device is considered using moving boundary conditions, whereas dissolution processes are neglected. Experiments proved the applicability of the theory. The prac tical benefit of the new model is to calculate the required shape and dimen sions of HPMC tablets to achieve a desired release profile.