J. Siepmann et al., A new model describing the swelling and drug release kinetics from hydroxypropyl methylcellulose tablets, J PHARM SCI, 88(1), 1999, pp. 65-72
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.