Quantifying sustained release kinetics from a polymer matrix including burst effects

The influence of drug distribution on bursting during release from rigid polymer matrices has been quantified using the generalized diffusion–dissolution model for the release kinetics developed in our earlier paper, J. Membr. Sci. 366 (2010) 104–115. It has been demonstrated that both the amount and distribution of amorphous drug and drug particles have a profound influence on the release kinetics. Higher amorphous concentrations in the top layer of the membrane lead to higher release rates and stronger initial bursting, and distributing more drug particles close to or at the membrane surface has the same effect. The presence of a boundary layer region in which the amorphous drug concentration drops to zero within very short time increases the contribution of amorphous drug to the burst effects, and also generates overall release profiles in close agreement with experimental data.