Release of mifepristone from biodegradable matrices: experimental and theoretical evaluations.

Diffusion of mifepristone in poly [(D,L) lactide-co-glycolide)] films was studied by release experiments. Five 50/50 copolymers of increasing molecular weights were used. The degradation effects were shown by gel permeation chromatography (GPC). Release kinetics show the effect of copolymer molecular weights on diffusion and degradation properties of loaded films. A new theoretical model for drug release from a biodegradable matrix was proposed with two assumptions: correlation of the diffusion coefficient with the polymer molecular weight and existence of a first order degradation kinetic. Higuchi's equation is verified at early time and the diffusion coefficient in the non-degraded polymer can be measured. The degradation constant is determined at long time and is compared with the results of GPC.