Solution-solubility dependency of controlled release of drug from polymer matrix: mathematical analysis.

Two types of drug release mechanisms-matrix controlled (Q - t1/2 relationship) and partition controlled (Q - t relationship)-were reported previously. The dependency of the transition between these two processes on the solution solubility of drug is now analyzed. Mathematical expressions are derived to treat the systemic effects of the addition of varying volume fractions of the cosolvent system on the concentration gradients across both the drug depletion zone and hydrodynamic diffusion layer as well as on the partitioning behavior at the polymer-solution interface. The results are in excellent agreement with reported experimental observations.