Modeling of dissolution-diffusion controlled drug release from planar polymeric systems with finite dissolution rate and arbitrary drug loading

A new approach for modeling the drug release from planar polymeric systems containing slowly dissolving drugs is presented. A distinctive feature of the proposed approach relates to the mathematical description of the drug above solubility. The drug remaining solid in the matrix is envisaged like a delta function-type dissolution sources releasing drug according to the Noyes–Whitney equation. Dissolution sources are inventoried in a unique mass balance equation governing the simultaneous dissolution and diffusion processes. This approach explicitly avoids solving multiple mass balances for the interwoven regions of solid and dissolved drugs, and makes easier the numerical solution. Another singular characteristic is related with the friendly manipulation of a broad variety of non-uniform drug loading, including particles size distributions. To make the numerical treatment versatile, the mathematical solution is expressed in terms of integral equations suitable to be numerically solved by a simple iterative scheme. The reliability of the mathematical and numerical procedures is ascertained by comparison of the simulation results with experimental and numerical data existing in the literature, and also matching, as asymptotic case, the solution of the diffusion equation with a continuum dissolution source described by the Noyes–Whitney equation. The versatility of the method to treat different architectures resembling multilayer laminate polymeric systems is shown.