Accessibility factors for diffusion-controlled drug delivery systems

The idea of accessibility factors or parameters is introduced to describe the ability of a planar or spherical controlled-release system to deliver a specific drug (with a known diffusion coefficient) within a desired period of time. The accessibility factors are the maximum and minimum values of the drug diffusion coefficient, the geometric dimensions of the system, and the release time. The solutions of the general diffusion equations are plotted as generalized diffusional diagrams, indicating the accessibility region for drug delivery. Deviations from the quasi-equilibrium conditions can be represented in these diagrams.