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.

Drug/polymer matrix swelling and dissolution.

The swelling and dissolution behavior of pharmaceutical systems containing a drug and a polymer can be analyzed by a mathematical model which predicts the drug released and the gel layer thickness as a function of time. It is possible to approximate the values of several of the physicochemical parameters of this model in order to obtain an order-of-magnitude analysis of the tablet dissolution process. Selected experimental results of tablet dissolution and drug release are analyzed and conclusions are made about the importance of the drug and polymer content and solubility in the release behavior.