A simple equation for description of solute release I. Fickian and non-fickian release from non-swellable devices in the form of slabs, spheres, cylinders or discs

Abstract

The simple exponential relation Mt/M∞ = ktn is introduced to describe the general solute release behavior of controlled release polymeric devices, where Mt/M∞ is the fractional solute release, t is the release time, k is a constant, and n is the diffusional exponent characteristic of the release mechanism. It is shown that this equation can adequately describe the release of drugs or other solutes from slabs, spheres, cylinders and discs (tablets), regardless of the release mechanism. It is shown that in cases of pure Fickian release the exponent n has the limiting values of 0.50, 0.45 and 0.43 for release from slabs, cylinders and spheres, respectively. For tablets, and depending on the aspect ratio, i.e., the ratio of diameter to thickness, the Fickian diffusion mechanism is described by 0.43 < 0.50. For drug release from spherical polymer particles of a wide distribution, the value of the exponent n for Fickian diffusion depends on the width of the distribution. © 1987.