Certain sustained release preparations contain a substance which, when exposed to an aqueous medium, forms a gel. Liquid will continue to penetrate the gel layer with time (θ) and the release of drug is both a function of liquid penetration rates (α) and diffusion of drug through the gelled layer (with a permeation coefficient of II). The thickness of the layer will be a function of time, because as liquid penetrates, more gel is formed. Development of this model leads to a third-power equation for the amount of drug released (m) as a function of time: m = aθ3 + bθ2 + cθ; the coefficients a, b and c contain an integral: f{hook}10 exp[(-π/α)(1/u)du which is evaluated graphically and found equal to 0.93 exp[-2.6π/α]. The data by Bamba et al. (1979) were used to demonstrate that the fit of experimental data to the third-power equation is a good as or superior to conventional plotting techniques. © 1979.
