Die invloed van enkele faktore op die terugdiffusie van geneesmiddels in 'n membraan in

Abstract

The objectives with this study were to present solutions to several problems related to drug diffusion through membranes, with spesific reference to the back-diffusion problem encountered by Dürrheim (1977) in his studies on drug diffusion through the skin. The problem of back-diffusion when using then-alcohols (ethanol to n-decanol) was confirmed. By maintaining better sink conditions in the receiver cell than that used by Dürrheim (1977) a higher permeability coefficient was obtained, especially with the higher alcohols (n-octanol and n-decanol) with which the problem of back-diffusion was particularly noticeable. From the available data it was not possible to infer the mechanism and factors that could have a quantitative effect on back-diffusion. To solve the problem of back-diffusion, a kinetic approach was followed. The data obtained from this study suggested that the diffusion process occured by means of two distinguishable processes, namely absorption or adsoption into or onto the membrane and a passive diffusion of the alcohol through the membrane. The back-diffusion phenomenon however still appears to be too complex to be solved from these data. Although in the kinetic study no sink conditions were maintained, it was possible to calculate a permeability coefficient of the same order as that obtained in the preliminary study. It is therefore concluded that sink conditions in the receiver cell are not an absolute requirement for the calculation of the correct permeability coefficient. This permeability coefficient was calculated by means of Fick's law, with due allowance for the varying concentration gradient. The concentration gradient was assumed to be constant in the preliminary study. Although the back-diffusion problem was not quantified in this study, the diffusion mechanism of n-octanol through a membrane is clarified to a somewhat greater extent and a more economical method was developed to determine the permeability coefficient accurately .