TRANSPORT OF DRUGS ACROSS POROUS ION-EXCHANGE MEMBRANES

Porous ion exchange membranes have potential applications for drug del ivery systems, Permeability of these membranes can be controlled by en vironmental factors like pH and ionic strength but also the drug prope rties have an important role in the permeation process. In this paper the influence of the drug charge, lipophilicity and molecular weight o n the diffusional drug flux is demonstrated. The membranes under study were poly(acrylic acid) (PAA) grafted porous poly(vinylidene fluoride ) (PVDF) membranes which are cation selective due to the partial ioniz ation of carboxyl groups in grafted PAA chains. At low pH the membrane pores are open and the drugs can diffuse through the membrane quite e asily. However, at pH 7 the grafted chains partially block the pores a nd the diffusional flux of bigger drug molecules (M-W 9400) decreases five orders of magnitude and also the flux of smaller molecules is cle arly reduced. When the influence of the drug charge on the diffusion o f the drugs across the membranes was studied, it turned out that the P AA-PVDF membranes facilitate the transport of cationic drugs and repel anionic ones. The presented mathematical model, based on Donnan equil ibrium and measured transport number data, predicted the observed tren ds reasonably well. (C) 1998 Elsevier Science B.V.