Influence of chloride ion exchange on the permeability and drug release of Eudragit RS 30 D films

The objective of this study was to investigate the permeability of the cationic acrylic copolymer Eudragit RS 30 D as a function of the anionic buffer species of the dissolution media with special emphasis on the chloride ion exchange of the polymer. Indirect impedance measurement on isolated Eudragit RS films was used to investigate the mechanisms controlling membrane permeability. The chloride ion exchange was determined using capillary electrophoresis during dissolution testing of Eudragit RS 30 D-coated theophylline beads. The dissolution media investigated included various concentrations of sodium acetate, succinic acid and di-sodium succinate. The results of this study demonstrated that the degree of polymer swelling and related drug release was a function of the chloride counterion interaction with the polymer's quarternary ammonium groups. Chloride exchange during the dissolution test with other anions including acetate or succinate ions, resulted in significant changes in the polymer diffusion properties. The ion exchange proved to be the responsible mechanism of controlling polymer permeability as a function of anionic species and concentration. The order of anion permeability enhancing effect was acetate>mono-succinate>disuccinate. The ion exchange could be inhibited significantly by the addition of chloride ions to the dissolution medium. (C) 2002 Elsevier Science B.V. All rights reserved.