Drug release from a porous ion-exchange membrane in vitro

The effect of environmental ionic strength on the rate of drug release from a cation exchange membrane was evaluated. Cationic propranolol-HCl, timolo l, sotalol-HCl, atenolol and dexmedetomidine-HCl and neutral diazepam were adsorbed onto a porous poly(vinylidene fluoride) (PVDF) membrane that was g rafted with bioadhesive poly(acrylic acid) chains (PAA-PVDF). Despite its p orosity, the PAA-PVDF membrane acted as a cation exchange membrane. The rel ease of adsorbed drug from the PAA-PVDF membrane was investigated by using a USP rotating basket apparatus. Adsorption of cationic drugs onto the PAA- PVDF membrane tended to increase with increasing lipophilicity of the drug. A decrease in the ionic strength of the adsorption medium increased the am ount of the cationic drugs adsorbed onto the membrane, but had no effect on diazepam adsorption. The release of cationic drugs from the PAA-PVDF membr ane was greatly affected by the ionic strength of both the adsorption mediu m and the dissolution medium, while ionic strengths did not affect diazepam release. Our results suggest that the ionic strength of both the adsorptio n and dissolution media substantially affects the release rate of a drug th at has been adsorbed onto the ion exchange membrane, primarily via electros tatic interactions, while ionic strength has no effect on the release of a drug which has been adsorbed onto the membrane via non-electrostatic forces . (C) 1999 Elsevier Science Ltd. All rights reserved.