Drug release from cation exchange membrane in rabbit eye.

Cations were adsorbed onto a poly(acrylic acid) (PAA) grafted poly(vinylidene fluoride) (PVDF) membrane that served as a cation exchange membrane. The aim of this study was to evaluate the effect of ionic strength of the adsorption medium on cation release from the PAA-PVDF membrane in the eye. Model cations, propranolol and timolol, were adsorbed onto the membranes in solutions with different ionic strengths (mu = 0.018 - 0.40) at pH 7.0. The circular drug-containing membranes were applied to both eyes of pigmented rabbits in the lower conjunctival sac. The membranes were well tolerated and well retained in the rabbit eye. Membranes containing either propranolol or timolol were removed from the eyes at preset time intervals, and the remaining drug content in the membranes was determined. The release rates of both propranolol and timolol decreased with increasing ionic strength of the adsorption medium. This was probably due to cationic exchange properties, as well as swelling properties of the membrane.