Drug release from cation exchange membrane in rabbit eye

Cations were adsorbed onto a poly(acrylic acid) (PAA) grafted poly(vinylide ne 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 adso rption medium on cation release from the PAA-PVDF membrane in the eye. Mode l cations, propranolol and timolol, were adsorbed onto the membranes in sol utions with different ionic strengths (mu = 0.018 - 0.40) at pH 7.0. The ci rcular drug-containing membranes were applied to both eyes of pigmented rab bits in the lower conjunctival sac. The membranes were well tolerated and w ell retained in the rabbit eye. Membranes containing either propranolol or timolol were removed from the eyes at preset time intervals, and the remain ing drug content in the membranes was determined. The release rates of both propranolol and timolol decreased with increasing ionic strength of the ad sorption medium. This was probably due to cationic exchange properties, as well as swelling properties of the membrane.