In-vitro assessment of a matrix system of levobunolol

In order to study the feasibility of systemic delivery of levobunolol transdermally, a matrix-type delivery system was fabricated using a silicone elastomer. The relationship between loading dose and skin permeation rate was evaluated in-vitro using hairless mouse skin mounted on the stirred receptor compartment of the Keshary-Chien glass diffusion cell maintained at 37 degrees C. The concentration of levobunolol in the receptor compartment was determined by HPLC. A similar study without using the skin was carried out to determine the effect of loading dose on the release of levobunolol from discs. It was observed that the release of drug from disc followed a matrix-diffusion controlled (Q) vs square root of time relationship at different loading doses. In contrast, the results of skin permeation of levobunolol from transdermal discs containing different loading doses showed a linear Q vs time relationship indicating a constant zero order skin permeation rate at each loading dose. Skin permeation of levobunolol appeared to reach a plateau at a 5% (w/w) loading dose in the disc indicating the attainment of equilibrium concentration of levobunolol in the skin.