Determination of ethoxzolamide in the iris/ciliary body of the rabbit eye by high-performance liquid chromatography: comparison of tissue levels following intravenous and topical administrations.

A specific high-performance liquid chromatographic method is described for ethoxzolamide following the extraction of the material from iris/ciliary body eye tissue in rabbits. The steps consist of base extraction and protein and enzyme deactivation, followed by acid treatment, extraction into ethyl acetate, evaporation, and solubilization with a 50% aqueous methanol solution. The samples were chromatographed on a reverse-phase phenyl column with a mobile phase consisting of 50% methanol in 1% acetic acid. The recovery was 74.3% over a 10-fold range of tissue concentrations. The sensitivity was 0.03 microgram/mL, and the response was linear over the concentration range (0.03-0.5 microgram/mL) used in the study. Intravenous (2.0- and 6.0-mg/kg) and topical (1% suspension) doses of ethoxzolamide were administered to rabbits. Iris/ciliary body tissues were excised 45 min after drug administration. The tissue levels after a dose of 6 mg/kg were statistically greater than the levels obtained after a dose of 2 mg/kg. The smaller intravenous dose represented the lowest dose for which a reduction in intraocular pressure could be measured. An initial transitory drop in intraocular pressure was detected for the topical dose. Iris/ciliary body levels in the treated eye could be detected for the 2-mg/kg iv and topical doses.