Ocular Metabolism of Levobunolol: Historic and Emerging Metabolic Pathways.

Although ocular transport and delivery have been well studied, metabolism in the eye is not well documented, even for clinically available medications such as levobunolol, a potent and nonselective ß-adrenergic receptor antagonist. Recently, we reported an in vitro methodology that could be used to evaluate ocular metabolism across preclinical species and humans. The current investigation provides detailed in vitro ocular and liver metabolism of levobunolol in rat, rabbit, and human S9 fractions, including the formation of equipotent active metabolite, dihydrolevobunolol, with the help of high-resolution mass spectrometry. 11 of the 16 metabolites of levobunolol identified herein, including a direct acetyl conjugate of levobunolol observed in all ocular and liver fractions, have not been reported in the literature. The study documents the identification of six human ocular metabolites that have never been reported. The current investigation presents evidence for ocular and hepatic metabolism of levobunolol via non-cytochrome P450 pathways, which have not been comprehensively investigated to date. Our results indicated that rat liver S9 and human ocular S9 fractions formed the most metabolites. Furthermore, liver was a poor in vitro surrogate for eye, and rat and rabbit were poor surrogates for human in terms of the rate and extent of levobunolol metabolism.

Membrane electrodes for determination of some beta-blocker drugs.

Five poly(vinyl chloride) (PVC) matrix membrane electrodes responsive to the beta-blockers atenolol (AT), bisoprolol fumarate (BI), timolol maleate (TI), and levobunolol HCl (LV) were developed and characterized. A precipitation-based technique with ammonium reineckate anion as an electroactive material in PVC matrix with AT, BI, TI, and LV cations was used for fabrication of Electrodes 1-4, respectively. Electrode 5 fabrication was based on precipitation of LV cation with tungstophosphate anion as an electroactive material. Fast and stable Nernstian responses at 1 x 10(-2)-1 x 10(-7) M for different beta-blockers over the pH range of 2-8 were found for these electrodes, which were evaluated according to International Union of Pure and Applied Chemistry recommendations. The method was successively applied for the determination of beta-blockers in their pharmaceutical formulations. Validation of the method according to quality assurance standards showed the suitability of the proposed electrodes for use in the quality control assessment of these drugs. The recoveries for the determination of the beta-blocker drugs by the 5 proposed selective electrodes were 100.1 +/- 0.7, 99.9 +/- 0.8, 100.0 +/-1.1, 100.5 +/- 1.1, and 100.6 +/- 0.7% for Sensors 1-5, respectively. Statistical comparison between the results obtained by this method and the official method of the drugs was performed and no significant difference was found.