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A. Asero, A.R. Blanco, V. Moschetti, C. Civiale, M.G. Mazzone; Ocular Distribution of Topically Applied Azithromycin Eye Drop in Rabbits . Invest. Ophthalmol. Vis. Sci. 2005;46(13):4915.
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Purpose: To investigate the distribution of azithromycin into the conjunctiva, cornea, and aqueous humor after its ocular administration as eye drops in albino rabbits. Methods: Twelve male white New Zealand rabbits (weighing 1.8–2.3 kg) were randomly distributed in three equal Groups (I, II, III). All rabbits received 50 µl of an ophthalmic aqueous formulation of azithromycin (2%; w/v) into the lower conjunctival cul–de–sac of both eyes, every two hours up to a total of three (Group I) and six (Groups II, III) instillations, respectively. Two hours after the last dose, rabbits from Groups I and II were sacrificed by an overdose of TanaxR injected into the marginal ear vein. Animals in Group III were sacrificed twelve hours after last dosing. Eyes treated with azithromycin were washed with phosphate–buffered saline (PBS 0.1M; pH 7), aqueous humor was drawn away and each conjunctiva was surgically removed. After enucleation the cornea was excised at the limbus and removed from the eyeball. The linear relationship between log10 of azithromycin concentration and its related inhibition zone against S. aureus ATCC 29213 was utilized as bioassay method for determining tissue or aqueous humor concentrations of azithromycin. Results: After six instillations azithromycin was found in both conjunctiva and cornea: 545.0±143 and 222.5± 68.7 µg/g (mean±s.e.m.) of tissue, respectively. In addition, tissue concentrations of azithromycin into the conjunctiva (420.0±115 µg/g) and cornea (169.3±34.2 µg/g) were maintained above MIC90 for S. aureus (2.25 µg/ml) also in the Group III, left untreated for twelve hours before sacrifice. Azithromycin concentration was not revealed in aqueous humor because of bioassay detection limit (≥3.8 µg/ml). Conclusions: These preliminary results, to be further confirmed by additional analytical and pharmacokinetic studies, are promising for using aqueous azithromycin eye drops as topical ophthalmic drug in the treatment of ocular surface bacterial infections.
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