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E. C. Si, P. S. Cheung, L. M. Bowman, K. Hosseini; Ocular Distribution of a DuraSite Formulation Containing 2% Azithromycin in Rabbit Eyes. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2660.
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The ocular bioavailability of a 2% ophthalmic solution of azithromycin in DuraSite was evaluated in pigmented rabbits.
Forty-two pigmented rabbits were divided into 7 dose groups, one for each of 7 time points, at 0.5, 1, 2, 4, 8, 13, and 24 hours post-dosing. At the zero hour time point, 25 µL of 2% azithromycin in DuraSite was instilled into both the right and left eyes of each animal. At the designated time points, animals were sacrificed, and tears, bulbar conjunctiva, cornea, and plasma were harvested. The level of azithromycin in these tissues were determined using an HPLC/MS/MS method.
High concentrations of azithromycin were detected in the cornea, bulbar conjunctiva, and tears. Peak tissue concentrations (Cmax) ranged from 50 µg/g in the cornea to 195 µg/g in tears between 0.5 and 4 hours post dosing. The t1/2 in these tissues were 20, 12, and 5 hours, respectively. At the end of 24 hours, ocular tissue concentrations exceeded the MIC breakpoint for the most common causative pathogens of bacterial conjunctivitis by at least 7-fold. In contrast, plasma azithromycin levels were generally 4 to 5 orders of magnitude lower than those in the ocular tissues.
The long half-lives and high tissue concentrations attained by topical application of the 2% azithromycin formulation in DuraSite suggest the possibility for a shorter dosing regimen against ocular infections.
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