Ocular pharmacokinetic study following single and multiple azithromycin administrations in pigmented rabbits

Purpose: The aim of this study was to investigate whether the ocular pharmacokinetic parameters observed following systemic administration are also seen following topical administration. Methods: Azithromycin concentrations were measured by HPLC-MS in pigmented rabbits' tears, cornea, bulbar conjunctiva, and aqueous humor following single instillation and twice-daily instillations for three consecutive days of topical 1.50% azithromycin dihydrate solution. Results: Following a single administration, azithromycin levels were higher than the MIC 4 mu g/g breakpoint for susceptible germs for at least 4 hr in tears, 1 hr in conjunctiva, and 1 hr in cornea after instillation. Following multiple administrations, azithromycin levels were higher than the MIC 4 mu g/g for at least 16 hr in tears, 24 hr in conjunctivae, and 1 week in cornea after the last instillation. Conclusions: Both dosage regimens resulted in adequate and long-lasting azithromycin levels in the conjunctiva, the ocular target tissue relative to the expected therapeutic indication in man (bacterial conjunctivitis), and also in the cornea and tears.