Pharmacokinetics of azithromycin in rabbit lacrimal glands and conjunctiva

Purpose and Background: To measure azithromycin levels in rabbit lacrimal a nd Harder glands, conjunctiva and plasma after a single oral dose of 20 mg/ kg. Drug levels in lacrimal gland tissue are significant in trachoma becaus e the gland may be involved in the disease process and it is the source of tears by which the drug is carried to the external eye. Methods: Lacrimal a nd Harder glands, conjunctiva and plasma were collected from New Zealand wh ite female rabbits at 24, 48, 72, 96 and 144 h following a single oral dose of azithromycin (20 mg/kg). Azithromycin levels in tissue and plasma were measured using high-performance liquid chromatography (HPLC) electrochemica l detection. Results: Azithromycin levels peaked within the first 24 h in a ll tissues and plasma assayed. The highest concentration was in the lacrima l gland (6.2 mu g/g, SD +/- 0.8), followed by Harder gland (4.4 mu g/g, SD +/- 0.8), conjunctiva (0.9 mu g/g, SD +/- 0.5) and plasma (0.06 mu g/ g, SD +/- 0.03). These concentrations reached their lowest measured levels at 12 0 and 144 h. Conclusion: Azithromycin levels measured throughout the 144 h after dosing were consistently above the minimum inhibitory range (MIC) for Chlamydia trachomatis (0.03-0.25 mu g/ml) in the lacrimal glands, while th e conjunctiva maintained a concentration above the MIC for 96 h and stayed within MIC levels for 144 h.