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Abstract
A simple, rapid, sensitive, and selective liquid chromatography–tandem mass spectrometry method was developed and validated for the quantification of azithromycin in rabbit plasma, tear fluid, cornea, and conjunctiva tissues using roxithromycin as internal standard. Following a deproteinization procedure, the samples were eluted isocratically at a flow rate of 1 mL/min with 10 mM ammonium acetate (adjusted pH with 0.1% acetic acid)–acetonitrile (25:75, v/v) as the mobile phase and a Sepax GP-Phenyl C18 column (150 mm × 4.6 mm, 5 µm). Azithromycin and its internal standard were determined using a triple-quadrupole mass spectrometer under the selected reaction monitoring (SRM) mode with precursor-to-product qualifier transition m/z 749.4 [M + 2H]+→591.4 and m/z 837.4 [M+H]+→679.4, respectively. The results demonstrated that there were good linearities for plasma, tear fluid, cornea, and conjunctiva samples. The intra- and inter-day precision (RSD) values were below 15% and accuracy (%) ranged from 90–110% at all QC levels, suggesting good precision and accuracy. The method was reliable for ocular pharmacokinetic quantitative analysis of azithromycin. The pharmacokinetic study and bioequivalence study showed the two 1-sided 90% confidence interval for the ratio of the In-transformed means of Cmax, AUC0–t and AUC0–∞ were in accordance with the acceptance limit. And it confirmed that the test formulation (1.0% (w/v) and 1.5% (w/v) azithromycin eye drops) were bioequivalent to the reference products, AzaSite® and Azyter®, in terms of rate and extent of absorption.
ACKNOWLEDGMENT
This study was supported by the “Fundamental Research Funds for the Central Universities” (Program No. JKQ2011018) and The National Natural Science Foundation of China (No. 81072588).