Abstract: A simple and sensitive liquid chromatography/tandem mass spectrometry method was developed and validated for determination of azithromycin in human plasma with erythromycin as the internal stan-dard. Chromatographic separation was performed on a Lichrospher CN column(4.6 mm×150 mm) with a mixture of acetonitrile and water(containing 0.1% formic acid and 0.1% ammonium acetate, volume ratio 40∶60) as mobile phase. Selected ion monitoring was specific for azithromycin and erythromycin(IS). The assay was linear over the mass concentration range 2.34—600 ng/mL and the correlation coefficients for the calibration curves ranged from 0.997 to 0.999. The intra- and inter-day precisions, calculated from quality control samples, were less than 10%. Protein precipitation with methanol was chosen for sample preparation method. The recoveries ranged from 94.13% to 97.04 % and matrix effect ranged from 92.50% to 107.87%. The method was applied to bioequivalence study after oral administration of 500 mg azithromycin to 24 healthy volunteers.

Key words: Azithromycin, Human plasma, Bioequivalence, HPLC-MS/MS