AIM To develop a HPLC-MS assay for determination of azithromycin in human plasma and to investigate the pharmacokinetics and bioequivalence of 2 azithromycin tablets in human. METHODS After being deproteined by methanol,plasma samples were separated by HPLC on a reversed-phase C 18 column with a mobile phase of 10 mmol·L -1 ammonium acetate buffer solution (pH 3.5)-methanol (31∶69,V/V).HPLC-MS was performed in the selected ion monitoring (SIM)mode using target ions at m/z 749.8 for azithromycin and m/z 837.8 for the internal standard. The fragmentor voltage was 120 V.A randomized crossover design was performed in 20 healthy volunteers.In the study periods,a single 500 mg dose of each tablet was administered to each volunteer. RESULTS Calibration curves were linear over the range of 1.0-1 627.2 μg·L -1.The limit of quantification for azithromycin in plasma was 1.0 μg·L -1.The main pharmacokinetic parameters T 1/2,t maxand c max were (39.0±4.5)h,(2.6±0.9)h and (513.6±231.9)μg·L -1for the reference tablet;(38.5±3.8)h,(2.5± 1.0)h and (518.8±239.9)μg·L -1for the test tablet,respectively.The relative bioavalability of the test tablet was (99.7±12.6)%.The results of variance analysis and two one-sided t-test showed that there was no significant difference between the reference and test formulations in the AUC and c max.CONCLUSION The assay is proved to be sensitive,accurate and convenient.The reference and test formulations are bioequivalent.