Sensitive and selective liquid chromatography-tandem mass spectrometry method for the quantification of azithromycin in human plasma

A simple, rapid, sensitive and selective liquid chromatography-tandem mass spectrometry method was developed and validated for the quantification of azithromycin, a broad-spectrum antimicrobial agent, in human plasma using erythromycin as internal standard. Following solid-phase extraction, the analytes were separated using an isocratic mobile phase on a reverse phase C18 column and analyzed by mass spectrometry in the multiple reaction monitoring mode using the respective [M + H]+ ions, m/z 749/591 for azithromycin and m/z 734/576 for the IS. The assay exhibited a linear dynamic range of 5-500 ng/mL for azithromycin in human plasma. The lower limit of quantification was 5 ng/mL with a relative standard deviation of less than 5%. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. A run time of 2.0 min for each sample made it possible to analyze more than 400 human plasma samples per day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.