Determination of erythromycin, clarithromycin, roxithromycin, and azithromycin in plasma by high-performance liquid chromatography with amperometric detection.

In this study, a high-performance liquid chromatographic method was developed for the quantitative determination of erythromycin (EM), roxithromycin (RXM), and azithromycin (AZM) in rat plasma with amperometric detection under a standardized common condition using clarithromycin (CAM) as an internal standard. This method was also proved to be applicable for the determination of CAM by employing RXM as an internal standard. Each drug was extracted from 150 microl of plasma sample spiked with internal standard under an alkaline condition with tert.-butyl methyl ether. The detector cell potential for the oxidation of the drugs was set at +950 mV. The linearity of the calibration curves were preserved over the concentration ranges of 0.1-10 microg/ml for EM and RXM, and 0.03-3.0 microg/ml for CAM and AZM. Coefficients of variation and relative error were less than 9% and +/-7%, respectively. The analytical method presented here was proved to be useful for the investigation of the pharmacokinetic characteristics of EM, CAM, RXM, and AZM in rats.