Simultaneous analysis of amoxicillin and sulbactam in human plasma by HPLC-DAD for assessment of bioequivalence

A simple and accurate high-performance liquid chromatography with diode array detection-based (HPLC-DAD) method has been developed and validated for simultaneous determination of amoxicillin and sulbactam in human plasma. Sample preparation was involved in protein precipitation with acetonitrile followed by one-step extraction procedure. Chromatographic separation was achieved on a C18 column with an isocratic mobile phase consisting of water (containing 30 mM potassium dihydrogen phosphate, pH 2.8) and acetonitrile. The detection wavelengths of a diode array detector were set at 210 nm for amoxicillin and sulbactam, and 263 nm for the internal standard (cefadroxil). The method was validated for linearity, accuracy, precision, and stability. The calibration curve was linear from 0.163 to 14.7 μg/mL with correlation coefficient squared of 0.9991 for amoxicillin and 0.250–15.0 μg/mL with correlation coefficient squared of 0.9988 for sulbactam using 500 μL plasma samples. The lower limit of quantification was 0.163 and 0.250 μg/mL for amoxicillin and sulbactam, respectively. The imprecisions of intra- and inter-day validations for amoxicillin and sulbactam were <11% and their accuracies (%) were within the range of 95.4–105.7%. Mean recoveries were 75.9, 72.8, and 70.0% for amoxicillin, sulbactam, and cefadroxil, respectively. The established method was successfully applied to a bioequivalence study of two combination formulations of amoxicillin and sulbactam pivoxil in healthy male volunteers.