Simultaneous determination of amoxicillin and ambroxol in human plasma by LC–MS/MS: Validation and application to pharmacokinetic study

A rapid, simple and sensitive LC–MS/MS method was developed for simultaneous determination of amoxicillin and ambroxol in human plasma using clenbuterol as internal standard (IS). The plasma samples were subjected to a simple protein precipitation with methanol. Separation was achieved on a Lichrospher C18 column (150 mm × 4.6 mm ID, dp 5 μm) using methanol (containing 0.2% of formic acid) and water (containing 0.2% of formic acid) as a mobile phase by gradient elution at a flow rate of 1.0 mL/min. Detection was performed using electrospray ionization in positive ion multiple reaction monitoring (MRM) mode by monitoring the ion transitions from m/z 365.9 → 348.9 (amoxicillin), m/z 378.9 → 263.6 (ambroxol) and m/z 277.0 → 203.0 (IS). Calibration curves were linear in the concentration range of 5–20,000 ng/mL for amoxicillin, and 1–200 ng/mL for ambroxol, with the intra- and inter-run precisions of <9% and the accuracies of 100 ± 7%. The method has been validated and applied to pharmacokinetic studies of compound amoxicillin and ambroxol hydrochloride tablets in healthy Chinese volunteers.