Simultaneous determination of meropenem and imipenem in rat plasma by LC-MS/MS and its application to a pharmacokinetic study.

An efficient and reliable method using LC-MS/MS was established and validated for the simultaneous quantification of meropenem and imipenem in rat plasma. An electronic spray ion source in the positive multiple reaction monitoring mode was used for the detection and the transitions were m/z 384.6 → m/z 141.2 for meropenem, m/z 300.1 → m/z 141.8 for imipenem and m/z 423.4 → m/z 207.1 for matrine (IS). The calibration curves of meropenem and imipenem were linear in the range of 0.50-200 μg/mL. Satisfactory separation was achieved with a total run time of 3.0 min, the injection volume was 3 μl. The retention times of meropenem, imipenem and IS were 1.19, 1.14 and 1.13 min, respectively. Meropenem and imipenem are easily hydrolyzed in plasma. HEPES was used as a stabilizer and added to the plasma samples immediately after centrifugation. Extractions of meropenem, imipenem and IS were carried out by protein precipitation with acetonitrile. The specificity, precision and accuracy, stability, recovery and matrix effects were within acceptance limits. This method was successfully applied to investigate the pharmacokinetics of intravenous injection of meropenem and imipenem single administration or combined with sulbactam in rats. We found that sulbactam has no influence on the pharmacokinetics behavior of meropenem or imipenem.