Development and validation of an UPLC–MS/MS method for simultaneous determination of meropenem and its open-ring metabolite in human serum and cerebrospinal fluid with application to clinical samples

Central nervous system (CNS) infections require adequate drug exposure at the site of action, yet antibiotic meropenem (MER) shows limited cerebrospinal fluid (CSF) penetration and easily undergoes non-enzymatic degradation to an inactive open-ring metabolite (ORM). In this study, we developed a simple, sensitive, and fast liquid chromatography tandem mass spectrometry (LC-MS/MS) method for the simultaneous determination of MER and ORM in human serum and CSF. Chromatographic separation was accomplished on an Agela Venusil MP C18 column, with MER-d6 and ORM-d6 as internal standards. Methanol was found to promote methanolysis, yielding a characteristic product ( m/z 416.2). Therefore, acetonitrile was selected as both the organic phase and the protein-precipitation solvent. Method validation was conducted according to the ICH M10 guideline. Follow validation, the method was successfully applied to 57 serum and 16 CSF samples. ORM concentrations in human CSF were reported for the first time. This method provides a valuable tool to support MER monitoring in patients with CNS infections.