LC-MS/MS quantification of omadacycline in human plasma for therapeutic drug monitoring: method development and...

Omadacycline, a third-generation tetracycline antibiotic, exhibits time-dependent pharmacokinetics. The ratio of the 24-hour area under the concentration-time curve to minimum inhibitory concentration (AUC_0-24/MIC) serves as the primary pharmacokinetic/pharmacodynamic (PK/PD) index for omadacycline, demonstrating strong correlation with therapeutic efficacy, particularly in critically ill patient populations. To facilitate routine therapeutic drug monitoring (TDM) in clinical practice, a high-performance liquid chromatography - tandem mass spectrometry (HPLC-MS/MS) method was developed for quantification of omadacycline in human plasma. An Agilent 1260 series liquid chromatograph and an API 4000 triple tandem quadrupole mass spectrometer were used for the determination of omadacycline and endocannabinoids. The separation was performed on a Phenomenex KINETEX XB-C18 column (2.6 μm, 3 × 50 mm) with 0.1% formic acid-water and pure acetonitrile as the mobile phases. The LC-MS/MS separation was carried out using a gradient elution procedure at a flow rate of 0.4 mL/ min, and the total run time was 5 min. An electrospray ionization (ESI) was selected, and the detection ions of omadacycline and the internal standard (fexofenadine-d6) were determined by mass spectrometry scanning with multiple reaction monitoring (MRM) in positive ion mode as follows: m/z 557.4→453.4 and m/z 508.4→472.8, respectively. The established linear range (20-2000 ng/mL) effectively covers the plasma concentration range encountered in > 98% of clinical samples, making it suitable for routine therapeutic drug monitoring. The method demonstrated acceptable selectivity, recovery, and matrix effect. The results of intra-day precision and inter-day precision show that the relative standard deviation (RSD) is less than 10%, while the relative error (RE) is within ± 10.00%. In this study, we developed and validated a simple, sensitive and accurate method to quantify the concentration of omadacycline in human plasma using LC-MS/MS. This offers essential technical support for the rational clinical application of omadacycline.