HIGH-THROUGHPUT DETERMINATION OF LINEZOLID IN HUMAN PLASMA BY LIQUID CHROMATOGRAPHY-TANDEM MASS SPECTROMETRY

Abstract

A simple, high-throughput reversed-phase high performance liquid chromatography method with mass spectrometric detection (LC/MS/MS) was developed and validated for the quantification of linezolid in human plasma. After preparation, the sample was analyzed by isocratic elution on a Kinetex-C18 (50 × 2.1 mm, 2.6 µm) column. The mobile phase consisted of a mixture of acetonitrile: water containing 1 mM ammonium formate (25:75 V/V). Detection was performed in the multiple reaction monitoring (MRM) mode, using an electrospray ion source, positive ionization; the ion transition was monitored in the m/z 338.0 → m/z 296.2 range. Calibration was performed in the 0.256 to 20.130 µg/mL concentration range by using a quadratic least-squares regression, with a R2 higher than 0.995. The determined LOQ of linezolid in plasma was 0.256 µg/mL, the intra-day recoveries were in the 98.0 ± 4.5%–104.8 ± 4.5% range and the precision, for n = 5, was 4.5 to 8.6%. No interference was observed at the retention time (tR = 0.75 min) of linezolid. Linezolid showed good freeze-thaw, short-term, long-term, and post-preparative stability, as well. The short chromatographic run time and the simple and fast sample preparation make the method suitable to be used in therapeutic drug monitoring, clinical pharmacokinetics, and bioavailability studies.