Simultaneous Determination of Linezolid, PNU-142300, and PNU-142586 in Human Serum via Ion-Pairing Reversed-Phase Liquid Chromatography with UV Detection

In this study, we developed and validated a novel method of simultaneously measuring serum concentrations of linezolid (LZD) and its major metabolites, PNU-142300 and PNU-142586, in human serum using high-performance liquid chromatography coupled with an ultraviolet detector (HPLC-UV) for pharmacokinetic–pharmacodynamic analysis. LZD is an antibacterial agent, and its major metabolites are suspected to cause severe thrombocytopenia. To elucidate the relationship between the blood concentrations of these substances and platelet counts, an analytical method is needed that can simultaneously quantify LZD, PNU-142300, and PNU-142586 and be applied to clinical samples. We investigated an analytical method that shows high linearity at concentrations of 0.1–50 μg/mL (LZD and PNU-142300) and 0.2–50 μg/mL (PNU-142586), which covers the practical concentration range of clinical samples predicted through pharmacokinetic simulation. The intra- and inter-assay accuracies ranged above 88 % for LZD, PNU-142300, and PNU-142586. Furthermore, the precision of all intra- and inter- assays was less than 15 %. This is the first report on the simultaneous measurement of LZD concentrations and those of its major metabolites in human serum using an HPLC-UV system with a neutral isocratic mobile phase.