A validated UPLC-MS/MS method for the analysis of linezolid and a novel oxazolidinone derivative (PH027) in plasma and its application to tissue distribution study in rabbits

- UPLC-MS/MS method validation for two oxazolidinone antibiotics in plasma and tissues is reported.
- Comparative study of the matrix effect during the analysis of two oxazolidinone derivatives in plasma, muscles and liver.
- Determination of the tissue Lzd and PH027 concentrations using plasma calibration curve.
- Comparative tissue to plasma concentration ratios for two oxazolidinone antibiotics in rabbits are reported.

ObjectivesLinezolid is the first approved oxazolidinone antibacterial agent, whereas PH027 is a novel compound of the same class that exhibits good in vitro antibacterial activity. The objective of this study was to develop an UPLC-MS/MS assay for the analysis of linezolid and PH027 in plasma and to apply the method for comparative pharmacokinetic and tissue distribution studies of both compounds.MethodPlasma samples and calibrators were extracted with diethyl ether after addition of the internal standard solution. After evaporation of the ether layer, the residue was reconstituted in mobile phase and injected into UPLC-MS/MS. The mobile phase consisted of 2 mM ammonium acetate buffer solution and acetonitrile (70:30) at a flow rate of 0.2 ml/min. Separation was achieved using UPLC BEH C18 column, and quantitative determination of the analytes was performed using multiple-reaction monitoring (MRM) scanning mode. The method was validated by analyzing quality control tissue homogenate samples, and was applied to analyze tissue homogenate samples obtained following IV injections of linezolid and PH027 in rabbits.ResultsThe developed UPLC-MS/MS method was linear in the concentration range of 50-5000 ng/ml. Validation of the method proved that the method's precision, selectivity and stability were all within the acceptable limits. Linezolid and PH027 concentrations were accurately determined in the quality control tissue homogenate samples, and analysis of samples obtained following IV administration of the two compounds showed that the tissue to plasma concentration ratio of PH027 was higher than that of linezolid probably due to its higher lipophilicity.ConclusionsThe developed UPLC-MS/MS method for the analysis of linezolid and PH027 in rabbit's plasma can accurately determine the concentrations of these compounds in different tissues.