title: Quantification of linezolid in serum by LC-MS/MS using semi-automated sample preparation and isotope dilution internal standardization.
abstract: BACKGROUND
  Linezolid serum concentrations have been shown to be highly variable in critically ill patients with often sub-therapeutic drug levels regarding minimal inhibitory concentrations for relevant pathogens. Consequently, therapeutic drug monitoring of linezolid must be considered, requiring a reliable and convenient analytical method. We therefore developed and validated an LC-MS/MS method applying isotope dilution internal standardization and on-line solid phase extraction for serum linezolid quantification.
  
  
  METHODS
  Sample preparation was based on protein precipitation and on-line solid phase extraction with two-dimensional liquid chromatography and column switching. Three-fold deuterated linezolid was used as the internal standard. The method was validated involving two separate LC-MS/MS systems covering the concentration range of 0.13-32 mg/L. The run time was 4 min.
  
  
  RESULTS
  Validation revealed good analytical performance, with inaccuracy <6% and imprecision of <7.3% (CV) for six quality control samples (0.38-16.0 mg/L). The method was found to be robust during the validation process and during a pharmacokinetic study so far involving 600 samples. Comparative measurements on two LC-MS/MS systems revealed close agreement.
  
  
  CONCLUSIONS
  This LC-MS/MS assay described herein is a convenient, robust and reliable method for linezolid quantification in serum which can be routinely applied using different LC-MS/MS systems. The method can be used for clinical studies and subsequent TDM of linezolid.
authors.forename: Johannes
authors.initials: J
authors.lastname: Zander
authors.forename: Barbara
authors.initials: B
authors.lastname: Maier
authors.forename: Michael
authors.initials: M
authors.lastname: Zoller
authors.forename: Daniel
authors.initials: D
authors.lastname: Teupser
authors.forename: Michael
authors.initials: M
authors.lastname: Vogeser
mesh_terms: D000081:Acetamides / Q000097:blood* / Q000302:isolation & purification*; D053000:Analytic Sample Preparation Methods / Q000379:methods*; D001331:Automation; D001774:Blood Chemical Analysis / Q000379:methods* / Q000592:standards*; D002853:Chromatography, Liquid; D006801:Humans; D000069349:Linezolid; D023303:Oxazolidinones / Q000097:blood* / Q000302:isolation & purification*; D011865:Radioisotope Dilution Technique; D012015:Reference Standards; D015203:Reproducibility of Results; D052616:Solid Phase Extraction; D053719:Tandem Mass Spectrometry
chemical_list: D000081:Acetamides; D023303:Oxazolidinones; D000069349:Linezolid