title: Evaluation of the MassTrak Immunosuppressant XE Kit for  the determination of everolimus and cyclosporin A in human  whole blood employing isotopically labeled internal standards.
abstract: BACKGROUND
  Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is widely used for therapeutic drug monitoring of immunosuppressants given to transplant recipients. This study evaluated the performance of the newly introduced MassTrak Immunosuppressant XE Kit (Waters Corporation; "the Kit") in the determination of everolimus and cyclosporin A (CsA) using LC-MS/MS.
  
  
  METHODS
  The linearity, precision, detection limit, carryover and matrix effect of the Kit and comparison of the in-house method and Kit procedure were evaluated according to Clinical and Laboratory Standards Institute guidelines.
  
  
  RESULTS
  The Kit afforded good linearity in the measurement of everolimus from 2 to 26 ng/mL (R² = 0.996) and of CsA from 42.6 to 1407 ng/mL (R² = 0.995). The between- and within-run assay coefficients of variation were 2.3% - 8.0% for everolimus and 1.1% - 3.1% for CsA. The lower limit of quantitation of everolimus and CsA were 1.1-4.1 ng/mL, respectively. A comparison of CsA values obtained using inhouse reagents indicated good correlation with Kit results (R = 0.9909). The average matrix effect ranged from 15% - 39% for everolimus and 3% -10% for CsA, and ion enhancement was mostly observed for the matrix effect. The effect on analyte/internal standard ratios ranged from 1%-8% for everolimus and 1%-16% for CsA.
  
  
  CONCLUSIONS
  The Kit employing isotopically labeled internal standards provides reliable measurements of immunosuppressant levels over a broad range of concentrations.
authors.affiliation: Department of Laboratory Medicine, University of Ulsan College of Medicine and Asan Medical Center, Seoul, Republic of Korea.
authors.forename: Misuk
authors.initials: M
authors.lastname: Ji
authors.forename: Sollip
authors.initials: S
authors.lastname: Kim
authors.forename: Hee-Jung
authors.initials: HJ
authors.lastname: Chung
authors.forename: Woochang
authors.initials: W
authors.lastname: Lee
authors.forename: Sail
authors.initials: S
authors.lastname: Chun
authors.forename: Won-Ki
authors.initials: WK
authors.lastname: Min
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000592:standards; D016572:Cyclosporine / Q000097:blood* / Q000592:standards; D000068338:Everolimus; D006801:Humans; D007166:Immunosuppressive Agents / Q000097:blood* / Q000592:standards; D007553:Isotope Labeling; D011933:Reagent Kits, Diagnostic; D012015:Reference Standards; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000097:blood / Q000592:standards; D053719:Tandem Mass Spectrometry / Q000592:standards
chemical_list: D007166:Immunosuppressive Agents; D011933:Reagent Kits, Diagnostic; D016572:Cyclosporine; D000068338:Everolimus; D020123:Sirolimus