title: Long-term cross-validation of everolimus therapeutic drug monitoring assays: the Zortracker study.
abstract: BACKGROUND
  This ongoing academic collaboration was initiated for providing support to set up, validate, and maintain everolimus therapeutic drug monitoring assays and to study long-term interlaboratory performance.
  
  
  METHODS
  This study was based on EDTA whole blood samples collected from transplant patients treated with everolimus in a prospective clinical trial. Samples were handled under controlled conditions during collection, storage and were shipped on dry ice to minimize freeze-thaw cycles. For more than 1.5 years, participating laboratories received a set of 3 blinded samples on a monthly basis. Among others, these samples included individual patient samples, patient sample pools to assess long-term performance, and patient samples pools enriched with isolated everolimus metabolites.
  
  
  RESULTS
  The results between liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) and the everolimus Quantitative Microsphere System (QMS, Thermo Fisher) assay were comparable. The monthly interlaboratory variability (coefficient of variation %) for cross-validation samples ranged from 6.5% to 23.2% (average of 14.8%) for LC-MS/MS and 4.2% to 26.4% (average of 11.1%) for laboratories using the QMS assay. A blinded long-term pool sample was sent to the laboratories for 13 months. The result was 5.31 ± 0.86 ng/mL (range, 2.9-7.8 ng/mL) for the LC-MS/MS and 5.20 ± 0.54 ng/mL (range, 4.0-6.8 ng/mL) for QMS laboratories. Enrichment of patient sample pools with 5-25 ng/mL of purified everolimus metabolites (46-hydroxy everolimus and 39-O-desmethyl everolimus) did not affect the results of either LC-MS/MS or QMS assays.
  
  
  CONCLUSIONS
  Both LC-MS/MS and QMS assays gave similar results and showed similar performance, albeit with a trend toward higher interlaboratory variability among laboratories using LC-MS/MS than the QMS assay.
authors.affiliation: *Department of Anesthesiology, iC42 Clinical Research and Development, University of Colorado Anschutz Medical Campus, Aurora; †Department of Pathology, University of Utah Health Sciences Center; ‡ARUP Institute for Clinical and Experimental Pathology, Salt Lake City, Utah; and §Novartis Pharmaceutical Corp, East Hanover, New Jersey.
authors.forename: Björn
authors.initials: B
authors.lastname: Schniedewind
authors.forename: Stefanie
authors.initials: S
authors.lastname: Niederlechner
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Galinkin
authors.forename: Kamisha L
authors.initials: KL
authors.lastname: Johnson-Davis
authors.forename: Uwe
authors.initials: U
authors.lastname: Christians
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Meyer
mesh_terms: D001774:Blood Chemical Analysis / Q000379:methods*; D016903:Drug Monitoring / Q000379:methods*; D000068338:Everolimus / Q000032:analysis* / Q000097:blood*; D006801:Humans; D007166:Immunosuppressive Agents / Q000032:analysis* / Q000097:blood*
chemical_list: D007166:Immunosuppressive Agents; D000068338:Everolimus