title: A rapid HPLC-mass spectrometry cyclosporin method suitable for current monitoring practices.
abstract: OBJECTIVE
  Cyclosporin is an immunosuppressant drug with a narrow therapeutic window. Trough and 2-h post-dose blood samples are currently used for therapeutic drug monitoring in solid organ transplant recipients. The aim of the current study was to develop a rapid HPLC-tandem mass spectrometry (HPLC-MS) method for the measurement of cyclosporin in whole blood that was not only suitable for the clinical setting but also considered a reference method.
  
  
  METHODS
  Blood samples (50 muL) were prepared by protein precipitation followed by C(18) solid-phase extraction while using d(12) cyclosporin as the internal standard. Mass spectrometric detection was by selected reaction monitoring with an electrospray interface in positive ionization mode.
  
  
  RESULTS
  The assay was linear from 10 to 2000 microg/L (r(2)>0.996, n=9). Inter-day analytical recovery and imprecision using whole blood quality control samples at 10, 30, 400, 1500, and 2000 microg/L were 94.9--103.5% and <7.7%, respectively (n=5). The assay had a mean relative recovery of 101.6%. Ion suppression was<8.0% of the total signal (n=15). Extracted samples were stable for 6 h. Patient samples, measured by this method and compared with a validated HPLC-UV assay, revealed a strong correlation (r=0.998) and excellent agreement with a mean percentage bias of 2.1% (n=60).
  
  
  CONCLUSIONS
  This high-throughput method provides accurate, precise, and specific measurement of cyclosporin in blood over a wide analytical range, thus making it suitable for current clinical monitoring strategies.
authors.affiliation: Australian Bioanalytical Services Pty. Ltd., Princess Alexandra Hospital, QLD, Australia.
authors.forename: Paul
authors.initials: P
authors.lastname: Salm
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Taylor
authors.forename: Stephen V
authors.initials: SV
authors.lastname: Lynch
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Warnholtz
authors.forename: Peter I
authors.initials: PI
authors.lastname: Pillans
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D016572:Cyclosporine / Q000097:blood*; D016903:Drug Monitoring / Q000379:methods*; D006801:Humans; D013058:Mass Spectrometry / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014466:Ultraviolet Rays
chemical_list: D016572:Cyclosporine