A rapid HPLC-mass spectrometry cyclosporin method suitable for current monitoring practices

Objectives: 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 mu L) 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 mu g/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 mu g/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). Conclusion: 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. (C) 2005 The Canadian Society of Clinical Chemists. All rights reserved.