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

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.

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.

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).

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.