12-hour area under the curve cyclosporine concentrations determined by a validated liquid chromatography-mass spectrometry procedure compared with fluorescence polarization immunoassay reveals sirolimus effect on cyclosporine pharmacokinetics.

Liquid chromatographic (LC) procedures have been applied to cyclosporine therapeutic drug monitoring (TDM) since the agent was introduced in 1983. In recent years, the advance to mass spectrometric (MS) detection has enhanced the capability of LC by providing more sensitive and selective detection, a wider analytical range, faster turnaround time, and relative ease of use. Although fluorescence polarization immunoassay (FPIA) is a widely popular technology for cyclosporine TDM, it is compromised by a limited analytical range and lack of selectivity for parent drug. Here, we present the validation of an LC-MS procedure that is equally applicable to use on single or tandem quadrupole instruments. An extensive method comparison with FPIA was performed using samples (n = 726) collected for full 12-hour pharmacokinetic studies on 121 renal transplant recipients. Patients were receiving either full-dose cyclosporine or primary sirolimus therapy complimented with low-dose cyclosporine. FPIA overestimated all cyclosporine concentrations to varying degrees depending on hour of collection (12 approximately 0 > 8 > 6 > 4 > 2-hour). The mean FPIA/LC-MS ratio was significantly higher at 0 hour in the presence of sirolimus (P = 0.008) and trended higher at the other collection times and for area under the curve. Sirolimus also had a significant effect on the FPIA/LC-MS ratio at 12 hour in studies with tmax at 2 hours (P = 0.042) but not 4 hours (P = 0.735). Use of LC-MS procedures for cyclosporine TDM provides for quantitation of approximately 20% more samples from patients receiving low-dose cyclosporine and reduces any errors in dosing that may occur because of the sirolimus effect on cyclosporine pharmacokinetics when combined with varying degrees of overestimation of cyclosporine concentrations by FPIA.