AN HPLC MS/MS ASSAY FOR TACROLIMUS IN PATIENT BLOOD-SAMPLES - CORRELATION WITH RESULTS OF AN ELISA ASSAY/

An HPLC/MS/MS assay for tacrolimus in whole blood using FR900520 as an internal standard was validated over the standard curve range of 0.10 0-10.040 ng ml(-1). The calibration curve for tacrolimus in human bloo d gave a slope of 0.2481, an intercept of 0.007, and a correlation coe fficient (r) of 0.9996, with no interference noted from human blood, a nalyte, or internal standard stock solutions. Use of EDTA or heparin a s the preservative in blood resulted in no significant differences. Sa mples were stable for at least the time required to assay the maximum number of samples that could be placed in the automated system. The li mit of sensitivity of the assay was set at the concentration of the lo west nonzero standard tested, i.e., 0.100 ng ml(-1). However, validati on of the assay to a limit of 0.010 ng ml(-1) is currently underway. T he within-run and between-run precision and accuracy of the method wer e determined for four quality control samples. The highest CV was seen at 0.1 ng ml(-1) (17.6% within-run and 15.9% between-run), with other CV < 5%. The recovery ranged 79.6-81.3% for tacrolimus over the range 0.3-8.0 ng ml(-1) and was 63.10 +/- 1.37% for FR900520. There was a l inear correlation (r(2)=0.963) between assay results by HPLC/MS/MS and ELISA in whole blood from atopic dermatitis patients treated with top ical tacrolimus ointment. The difference between the means +/- S.D. de termined by HPLC/MS/MS (1.22 +/- 1.46 ng ml(-1)) and ELISA (1.12 +/- 1 .29 ng ml(-1)) was significant by a paired t-test (P < 0.001). Similar ly, there was a linear correlation (r(2)=0.841) between assay results by HPLC/MS/MS and IMx in whole blood from solid organ transplant patie nts treated with tacrolimus. The difference between the means was sign ificantly higher (P < 0.001) for the IMx (15.80 +/- 8.37 ng ml(-1)) th an the HPLC/MS/MS (13.32 +/- 6.87 ng ml(-1)). 1997 Published by Elsevi er Science B.V.