Analysis of cyclosporin A, tacrolimus, sirolimus, and everolimus in dried blood spot samples using liquid chromatography tandem mass spectrometry

In the last few years, an increasing number of dried blood spot (DBS) sampling assays have been developed. With this increase, more insight is gained in the factors that possibly influence the performance of DBS assays. We have developed an assay for four commonly used immunosuppressants; some of them are possibly concomitantly prescribed: cyclosporin A (CsA), tacrolimus (TcR), sirolimus (SiR), and everolimus (EvE). Chromatographic separation from possible ion suppression was obtained within the total runtime of 4.2 min. Trifluoroacetic acid and ammonium acetate were used as mobile phase additives. The linearity ranged from 23.6 to 787, 1.14 to 30.3, 1.34 to 35.8, and 1.26 to 33.7 mu g/L, for CsA, TcR, SiR, and EvE, respectively. Between- and within-run accuracy and precision were all within 15 % and extensive validation for DBS samples, such as hematocrit, blood spot volume, and spot punch location was performed. None of these factors were found to be of influence on the performance of the DBS assay.