Abstract
Concentration monitoring and dose individualization is required to optimize either tacrolimus or cyclosporin therapy. In this study, the validation of a simple, rapid high-performance liquid chromatography-tandem mass spectrometry method for the simultaneous measurement of tacrolimus and cyclosporin in whole blood is reported. Blood samples (100 microL) were prepared by protein precipitation with zinc sulphate followed by acetonitrile (containing the internal standards ascomycin and cyclosporin D). The chromatographic run time was 1.5 minutes per sample. Mass spectrometric detection was by selected reaction monitoring with an atmospheric pressure chemical ionization source in negative ionization mode (tacrolimus: m/z 802.5 --> 560.6, cyclosporin: m/z 1200.8 --> 1088.4). The assay had an analytical range of 1.0 to 30 mug/L (r > 0.998, n = 6) for tacrolimus and 25 to 2000 microg/L (r > 0.999, n = 6) for cyclosporin. Tacrolimus inter- and intraday inaccuracy and precision [coefficient of variation (CV)] using quality control samples (2.5, 12.5, 25 microg/L) was less than +/-10.0% and CV less than 5.0%, respectively (n = 5). Similarly, cyclosporin inter- and intraday inaccuracy and precision using quality control samples (70, 400, 1500 microg/L) was less than +/-2.0% and CV less than 5.0%, respectively (n = 5). The lower limit of quantification for tacrolimus was 1.0 mug/L and cyclosporin 25 microg/L. The assay had an absolute mean recovery of 86.7% for tacrolimus and 89.0% for cyclosporin (n = 15). Intersubject variability, as a measure of potential matrix effects on results, was less than 6.0% CV for both analytes (n = 15). Extracted samples were stable for at least 20 hours. Results obtained from external proficiency testing samples measured by this method compared with the mean of all liquid chromatography-tandem mass spectrometry methods used by scheme participants revealed a strong correlation and good agreement for tacrolimus (r = 0.993, mean bias = -10.3%, n = 19) and cyclosporin (r = 0.996, mean bias = 3.0%, n = 20). In conclusion, this is the first reported high-throughput method that uses negative atmospheric pressure chemical ionization for the simultaneous measurement of tacrolimus and cyclosporin in whole blood.
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