Evaluation of the MassTrak Immunosuppressant XE Kit for the determination of everolimus and cyclosporin A in human whole blood employing isotopically labeled internal standards.

BACKGROUND

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) is widely used for therapeutic drug monitoring of immunosuppressants given to transplant recipients. This study evaluated the performance of the newly introduced MassTrak Immunosuppressant XE Kit (Waters Corporation; "the Kit") in the determination of everolimus and cyclosporin A (CsA) using LC-MS/MS.

METHODS

The linearity, precision, detection limit, carryover and matrix effect of the Kit and comparison of the in-house method and Kit procedure were evaluated according to Clinical and Laboratory Standards Institute guidelines.

RESULTS

The Kit afforded good linearity in the measurement of everolimus from 2 to 26 ng/mL (R² = 0.996) and of CsA from 42.6 to 1407 ng/mL (R² = 0.995). The between- and within-run assay coefficients of variation were 2.3% - 8.0% for everolimus and 1.1% - 3.1% for CsA. The lower limit of quantitation of everolimus and CsA were 1.1-4.1 ng/mL, respectively. A comparison of CsA values obtained using inhouse reagents indicated good correlation with Kit results (R = 0.9909). The average matrix effect ranged from 15% - 39% for everolimus and 3% -10% for CsA, and ion enhancement was mostly observed for the matrix effect. The effect on analyte/internal standard ratios ranged from 1%-8% for everolimus and 1%-16% for CsA.

CONCLUSIONS

The Kit employing isotopically labeled internal standards provides reliable measurements of immunosuppressant levels over a broad range of concentrations.