Measurement of sirolimus in whole blood using high-performance liquid chromatography with ultraviolet detection

Background: Sirolimus, a potent immunosuppressive drug, exhibits intrapatient and interpatient variability of absorption and metabolism. Thus, therapeutic drug monitoring is important. Objective: This paper describes a reverse-phase high-performance liquid chromatography (HPLC) method, using ultraviolet (UV) absorption for detection, for measuring sirolimus levels in human whole-blood samples. Methods: The stability of sirolimus in whole blood was assessed under conditions likely to be encountered during transport of study samples to a central laboratory. The performance of the HPLC UV assay in measuring sirolimus was compared with that of 3 established, validated HPLC assays with tandem mass-spectrometric (MS/MS) detection. Results of the HPLC-UV assay also were compared with results produced by a prototype microparticle enzyme immunoassay (MEIA). Results: Inaccuracy for 3 in-house control samples was less than or equal to 4%, whereas within-assay repeatability (coefficient of variation [CV]) was less than or equal to 5% and between-assay reproducibility was less than or equal to 6.6%. Mean recovery of sirolimus from blood was 81.5% +/- 4.3%. The lower limit of quantification was set at 6.5 ng/mL, and the repeatability CV at this concentration was 4.2% (n = 6). Sirolimus-containing whole-blood samples were stable for 3 freeze/thaw cycles when stored at -20 degrees C and for greater than or equal to 2 days when stored at ambient temperature. The sample extract was shown to be stable for up to 54 hours at ambient temperature (similar to 22 degrees C) after extraction. Results of the HPLC-UV assay were consistent with those of the HPLC/ MS/MS assays but lower than those produced by MEIA. Conclusion: This HPLC-UV method is considered suitable for therapeutic drug monitoring of sirolimus.