A practical guide to the analysis of sirolimus using high-performance liquid chromatography with ultraviolet detection

Background Sirolimus, a new immunosuppressive agent, has recently been approved in the United States for use in combination with cyclosporine and corticosteroids in renal allograft transplantation. Therapeutic drug monitoring (TDM) of sirolimus is advocated by the drug's manufacturer in certain patient populations. Given the known pharmacokinetic interaction of sirolimus with cyclosporine and the requirement for patient compliance, physicians may wish to monitor steady-state trough levels of this agent. Several types of analytical methods have been investigated for use in TDM of sirolimus: immunoassay, high-performance liquid chromatography with ultraviolet detection (HPLC-UV), and HPLC with mass-spectrometric detection (HPLC-MS or HPLC/MS/MS). Objective This review identifies analytical parameters that are critical to clinical TDM of sirolimus when HPLC-UV is used. Methods Extraction of sirolimus from whole blood was performed using either liquid-liquid or solid phase techniques, whereas liquid chromatography was performed on reverse-phase analytical columns. The drug was detected at its UV extinction maximum. Calculated analytical parameters were evaluated according to current industry standards. Results HPLC-UV methods for the quantification of sirolimus meet or exceed industry standards of performance for clinical TDM. Comparison of the sirolimus levels in clinical samples analyzed by both HPLC-UV and HPLC/MS/MS indicated that the methods provided similar results. Conclusion HPLC-UV methods, although they use a less-sophisticated mode of detection than HPLC-MS or HPLC/MS/MS methods, provide an alternative means of performing TDM without sacrificing the analytical performance required for clinical monitoring of sirolimus.