Toward Analytical Performance Specifications for Immunosuppressive Drug Quantification in Transplantation: An Opinion Article

Background: Analytical methods require performance that meets the clinical needs. Different approaches for setting up permissible analytical imprecision goals (pCVA%) for drug analyses have been reported. The aim of this study was to calculate the pCV A % for cyclosporine, tacrolimus, everolimus, sirolimus, and mycophenolic acid using 4 alternative approaches, to compare the results and to critically discuss advantages and disadvantages of each model. Methods: The approaches to evaluate pCV A % were (A) based on biological variation observed in routine measurement results between 2022 and 2023 in the authors' laboratory, (B) derived from the terminal elimination half-life and dosing interval of the drugs, and (C and D) explored from the width of the therapeutic ranges (TR) by the 2 methods. For approach A, routine measurement data for cyclosporine and tacrolimus, obtained through liquid chromatography–tandem mass spectrometry and electrochemiluminescence immunoassays, were evaluated separately. Results: The 4 alternative approaches for deriving pCV A % yielded similar results, for cyclosporine and tacrolimus in an analytical method dependent manner. The average pCV A % was 5.2%, 5.6%, 5.1%, 4.8%, and 7.7% for cyclosporine, tacrolimus, everolimus, sirolimus, and mycophenolic acid, respectively. The most challenging goals were those using TR-related approaches, while those using the biological variation approach were most easily achievable. Approach B resulted in more stringent goals for drugs with longer elimination half-lives (eg, everolimus and sirolimus). Conclusions: There is no single ideal approach for setting goals of drug analysis. However, the pCV A % values derived from the various approaches are similar and confirm that a <6% target proposed by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology is adequate and realistic in combination with state-of-the-art measurement technologies. In the authors' opinion, approaches based on the width of the TR are preferable, as they represent a common basis for clinical decisions and reflect elements of biological variation and analytics used to establish the TR.