Determination of everolimus in whole blood using the Abbott IMx® sirolimus microparticle enzyme immunoassay

Objectives: Everolimus (Certican®) is a new immunosuppressant derived from sirolimus (Rapamune®) with a 2-hydroxyethyl chain at position 40 of the macrolide ring. The aim of our study was to evaluate the possible determination of everolimus in whole blood using a commercialized microparticle enzyme immunoassay for sirolimus determination. Design and methods: Everolimus concentrations were determined in blood samples from 11 kidney transplant patients (n = 51) and different control materials (n = 35) using the Seradyn Innofluor® Certican® fluorescence polarization immunoassay (FPIA) and the Abbott IMx® sirolimus microparticle enzyme immunoassay (MEIA). Results: The MEIA gave a concentration-dependent cross-reactivity with the everolimus, with a linear regression between the assigned values (y) for the Innofluor® Certican® calibrators and those obtained (x) using this immunoassay: y = 0.96x + 0.67 (ma68 = 0.21 μg/L, r = 0.974, p < 0.001). The within- and between-run coefficients of variation using the MEIA were ≤ 7.3%. In analyzing the different blood samples from patients and control materials using the MEIA and FPIA, a linear regression was found: MEIA = 0.99FPIA − 0.46 (ma68 = 0.32 μg/L, r = 0.967, p < 0.001). Correcting the MEIA results by means of the linear regression equation found between the assigned values for the Innofluor® Certican® calibrators and those obtained using this immunoassay led to a reduction in the deviation with respect to the FPIA values. The possible effect of the hematocrit on the results is analogous for both immunoassays. Conclusions: The Abbott IMx® sirolimus MEIA permits the simple and precise determination of everolimus in whole blood, making it a valid alternative for the therapeutic monitoring of this immunosuppressant agent