Analytic validation of the enzyme multiplied immunoassay technique for thedetermination of mycophenolic acid in plasma from renal transplant recipients compared with a high-performance liquid chromatographic assay

The analysis of mycophenolic acid (MPA) has proved a valuable adjunct to th e clinical care of organ transplant recipients. The analytic validation of the enzyme multiplied immunoassay technique (EMIT) for the determination of MPA in plasma is described. The EMIT MPA standard curve was 0 to 15.0 mug/ mL, and curve storage was maintained for 4 weeks. The MPA EMIT assay proved reliable and reproducible, as shown by the intra-assay and interassay coef ficients of variation (1.58-3.68% and 1.23-7.57%, respectively). Excellent linear correlation (r = 0.999) was observed for dilution linearity. The sen sitivity of the assay was 0.01 mug/mL. Recoveries of 99.4% to 104.29% were obtained by spiking aliquots of three controls of known MPA concentrations with MPA. No interference was observed for endogenous substances and coadmi nistered immunosuppressant drugs, and no cross-reactivity from the major me tabolite MPA glucuronide was found. The high-performance liquid chromatogra phy (HPLC) assay used protein precipitation and C18 ion-pair chromatography with ultraviolet detection at 304 nm. Plasma concentrations of MPA were me asured using EMIT and HPLC. A linear relationship was observed between EMIT and HPLC (EMIT = 1.091 x HPLC - 0.089; r(2) = 0.990, n = 129). These resul ts indicate that EMIT is a simple, rapid, and sensitive assay method for th e measurement of MPA in plasma.