FK506 MEASUREMENT - COMPARISON OF DIFFERENT ANALYTICAL METHODS

In this study, we used solid-phase extraction with Sep-Pak and a liqui d-liquid extraction with methylene chloride as two primary methods of extracting FK506 from plasma. The extracts were either analyzed direct ly by enzyme-linked immunosorbent assay (ELISA) or subjected to high-p erformance liquid chromatography (HPLC) separation and different fract ions were analyzed by ELISA. Serial blood samples were obtained from f our kidney transplant patients and four patients who underwent liver t ransplantation, from day 1 until day 30-35 posttransplantation. There was no significant difference in the FK506 plasma concentration as mea sured by all four methods in normal transplant patients. However, in l iver transplant patients, the solid-phase extraction method gave highe r FK506 concentrations than the methylene chloride extraction during t he early postoperative period. The concentrations measured after methy lene chloride extraction were higher than that after HPLC-ELISA. This higher FK506 concentration measured by direct ELISA could be attribute d to possible cross-reacting metabolites that were present in the plas ma of patients with abnormal liver functions. Once liver function retu rns to normal, all four methods give identical plasma concentrations f or FK506.