FALSELY ELEVATED SERUM VANCOMYCIN CONCENTRATIONS IN HEMODIALYSIS-PATIENTS

Fluorescence polarization immunoassay (FPIA) is the most widely used c linical vancomycin assay in the United States, Questions exist regardi ng the accuracy of this polyclonal assay in patients with end-stage re nal disease (ESRD). While several studies have reported discrepancies in vancomycin serum concentrations determined by FPIA compared with ot her vancomycin assays, no study has investigated the accuracy of vanco mycin serum concentrations determined by FPIA in patients with ESRD un dergoing maintenance hemodialysis, Therefore, we compared the assay pe rformance of FPIA and enzyme multiplied immunoassay technique (EMIT) i n six subjects with ESRD receiving high-efficiency hemodialysis, Subje cts underwent 6 consecutive weeks of hemodialysis treatment with a cel lulose acetate dialyzer (CA210) and received 1 g vancomycin intravenou sly once weekly during the last hour of dialysis. Vancomycin serum con centrations were determined by both EMIT and FPIA methodologies, From the serum concentration results of both assays, vancomycin dosing reco mmendations were calculated to achieve a desired steady-state peak con centration of 35 mg/L and trough concentration of 10 mg/L. Overall, va ncomycin serum concentrations reported by FPIA were significantly high er than those reported by EMIT, The mean difference between assays in the peak serum concentrations at weeks 1, 4, and 6 was 7.5, 11.5, and 11.2 mg/L, respectively. The mean difference in trough serum concentra tions at weeks 1, 4, and 6 was 4.2, 6.2, and 5.2 mg/L, respectively, T he FPIA overestimation of the EMIT values (calculated as FPIA - EMIT) varied widely among study subjects with a range of 0.0 mg/L to 27.0 mg /L for peak serum concentrations and 0.0 mg/L to 12.8 mg/L for trough serum concentrations, The mean doses calculated based on FPIA results were significantly lower than the EMIT-derived doses, No significant d ifference was observed in the calculated dosing intervals, These resul ts demonstrate that FPIA significantly overestimates vancomycin serum concentrations compared with EMIT in patients with ESRD undergoing hig h-efficiency hemodialysis, The overestimation by FPIA may result in si gnificantly different vancomycin dosing recommendations, leading to un derdosing and the potential for therapeutic failures. Due to the unpre dictability of the overestimation by FPIA, we were unable to formulate vancomycin dosing guidelines for institutions that use FPIA. Therefor e, we recommend that the EMIT vancomycin assay be used in patients wit h ESRD to ensure appropriate dosing. (C) 1996 by the National Kidney F oundation, Inc.