Fluorescence polarization immunoassay: Can it result in an overestimation of vancomycin in patients not suffering from renal failure?

It has been reported in scientific data that fluorescence polarization immu noassay (FPIA) results in overestimation of vancomycin in patients with ren al failure. This overestimation is caused by interference of the degradatio n product, CDP-1, in this assay. Increases in vancomycin levels have also b een reported in patients not suffering from renal failure (nonrenal failure patients) who are receiving vancomycin therapy for approximately 10 days o r more. The authors tested whether this increase in vancomycin in nonrenal failure patients is a result of CDP-1 interfering with FPIA or a change in the pharmacokinetics of the drug. Serum vancomycin ak and trough samples we re obtained from 10 adult (mean age SD: 55.9 years 17.5) nonrenal failure p atients (mean Cl-Cr +/- SD: 76.2 mL/min +/- 29.20) receiving vancomycin the rapy for at least 10 days. These peaks and troughs were obtained at steady state and again at approximately 10 days of therapy. All serum samples were analyzed initially by fluorescence polarization immunoassay (FPIA, TDx(R)) (Abbot Diagnostics; Irving, TX) and again by enzyme. multiplied immunoassa y (EMIT Vancomycin Assay) (Dade Behring; San Jose, CA). Statistical analysi s (Wilcoxon signed-rank test) determined that there was no difference betwe en the values obtained from the two assays. This demonstrates that the incr ease in vancomycin levels is not caused by the accumulation of CDP-1 and ma y be the result of a change in the pharmacokinetics of the drug.