Automated fluorescence polarization immunoassay for monitoring vancomycin

We have extended fluorescence polarization immunoassay (FPIA) technology for the measurement of drugs to include the complex amphoteric glycopeptide antibiotic vancomycin (molecular weight, 1,449). Fluorescein-labeled vancomycin was employed as a tracer, and antisera specific for vancomycin were raised in rabbits by conventional procedures. Tracer, sample, and diluted antiserum were combined, and the polarization of tracer fluorescence is determined in a specially designed fluorometer (Abbott TDx). Because of instrument design, the possibility of fluorescent interferences is minimized. The assay can measure as little as 0.6 mg/L of vancomycin and is free of interferences from hemolysis, lipemia, bilirubin, and changes in protein concentration. The coefficient of variation within assay was 3% (n = 5) and between assays was 5% (n = 5). The FPIA assay (TDx Vancomycin) was compared to a liquid chromatographic (LC) assay for vancomycin and to a commercially available radioimmunoassay (RIA) for 98 clinical specimens. A linear least-squares regression analysis gave a correlation coefficient for LC of 0.980 from the equation FPIA = 1.09 LC + 3.04, and a correlation coefficient for RIA of 0.957 from the equation FPIA = 1.036 RIA + 1.66.