Performance of a fluorescence polarization immunoassay system evaluated by therapeutic monitoring of four drugs.

Fluorescence polarization immunoassays (FPIA) for amikacin, gentamicin, quinidine, and theophylline (supplied by Roche Diagnostic Systems, made using a Cobas Fara centrifugal analyzer) were evaluated and compared with widely used monitoring analysis methods. For each drug, the between-assay imprecision was ascertained by calibration on the day of assay and by a stored calibration curve made at the beginning of the study. The precision of the amikacin and theophylline assays was acceptable [total coefficient of variation (CV) less than 7.5%] at all concentrations tested for each calibration mode. Imprecision of quinidine and gentamicin assays was significant at low concentrations (1.9 mg/L): total CV = 9.0% for quinidine assessed with stored calibration curve and total CV greater than 8.5% for gentamicin measured with the two calibration modes. The calibration curves for all four assays had a good stability (greater than 30 days). Linear regression analysis demonstrated close agreement between the FPIA (y) and the following comparative techniques (x): Abbott TDx assay for amikacin and gentamicin (r = 0.988, r = 0.974, respectively); Stratus fluorometric enzyme immunoassay for quinidine (r = 0.979); and EMIT Syva assay for theophylline (r = 0.993). It is concluded that fluorescence polarization immunoassay is a rapid and reliable method for the therapeutic monitoring of the four drugs tested. Moreover, the use of reagents on an instrument that can be implemented for a wide range of chemistries has significant advantages and cost benefits over dedicated instruments.