COMPARISON OF FLUORESCENCE POLARIZATION IMMUNOASSAY WITH LIQUID-CHROMATOGRAPHY FOR QUANTIFICATION OF PROCAINAMIDE AND N-ACETYLPROCAINAMIDE IN URINE

The objective of this study was to compare the precision and accuracy of fluorescence polarization immunoassay (FPIA) with highperformance l iquid chromatography (HPLC) for measurement of procainamide (PA) and N -acetylprocainamide (NAPA) concentrations in urine. To determine the c orrelation between FPIA and HPLC, urine PA and NAPA concentrations wer e assayed using both techniques in samples obtained from study patient s receiving PA and in spiked samples. In samples from patients, FPIA-d etermined PA and NAPA concentrations were 19 +/- 9% lower and 28 +/- 3 1% higher, respectively, than those determined by HPLC. The slope of t he FPIA-HPLC regression lines for PA and NAPA differed significantly f rom that of the line of unity (the slope that would result if FPIA and HPLC yielded identical concentrations). In spiked samples, FPIA-deter mined PA and NAPA concentrations were 15 +/- 2% and 11 +/- 2% lower th an HPLC-determined concentrations, respectively, and the slopes of the FPIA-HPLC regression lines differed significantly from the line of un ity. Therefore, FPIA cannot be recommended as a urine assay method whe n quantitative assessment of urine PA or NAPA excretion is needed for pharmacokinetic studies.