Comparison of Disposition Values Obtained by Two Assay Methods for Quinidine Gluconate in Patients with Ventricular Tachycardia

Eight patients with previously untreated ventricular tachycardia, age 48.54 +/- 28.02 years (mean +/- SD), were enrolled in a protocol evaluating the disposition of quinidine gluconate as determined by two assay methods. Patients received two infusions of 5 mg/kg over 30 minutes separated by 20-30 (24.9 +/- 4.0) minutes of electrophysiologic testing. Blood samples were obtained at 0.17 hours and just prior to the second infusion, and then at 0.17, 0.25, 0.33, 1.0, 6.0, 12.0, and 24.0 hours after the second infusion. Paired serum samples were assayed for quinidine concentrations by fluorescence polarization immunoassay and high-performance liquid chromatography. The two assays compared well, with a linear regression equation of Y = 0.927X + 0.247 with a correlation coefficient of 0.985. With the exception of the beta elimination rate constant and beta distribution volume, t test comparison of disposition values demonstrated no significant difference. Differences in the estimates of the beta elimination rate constant reflected differences in the two methods and indicated that even though both assays were comparable, subtle differences in specificity could be reflected in significant differences in this variable.