Pharmacokinetics of quinidine in dogs with congestive cardiac failure

Comparative disposition kinetics of two diastereomeric pairs of cinchona alkaloids in the dog

The comparative disposition kinetics of quinidine, quinine, cinchonine , and cinchonidine were investigated in five male, mongrel dogs after intravenous bolus injections of a 9.2-mmol/kg dose of each alkaloid base. Blood and plasma specimens were obtained at various times up to 6 h postdose and assayed for quinidine and quinine with a TLC-fluorometric procedure and for cinchonine and cinchonidine by HPLC. The plasma alkaloid concentration-time data were analyzed by weighted, nonlinear least-squares regression analysis to obtain the central compartment volume (Vc), disposition rate constants (alpha and beta), and corresponding half-life values (t1/2). Total body clearance (CL) and apparent volume of distribution (Vd) were estimated by nonparametric analysis. In this study, the highest plasma alkaloid concentrations were reached with quinidine and the lowest concentrations with the quinidine congener, cinchonine . The other congeneric pair, quinine and cinchonidine , exhibited plasma alkaloid concentrations that were comparable and intermediate to those of quinidine and cinchonine . With cinchonine and cinchonidine , the plasma and blood concentration-time curves were virtually superimposable. However, with quinidine and quinine, the plasma alkaloid concentrations of these diastereomers were approximately twice the corresponding blood concentrations. The total body clearance rate of quinidine was significantly slower than quinine and cinchonine clearance. No difference in clearance was observed between cinchonine and cinchonidine . The beta and t1/2 beta for quinidine were significantly smaller and larger, respectively, than the corresponding values obtained with the other alkaloids. No significant differences in alpha or Vc and Vd were found between and within the two diastereomeric pairs of alkaloids. The differences in disposition kinetics observed in this study were attributable to an interaction of stereochemical and 6'-methoxy group substitution effects.