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Circulation, Vol 55, 1-7, Copyright © 1977 by American Heart Association

ARTICLES

Pharmacokinetic studies of quinidine in patients with arrhythmias

KA Conrad, BL Molk and CA Chidsey

The absorption and disposition of quinidine were measured in nine patients following single oral and intravenous dosing. A new specific chromatographic method was used to measure the drug in plasma and urine. After intravenous administration, the plasma half-life (t1/2beta) was 7.8+/-0.7 h, the volume of distribution (Vd) was 3.0+/- 0.5 liters/kg, and the total body clearance was 4.8+/-0.8 ml/min/kg. After oral administration, 87+/-7% (mean+/-SEM) was available to the systemic circulation. Quinidine was removed primarily by hepatic metabolism, with the renal clearance averaging only 1.0+/-0.2 ml/min/kg. Mean quinidine concentrations were estimated in 42 patients on chronic therapy by averaging blood levels during a dosing interval. In patients without heart failure, these corresponded well to mean drug levels predicted from the pharmacokinetic parameters measured after a single intravenous dose, but in patients with heart failure, the values for mean quinidine concentrations were higher than predicted. This suggests that impaired elimination of the drug or a decreased volume of its distribution, or both, may develop in heart failure.