Greater quinidine-induced QTc interval prolongation in women

• Published in: Clinical pharmacology and therapeutics 2000-04, Vol.67 (4), p.413-418
• Main Authors: Benton, Robert E., Sale, Mark, Flockhart, David A., Woosley, Raymond L.
• Format: Article
• Language: English
• Subjects: Adult; Anti-Arrhythmia Agents - blood; Anti-Arrhythmia Agents - pharmacokinetics; Anti-Arrhythmia Agents - pharmacology; Area Under Curve; Biological and medical sciences; Cross-Over Studies; Drug toxicity and drugs side effects treatment; Electroencephalography - drug effects; Female; Heart Rate - drug effects; Humans; Infusions, Intravenous; Male; Medical sciences; Metabolic Clearance Rate; Pharmacology. Drug treatments; Quinidine - analogs & derivatives; Quinidine - blood; Quinidine - pharmacokinetics; Quinidine - pharmacology; Sex Factors; Single-Blind Method; Toxicity: cardiovascular system
• ISSN: 0009-9236; 1532-6535
• DOI: 10.1067/mcp.2000.105761

Background Prolongation of the electrocardiographic QT interval by drugs is associated with the occurrence of a potentially lethal form of polymorphic ventricular tachycardia termed torsades de pointes. Women are at greater risk than men for development of this adverse event when taking drugs that prolong the QT interval. To determine whether this may be the result of gender‐specific differences in the effect of quinidine on cardiac repolarization, we compared the degree of quinidine‐induced QT interval lengthening in healthy young men and women. Methods Twelve women and 12 men received a single intravenous dose of quinidine (4 mg/kg) or placebo in a single‐blind, randomized crossover trial. Total plasma and protein‐free concentrations of quinidine and 3‐hydroxyquinidine were measured in serum. QT intervals were determined and corrected for differences in heart rate with use of the method of Bazett (QTc = QT/RR1/2). Results As expected, the mean QTc interval at baseline was longer for women than for men (mean ± SD; 407 ± 7 versus 395 ± 9 ms, P < .05). The slope of the relationship between change in the QTc interval (ΔQTc) from baseline to the serum concentration of quinidine was 44% greater for women than for men (mean ± SE; 42.2 ± 3.4 versus 29.3 ± 2.6 ms/μg per mL, P < .001). These results were not influenced by analysis of 3‐hydroxyquinidine, free concentrations of quinidine and 3‐hydroxyquinidine, or the JT interval. Conclusions Quinidine causes greater QT prolongation in women than in men at equivalent serum concentrations. This difference may contribute to the greater incidence of drug‐induced torsades de pointes observed in women taking quinidine and has implications for other cardiac and noncardiac drugs that prolong the QTc interval. Adjustment of dosages based on body size alone are unlikely to substantially reduce the increased risk of torsades de pointes in women. (Clin Pharmacol Ther 2000;67:413‐8.) Clinical Pharmacology & Therapeutics (2000) 67, 413–418; doi: 10.1067/mcp.2000.105761