Dofetilide, A Novel Class III Antiarrhythmic Agent

Summary: Dofetilide is a potent and selective class III antiarrhythmic agent that is under development for the treatment of re-entrant tachyarrhythmias (ventricular tachycardia/ventricular fibrillation, atrial fibrillation/atrial flutter, and paraoxysmal supraventricular tachy-cardia). In animal studies, dofetilide selectively inhibits the rapid component of the time-dependent outward potassium current (Ikr) and therefore increases the effective refractory period and action potential duration without affecting the fast inward sodium current. Studies in dogs have shown that dofetilide (a) prolongs the effective refractory period in a dose-dependent manner, (b) elevates ventricular fibrillation threshold, (c) facilitates conversion of electrically induced ventricular fibrillation or fibrilloflutter to sinus rhythm, (d) does not influence conduction within the His-Purkinje system or within the myocardium, (e) does not impair cardiac contractility, and (f) reduces dispersion of ventricular repolarization. Dofetilide has been administered to healthy volunteers as well as to patients with ischemic heart disease or with supraventricular arrhythmias; the compound has generally been well tolerated. Side effects have occasionally been reported, but have generally been transient and mild and occur in placebo-treated subjects as well. No clinically significant changes in laboratory safety tests have been detected. The pharmacokinetic profile of dofetilide both in healthy volunteers and patients includes a linear dose-plasma concentration relationship and also a linear plasma concentration-QT. relationship. The terminal plasma elimination half-life is approximately 9-10 h and systemic bioavailability in the region of 100%. The elimination pattern is balanced, with 50% being excreted unchanged via the kidney, the remaining 50% being metabolized in the liver to inactive metabolites, with greater than 90% of circulating drug-related material being unchanged do fetilide. After intravenous administration of the compound. a slight hysteresis in the plasma drug level-QT. relationship has been detected. Pharmacodynamic data demonstrate dose- and concentration-dependdent effects on myocardial repolarization as evidenced by prolongations of the QT. interval. This is reflected in significant prolongations in the effective and functional refractory periods and monophasic action potential duration throughout the myocardium. No effects on sinus node function, conduction parameters, or cardiac contractility have been detected in any of the clinical studies, supporting the contention that dofetilide is a highly selective class III antiarrhythmic agent.