Effects of intravenous azimilide on cardiac performance, fibrillation threshold, and hemodynamics in anesthetized dogs.

The class III antiarrhythmic azimilide (E-1-[[[5-(4-chlorophenyl)-2-furanyl]methylene]-amino]-3-[4-(4-methyl-1- piperazinyl)butyl]-2,4-imidazolidinedione dihydrochloride; WHO No. 7299, CAS 149888-94-8), by slow infusion or stepwise bolus doses, was evaluated for effects on heart rate, blood pressure, and cardiac pump function, excitability, and refractoriness in anesthetized dogs. Infusion (0.6 mg/kg/min) in male beagles (n = 5) to a maximum dose of 54 mg/kg increased QTc more than 20 ms at 2.0 mg/kg. At a dose of 8.9 mg/kg i.v., QTc increased 34% above baseline and remained elevated throughout the subsequent infusion and for at least 60 min postinfusion. At this maximum class III dose, azimilide increased heart contractile force (HCF) 10% and +dP/dt 34% and decreased heart rate (HR) 12%, without significantly changing mean blood pressure (MBP), left ventricular end diastolic pressure, -dP/dt, stroke volume (SV), or cardiac output (CO). At the mean maximum 47 mg/kg i.v. dose, QTc remained elevated, but decreases were observed in HCF (-27%), +dP/dt (-24%), -dP/dt (-35%), SV (-16%), and CO (-52%). Cumulative intravenous bolus injections of azimilide (0.3, 1, 3, 10, and 30 mg/kg) in male mongrels (n = 5) increased effective refractory period (ERP) and +dP/dt (18% and 16%, respectively, at 10 mg/kg) as a function of dose and significantly decreased HR (-22% at 10 mg/kg). MBP decreased significantly (-23%) only at the highest dose. Ventricular fibrillation threshold (VFT) was unchanged at 30 mg/kg. Effects of dl- (n = 3) and d-sotalol (n = 4) on ERP and HR were similar to azimilide's, but both compounds caused a greater MBP depression and VFT elevation. These results suggest that azimilide is well tolerated by the cardiovascular system, providing an increase in contractility and a slight decrease in HR at intravenous doses that produced a large or maximum increase in cardiac refractoriness.