Effects of KT-362, a new Na and Ca influx and Ca release inhibitor, on canine ventricular arrhythmias.

Antiarrhythmic effects of the new drug KT-362, which was reported to suppress Na and Ca currents of cardiac cells and also to suppress intracellular Ca release in isolated smooth muscle preparations, were examined using two-stage coronary ligation-, digitalis- and adrenaline-induced ventricular arrhythmias in the dog. Intravenous KT-362 at 10 mg/kg suppressed coronary ligation arrhythmia both at 24 and 48 hr after ligation, and the minimum effective plasma concentrations for arrhythmias induced by 24 hr coronary ligation and 48 hr coronary ligation were 6.1 +/- 1.7 and 8.6 +/- 2.7 micrograms/ml, respectively. Antiarrhythmic effects were accompanied by transient hypotension. Oral administration of 70-100 mg/kg was also effective on 24 hr coronary ligation arrhythmia. However, there was no prominent hypotension in these experiments. Intravenous KT-362 at 3 mg/kg suppressed digitalis arrhythmia; and the minimum effective plasma concentration was 3.3 +/- 1.2 micrograms/ml, which was lower than the effective plasma concentrations for coronary ligation arrhythmias. Intravenous KT-362 at 1 mg/kg also suppressed adrenaline arrhythmia; and the minimum effective plasma concentration was 1.0 +/- 0.1 microgram/ml, the lowest among the effective plasma concentrations. These pharmacological profiles of KT-362 are quite different from those of class 4 Ca antagonists, but similar to those of class 1 drugs such as propafenone. Though KT-362 has a hypotensive effect, it is effective on canine ventricular arrhythmias; thus its clinical usefulness for supraventricular and ventricular arrhythmias is expected.