Effect of encainide, ODE, MODE, and flecainide on ADP/5-HT induced platelet aggregation and in the anesthetized dog coronary artery stenosis-occlusion model of intravascular thrombosis.

Encainide is a class 1C antiarrhythmic agent that is indicated for the treatment of life-threatening arrhythmias, such as sustained ventricular tachycardia. Furthermore, encainide possesses a moderate degree of antiserotonin activity, which was quantitated in this present study by determining displacement of [3H]spiperone binding from rat cortical 5-HT2 binding sites. The Ki for encainide in this model was 66.1 nM, compared to 2.6 nM for ketanserin. Two encainide metabolites, ODE and MODE, were also active, but were weaker than encainide. Additionally, these agents were found to inhibit platelet aggregation induced in vitro in human platelet-rich plasma by the combination of ADP and serotonin. In view of the fact that serotonin is one of a variety of humoral factors capable of activating blood platelets and has been recently implicated as playing a role in certain thrombotic syndromes, encainide, along with its two principal human metabolites, ODE and MODE, and another class 1C antiarrhythmic, flecainide, were evaluated in an in vivo model of intravascular thrombosis. Intraduodenal doses of 1 mg/kg of either encainide, ODE, or MODE significantly inhibited thrombosis in a canine model of coronary artery stenosis-occlusion.