Mibefradil is a tetralol calcium channel blocking agent that inhibits the influx of calcium ions across both the T (low-voltage) and L (high-voltage) calcium channels of cardiac and vascular smooth muscle, with a greater selectivity for T channels. Vasodilation occurs in vascular smooth muscle, causing a decrease in peripheral vascular resistance and a resulting decrease in blood pressure. Mibefradil causes a slight increase in cardiac output during chronic dosing. Mibefradil slows sinus and atrioventricular (AV) node conduction, producing a slight reduction in heart rate and a slight increase in the PR interval. It has also been shown to slightly lengthen the corrected sinus node recovery time and AH interval and to raise the Wenckebach point. The mechanism by which mibefradil reduces angina is not known, but is thought to be attributed to a reduction in heart rate, total peripheral resistance (afterload), and the heart rate_systolic blood pressure product at any given level of exercise. The result of these effects is a decrease in cardiac workload and myocardial oxygen demand.
Mibefradil belongs to a group of medicines called calcium channel blocking agents, or, more commonly, calcium channel blockers. Calcium channel blocking agents affect the movement of calcium into the cells of the heart and blood vessels. As a result, they relax blood vessels and increase the supply of blood and oxygen to the heart while reducing its workload. Mibefradil is a benzimidazoyl-substituted tetraline that selectively binds and inhibits T-type calcium channels.
The two metabolic pathways that mibefradil undergoes are esterase-catalyzed hydrolysis of the ester side chain (producing an alcohol metabolite) and cytochrome P450 3A4-catalyzed oxidation (that becomes less important during chronic dosing). The pharmacologic effect of the metabolite is approximately 10% of that of the parent mibefradil.