Which of the following calcium channel blockers has the most potent peripheral smooth muscle dilator effect?
A. diltiazem (Cardizem)
A. diltiazem (Cardizem)
B. nifedipine (Adalat CC)
C. nimodipine (Nymalize)
D. verapamil (Calan)
Correct Answer: B. nifedipine (Adalat CC)
Nifedipine has the strongest peripheral smooth muscle dilator effect of all the calcium channel blockers. Nifedipine inhibits the entry of calcium ions by blocking these voltage-dependent L-type calcium channels in vascular smooth muscle and myocardial cells. The reduced intracellular calcium, results in a reduction of peripheral arterial vascular resistance and dilatation of coronary arteries, leading to a reduction in systemic blood pressure and increased myocardial oxygen delivery. Other choices have less of a vasodilator effect.
Option A: Diltiazem is a non-dihydropyridine calcium channel blocker. Therapeutic effects occur through various mechanisms. Primarily, diltiazem inhibits the inflow of calcium ions into the cardiac smooth muscle during depolarization. Reduced intracellular calcium concentrations equate to increased smooth muscle relaxation resulting in arterial vasodilation and, therefore, decreased blood pressure.
Option C: During the depolarization of smooth muscle cells of blood vessels, there is an influx of calcium ions. The primary function of nimodipine is to block voltage-gated L-type calcium channels in their inactive conformation, avoiding this influx, to prevent vasoconstriction.
Option D: Verapamil is a non-dihydropyridine calcium channel blocker. Calcium channel blockers inhibit the entry of calcium ions into the slow L-type calcium channels in the myocardium and vascular smooth muscle during depolarization. This inhibition will produce relaxation of coronary vascular smooth muscle as well as coronary vasodilation, which is helpful in patients with hypertension.