Which of the following is an example of a calcium channel blocker?

Amlodipine is a well-known calcium channel blocker that is primarily used to treat hypertension and angina. Calcium channel blockers work by inhibiting the influx of calcium ions into vascular smooth muscle and cardiac muscle. This action leads to relaxation of blood vessels, resulting in decreased vascular resistance and lower blood pressure. By preventing calcium entry, these medications help to dilate blood vessels and reduce the workload on the heart.

In contrast, the other medications listed are not calcium channel blockers. Metoprolol is a beta-blocker that reduces heart rate and contractility. Losartan is an angiotensin II receptor blocker that modifies the effects of angiotensin II, a substance that can constrict blood vessels. Hydrochlorothiazide is a thiazide diuretic that helps lower blood pressure by promoting water and sodium excretion, which decreases blood volume. Each of these alternatives works through different mechanisms to manage blood pressure, making amlodipine the correct choice as a calcium channel blocker.