Which of the following is a calcium channel blocker?

The correct choice is Isoptin, which is a brand name for verapamil, a medication that functions as a calcium channel blocker. Calcium channel blockers work by inhibiting the influx of calcium ions through L-type calcium channels in cardiac and smooth muscle cells. This action results in relaxation of vascular smooth muscle, leading to a decrease in peripheral vascular resistance and helping to lower blood pressure. Additionally, calcium channel blockers can reduce heart rate and myocardial oxygen demand, making them useful in managing conditions such as hypertension and angina.

Lispro is a rapid-acting insulin used in diabetes management, Metformin is an oral antidiabetic medication that improves insulin sensitivity, and Simvastatin is a statin used to lower cholesterol levels. These medications do not share the mechanism of action characteristic of calcium channel blockers, which is why Isoptin is the appropriate answer to this question.