Which of the following drugs is an antihypertensive calcium channel blocker?

Verapamil Hydrochloride is a calcium channel blocker that is specifically used as an antihypertensive medication. It works by relaxing blood vessels, which decreases blood pressure and makes it easier for the heart to pump blood. Calcium channel blockers like verapamil inhibit the influx of calcium ions into the smooth muscle of the vascular system and the heart, leading to vasodilation and reduced heart rate. This mechanism makes it effective for managing hypertension.

In contrast, the other options provided do not serve this purpose. Temazepam is a benzodiazepine primarily used to treat insomnia. Eszopiclone is also a sleep aid and is not related to blood pressure management. Chlorpheniramine is an antihistamine used to relieve allergy symptoms and does not have antihypertensive properties. This distinction highlights why verapamil hydrochloride is the appropriate choice for an antihypertensive calcium channel blocker.