Which of the following is a calcium channel blocker?

• A. Lidocaine
• B. Epinephrine
• C. Atropine
• D. Nifedipine

Answer: (D)

Calcium channel blockers prevent calcium from entering cells through L-type channels in vascular smooth muscle and the heart, which relaxes smooth muscle and reduces vascular resistance. Nifedipine is a dihydropyridine calcium channel blocker that mainly targets vascular smooth muscle, causing vasodilation and lower blood pressure. The other drugs act by different mechanisms: lidocaine blocks sodium channels, epinephrine stimulates adrenergic receptors, and atropine blocks muscarinic receptors. So nifedipine is the calcium channel blocker.