Which two drugs have a clinically significant interaction when used together, such as a calcium channel blocker with a beta-blocker?

• A. Verapamil and Amlodipine
• B. Metoprolol and Amlodipine
• C. Verapamil and Metoprolol
• D. Clopidogrel and Omeprazole

Answer: (C)

Two drugs that both slow the heart’s electrical conduction and its pumping can interact in a way that magnifies those effects, leading to dangerous bradycardia and low blood pressure. Verapamil is a non-dihydropyridine calcium channel blocker that reduces heart rate and slows AV nodal conduction. Metoprolol is a beta-blocker that also lowers heart rate, decreases AV nodal conduction, and weakens cardiac contractility. When used together, their effects on the heart add up, raising the risk of marked bradycardia, AV block, and hypotension, especially in people with preexisting conduction system disease, heart failure, or the elderly. This is why clinicians monitor heart rate and blood pressure closely and may adjust dosing or choose alternatives if needed. The other listed combinations either don’t produce the same level of additive heart-conduction effects or involve interactions that are pharmacokinetic rather than hemodynamic; for example, a proton pump inhibitor with clopidogrel can affect antiplatelet activation but doesn’t create the same acute risk of bradycardia and hypotension.