Which drug is a nonselective antagonist at both alpha-1 and beta receptors?

• A. Propranolol
• B. Atenolol
• C. Labetalol
• D. Prazosin

Answer: (C)

Blocking both alpha-1 and beta receptors produces two simultaneous effects: alpha-1 blockade lowers peripheral vascular resistance (vasodilation), while beta blockade reduces heart rate, contractility, and renin release. Labetalol has this dual action, acting as a nonselective beta blocker with additional alpha-1 blocking activity, so it combines decreases in vascular resistance with reduced cardiac output. That makes it the best choice for a drug that antagonizes both receptor types. Propranolol blocks beta receptors without alpha-1 blockade, so it lowers heart rate and contractility but doesn’t directly cause alpha-mediated vasodilation. Prazosin blocks only alpha-1 receptors, lacking beta-blocking effects. Atenolol blocks only beta-1 receptors, with no alpha-1 blockade.