Labetalol is preferred in hypertensive emergencies of pregnancy partly because it blocks both alpha-1 and beta receptors. What is the approximate ratio of alpha-1 to beta blockade when labetalol is given intravenously?
- A 1:10, predominantly alpha-1 blockade
- B 1:3, predominantly beta blockade ✓
- C 1:1, equal alpha and beta blockade
- D 3:1, predominantly alpha-1 blockade
Correct answer: B. 1:3, predominantly beta blockade
Explanation
Labetalol blocks beta-1 and beta-2 receptors non-selectively along with alpha-1 receptors. After intravenous administration the ratio of alpha-1 to beta blockade is about 1:3, meaning beta blockade predominates, while orally the ratio shifts to roughly 1:7. This combined action lowers peripheral resistance without reflex tachycardia, making it useful in pregnancy-related severe hypertension. Equal or alpha-predominant ratios describe other agents and are incorrect for labetalol by either route.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.