In the management of acute severe hypertension in pregnancy, a labetalol infusion is initiated. A woman develops bradycardia and hypotension despite dose reduction. Which receptor-binding profile of labetalol explains this adverse effect combination?

• A Selective β1 blockade with peripheral α2 agonism
• B Non-selective β blockade (β1:β2 ratio 3:1) and α1 blockade (α:β ratio 1:7) ✓
• C Selective α1 blockade with reflex tachycardia prevention
• D Calcium channel blockade in combination with β1 selectivity

Explanation

Labetalol is a combined α1- and non-selective β-blocker with an oral α:β ratio of approximately 1:3 and an IV ratio of approximately 1:7. Non-selective β blockade (affecting both β1 and β2) causes bradycardia (β1 effect) and can worsen bronchoconstriction (β2 effect), while α1 blockade causes vasodilation contributing to hypotension. The combined effect explains the bradycardia-hypotension syndrome seen with excessive dosing.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.