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Adrenaline Dose-Dependent Effects — FRCA Primary MCQ

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HardPharmacology - CardiovascularAdrenaline Dose-Dependent EffectsFRCA Primary

A patient taking propranolol receives adrenaline for anaphylaxis. Bronchospasm improves only slightly, but blood pressure rises abruptly to 230/120 mmHg and the pulse falls to 42 min−1. Which receptor interaction best explains this pattern?

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Correct answer: C — Unopposed alpha vasoconstriction with baroreflex-mediated bradycardia

The best answer is “Unopposed alpha vasoconstriction with baroreflex-mediated bradycardia”. Non-selective beta blockade antagonises adrenaline’s cardiac and bronchodilator beta effects while alpha vasoconstriction persists. The resulting marked increase in vascular resistance can cause severe hypertension with baroreflex-mediated bradycardia. This interaction also helps explain reduced response of bronchospasm to adrenaline. The other mechanisms assign the wrong receptor action or predict vasodilatation rather than hypertension.

Reference: Adrenaline 1 mg/mL solution for injection, UK SmPC: https://www.medicines.org.uk/emc/product/3673/smpc; Royal College of Anaesthetists, Primary FRCA syllabus v2.2: https://www.rcoa.ac.uk/sites/default/files/documents/2026-01/Primary-FRCA-Syllabus.pdf