Autonomic Pharmacology USMLE Step 1 Practice Question
A 45-year-old man presents with sudden severe headache, profuse diaphoresis, and palpitations. Vital signs: BP 220/140 mmHg, HR 118/min, RR 16/min, Temp 37.2°C. Labs show elevated plasma free metanephrines (1,200 pg/mL; normal <90). CT abdomen reveals a 3-cm right adrenal mass. He denies chest pain. Prior to surgical removal, he receives phentolamine followed by propranolol. Why is this sequential drug administration order critical for patient safety?
Answer choices
- AThe order is irrelevant if both drugs are given before surgery
- BPropranolol must precede phentolamine to prevent tachycardia
- CPropranolol potentiates phentolamine's hypotensive effect
- DPhentolamine must precede propranolol to prevent unopposed alpha effectsCorrect answer
- EPhentolamine causes reflex tachycardia that propranolol prevents when given first
- FPropranolol reduces catecholamine synthesis, allowing phentolamine to work more effectively
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