A patient with pheochromocytoma is prepared for surgery. Why is it essential to establish adequate alpha-adrenergic blockade with phenoxybenzamine BEFORE adding a beta-blocker?
- A Beta-blockade without prior alpha-blockade can cause paradoxical severe hypertension due to unopposed alpha-mediated vasoconstriction ✓
- B Phenoxybenzamine has a short half-life requiring pre-loading before beta-blockers
- C Beta-blockers directly stimulate adrenal catecholamine release
- D Alpha-blockade is needed to prevent phenoxybenzamine-induced tachycardia
Correct answer: A. Beta-blockade without prior alpha-blockade can cause paradoxical severe hypertension due to unopposed alpha-mediated vasoconstriction
Explanation
In pheochromocytoma, excess catecholamines activate both alpha and beta receptors. If a beta-blocker is given first, the cardiac beta-2 vasodilatory tone is removed while vascular alpha receptors remain stimulated by tumor catecholamines, resulting in unopposed peripheral vasoconstriction and potentially lethal hypertensive crisis. Alpha-blockade first expands volume and prevents this phenomenon; only then is beta-blockade safe to add for rate control.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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Written and medically reviewed by the StethoPrep medical team.