In a patient with pheochromocytoma undergoing preoperative preparation, which pharmacological principle justifies initiating an alpha-blocker BEFORE a beta-blocker?

• A Alpha-blockers lower catecholamine synthesis in the tumor
• B Alpha-blockade is necessary to prevent beta-blocker induced tachycardia
• C Alpha-blockers reduce tumor size preoperatively
• D Beta-blockade without prior alpha-blockade causes severe hypertensive crisis by leaving alpha-mediated vasoconstriction unopposed ✓

Explanation

Pheochromocytoma secretes excess catecholamines that cause hypertension through alpha-1 receptor mediated vasoconstriction and tachycardia via beta-1 receptors. If a beta-blocker is given first, the vasodilatory component from beta-2 receptors in skeletal muscle is blocked, leaving the full alpha-1 vasoconstriction unopposed, precipitating a severe hypertensive crisis. Phenoxybenzamine (irreversible alpha-blocker) is therefore always started first, followed by a beta-blocker only if tachycardia persists.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.