A patient with a biochemically confirmed catecholamine-secreting tumour is being prepared for adrenalectomy. Why must an irreversible alpha-adrenergic blocker be started before any beta blocker?
- A Beta blockers accelerate tumour catecholamine synthesis
- B Alpha blockade is required to prevent rebound tachycardia after tumour removal
- C Unopposed alpha-mediated vasoconstriction can precipitate a hypertensive crisis ✓
- D Beta blockers interfere with urinary metanephrine measurement used to confirm cure
Correct answer: C. Unopposed alpha-mediated vasoconstriction can precipitate a hypertensive crisis
Explanation
Phenoxybenzamine is given first because blocking beta-2 mediated vasodilation while alpha-1 receptors remain open removes peripheral vasodilatory tone and can precipitate severe hypertension and pulmonary oedema. Only after adequate alpha blockade (evidenced by orthostatic hypotension) is a beta blocker added for reflex tachycardia or arrhythmias. Beta blockers do not affect metanephrine assays and do not alter tumour catecholamine synthesis.
Reference: Katzung's Basic and Clinical Pharmacology, 16th ed.
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