A 55-year-old man with pheochromocytoma is prepared for surgery. Phenoxybenzamine is started 10-14 days preoperatively. The drug produces a non-competitive, irreversible alpha-adrenergic blockade. What is the clinical consequence of this irreversibility during surgical tumour manipulation?
- A Persistent tachycardia post-operatively due to unopposed beta-receptor stimulation
- B Severe reflex bradycardia because alpha blockade unmasks vagal tone at the heart
- C Blunted hypertensive surges during tumour handling because displaced drug cannot be overcome by catecholamine floods ✓
- D Malignant hyperthermia triggered by catecholamine-induced rhabdomyolysis
Correct answer: C. Blunted hypertensive surges during tumour handling because displaced drug cannot be overcome by catecholamine floods
Explanation
Phenoxybenzamine forms a covalent bond with the alpha-adrenoceptor, making blockade insurmountable; even massive catecholamine release during tumour manipulation cannot displace the drug and overcome the blockade, thereby preventing dangerous hypertensive crises. This is the pharmacological rationale for its preoperative use in phaeochromocytoma. Post-operative hypotension is a recognised concern, not tachycardia. Beta-blockers are added only after adequate alpha blockade to control reflex tachycardia, not phenoxybenzamine alone.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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