Phenoxybenzamine produces irreversible alpha-blockade. The clinical implication of this irreversibility compared to phentolamine is:
- A Phenoxybenzamine is preferred for preoperative preparation in pheochromocytoma because its prolonged action provides stable blockade ✓
- B Phenoxybenzamine cannot be used for hypertensive emergencies due to unpredictable duration
- C Phentolamine is preferred for long-term management of pheochromocytoma
- D Irreversibility means phenoxybenzamine cannot be overcome by releasing more norepinephrine from the tumor
Correct answer: A. Phenoxybenzamine is preferred for preoperative preparation in pheochromocytoma because its prolonged action provides stable blockade
Explanation
Phenoxybenzamine alkylates the alpha receptor irreversibly, giving a prolonged effect (24-48 hours) that cannot be overcome even by massive catecholamine surges from a pheochromocytoma during surgical manipulation. This makes it the preferred agent for preoperative preparation of pheochromocytoma patients over 10-14 days. Phentolamine (competitive, reversible) is used for acute hypertensive crises in the perioperative period but is unsuitable for prolonged pre-op blockade due to its short duration (15-30 min IV).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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