A 45-year-old man receives phenoxybenzamine before adrenalectomy for pheochromocytoma. Unlike phentolamine, phenoxybenzamine is preferred because it:
- A Is a reversible competitive α-blocker with longer half-life
- B Irreversibly alkylates the α-receptor, providing sustained blockade that cannot be overcome by catecholamine surges ✓
- C Selectively blocks α2 receptors, preventing reflex tachycardia
- D Blocks β1 receptors in addition to α receptors, preventing arrhythmias
Correct answer: B. Irreversibly alkylates the α-receptor, providing sustained blockade that cannot be overcome by catecholamine surges
Explanation
Phenoxybenzamine is a non-selective, irreversible (covalent haloalkylamine) α-blocker. Its irreversible binding means that even massive surges of catecholamines released during tumor manipulation cannot displace the drug and overcome the block, making it superior for pre-operative preparation. Phentolamine is a reversible competitive blocker that can be overcome by catecholamine excess. Phenoxybenzamine does not selectively block α2 or β1 receptors.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.