Phenoxybenzamine differs from phentolamine in that it:
- A Is a competitive antagonist at alpha-1 and alpha-2 adrenoceptors
- B Selectively blocks only alpha-1 receptors without affecting alpha-2 receptors
- C Forms a covalent bond with the adrenoceptor, producing irreversible blockade ✓
- D Has a shorter duration of action due to rapid hepatic metabolism
Correct answer: C. Forms a covalent bond with the adrenoceptor, producing irreversible blockade
Explanation
Phenoxybenzamine is a haloalkylamine that alkylates the alpha-adrenoceptor, producing an irreversible (non-equilibrium) blockade lasting 24–48 hours. Phentolamine is a competitive (reversible) antagonist at both alpha-1 and alpha-2 receptors. Neither drug is selective for alpha-1 alone among these options.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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