Which drug would be MOST appropriate for rapid reversal of the hypotension caused by a phentolamine overdose?
- A Epinephrine (adrenaline)
- B Norepinephrine (noradrenaline) ✓
- C Isoproterenol
- D Dopamine at low dose
Explanation
Phentolamine is a competitive (reversible) non-selective alpha-1/alpha-2 blocker. Its hypotension is mediated by alpha-1 vasodilation (and also alpha-2 blockade that can increase NE release via lost feedback). To reverse the hypotension, an agent with primarily alpha-1 agonist activity is needed. Norepinephrine, acting on alpha-1 and alpha-2 with minimal beta-2, is the preferred vasopressor. Epinephrine would be problematic because its beta-2 vasodilating effect (on top of alpha blockade from phentolamine) could worsen hypotension ('epinephrine reversal'). Isoproterenol has no alpha activity. This principle — epinephrine reversal in presence of alpha-blockers — is a classic pharmacology concept.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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