Management of phentermine overdose causing hypertensive emergency?

• A. Administer benzodiazepine
• B. Administer diuretic
• C. Administer phentolamine
• D. Administer naloxone

Answer: (C)

Phentermine overdose triggers a surge of sympathetic activity with excessive norepinephrine causing marked peripheral vasoconstriction and a hypertensive emergency. The key treatment is counteracting that adrenergic effect directly. Administering phentolamine, a nonselective alpha-adrenergic antagonist, rapidly blocks alpha receptors on vascular smooth muscle, leading to vasodilation and a swift drop in blood pressure. This directly addresses the cause—alpha-adrenergic–mediated vasoconstriction from sympathetic overactivity.

Benzodiazepines can calm agitation and reduce sympathetic outflow somewhat, but they don’t promptly reverse the vasoconstriction driving the crisis. Diuretics reduce volume rather than counteracting the vasoconstrictive state and aren’t appropriate for an acute hypertensive emergency caused by sympathetic excess. Naloxone treats opioid overdose, not this scenario.