Phentolamine (Regitine) is a reversible nonselective alpha-adrenergic antagonist.

Mechanism

Its primary action is vasodilation due to α₁ blockade.

It also can lead to reflex tachycardia because of hypotension and α₂ inhibition, which increases sympathetic tone.

Uses

The primary application for phentolamine is for the control of hypertensive emergencies, most notably due to phaeochromocytoma (pheochromocytoma).

It also has usefulness in the treatment of cocaine induced hypertension, where one would generally avoid beta blockers and where calcium channel blockers are not effective. In this context it is probably most safely given by infusion since bolus doses have a propensity towards causing precipitous falls in blood pressure.

When given by injection it causes blood vessels to expand, thereby increasing blood flow. When injected into the penis (intracavernosal), it increases blood flow to the penis, which results in an erection.

It may be stored in crash carts to counteract severe peripheral vasoconstriction secondary to extravasation of peripherally placed vasopressor infusions, typically of norepinephrine. Epinephrine infusions are less vasoconstrictive than norepinephrine as they primarily stimulate beta receptor more than alpha receptors, but the effect remains dose dependent.

Phentolamine also has diagnostic and therapeutic roles in complex regional pain syndrome (reflex sympathetic dystrophy).

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