phentolamine

Phentolamine is a reversible, nonselective alpha-adrenergic receptor antagonist that blocks both α1 and α2 receptors. By inhibiting vascular α-adrenergic activity, it produces vasodilation and lowers systemic vascular resistance, leading to a drop in blood pressure.

Medical uses include management of hypertensive crises due to catecholamine excess, such as those associated with pheochromocytoma. It is used in the preoperative management of pheochromocytoma to control blood pressure and minimize intraoperative hypertensive events. Phentolamine is also employed to treat vasopressor extravasation injuries by local administration around the infiltrated area to reverse vasoconstriction and restore perfusion.

Mechanism and effects: α1 blockade on vascular smooth muscle leads to vasodilation, while α2 blockade can increase norepinephrine release, which may blunt the blood pressure decline while potentially contributing to tachycardia and other cardiovascular effects. The net result is a rapid reduction in blood pressure with possible reflex tachycardia.

Administration and pharmacokinetics: Phentolamine is typically given intravenously in acute settings, with a rapid onset and a short duration of action (usually minutes). It may be used orally in some historical or specific contexts, but IV administration is standard for emergencies and perioperative care, under careful hemodynamic monitoring.

Adverse effects and contraindications: Common side effects include hypotension, reflex tachycardia, headache, dizziness, flushing, and edema. It is contraindicated in patients with hypotension or significant cardiovascular instability and should be used with caution in those with coronary artery disease, heart failure, or arrhythmias.

Brand name and availability: Phentolamine is marketed under several names, including Regitine, and remains a specialized medication used in controlled clinical settings.