Phentolamine is a reversible nonselective alpha-adrenergic antagonist. The primary application for phentolamine is for the control of hypertensive emergencies, most notably due to 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. Beta-blockers or combined alpha and beta adrenergic blocking agents should be avoided in patients with a history of cocaine abuse. They can cause an unopposed alpha-adrenergic mediated coronary vasoconstriction, causing the worsening of myocardial ischemia and hypertension. It is also used in the treatment of pheochromocytoma prior to the administration of beta blockers to avoid unopposed alpha-stimulation. Phentolamine, 2-[[N-(3′-hydroxyphenyl)-para-toluidion]methyl]-2-imidazoline, is synthesized by alkylation of 3-(4-methylanilino)phenol using 2-chloromethylimidazoline.
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