Phentolamine

Phentolamine Structural Formulae

Phentolamine-space-filling

Phentolamine (brand name: Regitine) is a nonselective alpha-adrenergic antagonist, notable for its reversible effects on the body. It exerts its primary action by inhibiting certain receptors in the body, leading to various therapeutic effects.

Mechanism of Action

Phentolamine functions primarily by inducing vasodilation, a widening of blood vessels, due to its antagonistic action on α₁ receptors. This drug also possesses the ability to trigger reflex tachycardia, a rapid heart rate, resulting from hypotension (low blood pressure) and the inhibition of α₂ receptors, which then intensifies sympathetic tone.

Therapeutic Uses

• Hypertensive Emergencies: Phentolamine is a primary agent used in controlling hypertensive emergencies, particularly those arising from pheochromocytoma, a tumor of the adrenal gland.
• Cocaine-Induced Hypertension: The drug serves a vital role in managing hypertension resulting from cocaine use, given that beta blockers are typically avoided in such scenarios. Beta-blockers, such as metoprolol, can lead to serious complications in individuals with a history of cocaine use, including uncontrolled tightening of the coronary arteries.
• Pheochromocytoma Treatment: Before administering beta blockers for pheochromocytoma, phentolamine is used to prevent any undue alpha stimulation.
• Erection Induction: When phentolamine is directly injected into the penis (intracavernosal), it enhances blood flow, causing an erection.
• Peripheral Vasoconstriction Management: The drug can be present in crash carts to manage severe peripheral vasoconstriction that arises from extravasation of certain drugs.
• Complex Regional Pain Syndrome: Phentolamine has demonstrated efficacy in diagnosing and treating complex regional pain syndrome or reflex sympathetic dystrophy.
• Local Anesthetic Reversal: Recently introduced in dentistry, Phentolamine is used as a local anesthetic reversal agent under the brand name OraVerse.

Chemical Synthesis

Phentolamine's chemical synthesis can be described through its full chemical name: 2-[[N-(3′-hydroxyphenyl)-para-toluidion]methyl]-2-imidazoline. Its synthesis involves the alkylation of 3-(4-methylanilino)phenol using 2-chloromethylimidazoline.

• K. Miescher, A. Marxer, E. Urech, U.S. patent 2,503,059 (1950).
• E. Urech, A. Marxer, K. Miescher, Helv. Chim. Acta, 33, 1386 (1950).

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