Phentolamine

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Phentolamine Structural Formulae
Phentolamine-space-filling

Phentolamine (brand name: Regitine) is a nonselective alpha-adrenergic antagonist, notable for its reversible effects on the body.[1] It exerts its primary action by inhibiting certain receptors in the body, leading to various therapeutic effects.

Mechanism of Action[edit | edit source]

Phentolamine functions primarily by inducing vasodilation, a widening of blood vessels, due to its antagonistic action on α1 receptors.[2] 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.[3]

Therapeutic Uses[edit | edit source]

  • Hypertensive Emergencies: Phentolamine is a primary agent used in controlling hypertensive emergencies, particularly those arising from pheochromocytoma, a tumor of the adrenal gland.[4]
  • 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.[5]
  • 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.[6]
  • Local Anesthetic Reversal: Recently introduced in dentistry, Phentolamine is used as a local anesthetic reversal agent under the brand name OraVerse.[7]

Chemical Synthesis[edit | edit source]

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.

File:Phentolamine synthesis.png
  • 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).

References[edit | edit source]

  1. ↑
  2. ↑ Brock G. Oral phentolamine (Vasomax). Drugs Today (Barcelona). 2000 Feb-Mar;36(2-3):121-4.
  3. ↑
  4. ↑ Tuncel M, Ram VC. Hypertensive emergencies. Etiology and management. American Journal of Cardiovascular Drugs. 2003;3(1):21-31.
  5. ↑ Bella AJ, Brock GB. Intracavernous pharmacotherapy for erectile dysfunction. Endocrine. 2004 Mar-Apr;23(2-3):149-55.
  6. ↑ Rowbotham MC. Pharmacologic management of complex regional pain syndrome. Clinical Journal of Pain. 2006 Jun;22(5):425-9.
  7. ↑ http://www.novalar.com/oraverse-dental-specialty-pharmaceutical


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Contributors: Prab R. Tumpati, MD