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File:Phentolamine Structural Formulae.svg
Systematic (IUPAC) name
3-[4,5-dihydro-1H-imidazol-2-ylmethyl- (4-methylphenyl)-amino]phenol
Clinical data

Routes of
Usually IV or IM
Pharmacokinetic data
Metabolism Hepatic
Biological half-life 19 minutes
CAS Number 50-60-2
ATC code C04AB01 (WHO) G04BE05
PubChem CID 5775
DrugBank APRD00615
Chemical data
Formula C17H19N3O
Molar mass 281.352 g/mol[[Script error: No such module "String".]]
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Phentolamine (Regitine) is a reversible[1] nonselective alpha-adrenergic antagonist. [2]


Its primary action is vasodilation due to α1 blockade.[3]

It also can lead to reflex tachycardia because of hypotension and α2 inhibition, which increases sympathetic tone.[4]


The primary application for phentolamine is for the control of hypertensive emergencies, most notably due to pheochromocytoma.[5]

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 (i.e. metoprolol) or combined alpha and beta adrenergic blocking agents (i.e. labetalol) 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.

[6][7] 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.[8]

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).[9]

Phentolamine has recently been introduced in the dental field as a local anesthetic reversal agent. Distributed by Novalar, OraVerse is a Phentolamine Mesylate injection designed to reverse the local vasoconstrictor properties used in many local anesthetics to prolong anesthesia.[10] OraVerse has been shown to accelerate the reversal of the lingering soft-tissue numbness associated with the widely used anesthetic-vasoconstrictor combinations.[11]


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  1. Jewell, John R.; Longworth, David L.; Stoller, James K.; Casey, David (2003). The Cleveland Clinic internal medicine case reviews. Hagerstown, MD: Lippincott Williams & Wilkins. p. 32. ISBN 0-7817-4266-8. 
  2. MeSH Phentolamine
  3. Brock G. Oral phentolamine (Vasomax). Drugs Today (Barcelona). 2000 Feb-Mar;36(2-3):121-4.
  4. Shen, Howard (2008). Illustrated Pharmacology Memory Cards: PharMnemonics. Minireview. p. 14. ISBN 1-59541-101-1. 
  5. Tuncel M, Ram VC. Hypertensive emergencies. Etiology and management. American Journal of Cardiovascular Drugs. 2003;3(1):21-31.
  6. Hollander JE, Henry TD. Evaluation and management of the patient who has cocaine-associated chest pain. Cardiology Clinics. 2006 Feb;24(1):103-14.
  7. Chan GM, Sharma R, Price D, Hoffman RS, Nelson LS. Phentolamine Therapy for Cocaine-Association Acute Coronary Syndrome (CAACS). Journal of Medical Toxicology. 2006 Sep;2(3):108-11.
  8. Bella AJ, Brock GB. Intracavernous pharmacotherapy for erectile dysfunction. Endocrine. 2004 Mar-Apr;23(2-3):149-55.
  9. Rowbotham MC. Pharmacologic management of complex regional pain syndrome. Clinical Journal of Pain. 2006 Jun;22(5):425-9.
  11. Malamed S. What's new in local anaesthesia? Society For The Advancement Of Anaesthesia In Dentistry Digest. 2009 Jan;25:4-14.