Phentolamine

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Phentolamine
Phentolamine Structural Formulae.svg
INN
Drug class
Routes of administration Intravenous, Intramuscular, Intracavernosal
Pregnancy category
Bioavailability
Metabolism Liver
Elimination half-life ~19 minutes
Excretion Urine
Legal status
CAS Number 50-60-2
PubChem 4757
DrugBank DB00692
ChemSpider
KEGG


Phentolamine (brand names: Regitine, OraVerse) is a nonselective alpha-adrenergic antagonist used primarily in the management of hypertensive emergencies, pheochromocytoma, and erectile dysfunction.[1] It works by blocking alpha receptors, leading to vasodilation and a subsequent decrease in blood pressure.

Mechanism of Action[edit]

Phentolamine acts as a competitive, reversible alpha-adrenergic antagonist, blocking both α1 and α2 receptors:

  • α1 receptor blockade: Causes vasodilation, reducing vascular resistance and blood pressure.[2]
  • α2 receptor blockade: Inhibits negative feedback on norepinephrine release, leading to increased sympathetic activity, which may cause reflex tachycardia.[3]

Therapeutic Uses[edit]

Phentolamine is utilized in various clinical scenarios, including:

1. Hypertensive Emergencies[edit]

  • Used in pheochromocytoma crises to rapidly lower blood pressure.[4]
  • Preferred in cocaine-induced hypertension, where beta-blockers are contraindicated to avoid unopposed α-adrenergic stimulation.

2. Pheochromocytoma Treatment[edit]

  • Administered before beta-blockers to prevent hypertensive crises.

3. Erectile Dysfunction (ED)[edit]

  • When injected intracavernosally, phentolamine increases penile blood flow, aiding erection induction.[5]

4. Peripheral Vasoconstriction Reversal[edit]

  • Used in cases of extravasation of vasopressors (e.g., norepinephrine, dopamine), preventing tissue necrosis.

5. Complex Regional Pain Syndrome (CRPS)[edit]

  • Phentolamine infusion can help diagnose and manage CRPS (Reflex Sympathetic Dystrophy).[6]

6. Local Anesthetic Reversal[edit]

  • Marketed as OraVerse, phentolamine is used in dentistry to reverse local anesthetic effects, restoring normal sensation more quickly.[7]

Chemical Synthesis[edit]

Phentolamine's full chemical name is 2-[[N-(3′-hydroxyphenyl)-para-toluidino]methyl]-2-imidazoline.

Its synthesis involves: 1. Alkylation of 3-(4-methylanilino)phenol. 2. Reaction with 2-chloromethylimidazoline.

Patent and Research[edit]

  • 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).

Pharmacokinetics[edit]

  • Absorption: Rapid onset (IV: ~2 minutes)
  • Half-life: ~19 minutes
  • Metabolism: Liver (hepatic enzymatic degradation)
  • Excretion: Primarily in urine

Adverse Effects[edit]

Common side effects include:

  • Hypotension (low blood pressure)
  • Reflex tachycardia
  • Dizziness, flushing
  • Nasal congestion (due to vasodilation)

Serious adverse effects:

  • Severe hypotension
  • Arrhythmias
  • Myocardial ischemia (rare)

Contraindications[edit]

Phentolamine should not be used in:

  • Myocardial infarction (increases cardiac workload)
  • Coronary artery disease
  • Severe hypotension
  • Hypersensitivity to phentolamine

Drug Interactions[edit]

  • Beta-blockers – Risk of unopposed α-adrenergic effects.
  • Vasodilators (e.g., nitroglycerin, hydralazine) – Additive hypotensive effect.
  • Sympathomimetics (e.g., epinephrine) – Can lead to unpredictable blood pressure responses.

See Also[edit]


Sympatholytic (and closely related) antihypertensives (C02)
Sympatholytics
(antagonize α-adrenergic
vasoconstriction)
Other antagonists


Peripheral vasodilators (C04)
Phenylethanolamine derivatives
Alpha blockers
Niacin and derivatives
Purine derivatives
Ergot alkaloids


Drugs for erectile dysfunction (G04BE) and premature ejaculation
For erectile dysfunction
For premature ejaculation



Adrenergic receptor modulators
α1
Agonists
Antagonists
* Abanoquil
α2
Agonists
Antagonists
β
Agonists
* Abediterol
Antagonists
* Acebutolol


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  1. ↑ {{{last}}}, Jewell, John R.; Longworth, David L.; Stoller, James K.; Casey, David, The Cleveland Clinic Internal Medicine Case Reviews, Lippincott Williams & Wilkins, 2003, ISBN 0-7817-4266-8,
  2. ↑ Brock G. Oral phentolamine (Vasomax). Drugs Today (Barcelona). 2000 Feb-Mar;36(2-3):121-4.
  3. ↑ {{{last}}}, Shen, Howard, Illustrated Pharmacology Memory Cards: PharMnemonics, Minireview, 2008, ISBN 1-59541-101-1,
  4. ↑ Tuncel M, Ram VC. Hypertensive emergencies. 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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