Phentolamine
Nonselective alpha-adrenergic antagonist
| Phentolamine | |
|---|---|
| |
| 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
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
Phentolamine is utilized in various clinical scenarios, including:
1. Hypertensive Emergencies
- 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
- Administered before beta-blockers to prevent hypertensive crises.
3. Erectile Dysfunction (ED)
- When injected intracavernosally, phentolamine increases penile blood flow, aiding erection induction.[5]
4. Peripheral Vasoconstriction Reversal
- Used in cases of extravasation of vasopressors (e.g., norepinephrine, dopamine), preventing tissue necrosis.
5. Complex Regional Pain Syndrome (CRPS)
- Phentolamine infusion can help diagnose and manage CRPS (Reflex Sympathetic Dystrophy).[6]
6. Local Anesthetic Reversal
- Marketed as OraVerse, phentolamine is used in dentistry to reverse local anesthetic effects, restoring normal sensation more quickly.[7]
Chemical Synthesis
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
- 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
- Absorption: Rapid onset (IV: ~2 minutes)
- Half-life: ~19 minutes
- Metabolism: Liver (hepatic enzymatic degradation)
- Excretion: Primarily in urine
Adverse Effects
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
Phentolamine should not be used in:
- Myocardial infarction (increases cardiac workload)
- Coronary artery disease
- Severe hypotension
- Hypersensitivity to phentolamine
Drug Interactions
- 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
| Sympatholytic (and closely related) antihypertensives (C02) | ||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
| Peripheral vasodilators (C04) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
| Drugs for erectile dysfunction (G04BE) and premature ejaculation | ||||
|---|---|---|---|---|
* See also: Sexual dysfunction pharmacotherapies
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- ↑ {{{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,
- ↑ Brock G. Oral phentolamine (Vasomax). Drugs Today (Barcelona). 2000 Feb-Mar;36(2-3):121-4.
- ↑ {{{last}}}, Shen, Howard, Illustrated Pharmacology Memory Cards: PharMnemonics, Minireview, 2008, ISBN 1-59541-101-1,
- ↑ Tuncel M, Ram VC. Hypertensive emergencies. American Journal of Cardiovascular Drugs. 2003;3(1):21-31.
- ↑ Bella AJ, Brock GB. Intracavernous pharmacotherapy for erectile dysfunction. Endocrine. 2004 Mar-Apr;23(2-3):149-55.
- ↑ Rowbotham MC. Pharmacologic management of complex regional pain syndrome. Clinical Journal of Pain. 2006 Jun;22(5):425-9.
- ↑ http://www.novalar.com/oraverse-dental-specialty-pharmaceutical
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