Phentolamine

Phentolamine

Clinical data
Trade names	Regitine
AHFS/Drugs.com	Micromedex Detailed Consumer Information
Pregnancy category	US: C (Risk not ruled out)
Routes of administration	Usually IV or IM
ATC code	C04AB01 (WHO) V03AB36 (WHO)
Legal status
Legal status	US: ℞-only
Pharmacokinetic data
Metabolism	Liver
Biological half-life	19 minutes
Identifiers
IUPAC name 3-[(4,5-Dihydro-1H-imidazol-2-ylmethyl)(4-methylphenyl)amino]phenol
CAS Number	50-60-2 Y
PubChem (CID)	5775
IUPHAR/BPS	502
DrugBank	DB00692 Y
ChemSpider	5571 Y
UNII	Z468598HBV Y
KEGG	D08362 Y
ChEBI	CHEBI:8081 N
ChEMBL	CHEMBL597 Y
ECHA InfoCard	100.000.049
Chemical and physical data
Formula	C17H19N3O
Molar mass	281.352 g/mol
3D model (Jmol)	Interactive image
SMILES Oc3cc(N(c1ccc(cc1)C)CC/2=N/CCN\2)ccc3
InChI InChI=1S/C17H19N3O/c1-13-5-7-14(8-6-13)20(12-17-18-9-10-19-17)15-3-2-4-16(21)11-15/h2-8,11,21H,9-10,12H2,1H3,(H,18,19) Y Key:MRBDMNSDAVCSSF-UHFFFAOYSA-N Y
NY (what is this?)

Phentolamine (Regitine) is a reversible nonselective α-adrenergic antagonist.

Its primary action is vasodilation due to α₁ blockade.

Non-selective α-blockers can cause a much more pronounced reflex tachycardia than the selective α₁ blockers. Like the selective α₁ blockers, phentolamine causes a relaxation of systemic vasculature, leading to hypotension. This hypotension is sensed by the baroreceptor reflex, which results in increased sympathetic nerve firing on the heart, releasing norepinephrine. In response, the β₁ adrenergic receptors on the heart increase its rate, contractility, and dromotropy, which help to offset the decrease in systemic blood pressure. Unlike the α₁ selective blockers, phentolamine also inhibits the α₂ receptors, which function predominantly as presynaptic negative feedback for norepinephrine release. By abolishing this negative feedback phentolamine leads to even less regulated norepinephrine release, which results in a more drastic increase in heart rate.

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

It also has usefulness in the treatment of cocaine-induced cardiovascular complications, where one would generally avoid β-blockers (e.g. metoprolol), as they can cause unopposed α-adrenergic mediated coronary vasoconstriction, worsening myocardial ischemia and hypertension. It is important to note that phentolamine is not a first-line agent for this indication. Phentolamine should only be given to patients who do not fully respond to benzodiazepines, nitroglycerin, and calcium channel blockers.