Phentolamine

Source: Wikipedia, the free encyclopedia.
Phentolamine
Clinical data
Trade namesRegitine, Oraverse
AHFS/Drugs.comMonograph
Routes of
administration		intravenous, intramuscular, eye drops
ATC code
Legal status
Legal status
Pharmacokinetic data
MetabolismLiver
Elimination half-life19 minutes
Identifiers
  • 3-[(4,5-Dihydro-1H-imidazol-2-ylmethyl)(4-methylphenyl)amino]phenol
JSmol)
  • Oc3cc(N(c1ccc(cc1)C)CC/2=N/CCN\2)ccc3
  • 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) checkY
  • Key:MRBDMNSDAVCSSF-UHFFFAOYSA-N checkY
 ☒NcheckY (what is this?)  (verify)

Phentolamine, sold under the brand name Regitine among others, is a reversible[1] nonselective α-adrenergic antagonist.[2]

Mechanism

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

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 their 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.[4]

Uses

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 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.[6][7] 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.[8][9]

When given by injection it causes blood vessels to dilate, thereby increasing blood flow. When injected into the penis (intracavernosal), it increases blood flow to the penis, which results in an erection.[10]

It may be stored in

Epinephrine
infusions are less vasoconstrictive than norepinephrine as they primarily stimulate β receptor more than α receptors, but the effect remains dose-dependent.

Phentolamine also has diagnostic and therapeutic roles in complex regional pain syndrome (reflex sympathetic dystrophy).[11]

Phentolamine is marketed in the dental field as a local anesthetic reversal agent. Branded as OraVerse, it is a phentolamine mesylate injection designed to reverse the local vasoconstrictor properties used in many local anesthetics to prolong anesthesia.[12]

Chemistry

Phentolamine can be synthesized by alkylation of 3-(4-methylanilino)phenol using 2-chloromethylimidazoline:[13][14]

Adverse effects

References

  1. ISBN 0-7817-4266-8
    .
  2. ^ Phentolamine at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
  3. PMID 12879109
    .
  4. ISBN 978-1-59541-101-3
    .
  5. S2CID 1993954
    .
  6. S2CID 5282953
    .
  7. PMID 17933425
    .
  8. PMID 16326260
    .
  9. PMID 18072128
    .
  10. S2CID 13056029
    .
  11. S2CID 17837280
    .
  12. PMID 19267135
    .
  13. ^ US 2503059, Miescher K, Marxer A, Urech E, "2-(N:N-diphenyl-aminomethyl) imidazolines", issued 1950, assigned to Ciba Pharmaceuticals Products, Inc. 
  14. doi:10.1002/hlca.19500330539
    .
  15. ^ "Common Side Effects of Phentolamine Mesylate for Injection (Phentolamine Mesylate)". Drug Center - RxList.
Retrieved from "https://en.wikipedia.org/w/index.php?title=Phentolamine&oldid=1182222796"