ROGITAMINE
PHENTOLAMINE MESYLATE
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Source: Medicines Control Authority of Zimbabwe · fetched 2026-09-20 04:30:11 · updated 2026-09-23 04:30:09
Molecular reference: phentolamine
PubChem CID 5775Molecular formula: C17H19N3O
Mechanism of action
Phentolamine is a reversible, competitive antagonist at alpha-1 and alpha-2 adrenergic receptors. It causes vasodilation of vascular smooth muscles. Pupil dilation is primarily controlled by the radial iris dilator muscles surrounding the pupil, which are activated by the alpha-1 adrenergic receptors. Phentolamine reversibly binds to these receptors and reduces pupil diameter. By blocking alpha-1 adrenergic receptors, phentolamine can also be used to reverse mydriasis induced by muscarinic antagonists. Phentolamine inhibits responses to adrenergic stimuli by competitively blocking a-adrenergic receptors (primarily excitatory responses of smooth muscle and exocrine glands), but the action of the drug is relatively transient and a-adrenergic blockade is incomplete. Phentolamine has greater a-adrenergic blocking effects than does tolazoline. Phentolamine is more effective in antagonizing responses to circulating epinephrine and/or norepinephrine than in antagonizing responses to mediator released at the adrenergic nerve ending. The drug causes peripheral vasodilation and decreases peripheral resistance, primarily by direct relaxation of vascular smooth muscle, but a-adrenergic blockade also contributes to vasodilation. Phentolamine also stimulates beta-adrenergic receptors and produces a positive inotropic and chronotropic effect on the heart and increases cardiac output. DIFFERENCES IN PLASMA GLUCOSE & LACTOSE OBSERVED SUGGEST PROTECTION OF HEPATIC METABOLISM IN PHENTOLAMINE-TREATED ENDOTOXIC RATS (FASTED MALE RATS ADMIN E COLI ENDOTOXIN 25 MG/KG/IP) BY PREVENTION OF EXCESSIVE HEPATIC HYPOXIA. INFUSION OF PHENTOLAMINE AUGMENTED ACUTE INSULIN RESPONSE & GLUCOSE TOLERANCE. COMPARISON OF CARDIOVASCULAR ACTIONS OF DIHYDRALAZINE, PHENTOLAMINE, & PRAZOSIN IN SPONTANEOUSLY HYPERTENSIVE RATS IS DISCUSSED. For more Mechanism of Action (Complete) data for Phentolamine (8 total), please visit the HSDB record page.
Pharmacodynamics
Phentolamine produces an alpha-adrenergic block of a relatively short duration. Phentolamine induces vasodilatation of vascular smooth muscle and pupils. When used in an ophthalmic solution, the onset of pupil dilation generally occurred in 30 minutes, with the maximal effect seen in 60 to 90 minutes. Pupil dilation lasted for at least 24 hours. Phentolamine also has direct but less marked positive inotropic and chronotropic effects on cardiac muscle and vasodilator effects on vascular smooth muscle; however, phentolamine is not believed to affect contractile or adenyl cyclase function. Large doses can lead to a mild sympatholytic action. Some evidence suggests that phentolamine also stimulates beta-adrenergic receptors, thereby causing peripheral vasodilation. Phentolamine was shown to stimulate insulin secretion, possibly related to its blocking actions on ATP-sensitive K<sup>+</sup> channels.
Source: PubChem (NCBI) · pathways from PathBank, Reactome, WikiPathways & PharmGKB.