Phentolamine phaeochromocytoma

Phentolamine and phenoxybenzamine are older O -adrenoceptor antagonists, which may be used occasionally in course of the surgical removal of phaeochromocytoma, with the aim to suppress the vasoconstrictor effects of noradrenaline/adrenaline released from the tumor as a result of surgical manipulation. 

Alpha-adrenoceptor antagonists are used as antihypertensives and to reduce afterload in the treatment of heart failure. Urapidil and, to a lesser extent, ketanserin are used in the treatment of essential hypertension and acute perioperative hypertension. In contrast to other vasodilators urapidil does not increase intracranial pressure when given intravenously, making it preferable for use in neurosurgical interventions. The effects of the excessive catecholamine concentrations in patients with phaeochromocytoma can be treated by the non-selective ol- and o2-adrenoceptor antagonists phentolamine or phenoxybenzamine. 

Accidental overdose with adrenaline occurs occasionally. It is rationally treated by propranolol to block the cardiac p effects (cardiac arrhythmia) and phentolamine or chlorpromazine to control the a effects on the peripheral circulation that will be prominent when the P effects are abolished. Labetalol (a + p block) would be an alternative. P-adrenoceptor block alone is hazardous as the then unopposed a-receptor vasoconstriction causes (severe) hypertension (see Phaeochromocytoma, p. 494). Use of antihypertensives of most other kinds is irrational and some may also potentiate the adrenaline. 

Phentolamine is a nonselective a-adrenoceptor blocker. It is given i.v. for brief effect in adrenergic hypertensive crises, e.g. phaeochromocytoma or the MAOI-S5nnpathomimetic interaction. In addition to a-neceptor block it has direct vasodilator and cardiac inotropic actions. The dose for hypertensive crisis is 2-5 mg i.v. repeated as necessary (in minutes to hours). The use of phentolamine as a diagnostic test for phaeochromocytoma is appropriate only when biochemical measurements are impracticable, since it is less reliable. 

Phentolamine Erectile dysfunction Hypertensive episodes in phaeochromocytoma... 

The main indication of phentolamine is in the management of phaeochromocytoma but, unlike phenoxybenzamine, its action is reverable It belongs to the imidazoline class of compounds like xylometazoline but functions as an a-receptor antagonist rather than an agonist. It is diffi-cult to rationalise its antagonistic artivity on the basis of its structure. 

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