A major use of this drug is in the management of hypertension in pheochromocytoma prior to surgery. G. Pharmacology of Phentolamine and Tolazoline 1. Phentolamine and tolazoline are competitive antagonists of both alpha 1 and alpha 2 receptors. As such their effects on the cardiovascular system are similar to those of phenoxybenzamine just discussed. These drugs also have a parasympathomimetic effect on GI smooth muscle and gastric secretions.
Toxicity is like that of phenoxybenzamine.
Phentolamine is also used in the management of hypertension in cases of pheochromocytoma prior to surgery. It is also used intradermally to prevent dermal necrosis in cases of inadvertent extravasation of an alpha adrenergic agonist. It has also been used to treat the hypertensive crisis which sometimes results from rapid withdrawal from clonidine. H. Pharmacology of Prazosin and Related Drugs 1. Prazosin is the prototype of a family of potent and very selective alpha 1 receptor antagonists.