Use of phentolamine is of relatively little value:

Phentolamine is a competitive alpha-adrenergic blocking agent that has similar affinity for alpha1 and alpha2 receptors. It has a short duration of action. Its administration can prevent hypertension during surgical removal of pheochromocytoma (tumour of afrenal medulla that secretes excess of catecholamines). Abrupt withdrawal of clonidine results in rebound hypertension, which can be managed by phentolamine. In combination with papaverine this drug can be given directly into the cavernous in patients with erectile dysfunction. It is however not used to treat essential hypertension.