ABSTRACT
The intravenous phentolamine test. Phentolamine is an α1 and α2 adrenergic antagonist. It prevents excitation of noradrenaline-sensitive nociceptors. Phentolamine in normal saline (30 mg 100 ml-1) is infused over 20 min. If pain is relieved, it is believed that the pain is sympathetically maintained.
