The most appropriate next step in management is to begin treatment with an α-adrenoceptor antagonist, such as phenoxybenzamine. The purpose of preoperative α-blockade is to provide blood pressure control and decrease the risk of cardiovascular complications related to excessive catecholamine release during intraoperative manipulation of the tumor. Most patients are treated for 1 to 2 weeks before surgery with phenoxybenzamine with upward titration based on blood pressure. The target blood pressure is below 130/80 mm Hg seated and greater than 90 mm Hg (systolic) standing. Because of phenoxybenzamine's side effects including orthostasis, nasal stuffiness, fatigue, and retrograde ejaculation, some clinicians use short-acting specific α-antagonists, such as prazosin, doxazosin, or terazosin. In patients with tachycardia, β-blockers can be added after α-blockade is achieved. Labetalol, a combined α- and β-blocking agent, also can be used, especially in patients with tachyarrhythmias. A heart rate of 60 to 70/min seated and 70 to 80/min standing can be targeted in most patients. Patients with pheochromocytoma who are normotensive also should be treated with α-blockers because they often become hypertensive during surgical resection.

Increasing the dosage of lisinopril does not address the need for preoperative pharmacologic management of the patient's pheochromocytoma with α-blockade.

Although indicated for tumor localization following the biochemical diagnosis of pheochromocytoma, a contrast-enhanced adrenal CT scan should be avoided if possible until after an α-adrenoceptor antagonist has been initiated. Administering iodine contrast media to a patient who has not received α-blockade could incite a hypertensive crisis.

Similarly, the β-adrenoceptor antagonist propranolol should not be given prior to α-blockade because unopposed α-adrenoceptor stimulation could also precipitate a hypertensive crisis.