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Phenoxybenzamine
63%
81/128
Propranolol
13%
17/128
Phentolamine
5%
6/128
Tamsulosin
7/128
Atenolol
3%
4/128
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The most likely diagnosis in this patient is a pheochromocytoma in the setting of underlying multiple endocrine neoplasia (MEN) 2A. Phenoxybenzamine is used to prevent blood pressure spikes in patients with pheochromocytomas. The optimal management of pheochromocytoma-mediated hypertension includes alpha adrenergic blockade before any beta blockade. Phenoxybenzamine is an irreversible nonselective alpha adrenergic antagonist that is used as a first-line agent to prevent blood pressure spikes in patients with pheochromocytomas. This medication is started before any beta blocker is given in order to prevent unopposed alpha adrenergic activity from pheochromocytoma-secreted catecholamines, which would result in malignant hypertension. An alternative to phenoxybenzamine would be a mixed alpha/beta nonselective antagonist such as labetalol. Incorrect Answers: Answer 2: Propranolol is a non-selective beta-1 and beta-2 antagonist. Starting a pure beta-blocker without first starting an alpha-blocker in a patient with pheochromocytoma-mediated hypertension would lead to unopposed alpha blockade and malignant hypertension. Answers 3: Phentolamine is a reversible nonselective alpha adrenergic antagonist. Although its mechanism of action is similar to phenoxybenzamine's, the fact that it is reversible makes it less able to adequately control blood pressure in the setting of catecholamine hypersecretion. Clinically, phenoxybenzamine is started preoperatively in patients with pheochromocytomas to prevent malignant hypertension. Phentolamine is given intraoperatively since it is easier to titrate levels after the pheochromocytoma is removed. Answer 4: Tamsulosin is an alpha-1 selective antagonist. It selectively targets the bladder neck and is therefore optimal for benign prostatic hyperplasia. It is not indicated in the setting of pheochromocytoma due to this selectivity. Answer 5: Atenolol is a beta-1 selective antagonist. Starting a pure beta-blocker without first starting an alpha-blocker in a patient with pheochromocytoma-mediated hypertension would lead to unopposed alpha vasoconstriction activity and malignant hypertension. Bullet Summary: Phenoxybenzamine is an irreversible non-selective alpha adrenergic antagonist that is used to prevent blood pressure spikes in pheochromocytomas; it must be given before any pure beta blocker to prevent unopposed alpha adrenergic activity.
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