Pheochromocytoma Medication

Medical therapy is used for preoperative preparation prior to surgical resection, for acute hypertensive crises, and as primary therapy for patients with metastatic pheochromocytomas. Preoperative preparation requires combined alpha and beta blockade to control blood pressure and to prevent an intraoperative hypertensive crisis. Alpha-adrenergic blockade, in particular, is required to control blood pressure and prevent a hypertensive crisis. High circulating catecholamine levels stimulate alpha receptors on blood vessels and cause vasoconstriction.

Phenoxybenzamine (Dibenzyline) is the preferred alpha blocker in preparation for surgery. After effective alpha blockade, administer a beta blocker. Beta blockers are needed to control the tachycardia associated with high circulating catecholamine levels and alpha blockade.

Beta-adrenergic blockers are used if significant tachycardia occurs after alpha blockade. Only administer beta-adrenergic blockers after adequate alpha blockade, because unopposed alpha-adrenergic receptor stimulation can precipitate a hypertensive crisis. Noncardioselective beta blockers, such as propranolol (Inderal) or nadolol (Corgard), are often used; however, cardioselective agents, such as atenolol (Tenormin) and metoprolol (Lopressor), also may be used.

Labetalol (Trandate, Normodyne) is a noncardioselective beta-adrenergic blocker and selective alpha-adrenergic blocker that has been shown to be effective in controlling hypertension associated with pheochromocytoma. It has also been associated with paradoxic episodes of hypertension thought to be secondary to incomplete alpha blockade. Thus, its use in the preoperative treatment of patients with pheochromocytoma is controversial.

During surgery, intravenous phentolamine, a rapid-acting alpha-adrenergic antagonist, is used to control blood pressure. Rapid-acting intravenous beta blockers, such as esmolol, are also used to normalize blood pressure. Selective alpha1 blocking agents, such as prazosin (Minipress), terazosin (Hytrin), and doxazosin (Cardura), have more favorable adverse effect profiles and are used when long-term therapy is required (metastatic pheochromocytoma). These medications are not used to prepare patients for surgery because of their incomplete alpha blockade.

Class Summary

At low doses, alpha-adrenergic receptor blockers may be used as monotherapy in the treatment of hypertension. At higher doses, they may cause sodium and fluid to accumulate. As a result, concurrent diuretic therapy may be required to maintain the hypotensive effects of alpha-receptor blockers.

Phenoxybenzamine hydrochloride (Dibenzyline)

This is a long-acting adrenergic alpha-receptor blocker that can produce and maintain a chemical sympathectomy. Phenoxybenzamine hydrochloride lowers supine and upright blood pressure. It does not affect the parasympathetic nervous system.

Doxazosin mesylate (Cardura, Cardura XL)

Doxazosin mesylate is a quinazoline compound that is a selective alpha1-adrenergic antagonist. It inhibits postsynaptic alpha-adrenergic receptors, resulting in the vasodilation of veins and arterioles and a decrease in total peripheral resistance and blood pressure.

Phentolamine mesylate (OraVerse)

This is a nonselective alpha-adrenergic blocking agent. Its drug action is transient and alpha-adrenergic blockade incomplete. Phentolamine mesylate is often used immediately prior to or during adrenalectomy to prevent or control paroxysmal hypertension resulting from anesthesia, stress, or operative manipulation of the tumor. It is an alpha1- and alpha2-adrenergic blocking agent that blocks circulating epinephrine and norepinephrine action, reducing hypertension that results from catecholamine effects on alpha receptors.

Class Summary

Vasodilators reduce systemic vascular resistance, allowing more forward flow and improving cardiac output.

Nitroprusside (Nitropress)

Nitroprusside is a direct vasodilator that relaxes arterial vessels and venous smooth muscle. It has a short half-life and its effect disappears within 5 minutes of stopping infusion. The drug may be used to control paroxysmal hypertension intraoperatively. Nitroprusside produces vasodilation and increases inotropic activity of heart. At higher dosages, it may exacerbate myocardial ischemia by increasing the heart rate.

Class Summary

These agents compete with beta-adrenergic agonists for available beta-receptor sites.

Propranolol hydrochloride (Inderal LA, InnoPran XL)

This is a nonselective beta-adrenergic receptor blocker. After primary treatment with an alpha-receptor blocker, propranolol hydrochloride may be used as adjunctive therapy if control of tachycardia becomes necessary before or during surgery. It may be used to treat excessive beta-receptor stimulation in patients with inoperable metastatic pheochromocytoma. The drug has membrane-stabilizing activity and decreases the automaticity of contractions.

Propranolol hydrochloride is not suitable for the emergency treatment of hypertension; do not administer it intravenously in hypertensive emergencies.

Atenolol (Tenormin)

Atenolol selectively blocks beta1 receptors, with little or no affect on beta2 types.

Class Summary

These agents are used to inhibit catecholamine synthesis in pheochromocytoma.

Metyrosine (Demser)

Metyrosine inhibits tyrosine hydroxylase, the rate-limiting step in catecholamine synthesis. In patients with pheochromocytoma, administration of metyrosine reduces catecholamine biosynthesis by 35-80%, as measured by urinary catecholamine levels. It is indicated in patients with malignant pheochromocytoma or in cases of pheochromocytoma in which surgery is contraindicated. It can be useful in patients who are refractory to phenoxybenzamine therapy, or it can be administered as an adjunct to phenoxybenzamine therapy.