Pheochromocytoma Treatment
Pharmacotherapy
Alpha-Adrenergic Blockade
- First-line therapy used to minimize complications prior to surgery
Phenoxybenzamine
- Action: Powerful irreversible alpha-adrenergic blocker of the alpha receptors in the smooth muscles
- Effects: Oral administration results in an onset of action w/in a few hr & persists for up to 3-4 days
- Used to control the hypertension caused by excessive catecholamine release by pheochromocytoma
Selective Alpha1-Antagonists
- Eg Doxazosin
- Action: Selective blockade of alpha1-adrenoreceptors
- Effects: Limited use in pheochromocytoma, Phenoxybenzamine is more effective
- May be used to treat individual paroxysms
- May also may be used to treat hypertension while pheochromocytoma workup is ongoing
- Better tolerated than Phenoxybenzamine
- Prevent serious pressor crisis if pheochromocytoma is present
Beta-Blockers
- Eg Propranolol, Atenolol
- Administer only after alpha blockade has been induced
- W/o alpha blockade paradox increase in BP may occur
- Action: Competitive antagonists of catecholamines at beta-adrenergic receptors
- Effects: Used to treat tachycardia that may develop w/ alpha blockade
- Assist in preventing catecholamine-induced arrhythmias
- Low doses are usually sufficient
Calcium Channel Blockers
- Eg Nifedipine, Amlodipine
- Used as add-on treatment to alpha-adrenergic receptor blockers to further improve cardiovascular function peri-operatively
- Action: Blocks slow calcium channels to prevent calcium ion flow into the cell
- Effects: Vasodilatation, reduced afterload, peripheral resistance & blood pressure
Metirosine (Metyrosine)
- Action: Inhibits tyrosine hydroxylase which inhibits synthesis of catecholamines by the tumor
- Effects: Simplifies chronic management
- Should be used if other agents are ineffective or when tumor destruction will be marked