pheochromocytoma
PHEOCHROMOCYTOMA
Pheochromocytoma is a rare adrenal gland tumor that may precipitate life-threatening hypertension.
It can occur at any age but usually occurs during young to mid-adult life.
Majority of patients presents with ≥1 of the following hypertension resistant to standard antihypertensive treatment, hypertensive crisis with malignant hypertension, hypertensive encephalopathy, aortic dissection, or myocardial infarction and paroxysmal symptoms which suggest seizure disorder, anxiety attacks or hyperventilation.

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
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