USMLE

Phenoxybenzamine

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Alpha and Beta Blockers
  1. Phenoxybenzamine
  2. Phentolamine
  3. Alpha-1 Antagonists (Prazosin, Terazosin, Tamsulosin)
  4. Beta-1 Selective Blockers (Atenolol, Esmolol, Metoprolol)
  5. Combined Alpha-Beta Blockers (Carvedilol, Labetalol)
  6. Non-selective Beta-Blockers (Propranolol, Timolol)
  7. Nebivolol

Summary

Phenoxybenzamine is a non-selective alpha antagonist that blocks both alpha-1 and alpha-2 receptors. It is commonly used for the treatment of pheochromocytoma. The most common adverse effect is orthostatic hypotension due to alpha-1 blockade.

Key Points

  • Phenoxybenzamine
    • Mechanism of Action
      • Irreversible blockade of Alpha 1 and 2 Receptors
        • Alpha 1 Blockade → Decreased vasoconstriction → Decreased TPR → Decreased BP
    • Clinical Use
      • Pheochromocytoma
        • prevents hypertensive crisis from excess catecholamine release
    • Adverse Effects
      • Orthostatic Hypotension
        • Alpha 1 blockade → Decreased venous vasoconstriction → Decreased venous return against the effects of gravity from standing up
      • Reflex Tachycardia