Medicine & USMLE


Alpha & Beta Blockers (New)
  1. Phentolamine
  2. Phenoxybenzamine
  3. -osin Drugs
  4. Beta-1 Selective Beta Blockers
  5. Dual Alpha Beta Blockers
  6. Mirtazapine


Phenoxybenzamine is a non-selective alpha blocker that blocks both alpha-1 and alpha-2 receptors. The effects of phenoxybenzamine are irreversible. Clinically, this drug is used to treat pheochromocytoma. Phenoxybenzamine’s side effects include orthostatic hypotension and reflex tachycardia.

Key Points

  • Phenoxybenzamine
    • Mechanism
      • Blocks Alpha 1 and 2 Receptors (Nonselective)
        • Irreversible
          • compare vs. phentolamine which is reversible
    • Clinical Use
      • Pheochromocytoma
        • blockade of alpha-1 receptors stops vasoconstriction and prevents an increase in blood pressure caused by excess catecholamine release
    • Side Effects
      • Orthostatic Hypotension
        • Alpha 1 blockade → Decreased venous vasoconstriction → Decreased venous return against the effects of gravity from standing up
      • Reflex Tachycardia