Medicine & USMLE


Sympathomimetics and Sympatholytics (New)
  1. Isoproterenol
  2. Dobutamine
  3. Norepinephrine
  4. Alpha-Methyldopa
  5. Midodrine
  6. Clonidine & Guanfacine
  7. Phenylephrine


Isoproterenol is a sympathomimetic that works by equally activating beta-1 and beta-2 receptors. Physiologically, isoproterenol causes vasodilation, which leads to a decrease in blood pressure. It also increases the heart rate, which leads to an increase in cardiac output. Clinically, isoproterenol is used in the EP evaluation of tachyarrhythmias. Side effects of isoproterenol include an increase in cardiac oxygen demand, which can result in ischemia and angina in patients with underlying heart disease.

Key Points

  • Isoproterenol
    • Drug Class
      • Sympathomimetic
        • mimics the action of endogenous hormones on adrenergic receptors
    • Site of Action
      • Beta-1 Receptor Agonist
        • Acts on heart to increase cardiac output by increasing heart rate and contractility
      • Beta-2 Receptor Agonist
        • Acts on blood vessels to cause vasodilation, decreasing systemic vascular resistance and blood pressure
    • Physiologic Effects
      • Vasodilation
      • ↓ BP
        • due to vasodilation
      • ↑ HR
        • Through beta-1 action and reflex tachycardia (response to lowering of blood pressure)
      • ↑ CO
        • Due to an increase in HR
    • Clinical Use
      • EP evaluation of tachyarrhythmias
        • May provoke arrhythmias in patients
      • Heart Block and Bradycardia
        • Rarely used nowadays due to potential to cause ischemia and lower blood pressure
    • Side Effects
      • Increased myocardial oxygen demand (may worsen ischemia)
        • Increased cardiac output by beta-1 stimulation increases myocardial oxygen demand, which can induce ischemia