Medicine & USMLE


Sympathomimetics and Sympatholytics (Old)
  1. Dopamine
  2. Fenoldopam
  3. Dobutamine
  4. Epinephrine
  5. Norepinephrine
  6. Isoproterenol
  7. Midodrine
  8. Phenylephrine and Pseudoephedrine
  9. (Alpha) Methyldopa
  10. Clonidine (and Guanfacine)
  11. Tizanidine


Isoproterenol is a non-selective activator or agonist of beta-1 and beta-2 receptors. It is very rarely used in the clinical context for treatment of heart block.

Key Points

  • Isoproterenol
    • Mechanism
      • 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
    • Indications
      • Heart Block and Bradycardia
        • Increases dromotropy (AV nodal conduction) and heart rate
      • Electrophysiologic evaluation of tachyarrhythmias
        • May provoke tachyarrhythmias in patients
      • May worsen ischemia
        • Increased cardiac output by beta-1 stimulation increases myocardial oxygen demand, which can induce ischemia
    • Adverse Effects
      • Reflex Tachycardia
        • Beta-2 stimulated vasodilation reduces vascular resistance and blood pressure, which causes a compensatory increase in heart rate