Medicine & USMLE


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


Dopamine is a sympathomimetic drug that stimulates the fight-or-flight response. 

At low doses, dopamine activates D1 receptors, which dilates the renal arteries to increase renal perfusion. Dopamine may also activate D2 receptors in the brain, but the effects are less prominent due to low penetration of the blood-brain-barrier.

At medium doses, dopamine activates beta receptors, which can increase heart rate and contractility, leading to an overall increase in cardiac output.

At high doses, dopamine activates alpha receptors, causing vasoconstriction and an increase in blood pressure.

Clinically, dopamine is used to treat heart failure, shock, and unstable bradycardia. It is particularly useful for increasing renal blood flow in these patients.

Key Points

  • Dopamine
    • Drug Class
      • Sympathomimetic
        • Mimics the action of endogenous hormones on adrenergic receptors
    • Site of Action & Physiologic Effects
      • At low doses
        • Equally activates D1 & D2 receptors (D1 and D2 agonist)
          • Note: IV dopamine does not cross the blood-brain barrier. Since D2 receptors are mostly located in the brain, the D2 effects of administered dopamine are usually negligible
          • Renal artery vasodilation
            • D1 agonism causes dilation of most splanchnic vessel beds, including that of the renal arteries
      • At medium doses
        • Activates Beta (Beta agonist)
          • ↑ HR
          • Positive Inotropy (increased contractility)
          • ↑ CO
      • At high doses
        • Activates Alpha receptors (alpha agonist)
          • Vasoconstriction
          • ↑ BP (high doses)
    • Clinical Use
      • Treats (unstable) bradycardia
        • Due to positive inotropy mediated by beta-1 agonism
      • Treats shock
        • Due to vasoconstriction and increased BP mediated by alpha-1 agonism
      • Treats heart failure
        • Dopamine can increase cardiac output and may additionally improve renal function in cardiorenal syndrome