Medicine & USMLE

Norepinephrine

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

Summary

Norepinephrine, often abbreviated NE, is a sympathomimetic drug. It activates alpha-1 receptors at lower doses, alpha-2 receptors at medium doses, and beta-1 receptors at higher doses.

Physiologic effects of giving norepinephrine include vasoconstriction, leading to an increase in blood pressure. This may or may not lead to a decrease in heart rate. There may or may not be an increase in the cardiac output, depending on the patient.

Clinically, norepinephrine is used to treat hypotension and septic shock.

Side effects of norepinephrine include extravasation around the administration site, which can cause skin necrosis.

Key Points

  • Norepinephrine
    • Drug Class
      • Sympathomimetic
        • Mimics the action of endogenous norepinephrine on adrenergic receptors
    • Site of Action
      • Activates Alpha-1 Receptors (Alpha-1 Agonist) at low doses
        • Act on blood vessels to induce vasoconstriction
      • Activates Alpha-2 Receptors (Alpha-2 Agonist) at medium doses
        • Alpha-2 receptors are centrally located and cause weak inhibition of the sympathetic system; this effect is made clinically insignificant by strong alpha-1 agonism
      • Activates Beta-1 Receptors (Beta-1 Agonist) at high doses
        • Acts on heart to induce modest increase in myocardial contractility and heart rate
    • Physiologic Effects
      • Vasoconstriction
        • Increases vascular resistance
      • Increases Blood Pressure
        • Due to vasoconstriction
      • -/↓ HR
        • Reflex bradycardia caused by vasoconstriction and blood pressure increase may outweigh Beta-1 mediated increase in heart rate
      • -/↑ CO
        • Beta-1 mediated increase in heart rate and contractility may be blunted by reflex bradycardia or an increase in afterload
    • Clinical Use
      • Treats Hypotension
        • due to ability to increase blood pressure
      • Treats Septic Shock
        • due to vasoconstriction and increase in blood pressure
    • Side Effects
      • Local tissue necrosis at injection site (extravasation)
        • Due to local alpha-1 mediated vasoconstriction in blood vessels
        • Prevented by local injection of an alpha-1 blocking drug, such as phentolamine