Medicine & USMLE


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


Midodrine is a drug primarily used to treat low blood pressure. As a sympathomimetic drug, it works by activating alpha-1 receptors. This results in vasoconstriction, which causes an increase in blood pressure. This also slows the heart rate as a compensatory response. Clinically, midodrine is used to treat autonomic dysfunction and orthostatic hypotension. Side effects of midodrine include supine hypertension.

Key Points

  • Midodrine
    • Drug Class
      • Sympathomimetic
        • mimics the action of endogenous hormones on adrenergic receptors
    • Site of Action
      • Activates Alpha-1 (Alpha-1 Agonist)
    • Physiologic Effects
      • Vasoconstriction
      • ↑ BP
        • This is usually caused by arterial vasoconstriction and increased vascular resistance
      • ↓ HR
        • Due to compensatory baroreceptor reflex in response to increased blood pressure
      • -/↓ CO
        • Venous constriction increases venous return to the heart, which can increase cardiac output
        • Decreased HR however works to decrease cardiac output, so the effect may be no change at all
        • Conflicting studies here show that midodrine may even increase basal cardiac output
    • Clinical Use
      • Treats Orthostatic Hypotension
        • Alpha 1-mediated venous vasoconstriction helps maintain venous return despite the effects of gravity from standing up
      • Treats Autonomic Insufficiency
    • Side Effects
      • May exacerbate supine hypertension
        • Since activation of alpha-1 receptors leads to vasoconstriction, which increases blood pressure