Midodrine

Summary

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