What is midodrine and how is it used in cirrhosis-induced hyponatremia?

• A. A vasoconstrictor used to maintain mean arterial pressure in hyponatremic patients with low BP due to third-spacing of ascites
• B. A diuretic that reduces fluid overload
• C. A beta-blocker to reduce portal hypertension
• D. An ACE inhibitor to improve renal perfusion

Answer: (A)

In cirrhosis-related hyponatremia, the body’s effective arterial blood volume is reduced because fluid shifts into the abdomen (ascites) and elsewhere, triggering non-osmotic release of ADH and activation of the RAAS. Midodrine, an alpha-1 adrenergic agonist, causes vasoconstriction that raises systemic vascular resistance and mean arterial pressure. This improves renal perfusion and reduces the maladaptive neurohumoral drive that promotes water retention, helping the kidneys excrete free water and modestly correct the low sodium. It’s used specifically to maintain mean arterial pressure in hyponatremic patients who have low BP from third-spacing of ascites. It isn’t a diuretic, a beta-blocker for portal hypertension, or an ACE inhibitor; those agents don’t target the underlying low arterial volume and can worsen perfusion or hyponatremia in this setting.