Medicine & USMLE


Cardio Drugs - Diuretics
  1. Loop Diuretics
  2. Thiazide Diuretics
  3. Spironolactone
  4. Mannitol


Spironolactone is a diuretic that is used to remove excess fluid. By reducing blood volume, it can be effective in treating edema and hypertension. Importantly, spironolactone is a potassium-sparing diuretic, meaning that it increases potassium levels in the body and may even cause hyperkalemia at high doses, so you’ll want to keep a close eye on electrolyte levels. Since spironolactone causes fluid loss by way of urination, you’ll want to monitor the patient’s urine output, kidney function, and daily weights.

Key Points

  • Mechanism
    • Removes excess fluid (diuresis)
      • Aldosterone receptor antagonist
        • Blocks aldosterone and inhibits the sodium-potassium pump
      • Promotes sodium and water excretion and potassium retention at the distal tubule and collecting duct
        • Potassium-sparing diuretic
      • Relatively weak compared to other diuretics
    • Clinical Use
      • Hypertension
        • Decreased fluid volume = lower BP
        • Potassium-sparing diuretics are very weak diuretics, and are usually combined with other diuretics for the purposes of reducing potassium loss
      • Edema
        • Heart Failure
          • Spironolactone is the diuretic of choice for heart failure, as it has been proven to greatly reduce mortality
        • Ascites
          • Secondary to cirrhosis
      • Will lead to increased urination
        • Contraindicated in patients with renal failure
        • Watch for signs and symptoms of dehydration
        • Closely monitor intake and output as well as BUN and creatinine
        • Take in the morning to prevent nocturia
        • Record daily weights - sudden weight gain is usually due to fluid retention
      • Hypokalemia
        • Spironolactone is a very weak diuretic and is usually combined with other diuretics (e.g. thiazide, loop) to reduce potassium loss
      • High aldosterone levels
    • Side Effects and Adverse Reactions
      • Hyperkalemia
        • ACE inhibitors and ARBs also retain potassium and this combination can result in life-threatening hyperkalemia
        • Monitoring potassium levels is essential
        • Potassium supplements should be discontinued and potassium-rich foods should be avoided
      • GI distress
        • Take with food to decrease GI side effects
      • Endocrine effects
        • Gynecomastia, menstrual irregularities, erectile dysfunction, hirsutis
        • Not a perfect aldosterone-receptor blocker; off-target blockade of testosterone and androgen receptors inhibits the action of testosterone
      • Photosensitivity