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Spironolactone (Aldactone®)

By: Dr. Dawn Ruben

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  • Spironolactone is a diuretic drug that has a specific mechanism of action. Spironolactone inhibits the activity of the hormone aldosterone. This hormone is released in great quantity in heart failure and in some other medical disorders, such as Conn's syndrome.
  • Aldosterone is a hormone; its primary function is to retain sodium and excrete potassium in the kidneys.
  • Spironolactone inhibits this function of aldosterone, leading to increased sodium excretion in the urine. At the same time, potassium is retained in the body, giving this drug the label "potassium-sparing diuretic."
  • With increased sodium excretion, water is also excreted. This leads to increased urine production and the diuretic effect. Overall, the diuretic effect is mild.
  • Spironolactone also blocks the effects of aldosterone on the heart muscle. High concentrations of aldosterone are toxic to the heart.
  • Spironolactone is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.
  • This drug is not approved for use in animals by the Food and Drug Administration but it is prescribed legally by veterinarians as an extra-label drug.

    Brand Names and Other Names

  • This drug is registered for use in humans only.
  • Human formulations: Aldactone® (Searle) and various generic preparations
  • Veterinary formulations: None

    Uses of Spironolactone

  • Spironolactone is used to reduce fluid accumulation that may occur in disorders such as heart failure. It is also used in the treatment of abdominal fluid distention (ascites) associated with some liver diseases.

    Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, spironolactone can cause side effects in some animals.
  • Spironolactone should not be used in animals with known hypersensitivity or allergy to the drug.
  • Spironolactone should be avoided in animals with kidney impairment, liver disease or excessive blood potassium levels.
  • Adverse effects are few and typically mild. They generally subside once the drug is discontinued.
  • Spironolactone may interact with other medications. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with spironolactone. Such drugs include aspirin, enalapril, digoxin and other diuretics.
  • Some adverse effects associated with spironolactone include dehydration, low blood sodium, high blood potassium, lethargy, vomiting and diarrhea. These are more likely in animals also being treated with drugs called ACE inhibitors, such as enalapril or benazepril.

    How Spironolactone Is Supplied

  • Spironolactone is available in 25 mg, 50 mg and 100 mg tablets.

    Dosing Information

  • Medication should never be administered without first consulting your veterinarian.
  • Spironolactone is dosed at 0.5 to 2 mg per pound (1 to 4 mg/kg) one to two times daily.
  • The duration of administration depends on the condition being treated, response to the medication and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or prevent the development of resistance.

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