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Spironolactone for Veterinary Use
by Barbara Forney, VMD
Spironolactone is an aldosterone antagonist that is used as a potassium sparing diuretic. It is most commonly used in animals in congestive heart failure or for those with ascites. Spironolactone is an older drug but recent research still supports its use. This drug is approved for use in human medicine and is marketed under the brand name of Aldactone.
Spironolactone competitively inhibits aldosterone at the mineralocorticoid receptor of target cells in the distal renal tubules. It increases the excretion of sodium, chloride, and water, while sparing potassium, ammonium, and phosphate. It appears to have its greatest effect in animals with elevated aldosterone and to have less effect in animals with normal aldosterone levels. Spironolactone has been shown to have some additional cardioprotective effects in humans with elevated aldosterone. It may also act as a vasodilator through a mechanism similar to calcium channel blockers.
Spironolactone can be thought of as a prodrug as it is rapidly metabolized in the liver to canrenone and other active metabolites. It is primarily eliminated via the kidney. In humans, oral absorption is improved by administration with food. Spironolactone is not thought of as an emergency drug as peak diuresis may not occur until 2-3 days of therapy.
Dogs and Cats
Spironolactone is used to help manage refractory edema or fluid retention due to congestive heart failure, cirrhosis of the liver, ascites, hypertension, feline primary hyperaldosteronism, and nephrotic syndrome. It is used with furosemide, digoxin, and ACE 1 inhibitors in dogs with chronic congestive heart failure. The addition of spironolactone may allow a lower dose of furosemide. Research in both humans and in dogs would indicate improved survival when spironolactone is added to the conventional congestive heart failure treatment.
- The most common side effects are due to dehydration and/or electrolyte imbalances (hyperkalemia and hyponatremia). These are generally reversible by discontinuing the drug.
- Higher doses of spironolactone may cause anorexia, vomiting, and diarrhea
- Spironolactone should not be used in animals with hyperkalemia, significant kidney dysfunction, or Addison’s disease.
- Spironolactone crosses the placenta and has some anti-androgen properties in humans. It should only be used in pregnant or nursing animals when the benefits outweigh the risks due to the potential for feminization of fetuses. Spironolactone is found in maternal milk.
- The half life of digoxin may be increased. Additional monitoring may be warranted.
- Spironolactone should not be used with other potassium sparing diuretics or potassium supplements because of the possibility of hyperkalemia.
- Spironolactone may decrease the effects of mitotane.
- The diuretic effects of spironolactone may be decreased by salicylates.
- Spironolactone may increase the effects of neuromuscular blocking agents.
There is little information available on overdose in animals. If an oral overdose is recognized promptly, gut emptying protocol may be of benefit. Monitoring and support of hydration status and electrolyte status should be performed.
About the Author
Dr. Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania. She has a master's degree in animal science from the University of Delaware and graduated from the University of Pennsylvania School of Veterinary Medicine in 1982.
She began to develop her interest in client education and medical writing in 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
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