Drug Classification & Information

Spironolactone is a weak diuretic classified as a potassium sparing diuretic causing water loss through the kidneys.  It is never used as monotherapy for treatment of congestive heart failure (CHF) but often used in conjunction with other diuretics.  Spironolactone decreases effects of a hormone called aldosterone which has negative effects on the heart muscle (such as fibrosis).  Giving this medication with food may increase bioavailability.

Indications for Use

Spironolactone is indicated for the adjunctive therapy of CHF in animals (never alone).  May be helpful to delay onset to CHF in animals with occult (pre-CHF) dilated cardiomyopathy.  May be used in patients with abdominal fluid retention (ascites) not caused by cardiac disease.  As it can increase potassium levels, may be used to improve potassium blood levels in animals receiving other diuretics and who are unable to take oral potassium supplements.

Potential Drug Interactions

Should be used with caution in patients with high potassium levels or those with Addison’s disease.  Caution in patients with renal disease.  Spironolactone may increase blood levels of digoxin.  Caution when giving with oral potassium supplementation as may cause high potassium levels.

Drug Side Effects

Side effects are often mild and may include gastro-intestinal effects such as reduced appetite, vomiting.  Mild risk for dehydration – fresh water should always be readily available.    

Therapeutic Monitoring

Renal values (BUN, creatinine) and electrolytes should be monitored regularly when receiving this medication (1-2 weeks after any dose adjustment, then every 4-6 months). 

Dosage Forms

Human: 25, 50, 100 mg tablets; Spironolactone/hydrochlorothiazide (Aldactazide): 25/25 mg, 50/50 mg tablets