Spironolactone

Aldosterone Antagonist / Potassium-Sparing DiureticPODogsCats

Also known as: Aldactone · Aldactazide · Cardalis · Prilactone · espironolactona · SC-9420 · spirolactone · spironolactonum

Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference

1-2 mg/kg PO q12hPO· q12h

Body weight— 🐕

Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.

Dosing by species

🌎 NA — North America🌍 EU — Europe

Dogs

Indication	Dose	Route	Frequency	Duration	Region
As a diuretic in CHF (when furosemide and ACE inhibitors alone do not control fluid accumulation)	1-2 mg/kg PO q12h	PO	q12h	—	🌎 NA
As a diuretic in CHF (with other diuretics when hypokalemia is an issue)	2-4 mg/kg PO once daily	PO	q24h	—	🌎 NA
As a diuretic in CHF (to allow further reduction of furosemide dose)	0.5 mg/kg PO once daily to 2 mg/kg twice daily	PO	q24h to q12h	—	🌎 NA
For treating ascites (using fixed dose combination with hydrochlorothiazide)	0.5-1 mg/kg PO twice daily	PO	q12h	—	🌎 NA
For treating ascites (caused by right-sided heart failure)	1-2 mg/kg PO q12h	PO	q12h	—	🌎 NA
For adjunctive treatment of hypertension	1-2 mg/kg PO q12h	PO	q12h	—	🌎 NA
For adjunctive treatment of hypertension (Step 4 drug)	1-2 mg/kg twice daily	PO	q12h	—	🌎 NA
Congestive heart failure, ascites, hyperaldosteronism	2-4 mg/kg	PO	q24h	Continuous	🌍 EU

As a diuretic in CHF (when furosemide and ACE inhibitors alone do not control fluid accumulation): Refractory CHF
As a diuretic in CHF (to allow further reduction of furosemide dose): 0.5 mg/kg once daily for aldosterone blockage (weak diuretic effect); 2 mg/kg twice daily for stronger diuretic effect.
For treating ascites (using fixed dose combination with hydrochlorothiazide): Empirical dosage based on the spironolactone component of Aldactazide.
For treating ascites (caused by right-sided heart failure): Added to optimized furosemide and ACE inhibitor therapy.
For adjunctive treatment of hypertension (Step 4 drug): For systolic >160 mmHg, diastolic >120 mmHg after enalapril/benazepril and amlodipine.
Congestive heart failure, ascites, hyperaldosteronism: Licensed for use in combination with standard therapy for treatment of CHF caused by valvular regurgitation in dogs.

Cats

Indication	Dose	Route	Frequency	Duration	Region
As a diuretic in CHF (when furosemide and ACE inhibitors alone do not control fluid accumulation)	1-2 mg/kg PO q12h	PO	q12h	—	🌎 NA
As a diuretic in CHF (when serum potassium is low)	1 mg/kg q12h PO	PO	q12h	—	🌎 NA
For adjunctive treatment of hypertension	1-2 mg/kg PO q12h	PO	q12h	—	🌎 NA
For adjunctive treatment of hypertension (Step 3 drug)	1-2 mg/kg twice daily	PO	q12h	—	🌎 NA
For adjunctive treatment of primary hyperaldosteronism	1-2 mg/kg PO twice daily	PO	q12h	—	🌎 NA
Congestive heart failure, ascites, hyperaldosteronism	2-4 mg/kg	PO	q24h	Continuous	🌍 EU

As a diuretic in CHF (when furosemide and ACE inhibitors alone do not control fluid accumulation): Refractory CHF
For adjunctive treatment of hypertension (Step 3 drug): When systolic BP >160 mmHg, diastolic >120 mmHg after amlodipine and ACE inhibitor.
For adjunctive treatment of primary hyperaldosteronism: If potassium supplementation alone does not control clinical signs.
Congestive heart failure, ascites, hyperaldosteronism: Severe ulcerative facial dermatitis has been reported in Maine Coon cats.

Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.

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Overview

Spironolactone is a synthetic aldosterone antagonist and potassium-sparing diuretic. In veterinary medicine, it is primarily used as an adjunctive treatment for congestive heart failure (CHF), ascites, systemic hypertension, and primary hyperaldosteronism (especially in cats).

Clinical Pearls & Pharmacological Context:

Aldosterone Escape: While its direct diuretic effect is relatively weak compared to loop diuretics like furosemide, spironolactone plays a crucial role in blocking the Renin-Angiotensin-Aldosterone System (RAAS). Even when patients are on ACE inhibitors, aldosterone levels can eventually rebound (a phenomenon known as "aldosterone escape"). Spironolactone mitigates this.
Cardioprotection: In human medicine, spironolactone is highly valued for its antifibrotic effects on the myocardium, helping to prevent detrimental cardiac remodeling. While the extent of this benefit in veterinary patients (like dogs with myxomatous mitral valve disease) has been debated, it is increasingly incorporated into standard multi-drug CHF protocols.
Bioavailability: Absorption is significantly enhanced when administered with food.

Mechanism of action

Spironolactone acts as a competitive antagonist at the mineralocorticoid receptor.

Mechanism: It competitively inhibits aldosterone binding in the distal renal tubules and collecting ducts.
Pathway: Blockade of the receptor → prevents the synthesis of aldosterone-induced proteins (such as Na+/K+ ATPase and epithelial sodium channels) → decreases sodium and chloride reabsorption while decreasing potassium, ammonium, and phosphate excretion.
Result: Mild diuresis with potassium retention. It does not affect carbonic anhydrase or proximal renal transport mechanisms.

Safety & warnings

Contraindications

Hyperkalemia
Addison's disease (hypoadrenocorticism)
Anuria
Acute renal failure
Significant renal impairment
Hyperkalaemia
Hyponatraemia
Concurrent use with NSAIDs in animals with renal insufficiency
Pregnancy
Lactation
Animals intended for breeding

Adverse effects

Facial dermatitis (notably reported in Maine Coon cats)
Hyperkalemia
Hyponatremia
Dehydration
Increased BUN and mild acidosis (in patients with renal impairment)
Gastrointestinal distress (vomiting, anorexia)
CNS effects (lethargy, ataxia)
Endocrine changes (anti-androgenic effects, e.g., gynecomastia in humans, feminization of male fetuses)
Hyponatraemia
Hyperkalaemia
Reversible prostatic atrophy (in entire male dogs)
Severe ulcerative facial dermatitis (in Maine Coon cats)
Hepatotoxicity (reported in humans)

Precautions

Hepatic & Renal Caution: Use cautiously in patients with hepatic disease (though often used to treat ascites). Use in patients with renal impairment may lead to hyperkalemia.

Reproductive Safety: FDA Category D for pregnancy. Spironolactone and its active metabolites cross the placenta and can cause feminization of male fetuses. Canrenone (active metabolite) is excreted in breast milk; use with caution in nursing animals.

Drug interactions

DigoxinModerate

Spironolactone may increase the half-life of digoxin; enhanced monitoring of digoxin serum levels is warranted. May also cause falsely elevated digoxin values if using a radioimmune assay (RIA).

Mitotane

Spironolactone may mute the effects of mitotane if given concurrently; monitor carefully.

Neuromuscular blockers, non-depolarizing

Possible increase in neuromuscular blockade effects.

Potassium-sparing diuretics (e.g., triamterene)

Increased risk of hyperkalemia.

Potassium supplementsMajor

Increased risk of hyperkalemia.

Salicylates (e.g., Aspirin)

Spironolactone's diuretic effects may be decreased if administered concomitantly.

Thiazide diureticsModerate

Potentiates diuretic effects

Loop diureticsModerate

Potentiates diuretic effects

ACE inhibitorsModerate

Increased risk of hyperkalaemia (though generally safe to use concurrently in practice; monitor potassium)

NSAIDsMajor

Increased risk of hyperkalaemia and nephrotoxicity

CiclosporinModerate

Increased risk of hyperkalaemia

Monitoring

Serum electrolytes (especially potassium and sodium)
BUN and creatinine
Hydration status
Blood pressure (if indicated)
Clinical signs of edema/ascites
Patient weight
Serum potassium
Serum sodium
Renal function (BUN, Creatinine)
Digoxin levels (if used concurrently)

Pharmacokinetics

Half-life

DogsSpironolactone: 1-2 hours; Canrenone (active metabolite): ~20 hours

Absorption

In fasted dogs, oral bioavailability is approximately 50%, but increases up to 90% when given with food. In humans, it is >90% bioavailable with peak levels reached within 1-2 hours.

Distribution

Spironolactone and its active metabolite, canrenone, are both about 98% bound to plasma proteins. Both cross the placenta, and canrenone is detected in breast milk.

Metabolism

Rapidly metabolized to several metabolites, including the active metabolite canrenone, which possesses diuretic activity.

Elimination

About 70% of a dose is found in the feces and 18% in the urine.

Overdose

Information on acute overdosage of spironolactone in veterinary patients is limited.

Management: Should an acute overdose occur, follow general guidelines for diuretic overdose (e.g., furosemide or chlorothiazide).
Treatment: Empty the stomach if ingestion was recent. Provide supportive care, monitor hydration status, and closely evaluate serum electrolytes (especially potassium and sodium).
Contact an animal poison control center for further guidance.

Available products

Formulations

Oral tablets
Oral suspension (compounded)
10 mg tablet
40 mg tablet
50 mg tablet
80 mg tablet
100 mg tablet
Compound preparations with benazepril (e.g., 2.5mg/20mg, 5mg/40mg, 10mg/80mg)

Veterinary

Cardalis (compound with benazepril)
Prilactone

Human-labeled

Spironolactone Oral Tablets: 25 mg, 50 mg & 100 mg; Aldactone® (Searle); generic
Spironolactone/Hydrochlorothiazide Oral Tablets: 25 mg/25 mg & 50 mg/50 mg; Aldactazide® (Searle); generic
Spironolactone generics

Regulatory status

European Union✓ ApprovedPrescription onlyEMA

🐕 Dogs

POM-V / POM

United Kingdom✓ ApprovedPrescription onlyVMD