Spironolactone
Spironolactone is a mineralocorticoid-receptor antagonist with modest potassium-sparing diuretic activity. Its principal veterinary role is adjunctive aldosterone blockade in congestive heart failure, particularly in dogs with valvular disease. It also has specialist applications in primary hyperaldosteronism and selected sodium-retaining or fluid-accumulating disorders.
Group
Aldosterone antagonist and potassium-sparing diuretic
Mechanism of Action
Spironolactone and its active metabolites antagonize aldosterone at mineralocorticoid receptors. Reduced distal nephron sodium reabsorption decreases sodium-retaining signals while limiting potassium excretion. Receptor blockade in cardiovascular tissues can also reduce aldosterone-associated inflammatory and fibrotic signaling. These effects explain its neurohormonal role in heart failure despite a comparatively modest direct diuretic action.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Heart failure adjunct | 2–4 mg/kg | PO | Every 24 h | Canine starting amount is 2 mg/kg/day; reported upper limit 4 mg/kg/day. Feline efficacy is uncertain and dermatitis may limit use. |
| Heart failure adjunct | 1–2 mg/kg | PO | Every 12 h | Divided alternative to the daily amount. |
| Aldosterone blockade | 0.5 mg/kg | PO | Every 24 h | |
| Hypertension adjunct | 1–2 mg/kg | PO | Every 12 h |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Heart failure adjunct | 2–4 mg/kg | PO | Every 24 h | Canine starting amount is 2 mg/kg/day; reported upper limit 4 mg/kg/day. Feline efficacy is uncertain and dermatitis may limit use. |
| Heart failure adjunct | 1–2 mg/kg | PO | Every 12 h | Divided alternative to the daily amount. |
| Hypertension adjunct | 1–2 mg/kg | PO | Every 12 h | |
| Primary hyperaldosteronism adjunct | 1–2 mg/kg | PO | Every 12 h | When potassium replacement alone is insufficient. |
| Heart failure with hypokalemia | 1 mg/kg | PO | Every 12 h |
Indications
- Adjunctive treatment of congestive heart failure in dogs, particularly failure associated with myxomatous mitral valve disease.
- Specialist aldosterone blockade in selected cats or other veterinary patients with primary hyperaldosteronism.
- Adjunctive management of selected ascites or other aldosterone-associated fluid retention.
- Selected adjunctive treatment of hypertension or cardiac disease when excess aldosterone activity is a relevant therapeutic target.
Contraindications
- Dehydration
- Gastric ulceration or significant GI disease
- Avoid high-potassium supplements.
Interactions
- ACE inhibitors, trimethoprim and NSAIDs can increase hyperkalemia/renal risk; may mildly interfere with digoxin assays.
Adverse effects
- Hyperkalemia; feline facial dermatitis and occasional endocrine effects.
Toxicity
Monitor potassium, hydration and renal function after excess exposure; hyperkalemia is a clinically important potential consequence.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Spironolactone 25 mg | Tablet | 25 mg / tablet | PO |
| Spironolactone 50 mg | Tablet | 50 mg / tablet | PO |
| Spironolactone 100 mg | Tablet | 100 mg / tablet | PO |
| Spironolactone suspension 5 mg/mL | Oral Liquid | 5 mg / mL | PO |
Monitoring and Administration
Monitor potassium and renal function, particularly with ACE inhibitors; assess feline skin reactions. Reported daily maximum is 4 mg/kg in dogs.
Aldactazide combination ascites amount is 0.5-1 mg/kg twice daily based specifically on the spironolactone component. Without complete product composition and compatible strengths, it is not assigned to a single-agent preparation. Hypertension step-up and ascites multidrug plans must retain coagent and renal-monitoring context.