Spironolactone is commonly prescribed for dogs to treat congestive heart failure as an adjunct diuretic and aldosterone blocker, particularly in mitral valve disease. Dosage is always weight-based — use the chart below as a reference and confirm the exact dose with your vet before administering.
Weight-Based Dosage Chart
| Weight | Typical Dose | Frequency / Notes |
|---|---|---|
| Under 10 lbs | 9–18 mg | once daily (2–4 mg/kg); adjunct to ACE inhibitor + furosemide; monitor potassium |
| 10–25 lbs | 20–45 mg | once daily; avoid in significant renal impairment |
| 26–50 lbs | 52–100 mg | once daily; available as fixed combination with benazepril (Cardalis) |
| Over 50 lbs | 91–180 mg | once daily; vet adjusts dose; do not use as sole diuretic in acute edema |
Doses above are general reference ranges for adult dogs. Puppies, kittens, seniors, and pets with kidney or liver conditions may require different dosing. All dosages are extra-label unless otherwise noted.
What Is Spironolactone?
Spironolactone is used in dogs to treat congestive heart failure as an adjunct diuretic and aldosterone blocker, particularly in mitral valve disease. It is typically available in tablet, capsule, or liquid form and is usually given orally. In most cases, a prescription from a licensed veterinarian is required.
Common Side Effects in Dogs
Watch for these signs and contact your vet if any appear or worsen:
Contact your vet immediately if your dog shows signs of a severe allergic reaction (facial swelling, difficulty breathing, collapse) or if side effects are severe or persistent.
How to Give Spironolactone to Your Dog
- Give with food to reduce stomach upset unless your vet instructs otherwise.
- Complete the full prescribed course even if your pet seems better.
- Store at room temperature away from moisture and heat.
- Never split or crush tablets unless your vet confirms it is safe for that formulation.
- If your pet vomits within 30 minutes of a dose, contact your vet before redosing.
⚠️ Important Safety Reminders
What If My Dog Misses a Dose?
If you miss a dose, give it as soon as you remember — unless it is almost time for the next dose. In that case, skip the missed dose and continue on schedule. Never double-dose. If you are unsure, call your vet or pharmacist.
Frequently Asked Questions
Dosage is always weight-based and varies by the condition being treated. Use the chart above as a reference guide, but always confirm the exact dose with your veterinarian before administering.
Most veterinary medications require a prescription. Even over-the-counter options can cause harm at the wrong dose or in combination with other medications. Always consult your vet first.
The most commonly reported side effects include hyperkalemia — elevated potassium (monitor with ace inhibitors), vomiting or diarrhea, lethargy. Contact your vet if side effects are severe, persistent, or you notice unexpected changes in your pet's behaviour.
Onset of action varies by medication and indication. Some drugs work within hours; others (such as behavioural medications) may take weeks. Follow your vet's guidance on expected timeline.
Call your vet or ASPCA Animal Poison Control (888-426-4435) immediately. Do not wait for symptoms to appear. Have the medication packaging and your pet's weight ready when you call.