Spironolactone for dogs: Uses, dosage, and safety

In this article:

• Uses
• Safety
• Dosage
• Alternatives
• Summary

In this article

• Uses
• Safety
• Dosage
• Alternatives
• Summary

Spironolactone (brand name: Aldactone) is a potassium-sparing diuretic that increases water and sodium excretion through urine. Veterinarians never use spironolactone on its own but always combine it with other medications. Pet parents can expect to give their dog one dose daily, either as a tablet or a specially prepared liquid. In some cases, spironolactone is a long-term or even lifelong treatment. 

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What is spironolactone used for in dogs?

In dogs, spironolactone is useful in treating congestive heart failure and other cardiovascular conditions when other drugs are not working well or causing potassium levels to fall too low. Veterinarians also use it for other purposes, including treating fluid buildup in the belly (ascites), treating high blood pressure, and reducing fluid buildup when the kidneys are having filtering problems. For all these conditions, veterinarians only use it with other medications.

Congestive heart failure (CHF)

Heart failure is a condition in which the heart cannot pump enough blood to the rest of the body. In dogs, as in humans, there are many causes of heart failure, including genetics, valve disease, fluid buildup around the heart, “back-leak” of the blood, high blood pressure, pulmonary hypertension, and heart structure abnormalities. Valve disease is the primary cause of heart failure in dogs, accounting for about 80% of cases.

Veterinarians choose medications based on the cause. Standard treatment of congestive heart failure includes diuretics such as furosemide to reduce fluid and drugs that dilate blood vessels, such as ACE inhibitors. Also commonly used is a drug that increases the strength of heart muscle contractions called pimobendan, and drugs that change the way the heart beats, such as digoxin, beta blockers, and calcium channel blockers.

Veterinarians use spironolactone if diuretic treatment is not effective or if the diuretics being used deplete too much potassium from the system. 

Ascites (abdominal fluid buildup)

Veterinarians call fluid buildup in the abdomen “ascites.” Ascites is a serious and potentially life-threatening condition caused by blocked liver veins. Blood vessel problems have several possible causes, including blood clots, strictures, swelling, compression, scarring, tumors, or other conditions that restrict blood flow through these vessels. These blood vessel problems are often a consequence of other conditions like heart failure, liver failure, or heart disease. 

For ascites, veterinarians treat the cause. They only use diuretics to reduce fluid buildup in the abdomen. Spironolactone is added to the treatment to reduce fluid buildup and maintain normal potassium levels. 

High blood pressure

A dog with systemic hypertension has blood pressures in the arteries that are high enough to damage blood vessels and organs over time. High blood pressure is common among people. The CDC reports that 49% of adults in the U.S. have high blood pressure. Most cases involve primary hypertension, that is, high blood pressure that isn’t caused by any other medical condition. 

It’s not the same for dogs. High blood pressure is relatively uncommon in dogs. Dogs that do have high blood pressure are usually diagnosed with secondary hypertension, meaning high blood pressure that has an identifiable cause, such as kidney disease, adrenal gland problems, or other medical conditions. 

When a dog has high blood pressure, veterinarians usually treat the cause. To bring blood pressure back to normal, veterinarians use many of the same drugs doctors use in people, including ACE inhibitors such as benazepril, angiotensin-II receptor blockers (ARBs), beta blockers, calcium channel blockers, and diuretics. Spironolactone is not the first drug a veterinarian will use. Instead, it’s added if other drugs aren’t working or there’s a problem with low potassium levels. 

RELATED: How to manage high blood pressure in dogs

Glomerular disease

Glomerular disease is a type of kidney disease. The glomeruli are groups of small tubules in the kidneys. When blood passes through these small tubules, substances the body doesn’t need, such as water and waste, are filtered into the urine. Substances the body does need, like blood cells and proteins, are filtered so they don’t pass out of the body. Glomerular disease occurs when the glomeruli are damaged and cannot perform their functions, leading to fluid buildup in the body. 

Glomerular disease in dogs results from medical conditions such as diabetes, infections, drugs, autoimmune disorders, and other diseases. The veterinarian will primarily address these other causes. To reduce swelling and fluid buildup, veterinarians use diuretics to increase water loss. If potassium levels drop, spironolactone is added to diuretic therapy. 

Is spironolactone safe for dogs?

Veterinarians consider spironolactone safe in dogs as either a backup or adjunct treatment. Because spironolactone prevents the kidneys from eliminating potassium, it is not safe to give to dogs with high potassium levels. Some medical conditions, such as diabetes, Addison’s disease, and severe kidney disease, can cause high potassium levels, so spironolactone is avoided in dogs with these conditions. Veterinarians use spironolactone cautiously in dogs with liver disease or dysfunction.

Side effects of spironolactone in dogs

The most common side effects of spironolactone in dogs are:

• Thirst and increased drinking
• Increased urination
• Mild electrolyte abnormalities (low sodium or high potassium)
• Mild dehydration

Other possible spironolactone side effects in dogs include:

• Vomiting
• Diarrhea
• Loss of appetite
• Low energy
• Coordination problems

The most serious side effects of spironolactone in dogs are:

• Dehydration
• Severely high potassium

Call a veterinarian if mild side effects worsen or you notice symptoms of dehydration or high potassium (hyperkalemia), such as:

• Infrequent or no urination
• Straining to urinate
• Extreme thirst
• Dry gums
• Persistent vomiting
• Persistent diarrhea
• Weakness
• Loss of coordination
• Collapse

Interactions of spironolactone with other pet meds

Before the veterinarian prescribes any drug, always tell the veterinarian about any medications, remedies, or supplements you’re giving the dog. 

Drug interactions can be an issue when dogs are taking spironolactone. One reason is that spironolactone is always used with other drugs, never by itself. Some of the other drugs used can interact with spironolactone. 

Spironolactone may cause problems in dogs taking:

• Other diuretics. Spironolactone is frequently used with other diuretics, but it increases the risk of dehydration. Make sure the dog has easy access to plenty of water.
• Other potassium-sparing diuretics. Giving a dog two potassium-sparing diuretics increases the risk of both dehydration and high potassium.
• Potassium supplements. Combining potassium supplements with spironolactone increases the risk of high potassium.
• Digoxin. Digoxin may be used to treat heart failure in dogs, but spironolactone may increase the concentration of digoxin in the dog’s system, raising the risk of side effects.
• Mitotane. Most dog caregivers won’t encounter mitotane. Veterinarians use it to treat adrenal gland problems such as Cushing’s disease. Spironolactone may reduce the concentration of mitotane in the blood, decreasing its effectiveness.
• Aspirin and other salicylates. Aspirin and similar drugs, called salicylates, could reduce the effectiveness of spironolactone.

Spironolactone dosage for dogs

The standard spironolactone dosage for dogs is 1–2 mg/kg daily, which may be taken once or twice daily.

• For heart failure: 1–2 mg/kg once or twice per day, but dosages can vary depending on other drugs being used
• For ascites: 0.5–2 mg/kg twice daily, but the dosage could be higher in some circumstances
• For hypertension: 1–2 mg/kg once or twice per day 
• For glomerular disease: 1–2 mg/kg once per day 

Spironolactone is not formulated for dogs. For humans, the smallest tablet is 10 mg, which may be too large for small dogs. The veterinarian can use tablets or oral suspensions specially prepared by a compounding pharmacy.

Can dogs overdose on spironolactone?

Do not give a dog more spironolactone than prescribed. A spironolactone overdose in dogs could cause serious dehydration, so call a veterinarian if your dog ate spironolactone or ingested too much. If you’re unsure, signs of a spironolactone overdose include:

• Excessive thirst
• Excessive urination
• Vomiting

 The warning signs of dehydration in a dog include:

• Dry tongue and gums
• Thick, ropey saliva
• Dry, sunken eyes
• Loss of skin turgor

RELATED: See more on spironolactone dosages

Can I give my dog spironolactone every day?

When veterinarians prescribe spironolactone, the dog must receive daily doses. Spironolactone could be a long-term or lifelong treatment for some dogs.

How to give your dog spironolactone

Diuretics are powerful drugs that increase urine production and reduce sodium retention. Both are crucial to maintaining life, so make sure to:

• Follow all the veterinarian’s instructions. 
• Do not miss doses or give them too frequently. Spironolactone typically requires only one dose per day.
• The veterinarian may need to examine the dog regularly and perform blood tests to monitor the treatment’s effectiveness and detect potential problems. Keep all follow-up appointments.
• Make sure the dog has easy access to drinking water unless the veterinarian instructs otherwise.

To give a dog spironolactone tablets or oral suspension:

• The dog can take a dose with food or on an empty stomach. If the dog vomits up the dose, give the next dose with food.
• If you don’t know how to give a dog a tablet, ask a veterinary assistant to demonstrate.
• Measure the spironolactone liquid using the provided dosing syringe. If it’s missing, ask the veterinarian or a pharmacist for one. Shake the spironolactone bottle before measuring a dose.
• If a dose is missed, give it when remembered. If it’s almost time for the next dose, skip the missed dose and give the next dose as scheduled. Do not give the dog two doses to make up for a missed dose.
• Store spironolactone tablets at room temperature in tight, light-resistant containers. 
• Spironolactone liquid should be stored in a refrigerator. Throw out any unused medication after 30 days.

Spironolactone alternatives for dogs

Spironolactone has very narrow uses in veterinary medicine. When a diuretic is needed, veterinarians usually turn first to thiazide diuretics or loop diuretics. In dogs, veterinarians use spironolactone as an alternative or add-on treatment to induce urine production while maintaining normal potassium levels. 

Given the narrow use of spironolactone, the only alternative to spironolactone is another potassium-sparing diuretic used in dogs. That narrows the choices down to triamterene. 

Summary

Veterinarians use spironolactone along with other medications for serious conditions like heart failure, ascites, and high blood pressure. It’s not a first choice, but a useful alternative if other medications don’t work or diuretics are causing low potassium. Treatment can be long-term or even lifelong. Doses must be given every day.