Spironolactone for dogs: Uses, dosage, and safety

In this article:

• What is spironolactone used for in dogs?
• Is spironolactone safe for dogs?
• Spironolactone dosage for dogs
• Spironolactone alternatives for dogs
• Summary

In this article

• What is spironolactone used for in dogs?
• Is spironolactone safe for dogs?
• Spironolactone dosage for dogs
• Spironolactone alternatives for dogs
• Summary

Spironolactone (brand name: Aldactone) is a potassium-sparing diuretic that increases water and sodium excretion through urine. Veterinarians never use spironolactone by itself 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. 

RELATED: Save up to 80% on spironolactone

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 describes any situation 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 fluids, drugs that dilate blood vessels such as ACE inhibitors or 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 does not work well or the diuretics being used deplete too much potassium from the system. Spironolactone does not seem to have any other benefit in treating heart failure in dogs other than maintaining normal potassium levels.

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 any other problem that restricts blood flow through these veins. 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 the fluid building up in the abdomen. Spironolactone is added to the treatment to both reduce fluid buildup and keep potassium at normal 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 48% of adults 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. Most dogs are 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—like water and waste—pass through them into the urine. Stuff the body does need—like blood cells and proteins—are filtered so they don’t pass out of the body. Glomerular disease describes what happens when that process doesn’t work, so the urine gets foamy or discolored, and fluid builds up in the body. 

Glomerular disease in dogs is always a result of medical conditions like diabetes, infection, drugs, autoimmune disorders, or 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 get low, spironolactone is added to diuretic treatment. 

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 kidney problems, cause high potassium, so spironolactone is contraindicated in dogs with those 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 side effects 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 there’s an increased 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 owners won’t encounter mitotane. Veterinarians use it to treat adrenal gland problems such as Cushing’s disease. Spironolactone may increase the concentration of mitotane in the blood, increasing the risk of side effects

• Aspirin and other salicylates. Aspirin and similar drugs called salicylates could decrease the effects 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, much larger than the standard dosage for dogs. The veterinarian may 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. An overdose could cause serious dehydration, so call a veterinarian if a dog has ingested too much spironolactone. 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

Can I give my dog spironolactone every day?

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

How to give your dog spironolactone

Diuretics are powerful drugs that decrease water and sodium. 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 effectiveness of the treatment and look for 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 with the dosing syringe provided. 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 keeping potassium levels normal. 

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 instead a useful alternative if other medications don’t work or other diuretics are causing low potassium. Treatment can be long-term or even lifelong. Doses must be given every day.