This commonly used diuretic is used for treating conditions that cause fluid buildup in the body, such as heart disease.
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dog drinking water; furosemide for dogs
Credit: Jason Donnelly

If your vet has prescribed furosemide, you've probably been dealing with a pretty serious health scare with your dog. We feel you. Any health concern can be scary, but when you hear your vet say something like "fluid in the chest" or "heart failure," you're bound to worry.

Fortunately, furosemide for dogs can help treat a handful of conditions when closely monitored by a veterinarian. Here's what you should know.

What Is Furosemide?

Furosemide is a diuretic commonly used in veterinary medicine. It's often prescribed to treat heart disease and other conditions that cause the body to retain fluid. Common brand names for furosemide include Lasix and Salix, but generic forms are available as well with a prescription from your vet.

Furosemide and similar diuretics can reduce various forms of edema (fluid accumulation in the tissues) and relieve many associated symptoms. The medication acts in the kidneys, a set of two complex organs responsible for maintaining hydration, electrolyte balance, and blood pressure through systems of filtration and excretion. Loop diuretics such as furosemide work by making the kidneys pass more fluids, minerals, and electrolytes, thus producing more urine. This draws fluid that has accumulated in the body into the bloodstream, replacing the fluid passed by the kidneys.

What Is Furosemide Used for in Dogs?

Furosemide is used to remove any excess fluid in the body by helping your dog pee more frequently. The fast-acting medication typically increases your dog's urination within an hour or two, a sign that the drug is working to expel excess fluid.

Furosemide can be beneficial, even life-saving, to dogs with several health conditions, including:

Congestive Heart Failure

Congestive heart failure is a form of heart disease that often causes fluid accumulation or congestion in the chest, abdominal cavities, or the lung tissue (a condition called pulmonary edema). This fluid buildup can make it difficult for the dog to breathe properly.

Because furosemide helps the kidneys expel fluid from the bloodstream, it can enable excess fluid in the tissues to travel to the bloodstream and leave the body via urine.

Edema

Edema is swelling caused by excess fluid in the body's tissues. Furosemide can help remove fluid from body cavities or other tissues even if the cause is not heart failure. 

Bronchitis

In addition to its diuretic properties, furosemide can also act as a respiratory airway dilator to reduce coughing in dogs. Dogs with chronic bronchitis may benefit from furosemide, but it's not typically used alone to treat this condition.

Kidney Disease

Kidney disease causes uremia, a buildup of waste products in the bloodstream that are normally eliminated by the kidneys. Furosemide helps the kidneys produce more urine to filter out these waste products. Additionally, furosemide may be used in combination with other medications to stimulate urine production if the kidneys are not producing enough.

Hypercalcemia

Calcium is one of the minerals passed through the kidneys, and furosemide encourages the organs to pass more of it. So, furosemide can reduce blood calcium levels if they become dangerously elevated (a condition called hypercalcemia). Other drugs, such as prednisone, may be used with furosemide to promote calcium excretion.

Hyperkalemia

Furosemide can also be helpful in reducing high potassium blood levels (hyperkalemia). This condition is often related to kidney disease.

Furosemide Dosage for Dogs

Furosemide is available in both oral and injectable forms. Injections are typically given in the hospital, but your veterinarian may prescribe tablets or liquid to be given at home. 

Tablets come in several strengths so your vet can prescribe an accurate dose. The liquid form is helpful for small dogs or those who don't take pills well. And while furosemide is available in both veterinary and human formulations, both are OK to give Fido.

Your vet calculates your dog's furosemide dosage based on his weight and the specific condition being treated. This is usually somewhere from 1–4 milligrams per kilogram of body mass every 8–12 hours. Accurate dosing is important to prevent adverse effects, so don't adjust your dog's dose without talking to your vet first.

If you miss a dose of furosemide, give it right away unless the next dose is almost due. Then, resume the recommended schedule. Do not double up on doses.

Wash your hands after handling furosemide so you don't absorb any of this drug into your skin. If you are allergic to sulfa drugs (sulfonamides), wear gloves when handling.

Side Effects of Furosemide for Dogs

Furosemide can cause several side effects in dogs, some worse than others. Make sure your dog drinks enough water while on furosemide in order to reduce the likelihood of some of these effects. The most common side effects of furosemide in dogs include:

  • Increased urination (this is expected, but contact your vet if it's extreme)
  • Increased thirst
  • Dehydration
  • Electrolyte imbalances (especially low sodium)
  • Mineral deficiencies (low calcium, magnesium, or potassium)
  • Diarrhea
  • Constipation

The following side effects are less common in dogs but can be serious:

  • Anemia (low red blood cells)
  • Leukopenia (low white blood cells)
  • Lethargy
  • Weakness
  • Restlessness
  • Rapid heart rate
  • Hypoglycemia (low blood sugar)
  • Hearing loss (at very high doses)

Contact your vet if you notice these or any other unusual signs in your dog while on furosemide. It's important for your veterinarian to monitor your dog regularly during treatment. Your dog will need follow-up exams and lab work periodically to prevent serious side effects.

Can Dogs Overdose on Furosemide?

It's possible for dogs to overdose on furosemide, especially if they get into the whole bottle. Always keep all medicines out of your dog's reach to prevent toxicity.

A furosemide overdose can cause serious issues with hydration and electrolyte balance as well as central nervous system problems (like seizures and even a coma) and heart failure. Contact a vet immediately if your dog accidentally gets too much furosemide. You can call your local vet, an animal emergency service, or a pet poison control service like ASPCA Animal Poison Control at (888) 426-4435 or Pet Poison Helpline at (855) 764-7661 for professional advice.

Precautions and Warnings

Furosemide should not be used in dogs with anuria, a state in which the kidneys can no longer produce urine. Dogs with kidney disease should be closely monitored during treatment. Furosemide should be used with caution in dogs with a history of diabetes mellitus, liver disease, and electrolyte imbalance.

Several drug interactions have either been reported or are theoretically possible in dogs on furosemide. Be sure to tell your vet about all medications and supplements you give your pup. The following drugs may interact with furosemide:

  • Ace inhibitors like enalapril and benazepril may lead to high blood pressure.
  • Aminoglycosides like gentamicin and amikacin may increase the risk of hearing loss.
  • Amphotericin B may increase the risk of high potassium and kidney damage.
  • Corticosteroids like prednisone may increase the risk of GI ulcers and high potassium.
  • Digoxin, also used for heart disease, may increase the risk of toxicity when used in conjunction with furosemide.
  • Some muscle relaxants may work differently when taken with furosemide.