Furosemide is a generic drug that vets prescribe to treat dogs with heart conditions and other conditions involving fluid buildup in the body. It’s also known by the brand names Salix and Disal.

Furosemide is a diuretic that works on a dog’s kidneys to help them excrete water, minerals, and electrolytes. This is important in conditions where fluid buildup is a problem.

Furosemide is available in these forms:

  • Oral solution: 8 milligrams per milliliter (mg/mL) or 10 mg/mL
  • Tablets: 12.5 mg, 20 mg, 40 mg, 50 mg, and 80 mg
  • Injectable (veterinarian use only): 50 mg/mL

Researchers have also developed a furosemide oral disintegrating film (ODF) that dissolves in the mouth and may be easier to give than a tablet. The Food and Drug Administration (FDA) has not yet approved the ODF form.

Brand-name versions of furosemide are available: Salix and Disal. Salix was previously called Lasix.

This article explains how to use furosemide safely, what conditions it treats, how it works in your dog’s body, and what side effects to watch for.

How to use furosemide for a dog

  • Check the dosage: Read your dog’s prescription carefully to be clear about how much they need.
  • Timing: Because furosemide makes dogs urinate, avoid giving the last dose too close to bedtime.
  • Food: Your dog can have furosemide with or without food. If they experience digestive issues taking it without food, try giving it with food next time.
  • Giving oral tablets:
    • Cup your dog’s upper snout and put the tablet at the back of their mouth quickly before closing their snout. You can also squash the tablet into a treat.
  • Giving oral medication:
    • Use the dosing syringe to measure the exact amount of liquid the vet has prescribed.
    • Cup the upper snout and empty the syringe contents into your dog’s mouth.
  • Missed doses: If you miss a dose, give it when you remember. However, if it is close to the next scheduled dose, just skip the missed one. Do not double up the dose.
  • Storage: Store furosemide at room temperature away from direct light. Do not freeze it.

Furosemide is a “loop diuretic” that works in a part of the kidney called the loop of Henle. The kidneys normally filter blood and balance salts like sodium and chloride, but furosemide stops the kidneys from reabsorbing these salts.

Because water tends to follow salt, when the sodium stays in the urine to be flushed out, water stays with it. This causes your dog to produce more urine, reducing the volume of fluid in the blood and tissues and relieving pressure on the heart and lungs.

Furosemide has various uses, but it is best-known for treating fluid buildup caused by heart conditions. Its uses include:

  • Congestive heart failure (CHF): When a dog has heart failure, the heart cannot pump blood effectively. This leads to fluid accumulation, often in the lungs (pulmonary edema) or the belly (ascites). Furosemide helps drain this fluid, so the dog can breathe more easily.
  • Edema: Furosemide can treat fluid swelling in body tissues or cavities caused by other medical issues.
  • Chronic bronchitis: For dogs with chronic bronchitis, furosemide can help dilate the airways, although vets typically recommend other medications first.
  • Hypercalcemia: This condition occurs when calcium levels in the blood are too high, which can damage the kidneys. Furosemide helps the body to get rid of excess calcium in the urine.
  • Acute kidney failure: In emergencies where the kidneys are shutting down and stopping urine production, a vet may use furosemide to try to stimulate the kidneys to resume function.
  • Hyperkalemia: This refers to dangerously high potassium levels in the blood, which furosemide can help lower.

The dosage of furosemide can vary depending on the severity of the disease and the dog’s size. Always follow the vet’s dosage instructions for your dog.

For home use, furosemide is available in tablet sizes of 12.5 mg, 20 mg, 40 mg, 50 mg, and 80 mg. It’s also available as a liquid that’s given using a dosing syringe.

Your dog’s vet will tell you how much furosemide to give and at what intervals based on your dog’s condition, weight, and other factors.

Your vet may adjust the dose based on how your dog responds to the treatment.

Injectable furosemide is used by vets in emergency situations, such as severe heart failure. It is typically given by a vet in a clinical setting and is not available for home use.

Because furosemide changes how the kidneys handle water and salt, side effects are often related to hydration and electrolytes.

  • Thirst and urination: The most common side effects are drinking more water (polydipsia) and peeing more (polyuria). This is actually proof that the drug is working. You may need to let your pet out more often to urinate to avoid accidents in the house.
  • Electrolyte imbalance: Furosemide causes the body to lose potassium, sodium, and chloride. Low potassium (hypokalemia) can make a dog feel weak or lethargic.
  • Dehydration: If the dog loses too much fluid and doesn’t drink enough, they can become dehydrated.
  • Increased blood sugar: Furosemide can raise blood sugar levels, which is important to monitor if your dog has diabetes.
  • Hearing Loss: Hearing loss is a rare side effect of furosemide.

If you notice concerning changes in your dog’s health, contact a vet right away.

Medical Perspective

“Signs that your pet may be feeling ill include decreased appetite and thirst, isolating, vomiting and/or diarrhea, lethargy, difficulty breathing, restlessness and excessive vocalization.

If your pet’s resting respiratory rate is greater than 40 breaths per minute, their gums are pale or blue, they cannot get up or are not responding to normal cues, or they are acting confused/disoriented, they may be experiencing a medical emergency.”

— Vincent J. Tavella DVM, MPH

Learn about warning signs you should take your dog to the vet.

Quotes represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

Furosemide is not suitable for all dogs, particularly those with certain health conditions or those taking other medications.

Your vet will assess your dog’s health before prescribing furosemide to reduce the chance of adverse side effects. Remember to tell them about any changes in your dog’s health during treatment.

Which dogs should not have furosemide?

If any of the following criteria apply to your dog, it may be unsafe for them to take furosemide:

  • dehydration
  • being prone to calcium oxalate stones
  • diabetes
  • kidney failure

What should I avoid giving my dog alongside furosemide?

Furosemide can interact with other drugs, so tell your vet about everything you give your dog. A vet will avoid combining the following medications with furosemide unless absolutely necessary:

  • ACE inhibitors: Combining these common heart drugs, such as enalapril and benazepril, with furosemide can worsen dehydration and cause kidney failure. If a vet prescribes them together, they will give the lowest effective dose and monitor your dog’s kidney function closely.
  • Prednisone: Using this steroid with furosemide can increase the risk of potassium loss.
  • Theophylline: This airway medication may reach toxic levels in the blood when taken with furosemide, so the dose may need to be adjusted.
  • Aminoglycoside antibiotics: These antibiotics, such as amikacin and gentamicin, can be toxic to the ears and kidneys, and furosemide increases that risk.

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Furosemide is a diuretic used to treat heart failure and fluid buildup in dogs by helping the kidneys flush excess water and salt from the body.

It comes in tablet, liquid, and injectable forms. Possible side effects include increased thirst, urination, and electrolyte changes.

Always follow your vet’s dosing instructions closely and monitor your dog for signs of weakness or dehydration.

Disclaimer: This article provides information about medications for pets. Do not use human medications for pets, or pet medications for humans, as dosages, strengths, and ingredients may be different and can lead to serious harm. Always use medications under the guidance of a licensed veterinarian or doctor.