Furosemide for cats: Dosage and safety

In this article:

• What is furosemide used for in cats?
• Safety
• Dosage
• Alternatives
• Summary

In this article

• What is furosemide used for in cats?
• Safety
• Dosage
• Alternatives
• Summary

Furosemide is a generic diuretic widely used in veterinary medicine. While it’s used for various conditions in other animals, veterinarians give furosemide to cats as part of a multidrug treatment of congestive heart failure (CHF). Furosemide increases urine production in cats, eliminating excess water that builds up in the lungs, belly, and other tissues due to heart failure. Unlike other animals, cats are particularly sensitive to the effects of furosemide, so dosages are small and need to be carefully calibrated.

RELATED: Save up to 80% on furosemide

What is furosemide used for in cats?

Veterinarians primarily use furosemide to reduce fluid retention in cats with congestive heart failure. Veterinarians may also use it to treat fluid build-up in the lungs (pulmonary edema) or other problems with fluid accumulation.

Congestive heart failure

Congestive heart failure is a condition in which the heart can’t pump enough blood to the rest of the body. The most significant consequence of heart failure is congestion. Fluid backs up in the body, usually the lungs and the abdomen. Fluid in the lungs, called pulmonary edema, interferes with the cat’s breathing ability. Fluid build-up in the belly (ascites) is associated with liver problems.

Furosemide is the diuretic of choice for congestive heart failure in cats. Other drugs, including ACE inhibitors or angiotensin II receptor blockers, will also be used to widen blood vessels and reduce blood pressure. The cat may also need to take pimobendan to strengthen heartbeats and lower blood pressure.

Furosemide increases the amount of water and salts excreted through the urine to help drain excess fluid. Called a loop diuretic, it increases electrolytes in the urine to draw more water into it. 

Furosemide works very quickly. About 30 minutes after a dose is swallowed, the cat should start urinating more. The effects peak in about one to two hours.

Edema

Veterinarians use furosemide for serious fluid retention problems such as pulmonary edema or ascites. Edema and ascites can be symptoms of heart failure or due to other disease processes. Dosages vary, but they will probably be similar to those used for heart failure.

Is furosemide safe for cats?

The U.S. Food and Drug Administration (FDA) has approved furosemide for use in cats with serious medical conditions such as heart failure. 

Furosemide is never given to cats that are not urinating (anuria) or allergic to the drug. 

If the cat has electrolyte abnormalities or severe liver disease (hepatic coma), the veterinarian will have to correct these problems before furosemide can be given. 

Veterinarians will use furosemide cautiously in cats with:

• Electrolyte imbalances
• Diabetes mellitus

Veterinarians will regularly monitor blood pressure and electrolytes to make sure that the cat doesn’t get dehydrated or that electrolytes don’t get too low. However, pet parents should also monitor the cat for signs of dehydration or electrolyte depletion. 

Signs that a cat is dehydrated include:

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

Signs of electrolyte imbalances include:

• Excessive thirst
• Lack of energy
• Drowsiness
• Fatigue
• Rapid heart rate
• Decreased urination

Cats are particularly sensitive to furosemide. High doses of furosemide can cause hearing loss in the cat. 

Side effects of furosemide in cats

The most common side effects of furosemide in cats are increased urination and thirst. 

Serious adverse effects include:

• Dehydration
• Electrolyte imbalances
  • Low sodium
  • Low potassium
  • Low calcium
  • Low chloride
• Elevated blood sugar
• Low blood pressure
• Hearing loss

Cat parents should call or visit a veterinarian or veterinary hospital if they notice the cat:

• Is urinating less frequently or not at all
• Is excessively thirsty
• Lacks energy
• Is sleepy or weak
• Has a dry tongue or gums
• Has sunken or dry eyes
• Has skin that, when pushed on by a finger, forms a dimple that doesn’t return to normal
• Is vomiting

Interactions of furosemide with other pet meds

Furosemide has many drug interactions, so make sure the veterinarian knows about all prescription drugs, over-the-counter medications, dietary supplements, and herbal remedies the cat is being given. 

Furosemide can cause significant problems in a cat when it’s combined with:

• Angiotensin-converting enzyme (ACE) inhibitors: Blood pressure could get too low if furosemide is taken with ACE inhibitors, such as enalapril.

• Corticosteroids: Blood potassium could drop too low if furosemide is taken with corticosteroids.

• Antiarrhythmics: Antiarrhythmics such as digoxin can cause blood potassium to drop too low.

• The antifungal drug amphotericin B: If furosemide is taken with the antifungal amphotericin B, blood potassium could drop too low, resulting in the risk of kidney damage.

• Aminoglycoside antibiotics: Combining furosemide with aminoglycoside antibiotics increases the risk of ear damage and hearing loss in a cat.

• Insulin: Furosemide can increase blood sugar levels, requiring insulin dosage modifications.

• Bronchodilators: If taken with furosemide, the cat is more likely to experience side effects from bronchodilators, such as theophylline.

Furosemide dosage for cats

The standard furosemide dosage for cats is 1–2 mg/kg every 12–24 hours.

However, it’s not that easy. Veterinarians will individualize the dose based on the severity of the condition and the cat’s response to treatment. 

The initial doses are usually given as injections and are often higher than continued daily dosing. The veterinarian may then send the cat home with oral furosemide at a lower dose.

Published furosemide dosages for cats include:

• Initial doses for heart failure: 2.75 mg/kg intravenous or intramuscular injection given every 12 hours; doses can increase to as much as 5 mg/kg given every 12 to 24 hours
• Maintenance doses for heart failure: Dose can vary greatly depending on each individual cat’s response to treatment and stage of disease. Doses range from 1 mg/kg given by mouth every 2-3 days to 2 mg/kg given orally every eight to 12 hours 
• For long-term treatment of pulmonary edema: 1–2 mg/kg given by mouth every 12–24 hours

For dosing at home, the veterinarian will likely send pet owners home with furosemide tablets or liquid formulated especially for small animals. Cats can also take the same furosemide that humans take, but they will need their own prescription. Veterinarians may also have furosemide compounded into treats or flavored liquid specific for an individual cat at the dose needed.

Can cats overdose on furosemide?

Cats are more sensitive to furosemide than dogs, so pet owners should take special care to measure doses accurately. A furosemide overdose could cause dehydration, electrolyte problems, or hearing loss in a cat. Veterinarians are cautioned never to exceed a dose of 5 mg per kilogram of body weight when giving cat furosemide.

Call a veterinarian or take the cat to a veterinary hospital if you think the cat has been given too much furosemide. You should also take action if you notice symptoms such as:

• Excessive urination
• Excessive thirst
• Vomiting
• Rapid or unusual heartbeats
• Loss of interest in food

Can I give my cat furosemide every day?

Veterinarians give cats furosemide for serious medical conditions, including heart failure and pulmonary edema. It can cause many side effects, some serious, and has many significant drug interactions. However, its benefits outweigh its risks.

If a cat is sent home with furosemide, doses are given once or twice a day. Since heart failure is potentially a lifelong condition, the cat may need furosemide long-term. 

Furosemide treatment requires vigilance on the part of veterinary professionals and pet parents. Veterinary professionals will regularly see the cat to assess the effectiveness of treatment and do tests for side effects and other problems. 

Pet parents will need to watch for unusual symptoms and take action when it looks like the cat is experiencing side effects. They will need to make sure that the cat has enough water to stay hydrated. In some cases, they may need to put their pet on cat food specially formulated for cats with heart disease or kidney disease to ensure the cat gets enough nutrition.

Furosemide can damage a cat’s ears, so parents should also watch for any signs that the cat is losing hearing and contact the veterinarian.

How to give your cat furosemide

Cat owners should remember that furosemide is a powerful drug. It works very well but can cause problems if dosed incorrectly. Here are a few tips to make sure the cat gets its medicine safely:

• Follow all the veterinarian’s instructions. 
• Understand the dosing schedule. Missing a dose is as serious as giving too many doses. Both are easy to do. 
• The veterinarian may need to examine the cat and run tests regularly. Make sure to keep all follow-up appointments.
• If you’re giving the cat tablets, the veterinarian tablets must be split in two. Make sure you understand how to divide the tablets correctly.
• Furosemide tablets and oral solutions can be given with or without food.
• Ask a veterinary technician to demonstrate if you don’t know how to give a cat a tablet.
• If you are using the oral suspension:
  • You may need to shake the bottle before measuring out a dose.
  • Only use the calibrated oral syringe that comes with this medicine. Do not use tableware or kitchen measuring devices.
• If a dose of furosemide is missed, give it when remembered. Then, provide the next dose after the prescribed interval. For instance, if instructed to give a dose every 8 hours, then give the missed dose and wait 8 hours for the next dose.
• There is no need to taper the dose when this drug is discontinued.
• Store furosemide tablets at room temperature.
• Ask the veterinarian or veterinary pharmacist how to store furosemide liquid. 
  • The liquid may only be good for a limited period. If you’re unsure, ask the veterinarian or pharmacist.

Furosemide alternatives for cats

Veterinarians prescribe furosemide and other loop diuretics for serious conditions. If furosemide can’t be used, they may prescribe bumetanide or torsemide as an alternative loop diuretic.

Not all diuretics are appropriate for heart failure. In the veterinary literature, thiazide diuretics and spironolactone, a potassium-sparing diuretic, are the most common alternative diuretics for heart failure.

Summary

Furosemide is a first-line drug for treating heart failure in cats. As a diuretic, it reduces fluid accumulation in the lungs, belly, and other tissues due to heart failure. Cats are very sensitive to the effects of furosemide, so pet owners should be cautious when dosing the cat and look for side effects such as dehydration or electrolyte imbalances.