By Rania Gollakner, BS, DVM, MPH

What is furosemide?

Furosemide (brand names: Lasix®, Salix®, Frusemide®, Disal®, Uritol®) is a loop diuretic used to treat conditions such as congestive heart failure, lung fluid retention, and certain kidney diseases.

It can also be used to aid in the treatment of high blood potassium and high blood pressure. In racehorses, it has been used to prevent exercise-induced lung bleeding.

Its use in cats and dogs at labeled doses is FDA approved, however, its use at other doses or use in ferrets and other small mammals, horses, birds, and reptiles to treat various conditions is ‘off label’ or ‘extra label’. Many drugs are commonly prescribed for off label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully as their directions may be significantly different from those on the label.

How is furosemide given?

Furosemide is given by mouth in the form of a tablet or liquid. It may be given with or without food; however, if vomiting occurs when dosed on an empty stomach, give future doses with food or a treat. Measure liquid doses carefully. It can also be given by injection in the hospital or clinic setting.

Ensure your pet has access to plenty of fresh, clean water at all times while on this medication. Because this medication will cause frequent urination, avoid dosing this medication close to bedtime. If you are allergic to sulfa medications, you should wear gloves when handling this medication.

This medication will take effect quickly, in about 1 to 2 hours, and improvement in clinical signs should follow.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time, and return to the regular dosing schedule. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

The most common side effect is an increase in urination. Other possible side effects include diarrhea or constipation. Serious side effects include weakness, collapse, head tilt, balance problems, electrolyte imbalance, lack of urine production, or a racing heart rate. This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Furosemide should not be used in pets that are allergic to it or in those that are unable to make urine. It should also not be used, or be discontinued in pets that have worsening kidney disease. Furosemide should be used cautiously in pets with dehydration, electrolyte imbalance, liver or kidney disease, and diabetes mellitus and in pets that are actively vomiting or having diarrhea, or in pets that are pregnant or lactating. Pets that are allergic to sulfonamides may also be sensitive to furosemide, so caution must be taken.

Are there any drug interactions I should be aware of?

The following medications should be used with caution when given with furosemide: ACE inhibitors, aminoglycosides, amphotericin B, cisplatin, corticosteroids, digoxin, insulin, nondepolarizing muscle relaxants, probenecid, salicylates, succinylcholine, or theophylline. Any drugs that cause kidney or ear toxicity should be used carefully in conjunction with furosemide. Furosemide can also cause a falsely elevated Free T4 lab value.

Be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring that needs to be done with this medication?

Electrolyte levels, kidney values, blood sugar levels, and hydration should all be monitored. Blood pressure, weight, and ear function may also be monitored if indicated. Your veterinarian may monitor your pet to be sure that the medication is working.

How do I store furosemide?

Store at room temperature and protect from light and freezing.

What should I do in case of emergency?

If you suspect an overdose or an adverse reaction to the medication, call your veterinary office immediately. If they are not available, follow their directions in contacting an emergency facility.

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