Furosemide for Veterinary Use

Therapeutic Class: Loop Diuretic

Species: Dogs, cats and horses

May Be Prescribed For:
Dogs and cats: Congestive heart failure (CHF), pulmonary edema, uremia, hyperkalemia, hypertension.
Horses: Exercise induced pulmonary hemorrhage, acute renal failure, edema due to a variety of causes.

Furosemide is a potent loop-diuretic that acts within the kidney to produce a dose-dependent increase in urine output with increased urinary excretion of sodium, potassium, calcium, chloride, magnesium, hydrogen, ammonium, and bicarbonate. Furosemide increases blood flow to the kidney, and causes a transient increase in the glomerular filtration rate. It has no effect on carbonic anhydrase and does not have an antagonistic effect on aldosterone. Although the urinary loss of electrolytes is substantial, they are usually replaced within 24 hours by re-absorption by the kidneys and within the GI tract.

Furosemide may be administered orally, intramuscularly, subcutaneously, or intravenously. Onset of action after oral administration is approximately one hour. Onset of action after intravenous administration is five minutes with peak effect at approximately 30 minutes. Constant rate infusion may be helpful in the initial phase of treatment of animals with life-threatening CHF.

Furosemide is used in dogs and cats to promote diuresis and manage fluid retention. It is commonly used to treat pulmonary edema due to CHF. Other uses include diuresis in acute renal failure, management of ascites, hypercalcemia, or hyperkalemia. Although furosemide also lowers blood pressure through vasodilation, it is not considered a primary treatment for hypertension.

Cats are more sensitive to furosemide than dogs or other species and may need lower doses. Cats are also more likely to develop hypokalemia, azotemia and ototoxicity.

Furosemide is used in general equine practice to manage fluid retention and edema. It is commonly used in racehorses to reduce the incidence of exercise-induced pulmonary hemorrhage (EIPH) and epistaxis. The mechanism of action is through the dose-dependent reduction in right atrial, pulmonary arterial, and pulmonary capillary pressures. Furosemide has been shown to cause bronchodilation, which may also play a role in the prevention of epistaxis.

• The most-common side effects relate to volume depletion or electrolyte imbalances, the most serious being hyponatremia. Potassium, calcium, magnesium and sodium levels may need to be monitored. Animals that are eating and drinking normally have a reduced risk for dehydration or electrolyte depletion.

• Ototoxicity may occur, particularly in cats or in other species with high dose intravenous treatment.

• Other less common side effects include GI upset, hematologic changes, restlessness or weakness.

• Furosemide should not be used in animals that are unable to produce urine (anuric), or those with serious electrolyte imbalances or electrolyte depletion.

• Furosemide should be used with caution in animals that are dehydrated, have decreased liver function or diabetes mellitus.

• Animals that are vomiting or have diarrhea should be monitored closely because they may develop electrolyte imbalances that could be exacerbated by furosemide.

• Humans that are hypersensitive to sulfonamides may also be hypersensitive to furosemide. This work has not been repeated in animals.

• Furosemide has been shown in laboratory animals to present some risk to fetuses. It is also found in breast milk.

There are a number of possible drug interactions with furosemide:

• Increased potential for nephrotoxicity and ototoxicity when used with aminoglycoside antibiotics (amikacin or gentamicin).

• Increased risk of hypotension and acute renal failure when used with ACE inhibitors (enalapril or benazapril).

• Furosemide may increase serum digoxin levels, or decrease digoxin excretion. Decreased serum potassium or magnesium levels due to furosemide can increase the cardio toxic effects of digoxin. Additional monitoring of digoxin levels and electrolyte levels may be indicated.

• Concurrent use with corticosteroids may increase risk of GI ulceration or hypokalemia.

• Decreased serum potassium due to furosemide can decrease the antiarrhythmic effects of lidocaine. Electrolyte monitoring and possible potassium supplementation may be indicated in this situation.

• The diuretic effects of furosemide may increase renal loss of bromide, allowing for seizure breakthrough.

• Furosemide may alter insulin requirements.

• Other drugs that may cause interactions include: amphotericin B, atracurium, turbocurarine, probenicid, salicylates, succinylcholine,, and theophylline.

• Acute overdose with furosemide may cause electrolyte and fluid imbalances, central nervous system signs, and cardiovascular collapse. Electrolyte and fluid balance should be monitored and supported.

• If an oral overdose is recognized promptly, gut emptying may be warranted.