Drug Classification & Information

Furosemide is a loop diuretic (‘water pill’) and is the first line of therapy for congestive heart failure (CHF) in veterinary species.  It causes loss of electrolytes and water from the body through the kidneys. Ensure animals are eating and drinking normally while taking this medication.  Injectable furosemide is sometimes prescribed for at-home administration (subcutaneous) in refractory cases or in cats intolerant to oral therapy.

Indications for Use

CHF in animals.  May also be considered for treatment of fluid accumulations for other causes besides heart disease.  Occasionally used at low dosages for anti-tussive and bronchodilating effects in patients with airway disease such as collapsing trachea and chronic bronchitis. 

Potential Drug Interactions

May increase risk for digoxin toxicity by causing loss of potassium.  May affect insulin requirements in Diabetic patients (increases glucose levels).  Can result in hypotension when given with vasodilators.  NSAIDs may reduce diuretic effect.  Combination with NSAIDs may increase risk for renal dysfunction.

Drug Side Effects

Furosemide can lead to significant dehydration and electrolyte loss and may lead to renal dysfunction (azotemia).  Regular access to fresh drinking water is essential when receiving furosemide (do not limit water intake).  Furosemide will increase both thirst and urination.  May cause hearing loss at high dosages.  May result in some GI upset (reduced appetite, vomiting) and weakness.  It should be used with caution in patients with pre-existing renal disease.

Therapeutic Monitoring

Renal values (BUN, creatinine) and electrolytes should be monitored regularly when receiving this medication (1-2 weeks after any dose adjustment, then every 4-6 months). 

Dosage Forms

Human: 20, 40, 80 mg tablets (Lasix – brand, generic)

Veterinary:  12.5, 50 mg (Salix) tablets; 10 mg/mL liquid suspension for oral administration

50 mg/mL for injection (subcutaneous)