Furosemide

Furosemide in Dogs and Cats: Uses, Dosage and Side Effects

Overview

• Loop diuretic, inhibiting the Na+/K+/Cl– cotransporter in the thick ascending limb of the loop of Henle.
• The net effect is a loss of sodium, potassium, chloride and water in the urine.
• It also increases the excretion of calcium, magnesium and hydrogen as well as renal blood flow and glomerular filtration rate.
• Transient vasodilation may occur following i.v. administration and in some species,
  bronchodilation may occur; the exact mechanism for both is unclear.

Uses of Furosemide

• Management of congestive heart failure (acute and chronic).
• The use of diuretic monotherapy for the chronic management of heart failure due to mild regurgitation or dilated cardiomyopathy in dogs is not recommended, as patients
  receiving concomitant therapy with pimobendan, ACE inhibitors (and spironolactone in dogs with mitral regurgitation) have a better clinical outcome.
• Treatment of hypercalcemia.
• Promotion of diuresis in acute renal failure (questionable efficacy).

Dose of Furosemide in Dogs and Cats

Dogs, Cats:

Acute, life-threatening congestive heart failure:

• 1–2 mg/kg i.v., i.m. q0.5–4h as required, based on improvement in respiratory rate and effort.
• Once clinical signs improve, increase the dosing interval to q6–12h, monitor urea, creatinine and electrolytes, and start oral therapy once tolerated.
• Use the lower end of the dose range for cats and monitor response.
• Ensure no pleural effusion present.

Chronic, congestive heart failure:

• 1–5 mg/kg p.o. q6–12h.
• Typical maintenance doses for mild to moderate CHF are 1–2 mg/kg p.o. q8–24h (dogs) and 1–2 mg/kg p.o. q12–48h (cats).
• The goal is to use the lowest dose of furosemide that effectively controls clinical signs.
• Doses in excess of 12 mg/kg/day are unlikely to be beneficial and warrant the addition of a different class of diuretic (e.g. thiazide) or transfer to an alternative diuretic
  (e.g. torasemide) to control refractory failure.
• In patients with ascites, the use of s.c. instead of p.o. furosemide can have a marked
  clinical benefit due to improved bioavailability.

Hypercalcaemia:

• hydrate before therapy.
• Give 2–4 mg/kg i.v., s.c., p.o. q8–24h.
• Maintain hydration status and electrolyte balance with normal saline and added KCl.
• Furosemidegenerally reduces serum calcium levels by 0.5–1.5 mmol/l.

Acute renal failure/oliguria:

• Replace fluid deficit and subsequently closely monitor fluid input and output.
• Give furosemide at 2 mg/kg i.v.
• If no diuresis within 1 hour, repeat the dose at 2–4 mg/kg i.v.
• If no response within 1 hour give another dose at 2–4 mg/kg i.v. Alternatively, a bolus dose with 1–2 mg/kg i.v. followed by constant rate infusion at 0.1–2 mg/kg/h.

Side Effects of Furosemide in Dogs and Cats

• Hypokalaemia, hypochloraemia, hypocalcaemia, hypomagnesaemia and hyponatraemia; dehydration, polyuria/polydipsia and prerenal azotaemia occur readily.
• A marked reduction in cardiac output can occur in animals with severe pulmonary
  disease, low-output heart failure, hypertrophic cardiomyopathy, pericardial or myocardial disorders, cardiac tamponade and severe hypertension.
• Other adverse effects include ototoxicity (especially in cats), GI disturbances, leucopenia, anaemia, weakness and restlessness.

Contraindications of Furosemide in Dogs and Cats

• Dehydration and anuria.
• Do not use in pericardial effusion where cardiac tamponade is confirmed.
• Can be used post-effusion drainage to assist in the management of right-sided heart failure symptoms if necessary.

Some Notes:

• Use with caution in patients with severe electrolyte depletion, hepatic failure and diabetes mellitus.
• Evidence for efficacy in non-cardiogenic pulmonary oedema is lacking.
• Nephrotoxicity/ototoxicity associated with aminoglycosides may be potentiated when furosemide is also used.
• Furosemide may induce hypokalaemia, thereby increasing the risk of digoxin toxicity.
• Increased risk of hypokalaemia if furosemide is given with acetazolamide, corticosteroids, thiazides and theophylline.
• Concurrent administration of NSAIDs with furosemide may decrease efficacy and
  may predispose to nephrotoxicity, particularly in patients with poor
  renal perfusion.
• Furosemide may inhibit the muscle relaxation qualities of tubocurarine, but increase the effects of suxamethonium.