Furosemide (Frusemide)

Furosemide, also spelled frusemide, is a potent loop diuretic widely used to relieve fluid accumulation in veterinary patients. Its principal small-animal application is pulmonary edema and other congestion associated with heart failure. Additional uses include selected electrolyte disorders, edema in large animals and reduction of exercise-induced pulmonary hemorrhage in horses.

Group

Loop diuretic

Mechanism of Action

Furosemide inhibits the sodium–potassium–chloride cotransporter NKCC2 in the thick ascending limb of the loop of Henle. This reduces sodium chloride reabsorption and the medullary concentrating gradient, increasing urinary salt and water loss. Reduced circulating volume and venous pressures help relieve congestion. Increased urinary calcium and potassium excretion contributes to selected electrolyte-management uses.

Dose Rates

Dog

Use / stage	Dose	Route	Schedule	Instructions
Edema	2–6 mg/kg	IV, IM, SC, PO	Every 8–12 h
Heart failure — Initial	2 mg/kg	PO	Every 12 h
Heart failure — Maintenance	1–2 mg/kg	PO	Every 12 h
Acute pulmonary edema	2 mg/kg	IV	Every 0.5 h	Intensive monitored treatment; repeat until clinical improvement, reassessing hydration and perfusion.
Diuretic infusion — Loading	0.66 mg/kg	IV
Diuretic infusion — Maintenance	0.66 mg/kg/hour	IV	Continuous	Infuse for 8 hours.
Alternative diuretic infusion	0.25 mg/kg/hour	IV	Continuous	Equivalent to a total 2 mg/kg infused over 8 hours in 5% glucose.

Cat

Use / stage	Dose	Route	Schedule	Instructions
Edema	1–4 mg/kg	IV, IM, SC, PO	Every 8–24 h	Start at 1 mg/kg and titrate to response.

Horse

Use / stage	Dose	Route	Schedule	Instructions
Edema	1 mg/kg	IM, IV	Every 8 h
Edema	250–500 mg/animal	IM, IV	Every 6–8 h
Diuretic infusion — Loading	0.12 mg/kg	IV
Diuretic infusion — Maintenance	0.12 mg/kg/hour	IV	Continuous
EIPH prevention	0.5 mg/kg	IV	Once	Reported timing is 4 hours before exercise or 24 hours before racing; competition rules require separate verification.
EIPH prevention	1 mg/kg	IV	Once	Reported timing is 4 hours before exercise or 24 hours before racing; competition rules require separate verification.
Heart failure — Maintenance	0.5–2 mg/kg	PO, IM	Every 8–12 h

Cattle

Use / stage	Dose	Route	Schedule	Instructions
Edema	500 mg/animal	IM, IV	Every 24 h
Edema	250 mg/animal	IM, IV	Every 12 h

Ferret

Use / stage	Dose	Route	Schedule
Acute heart failure — Initial	2–3 mg/kg	IV, IM
Heart failure — Maintenance	1–2 mg/kg	PO	Every 12 h
Heart failure	1–4 mg/kg	PO, SC, IM, IV	Every 8–12 h

Rabbit

Use / stage	Dose	Route	Schedule	Instructions
Heart failure	2–5 mg/kg	PO, SC, IM, IV	Every 12 h
Pulmonary edema	1–4 mg/kg	IV, IM	Every 4–6 h

Reptile

Use / stage	Dose	Route	Schedule	Instructions
Diuresis	5 mg/kg	IV, IM	As needed

Bird

Use / stage	Dose	Route	Schedule	Instructions
Diuresis	0.1666666667 mg/kg	IM	Every 12 h	Equivalent to 0.05 mg per 300 g; lories are particularly sensitive to overdose.

Indications

Treatment of cardiogenic pulmonary edema and other congestive manifestations of heart failure in dogs and cats.
Management of selected noncardiac edema or effusions when removal of retained fluid is clinically appropriate.
Adjunctive promotion of calcium excretion in selected hypercalcemic patients after restoration of hydration.
Adjunctive enhancement of potassium excretion in selected hyperkalemic patients with adequate renal urine production.
Reduction of exercise-induced pulmonary hemorrhage in horses within an appropriate equine treatment program.
Treatment of selected edema syndromes in cattle, including udder edema.

Contraindications

Use cautiously with volume depletion, electrolyte depletion or concurrent ACE inhibition.

Interactions

Aminoglycosides and amphotericin increase renal/ototoxic risk.
NSAIDs may reduce response.
Acidic mixtures can cause precipitation.

Adverse effects

Dehydration, azotemia and electrolyte losses
RAAS activation and reduced response with repeated dosing
SC injection discomfort

Preparations

Preparation	Form	Strength	Route
Furosemide (Frusemide) 12.5 mg	Tablet	12.5 mg / tablet	PO
Furosemide (Frusemide) 20 mg	Tablet	20 mg / tablet	PO
Furosemide (Frusemide) 40 mg	Tablet	40 mg / tablet	PO
Furosemide (Frusemide) 50 mg	Tablet	50 mg / tablet	PO
Furosemide (Frusemide) 80 mg	Tablet	80 mg / tablet	PO
Furosemide oral solution 10 mg/mL	Oral Liquid	10 mg / mL	PO
Furosemide injection 50 mg/mL	Injection	50 mg / mL	IV, IM, SC

Monitoring and Administration

Monitor hydration, urine output, electrolytes and renal parameters. Increased urine production does not establish improved AKI outcome.

Equine oral absorption is poor. Avoid acidic admixtures and discard discolored solutions.