Furosemide
4-chloro-2-(furan-2-ylmethylamino)-5-sulfamoylbenzoic acid
Also known as: Lasix · Salix · Disal · Dimazon · Frusecare · Frusedale · Libeo · Frusol · frusemide · furosemidum · LB-502
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Structured calculator evidenceInjection
Verified clinician required
Combined schedule constraints — all apply
- q12-24h
- q6-8h
NA
Governing clinical context (2)
- NOTE: Watch units closely when calculating doses. Do not confuse CRI dosages using mg/kg/hour with μg/kg/minute.
- Furosemide injection should be stored at room temperature. A precipitate may form if the injection is refrigerated, but it will resolubilize when warmed without alteration in potency. The human injection (10 mg/mL) should not be used if it has a yellow color. The veterinary injection (50 mg/mL) normally has a slight yellow color.
Adjunctive therapy for systemic hypertension
- q8-24h
NA
Governing clinical context (3)
- NOTE: Watch units closely when calculating doses. Do not confuse CRI dosages using mg/kg/hour with μg/kg/minute.
- ■ Furosemide may be given with or without food. If your animal vomits or acts sick after receiving this medicine on an empty stomach, try giving the next dose with food or a small treat. If vomiting continues, contact your veterinarian.
- Store furosemide protected from light at room temperature up to 25°C (77°F). Furosemide tablets should be protected from moisture and stored in light-resistant, well-closed containers. Tablets may discolor with exposure to light, and discolored tablets should be discarded. The oral solution should be stored at room temperature and protected from light and freezing; discard opened bottles after 90 days.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Furosemide is a potent, rapidly acting loop diuretic widely used in veterinary medicine to manage fluid overload conditions. It is the cornerstone of therapy for congestive heart failure (CHF) and pulmonary edema across multiple species. By promoting profound diuresis, it rapidly reduces cardiac preload and relieves venous congestion.
Beyond its primary cardiac applications, furosemide is utilized for:
- Oliguric renal failure: To convert oliguria to polyuria and promote urine flow.
- Hypercalcemia: To promote renal calcium excretion (requires prior volume expansion).
- Exercise-Induced Pulmonary Hemorrhage (EIPH): Used prophylactically in racehorses to reduce epistaxis.
- Udder edema: FDA-approved for post-parturient use in cattle.
Because of its potency, furosemide can lead to significant fluid and electrolyte shifts, necessitating careful monitoring of hydration status and serum electrolytes (especially potassium).
Mechanism of action
Furosemide acts primarily on the thick ascending limb of the loop of Henle in the nephron.
- Inhibition of NKCC2: It reversibly binds to and inhibits the Na⁺/K⁺/2Cl⁻ cotransporter on the luminal membrane → prevents the reabsorption of sodium, potassium, and chloride.
- Loss of Medullary Hypertonicity: This disruption abolishes the hypertonic medullary interstitium → impairs the kidney's ability to concentrate urine → results in profound, dose-dependent diuresis.
- Electrolyte Excretion: It significantly increases the renal excretion of water, Na⁺, K⁺, Cl⁻, Ca²⁺, Mg²⁺, H⁺, NH₄⁺, and bicarbonate.
- Hemodynamic Effects: Furosemide induces mild renal venodilation and transiently increases glomerular filtration rate (GFR) via prostaglandin release. This venodilation provides rapid relief in acute cardiogenic pulmonary edema, often before the onset of significant diuresis.
Safety & warnings
Contraindications
- Anuria
- Hypersensitivity to furosemide
- Progressive renal disease if increasing azotemia and oliguria occur during therapy
- Seriously depleted electrolytes
- Severe dehydration
- Severe electrolyte depletion
- Hepatic coma
- Pericardial effusion where cardiac tamponade is confirmed
Adverse effects
- Fluid and electrolyte abnormalities (hyponatremia, hypokalemia, hypocalcemia, hypomagnesemia)
- Prerenal azotemia (secondary to dehydration)
- Ototoxicity (especially in cats with high-dose IV therapy)
- Gastrointestinal distress
- Hematologic effects (anemia, leukopenia)
- Weakness and restlessness
- Hypokalaemia
- Hypochloraemia
- Hypocalcaemia
- Hypomagnesaemia
- Hyponatraemia
- Polyuria/polydipsia (PU/PD)
- Prerenal azotaemia
- Gastrointestinal disturbances
- Leucopenia
- Anaemia
- Electrolyte depletion (hypokalemia, hyponatremia, hypochloremia)
- Polyuria and polydipsia
Precautions
Use with caution in patients with pre-existing electrolyte or water balance abnormalities, impaired hepatic function (may precipitate hepatic coma), and diabetes mellitus. Monitor carefully in patients with conditions leading to fluid loss (e.g., vomiting, diarrhea). Patients hypersensitive to sulfonamides may also be hypersensitive to furosemide. Ensure animals have normal food and water intake to prevent imbalances.
Drug interactions
Increased risks for hypotension, particularly in patients who are volume or sodium depleted secondary to diuretics
Increased risk for ototoxicity
Loop diuretics may increase the risk for nephrotoxicity development; hypokalemia
Increased risk for GI ulceration; hypokalemia
Furosemide-induced hypokalemia may increase the potential for digoxin toxicity
Furosemide may alter insulin requirements
Furosemide may prolong neuromuscular blockade
Furosemide can reduce uricosuric effects
Loop diuretics can reduce the excretion of salicylates
Furosemide may potentiate effects
Pharmacologic effects of theophylline may be enhanced when used with furosemide
Potentiates nephrotoxicity and ototoxicity
Increased risk of hypokalaemia
Increased risk of hypokalaemia
Decreased diuretic efficacy and predisposes to nephrotoxicity, particularly with poor renal perfusion
Inhibits muscle relaxation qualities
Increases the effects of suxamethonium
Increased risk of hypotension and renal impairment; however, concurrent use is standard of care for heart failure with appropriate monitoring.
Increased risk of ototoxicity and nephrotoxicity.
Monitoring
- Serum electrolytes (especially potassium, sodium, calcium, magnesium)
- Blood glucose
- Hydration status
- Blood pressure, if indicated
- Clinical signs of edema, patient weight, if indicated
- Evaluation of ototoxicity, particularly with prolonged therapy or in cats
- Resting respiratory rate (at home by owner)
- Serum electrolytes (Potassium, Sodium, Chloride, Calcium, Magnesium)
- Renal parameters (BUN, Creatinine)
- Clinical signs of ototoxicity (especially in cats)
- Serum electrolytes (especially Potassium, Sodium, Chloride)
- Renal function (BUN, Creatinine)
- Clinical signs of edema/heart failure resolution
Pharmacokinetics
Half-life
Absorption
In dogs, oral bioavailability is approximately 77%. In humans, 60-75% absorbed following oral administration. Diuretic effect takes place within 5 minutes after IV administration and within 1 hour after oral dosing. Peak effects occur ~30 minutes after IV and 1-2 hours after PO.
Distribution
Approximately 95% bound to plasma proteins in both azotemic and normal patients.
Metabolism
Undergoes some hepatic metabolism (glucuronidation).
Elimination
Excreted primarily via the kidneys.
Overdose
The LD50 in dogs after oral administration is >1000 mg/kg; after IV injection >300 mg/kg. Chronic overdosing at 10 mg/kg for six months in dogs led to development of calcification and scarring of the renal parenchyma.
Acute overdosage may cause severe electrolyte and water balance problems, CNS effects (ranging from lethargy to coma and seizures), and cardiovascular collapse.
Treatment:
- Empty the gut after recent oral ingestion using standard protocols.
- Avoid concomitant cathartics as they may exacerbate fluid and electrolyte imbalances.
- Aggressively monitor and treat electrolyte and water balance abnormalities supportively.
- Monitor respiratory, CNS, and cardiovascular status.
Available products
Formulations
- Oral Solution (Syrup)
- Injection
- Oral tablets
- Injectable solution (IV/IM/SC)
- Injectable: 50 mg/ml solution
- Oral: 10 mg tablet
- Oral: 20 mg tablet
- Oral: 40 mg tablet
- Oral: 20 mg/5 ml sugar-free solution
- Oral: 40 mg/5 ml sugar-free solution
- Oral: 50 mg/5 ml sugar-free solution
Veterinary
- Furosemide Tablets: 12.5 mg, & 50 mg; Salix, Disal, generic
- Furosemide Oral Solution (Syrup): 10 mg/mL in 60 mL; generic
- Furosemide for Injection: 50 mg/mL (5%) in 50 mL & 100 mL vials; Disal Injection, Salix Injection, generic
- Dimazon 10 mg, 50 mg tablets
- Dimazon 5% injectable solution
- Frusecare 40 mg tablets
- Frusedale 40 mg tablets
- Libeo 10 mg, 40 mg chewable tablets
Human-labeled
- Furosemide Oral Tablets: 20 mg, 40 mg, & 80 mg; Lasix; generic
- Furosemide Oral Solution: 10 mg/mL in 60 mL & 120 mL; 40 mg/5 mL in 500 mL & UD 5 mL & 10 mL; generic
- Furosemide Injection: 10 mg/mL in 2 mL (20 mg), 4 mL (40 mg) & 10 mL (100 mg) single-dose vials; generic
- Lasix 20 mg, 40 mg tablets
- Lasix oral solution
- Lasix injectable solution
- Frusol
Regulatory status
POM-V classification in the UK.
POM-V, POM.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Tablets should be stored in light-resistant, well-closed containers. Oral solution should be stored at room temperature and protected from light and freezing. Injection should be stored at room temperature. A precipitate may form if the injection is refrigerated, but will resolubilize when warmed without alteration in potency. Unstable at an acid pH, but very stable under alkaline conditions.
Client information
Furosemide (often known by the brand name Lasix) is a potent diuretic or "water pill" used to help your pet's body eliminate excess fluid. It is most commonly prescribed for heart failure or fluid in the lungs.
Important: Because this medication removes water from the body, your pet will urinate much more frequently and in larger amounts. Always ensure your pet has free access to fresh drinking water to prevent severe dehydration.
- Monitoring at Home: If your pet is being treated for heart disease, your veterinarian may ask you to count your pet's resting respiratory rate (breaths per minute while sleeping). This is a crucial tool to ensure the medication dose is correct.
- When to Call the Vet: Contact your veterinarian immediately if you notice signs of dehydration or electrolyte imbalance, such as excessive thirst, extreme lethargy, weakness, restlessness, reduced urination, vomiting, or a very fast heart rate.
- Dosing: Follow your veterinarian's dosing instructions exactly. Do not change the dose without consulting them, as the balance between clearing fluid and causing dehydration is delicate.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.