Furosemide

Loop Diuretic Sulfonamide derivative

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 2-5 mg/kg q8-12h Duration: Variable; adjust to effect
Notes: For chronic heart failure, start at lower end and titrate to lowest effective dose.
Dog IV/IM 1-2 mg/kg q1-2h as needed Duration: Acute management
Notes: IV administration for emergencies; monitor hydration and electrolytes.
Cat PO 1-2 mg/kg q12-24h Duration: Variable
Notes: Cats are more sensitive; use lower doses.
Cat IV/IM 0.5-1 mg/kg q1-2h as needed Duration: Acute management
Notes: Use with caution in cats with renal disease.
Horse IV 0.5-1 mg/kg q12-24h Duration: Variable
Notes: For EIPH prophylaxis, administer 4 hours before exercise.
Horse PO 1-2 mg/kg q24h Duration: Variable
Notes: Oral bioavailability is lower; adjust dose.
Cattle IV/IM 0.5-1 mg/kg q12-24h Duration: Variable
Notes: For udder edema, use 0.5-1 mg/kg IV or IM.
Cattle PO 1-2 mg/kg q24h Duration: Variable
Notes: Oral dose may be higher due to lower bioavailability.
Small Ruminants IV/IM 1-2 mg/kg q12-24h Duration: Variable
Notes: Use with caution; monitor electrolytes.
Rabbit PO/SC/IM 1-5 mg/kg q12-24h Duration: Variable
Notes: Doses up to 5 mg/kg may be used; monitor renal function.
Birds/Poultry IM/PO 0.1-0.5 mg/kg q12-24h Duration: Variable
Notes: Limited data; use with caution.

Clinical Indications & Species Uses

General Indications
  • Diuresis
  • Edema of various etiologies
  • Hypertension
  • Hypercalcemia
Dog (Canine)
  • Pulmonary edema (cardiogenic and non-cardiogenic)
  • Congestive heart failure (acute and chronic)
  • Ascites
  • Pleural effusion
  • Hypertension
  • Acute renal failure (oliguric)
  • Hypercalcemia
  • Cerebral edema
Cat (Feline)
  • Pulmonary edema
  • Congestive heart failure
  • Pleural effusion
  • Ascites
  • Hypertension
  • Acute renal failure (oliguric)
  • Hypercalcemia
Horse (Equine)
  • Pulmonary edema
  • Exercise-induced pulmonary hemorrhage (EIPH) prophylaxis
  • Congestive heart failure
  • Edema (e.g., ventral edema)
  • Hypercalcemia
Cattle (Bovine)
  • Pulmonary edema
  • Congestive heart failure
  • Udder edema
  • Ascites
  • Hypercalcemia
Small Ruminants (Sheep / Goat)
  • Pulmonary edema
  • Congestive heart failure
  • Edema
  • Ascites
Rabbit & Small Mammals
  • Pulmonary edema
  • Congestive heart failure
  • Ascites
  • Edema
Avian & Poultry
  • Pulmonary edema
  • Ascites
  • Edema
Exotic & Other Species
  • Edema
  • Ascites
  • Congestive heart failure (in some species)

Pharmacology & Mechanism of Action

Drug Class: Loop Diuretic | Pharmacological Group: Sulfonamide derivative

Mechanism of Action: Furosemide inhibits the Na+-K+-2Cl- symporter (NKCC2) in the thick ascending limb of the loop of Henle, reducing reabsorption of sodium and chloride, leading to increased excretion of water, sodium, chloride, potassium, calcium, and magnesium. It also stimulates renal prostaglandin synthesis, causing renal vasodilation and increased renal blood flow.

Pharmacodynamics: Furosemide produces a rapid and profound diuresis, with onset of action within minutes after IV administration and within 30-60 minutes after oral administration. It reduces extracellular fluid volume, decreases preload and afterload, and lowers blood pressure. It also reduces pulmonary capillary wedge pressure and pulmonary edema. Chronic use can lead to electrolyte imbalances and activation of the renin-angiotensin-aldosterone system.

⚑ Pharmacokinetics Summary

Absorption: Rapidly absorbed from the gastrointestinal tract in most species; oral bioavailability varies (dog: ~77%, horse: ~48%, cattle: ~50%).
Distribution: Widely distributed; crosses the placenta; small amounts enter milk. Volume of distribution is approximately 0.1-0.2 L/kg in dogs and cats.
Metabolism: Partially metabolized in the liver (glucuronidation) in some species; a significant fraction is excreted unchanged by the kidneys.
Excretion: Excreted primarily via the kidneys (glomerular filtration and tubular secretion); some biliary excretion in dogs. Renal excretion is rapid, with most eliminated within 24 hours.
Half-Life: Dog: 1-2 hours; Cat: 1-2 hours; Horse: 1-2 hours; Cattle: 1-2 hours; Rabbit: 1-2 hours.
Bioavailability: Oral bioavailability: Dog ~77%, Cat ~70%, Horse ~48%, Cattle ~50%.
Protein Binding: High protein binding (approximately 90-95% in dogs and cats).

Available Formulations & Strengths

Oral Tablet 12.5 mg, 20 mg, 40 mg, 50 mg, 80 mg (PO)
Oral Solution 10 mg/mL (PO)
Injectable Solution 10 mg/mL, 50 mg/mL (IV/IM)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to furosemide or sulfonamides
  • Anuria or severe renal failure with no urine output
  • Severe electrolyte depletion (e.g., hypokalemia, hyponatremia)
  • Hypovolemia or dehydration
  • Hepatic coma or pre-coma
  • Concurrent use of other ototoxic drugs (e.g., aminoglycosides) may increase risk of ototoxicity
Warnings & Clinical Precautions:
  • Use with caution in animals with hepatic cirrhosis, diabetes mellitus, or gout (hyperuricemia).
  • Monitor renal function, electrolytes (especially potassium, sodium, chloride), and hydration status during therapy.
  • May cause dehydration and electrolyte imbalances; ensure adequate water intake.
  • In animals with pre-existing renal disease, use lower doses and monitor closely.
  • May cause ototoxicity, especially with rapid IV administration or high doses.
  • In horses, use with caution in animals with electrolyte imbalances; may affect performance.
  • In food animals, observe withdrawal times.
  • Use in pregnant animals only if clearly needed; furosemide crosses the placenta.

Adverse Effects & Reactions

Common:

  • Increased urination
  • Electrolyte imbalances (hypokalemia, hyponatremia, hypochloremia)
  • Dehydration
  • Gastrointestinal upset (vomiting, diarrhea)
  • Weakness
  • Lethargy

Serious / Severe:

  • Ototoxicity (especially with rapid IV administration)
  • Renal dysfunction or failure
  • Cardiac arrhythmias (due to electrolyte disturbances)
  • Hypotension
  • Pancreatitis (rare)
  • Blood dyscrasias (rare)

Rare:

  • Allergic reactions (skin rash, anaphylaxis)
  • Bone marrow suppression
  • Hyperglycemia
  • Hyperuricemia
  • Calcium oxalate urolithiasis

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Aminoglycosides (e.g., gentamicin) Increased risk of ototoxicity and nephrotoxicity High
Corticosteroids Increased risk of hypokalemia Moderate
Digoxin Increased risk of digoxin toxicity due to hypokalemia High
NSAIDs (e.g., flunixin, carprofen) Reduced diuretic effect and increased risk of nephrotoxicity Moderate
ACE inhibitors (e.g., enalapril) Additive hypotensive effect; risk of hyperkalemia if potassium-sparing diuretics are used Moderate
Lithium Increased lithium levels and toxicity High
Suxamethonium (succinylcholine) Prolonged neuromuscular blockade Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe dehydration
  • Hypotension
  • Electrolyte depletion (hypokalemia, hyponatremia, hypochloremia)
  • Metabolic alkalosis
  • Cardiac arrhythmias
  • Weakness, collapse
  • Renal failure
  • Ototoxicity (deafness)

Emergency Treatment Protocol: Discontinue the drug. Provide supportive care: fluid and electrolyte replacement (IV fluids with appropriate electrolytes), monitoring of vital signs and ECG. In severe cases, consider hemodialysis or peritoneal dialysis. There is no specific antidote.

Food Animal Withdrawal Times

πŸ₯© Meat: 3 daysπŸ₯› Milk: 2 days

Withdrawal times may vary by country and formulation; consult local regulations. In the US, furosemide is not approved for food animals, but extra-label use requires extended withdrawal periods (e.g., 30 days for meat, 7 days for milk) as per FARAD guidelines.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25Β°C, excursions permitted to 15-30Β°C).

Light Sensitivity: Light-sensitive β€” protect from direct exposure.

Handling & Special Conditions: Protect from light and moisture. Keep in a tightly closed container.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for veterinary use in dogs, cats, and horses (e.g., Lasix).

Extra-Label (Off-Label) Use: In the US, furosemide is approved for use in dogs, cats, and horses. Extra-label use in food animals is permitted under AMDUCA with veterinary oversight, but requires extended withdrawal times. In the EU, similar regulations apply.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Furosemide is a potent loop diuretic commonly used in veterinary medicine for the management of edema, particularly pulmonary edema and congestive heart failure. It is essential to monitor hydration status, electrolytes, and renal function during therapy. Dosage should be individualized, starting with the lowest effective dose and titrating to effect. In emergency situations, IV administration provides rapid onset. For chronic therapy, oral administration is convenient. In horses, furosemide is used for EIPH prophylaxis, but it is prohibited in some competitions. In food animals, extra-label use requires careful attention to withdrawal times to ensure food safety. Always consider potential drug interactions and contraindications before use.

References & Literature

  • πŸ“š Plumb's Veterinary Drug Handbook
  • πŸ“š Papich Veterinary Pharmacology and Therapeutics
  • πŸ“š Compendium of Veterinary Products (CVP)