Torasemide — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	PO	0.1-0.2 mg/kg	q24h	Duration: Chronic as needed Notes: May be increased to 0.3 mg/kg q24h if needed. For acute heart failure, IV dose of 0.1-0.2 mg/kg can be used.
Cat	PO	0.1-0.2 mg/kg	q24h	Duration: Chronic as needed Notes: Use cautiously in cats with renal disease. Start at low end of dose range.
Horse	IV	0.1-0.2 mg/kg	Once, 4 hours before exercise	Duration: Single dose for EIPH Notes: For EIPH, administer 4 hours before exercise. Oral dosing is less reliable.
Cattle	IV	0.05-0.1 mg/kg	q12-24h	Duration: As needed Notes: Not approved; use with caution. Monitor electrolytes and hydration.
Small Ruminants	IV	0.05-0.1 mg/kg	q12-24h	Duration: As needed Notes: Not approved; use with caution. Monitor electrolytes and hydration.
Rabbit	PO	0.1-0.2 mg/kg	q24h	Duration: As needed Notes: Limited data; use with caution.
Bird/Poultry	IM	0.1-0.2 mg/kg	q12-24h	Duration: As needed Notes: Limited data; use with caution.
Exotic/Other	PO/IV	0.1-0.2 mg/kg	q24h	Duration: As needed Notes: Dose based on extrapolation; use with caution.

Clinical Indications & Species Uses

General Indications

Diuresis in conditions with fluid overload
Congestive heart failure
Pulmonary edema
Ascites
Hypertension (adjunctive)

Dog (Canine)

Congestive heart failure (pulmonary edema, pleural effusion)
Hypertension (adjunctive therapy)
Ascites due to right-sided heart failure
Oliguric acute kidney injury (off-label)

Cat (Feline)

Congestive heart failure (pulmonary edema, pleural effusion)
Hypertension (adjunctive therapy)
Ascites due to right-sided heart failure

Horse (Equine)

Exercise-induced pulmonary hemorrhage (EIPH) (off-label)
Pulmonary edema
Congestive heart failure (rare)

Pharmacology & Mechanism of Action

Drug Class: Loop Diuretic | Pharmacological Group: Sulfonylurea derivative

Mechanism of Action: Torasemide is a loop diuretic that inhibits the Na+-K+-2Cl- cotransporter in the thick ascending limb of the loop of Henle. This inhibition reduces sodium and chloride reabsorption, leading to increased excretion of water, sodium, chloride, and other electrolytes (potassium, calcium, magnesium). It also has a mild aldosterone antagonist effect, which may contribute to its potassium-sparing properties compared to other loop diuretics. The diuretic effect is dose-dependent and occurs rapidly after administration.

Pharmacodynamics: Torasemide produces a potent diuresis and natriuresis, with a rapid onset of action. It is more potent on a milligram basis than furosemide (approximately 10-20 times more potent in dogs). It also causes venodilation, reducing preload and cardiac filling pressures, which is beneficial in congestive heart failure. The aldosterone antagonism may reduce myocardial fibrosis and have additional benefits in heart failure. The diuretic effect peaks within 1-2 hours after oral administration and lasts for 6-12 hours depending on the species.

⚡ Pharmacokinetics Summary

Absorption: Torasemide is well absorbed after oral administration in dogs and cats, with bioavailability reported to be >90% in dogs. Food may slightly delay absorption but does not significantly affect the extent. In horses, oral bioavailability is lower (approximately 50-60%).

Distribution: Torasemide is widely distributed in the body. It is highly bound to plasma proteins (approximately 97-99% in dogs and humans). The volume of distribution is relatively small, consistent with its high protein binding. It crosses the placenta and is excreted in milk in small amounts.

Metabolism: Torasemide is extensively metabolized in the liver, primarily by cytochrome P450 enzymes (CYP2C9 in humans). The major metabolites are the carboxylic acid derivative (M1) and the hydroxylated metabolite (M5), which have minimal diuretic activity. In dogs, metabolism is similar, with the parent drug and metabolites excreted in urine and bile.

Excretion: Torasemide is eliminated primarily via the kidneys, with approximately 20-30% of the dose excreted unchanged in urine in dogs. The remainder is excreted as metabolites in urine and feces. In horses, renal excretion of the parent drug is higher. The elimination half-life is longer than furosemide, allowing for less frequent dosing.

Half-Life: Dogs: approximately 3-5 hours; Cats: approximately 4-6 hours; Horses: approximately 2-3 hours; Humans: 3-4 hours.

Bioavailability: Oral: >90% in dogs; approximately 50-60% in horses; not well documented in cats but likely high.

Protein Binding: Approximately 97-99% bound to plasma proteins in dogs and humans.

Available Formulations & Strengths

Oral Tablet 5 mg, 10 mg, 20 mg, 100 mg (PO)

Injectable Solution 10 mg/mL (2 mL, 5 mL vials) (IV, IM)

Contraindications & Clinical Warnings

Contraindications:

Hypersensitivity to torasemide or sulfonylureas
Anuria
Severe hepatic failure (may precipitate hepatic encephalopathy)
Severe electrolyte depletion (hypokalemia, hyponatremia)
Hypovolemia or dehydration
Concurrent use with aminoglycosides (increased ototoxicity risk)

Warnings & Clinical Precautions:

Use with caution in patients with renal impairment; monitor renal function and electrolytes.
May cause dehydration and electrolyte imbalances; ensure adequate hydration.
Monitor for signs of hypokalemia, hyponatremia, hypochloremia, and metabolic alkalosis.
In animals with hepatic disease, use with caution as it may precipitate hepatic encephalopathy.
May cause ototoxicity, especially with rapid IV administration or high doses.
Use with caution in animals with diabetes mellitus; may affect glucose tolerance.
In food animals, observe withdrawal times; not approved for use in food animals in many countries.
In horses, use with caution in animals with a history of renal disease or electrolyte imbalances.

Adverse Effects & Reactions

Common:

Increased urination
Electrolyte imbalances (hypokalemia, hyponatremia, hypochloremia)
Dehydration
Gastrointestinal upset (vomiting, diarrhea)
Increased thirst

Serious / Severe:

Ototoxicity (especially with rapid IV administration)
Renal failure (especially with concurrent nephrotoxic drugs)
Cardiac arrhythmias (due to electrolyte imbalances)
Hepatic encephalopathy in animals with liver disease
Severe hypotension

Rare:

Allergic reactions (skin rash, anaphylaxis)
Bone marrow suppression (thrombocytopenia, leukopenia)
Hyperglycemia
Hyperuricemia

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; monitor blood pressure	Moderate
Lithium	Increased lithium levels and toxicity	High
Anticoagulants (e.g., warfarin)	Potential increased anticoagulant effect (protein binding displacement)	Moderate

Overdose & Toxicity Management

Signs of Toxicity:

Severe dehydration
Electrolyte depletion (hypokalemia, hyponatremia, hypochloremia)
Hypotension
Cardiac arrhythmias
Weakness, lethargy
Collapse
Renal failure

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Discontinue the drug. Correct fluid and electrolyte imbalances with appropriate IV fluids and electrolyte supplementation. Monitor cardiac function and blood pressure. In severe cases, consider hemodialysis or peritoneal dialysis to remove the drug. There is no specific antidote.

Food Animal Withdrawal Times

🥩 Meat: 7 days🥛 Milk: 3 days

Withdrawal times are not established for torasemide in food animals in many countries. Use in food animals is off-label; consult regulatory guidelines. The values provided are estimates based on pharmacokinetic data and should be used with caution.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (20-25°C, 68-77°F). Protect from light and moisture.

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Keep in tightly closed container. Do not freeze injectable solution.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; approved for human use in some countries. In the US, it is available as a human drug (Demadex) and can be used extra-label in animals.

Extra-Label (Off-Label) Use: In the US, torasemide is not FDA-approved for veterinary use, but it can be used under the Animal Medicinal Drug Use Clarification Act (AMDUCA) for extra-label use in animals. For food animals, a valid veterinarian-client-patient relationship is required, and withdrawal times must be observed. In the EU, torasemide is not approved for food animals.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Torasemide is a potent loop diuretic that is increasingly used in veterinary medicine, particularly for congestive heart failure in dogs and cats. It offers advantages over furosemide, including higher oral bioavailability, longer duration of action, and less frequent dosing. It may be more effective in animals that are refractory to furosemide. However, it is not approved for veterinary use in many countries, so extra-label use is common. Close monitoring of renal function, electrolytes, and hydration is essential, especially during initial therapy or dose adjustments. In horses, torasemide is used off-label for EIPH, but its efficacy is debated. Always consider potential drug interactions and contraindications before prescribing. For food animals, strict adherence to withdrawal times is necessary to prevent drug residues.

References & Literature

📚 Plumb's Veterinary Drug Handbook
📚 Papich Veterinary Pharmacology and Therapeutics
📚 Compendium of Veterinary Products (CVP)