Torsemide to Furosemide Equivalency
When converting from furosemide (Lasix) to torsemide, use a standard conversion ratio of 4:1, meaning 40 mg of furosemide is equivalent to 10 mg of torsemide. 1
Conversion Table
| Furosemide Dose (mg) | Torsemide Dose (mg) |
|---|---|
| 20 mg | 5 mg |
| 40 mg | 10 mg |
| 80 mg | 20 mg |
| 120 mg | 30 mg |
| 160 mg | 40 mg |
Pharmacological Differences
Torsemide offers several advantages over furosemide:
- Bioavailability: Torsemide has higher oral bioavailability (>80%) compared to furosemide's variable bioavailability (10-100%) 1, 2
- Duration of action: Torsemide has a longer half-life (3-4 hours) compared to furosemide (6-8 hours for effect but shorter half-life) 1, 3
- Elimination: Torsemide is eliminated both hepatically (80%) and renally (20%), making it potentially advantageous in patients with renal dysfunction 2
Clinical Considerations
When switching between these medications:
- The European Society of Cardiology guidelines note that torsemide may improve natriuresis in patients with suboptimal response to furosemide 4
- Monitor closely after conversion:
- Urine output
- Electrolytes (particularly potassium)
- Renal function
- Symptoms of volume depletion
Evidence from Clinical Studies
Recent evidence from the TRANSFORM-Mechanism trial found that a dose equivalence of approximately 4:1 (furosemide:torsemide) resulted in similar natriuresis 5. This supports the standard conversion ratio recommended in clinical practice guidelines.
An earlier study found that 20 mg of torsemide was more effective than 40 mg of furosemide in reducing body weight and improving symptoms of congestive heart failure 6, suggesting the 4:1 ratio is clinically appropriate.
Cautions
- Despite theoretical advantages, recent evidence suggests no meaningful pharmacokinetic/pharmacodynamic advantages for torsemide versus furosemide 5
- Higher diuretic doses with torsemide may lead to greater neurohormonal activation and kidney dysfunction 5
- Both medications can cause similar adverse effects including electrolyte abnormalities, particularly hypokalemia
Remember to adjust dosing based on clinical response and monitor for adverse effects regardless of which loop diuretic is used.