Furosemide to Torsemide Conversion
When converting from furosemide to torsemide, the appropriate dose ratio is 4:1, meaning 40 mg of furosemide is equivalent to 10 mg of torsemide. 1, 2
Conversion Guidelines
According to the American College of Cardiology/American Heart Association guidelines, the standard conversion ratio between these loop diuretics is:
- 40 mg furosemide = 10 mg torsemide
- 80 mg furosemide = 20 mg torsemide
- 120 mg furosemide = 30 mg torsemide
- 160 mg furosemide = 40 mg torsemide
This 4:1 ratio is supported by clinical evidence and is reflected in the dosing tables provided in multiple heart failure guidelines 1.
Pharmacological Differences
Torsemide offers several advantages over furosemide:
- Longer duration of action (12-16 hours vs. 6-8 hours for furosemide) 1
- Better oral bioavailability (approximately 80% vs. variable 10-100% for furosemide) 3, 4
- Once-daily dosing capability due to extended half-life 1, 3
However, recent mechanistic studies have questioned some of the presumed pharmacokinetic advantages of torsemide. The TRANSFORM-Mechanism trial found that:
- Kidney bioavailability was actually lower with torsemide compared to furosemide
- Furosemide demonstrated a longer duration of kidney drug delivery and natriuresis 2
Clinical Considerations
When converting between these medications, consider:
- Patient's current response: If the patient has been stable on furosemide, maintain the equivalent diuretic effect with torsemide
- Renal function: No specific dose adjustments are needed for conversion based on renal function, but monitor closely after conversion
- Monitoring needs: Check electrolytes, especially potassium, after conversion
Practical Conversion Examples
| 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 |
Common Pitfalls to Avoid
- Underdosing: Using a 1:1 conversion ratio will result in significant underdosing of torsemide
- Overestimating potency: While torsemide is more potent on a mg-per-mg basis, the 4:1 ratio accounts for this difference
- Ignoring monitoring: After conversion, patients should be monitored for changes in fluid status, electrolytes, and renal function
The 4:1 conversion ratio is well-established in clinical practice and supported by multiple guidelines, making it the most reliable approach when switching patients from furosemide to torsemide 1.