Converting from Furosemide to Torsemide
Use a conversion ratio of approximately 4:1 (furosemide:torsemide) when switching patients between these loop diuretics, meaning 40 mg of furosemide is roughly equivalent to 10 mg of torsemide. 1
Evidence-Based Conversion Ratio
The most recent mechanistic study (TRANSFORM-Mechanism trial, 2025) definitively established that a 4:1 dose equivalence between furosemide and torsemide results in similar natriuresis and clinical outcomes 1. This contradicts older assumptions of a 2:1 ratio that many clinicians historically used.
- The 2:1 conversion ratio commonly cited in older literature results in excessive diuresis with torsemide, leading to greater neurohormonal activation (increased renin, aldosterone, norepinephrine) and mild kidney dysfunction without improving fluid status 1
- A 4:1 ratio produces equivalent natriuretic effects while avoiding these complications 1
Practical Conversion Examples
Common conversions using the 4:1 ratio:
- Furosemide 40 mg daily → Torsemide 10 mg daily 1
- Furosemide 80 mg daily → Torsemide 20 mg daily 1
- Furosemide 160 mg daily → Torsemide 40 mg daily 1
Administration Considerations
Torsemide offers pharmacokinetic advantages that may improve adherence:
- Bioavailability of torsemide is approximately 80% (compared to furosemide's variable 10-90% absorption), making oral and IV doses therapeutically equivalent 2
- Torsemide can be given without regard to meals, unlike furosemide whose absorption is reduced by food 2
- Once-daily dosing is standard for torsemide due to its 3.5-hour half-life and 6-8 hour duration of action 2
For heart failure patients on chronic diuretic therapy, the European Society of Cardiology recommends that when converting, the initial dose should be at least equivalent to their previous oral dose using appropriate conversion ratios 3
Critical Monitoring After Conversion
Monitor these parameters within the first week after switching:
- Urine output (target 0.8-1.5 mL/kg/hour) 4
- Daily weights (target 0.5-1.0 kg loss per day if volume overloaded) 5
- Serum electrolytes, particularly potassium and sodium 5, 3
- Renal function (serum creatinine, BUN) 4
- Blood pressure for hypotension 3
Common Pitfalls to Avoid
Do not use the 2:1 conversion ratio that appears in older literature and some clinician habits. The TRANSFORM-Mechanism trial demonstrated this results in approximately double the intended natriuresis, causing unnecessary neurohormonal activation and kidney dysfunction without improving plasma volume or body weight 1.
Avoid switching in patients with:
- Systolic blood pressure <90 mmHg 6
- Severe hyponatremia (sodium <120-125 mEq/L) 5
- Marked hypovolemia or dehydration 6
- Anuria or progressive acute kidney injury 5
Special Populations
In patients with renal impairment recovering from acute kidney injury, torsemide may demonstrate better dose-dependent diuretic effects compared to furosemide, though both are effective 4. However, the 4:1 conversion ratio should still be maintained to avoid excessive diuresis.
For patients with hepatic disease and ascites, while specific conversion data is limited, the European Association for the Study of the Liver recommends maintaining combination therapy with spironolactone when using loop diuretics, regardless of which agent is chosen 5.