Difference Between Furosemide 40mg and Torsemide 40mg
Torsemide 40mg delivers approximately 4 times the diuretic effect of furosemide 40mg, making them non-equivalent doses. The standard conversion ratio is 40mg furosemide = 10-20mg torsemide, meaning 40mg of torsemide represents a substantially higher diuretic dose than 40mg of furosemide 1.
Dose Equivalence and Potency
The established conversion ratio is 40mg furosemide = 10-20mg torsemide, with most recent mechanistic data supporting approximately a 4:1 ratio (40mg furosemide = 10mg torsemide) for equivalent natriuresis 1, 2.
In the TRANSFORM-Mechanism trial, when clinicians used a 2:1 conversion (prescribing similar mg doses of each drug), torsemide produced substantially greater natriuresis than furosemide, confirming that equal milligram doses are not equivalent 2.
Therefore, 40mg torsemide delivers roughly 4 times the sodium excretion compared to 40mg furosemide 2.
Pharmacokinetic Differences
Bioavailability
- Furosemide has variable oral bioavailability of approximately 64%, with significant inter-patient variability 3.
- Torsemide has superior and more consistent oral bioavailability of approximately 80%, with less inter-subject variation 4.
Duration of Action
- Both drugs have similar duration of diuresis of 6-8 hours, contrary to common assumptions about torsemide's longer action 3, 4, 2.
- The TRANSFORM-Mechanism trial found that furosemide actually had a longer duration of kidney drug delivery and natriuresis compared to torsemide 2.
Kidney Delivery
- Furosemide achieves higher kidney bioavailability (24.8%) compared to torsemide (17.1%), meaning a greater proportion of furosemide reaches the tubular site of action 2.
Clinical Outcomes and Safety
Efficacy
- The TRANSFORM-HF trial (2859 patients) found no difference in all-cause mortality or hospitalization between torsemide and furosemide strategies over 12 months 5.
- Patient-reported outcomes (Kansas City Cardiomyopathy Questionnaire scores) showed no significant difference between drugs at 1,6, or 12 months 5.
- Quality of life and symptom improvement were equivalent regardless of which loop diuretic was used 5.
Neurohormonal Activation
- Higher doses of torsemide (when using non-equivalent dosing) resulted in significantly greater activation of renin, aldosterone, and norepinephrine compared to furosemide 2.
- This increased neurohormonal activation with higher torsemide doses was associated with mild perturbations in kidney function 2.
Dose-Response Considerations
- Higher loop diuretic doses of either drug were independently associated with worse clinical outcomes, including increased all-cause mortality and hospitalization 6.
- The correlation between higher doses and worse outcomes was consistent regardless of which loop diuretic was used 6.
Guideline-Recommended Dosing
Heart Failure
- ESC guidelines recommend furosemide 40-240mg daily and torsemide 10-20mg daily as usual maintenance doses 7.
- For acute decompensated heart failure, guidelines recommend starting with at least twice the home oral dose intravenously 7.
Cirrhosis with Ascites
- EASL guidelines recommend torsemide for patients exhibiting weak response to furosemide in cirrhotic patients with ascites 7.
- In cirrhosis, torsemide induced greater cumulative 24-hour diuresis than furosemide in randomized trials 7.
Clinical Bottom Line
When prescribing 40mg of either drug, recognize that torsemide 40mg is approximately equivalent to 160mg furosemide in terms of natriuretic effect 1, 2. If switching between these agents:
- To convert from furosemide 40mg to torsemide: use 10mg torsemide 1.
- To convert from torsemide 40mg to furosemide: use 160mg furosemide 1.
Despite theoretical pharmacokinetic advantages of torsemide (better bioavailability), the most recent and highest-quality evidence shows no clinical superiority over furosemide for mortality, hospitalization, or quality of life when equivalent doses are used 2, 5. The key is using appropriate equivalent dosing and monitoring for response, rather than assuming one agent is inherently superior 2, 5, 6.