What is the equivalency ratio when converting from furosemide (Lasix) to torsemide?

Torsemide to Furosemide Equivalency

The most commonly used conversion ratio is 1:2 (torsemide:furosemide), meaning 10 mg of torsemide is equivalent to 20 mg of furosemide, though recent mechanistic data suggests a 1:4 ratio (10 mg torsemide to 40 mg furosemide) produces similar natriuresis. 1, 2

Standard Conversion Ratios

Traditional Clinical Practice

• The 2013 ACC/AHA guidelines list torsemide 10-20 mg once daily as equivalent to furosemide 20-40 mg once or twice daily, supporting an approximate 1:2 conversion ratio. 1
• The 2016 ESC guidelines recommend 10-20 mg IV torsemide as an alternative to 20-40 mg IV furosemide, again suggesting a 1:2 ratio. 1
• For cirrhosis patients, Korean guidelines explicitly state torsemide is used at one-quarter the dose of furosemide (1:4 ratio). 1

Recent Mechanistic Evidence

• The 2025 TRANSFORM-Mechanism trial found that a 4:1 dose equivalence (40 mg furosemide to 10 mg torsemide) resulted in similar natriuresis, challenging the traditional 2:1 conversion. 2
• When clinicians used the traditional 2:1 ratio in this trial, torsemide produced substantially greater natriuresis but also caused greater neurohormonal activation (increased renin, aldosterone, norepinephrine) and kidney dysfunction without improving plasma volume or body weight. 2

Pharmacokinetic Differences

Bioavailability

• Torsemide has approximately 80% bioavailability with minimal first-pass metabolism, while furosemide has variable bioavailability (10-100%, typically 40-50%). 3
• This higher and more predictable bioavailability means oral and IV torsemide doses are therapeutically equivalent, unlike furosemide where IV dosing is often preferred. 3

Duration of Action

• Torsemide has a longer half-life (3.5 hours) and duration of action (12-16 hours) compared to furosemide (6-8 hours). 1, 3
• However, the 2025 TRANSFORM-Mechanism trial contradicted this, showing furosemide actually had a longer duration of kidney drug delivery and natriuresis than torsemide. 2

Clinical Outcomes Data

Effectiveness

• The 2023 TRANSFORM-HF trial (2,859 patients) found no difference between torsemide and furosemide in all-cause mortality, all-cause hospitalization, or quality of life over 12 months. 4
• A 2025 Medicare study of 328,640 older adults showed torsemide had a slightly lower risk of the composite outcome (HR 0.97) and urgent IV diuretic visits (HR 0.88) compared to furosemide. 5

Safety Considerations

• Torsemide was associated with increased acute kidney injury risk (HR 1.12) compared to furosemide in the 2025 Medicare study. 5
• The TRANSFORM-Mechanism trial showed higher torsemide doses (using 2:1 conversion) caused perturbations in kidney function and significant neurohormonal activation. 2

Practical Conversion Recommendations

For Stable Outpatients

• Use a 1:2 ratio (10 mg torsemide = 20 mg furosemide) as the starting point, as this is supported by major guidelines and reflects real-world prescribing patterns. 1
• Monitor closely for over-diuresis given the mechanistic data suggesting this may produce excessive natriuresis. 2

For Hospitalized Patients

• Start with 10-20 mg IV torsemide as equivalent to 20-40 mg IV furosemide (1:2 ratio). 1
• For patients on chronic furosemide therapy, the initial IV torsemide dose should be at least half the oral furosemide dose. 1

Monitoring After Conversion

• Check spot urine sodium 2 hours after the first dose; values <50-70 mEq/L indicate insufficient diuretic response. 1
• Monitor hourly urine output (target >100-150 mL/hour in first 6 hours), daily weights, and renal function/electrolytes every 12-24 hours. 6
• Watch for signs of over-diuresis including worsening renal function, hypotension, or excessive neurohormonal activation. 2

Important Caveats

• The optimal conversion ratio remains uncertain, with guideline-based 1:2 ratios potentially causing over-diuresis based on recent mechanistic data suggesting 1:4 may be more appropriate. 1, 2
• Torsemide's longer duration of action may reduce dosing frequency but does not necessarily improve clinical outcomes. 3, 4
• In patients with advanced kidney disease (CKD stage 4-5), both diuretics show reduced efficacy, and higher doses may be needed regardless of the agent chosen. 1