What is the conversion dose from furosemide (Lasix) to torsemide?

Furosemide to Torsemide Conversion

The conversion ratio from furosemide to torsemide is approximately 4:1 (40 mg furosemide = 10 mg torsemide), based on the most recent mechanistic evidence demonstrating equivalent natriuresis at this ratio. 1

Evidence-Based Conversion Ratio

The TRANSFORM-Mechanism trial (2025) provides the highest quality evidence for conversion dosing:

• A 4:1 conversion ratio (40 mg furosemide to 10 mg torsemide) produces equivalent natriuresis and clinical outcomes. 1
• The commonly used 2:1 conversion ratio results in substantially greater natriuresis with torsemide, leading to neurohormonal activation, kidney dysfunction, and no improvement in fluid status despite higher diuretic effect. 1
• Torsemide demonstrated no meaningful pharmacokinetic or pharmacodynamic advantages over furosemide when dosed appropriately. 1

Guideline-Supported Dosing Ranges

The 2016 ESC Heart Failure Guidelines provide standard dosing ranges that align with the 4:1 conversion:

• Furosemide usual daily dose: 40-240 mg 2
• Torsemide usual daily dose: 10-20 mg 2
• Initial furosemide dose: 20-40 mg corresponds to initial torsemide dose: 5-10 mg 2

Practical Conversion Algorithm

When converting from furosemide to torsemide:

1. Calculate the 4:1 ratio: Divide the total daily furosemide dose by 4 to determine the equivalent torsemide dose. 1
2. Round to available tablet strengths: Torsemide is typically available in 5 mg, 10 mg, 20 mg, and 100 mg tablets. 3, 4
3. Monitor closely for the first 5-7 days: Check electrolytes (sodium, potassium), renal function (creatinine), blood pressure, and daily weights. 2
4. Assess for signs of over-diuresis: Watch for hypotension (SBP <90 mmHg), hypovolemia, worsening renal function, or severe hyponatremia. 2

Common Conversion Examples

• Furosemide 40 mg daily → Torsemide 10 mg daily 1
• Furosemide 80 mg daily → Torsemide 20 mg daily 1
• Furosemide 120 mg daily → Torsemide 30 mg daily (round to 20-40 mg based on clinical response) 1
• Furosemide 160 mg daily → Torsemide 40 mg daily 1

Critical Pitfalls to Avoid

• Do not use the 2:1 conversion ratio commonly cited in older literature, as this results in excessive diuresis, neurohormonal activation, and kidney dysfunction without improving fluid status. 1
• Avoid conversion in patients with SBP <90 mmHg, severe hyponatremia (sodium <120-125 mmol/L), or marked hypovolemia until these conditions are corrected. 2
• Do not assume torsemide is "more potent" based on older pharmacokinetic studies—the TRANSFORM-Mechanism trial demonstrates that kidney bioavailability is actually lower with torsemide (17.1% vs 24.8% for furosemide). 1

Pharmacokinetic Considerations

While older studies suggested advantages for torsemide, recent evidence clarifies:

• Torsemide has lower kidney bioavailability (17.1%) compared to furosemide (24.8%), meaning less drug reaches the tubular site of action. 1
• Furosemide has longer duration of kidney drug delivery and natriuresis compared to torsemide. 1
• Torsemide bioavailability is 80% versus furosemide's variable absorption, but this does not translate to clinical superiority. 5, 3, 4, 1
• Both drugs can be given once daily for chronic heart failure management. 2

Monitoring After Conversion

Within 5-7 days of conversion, check:

• Electrolytes: Sodium (target >135 mmol/L), potassium (target 3.5-5.0 mmol/L) 2
• Renal function: Creatinine should remain stable; stop if increase >0.3 mg/dL 2
• Blood pressure: Maintain SBP ≥90-100 mmHg 2
• Daily weights: Target 0.5-1.0 kg loss per day maximum 2
• Urine output: Should remain >0.5 mL/kg/h 2