Converting from Furosemide 80 mg to Torsemide
When converting a patient from furosemide 80 mg oral daily to torsemide, start with torsemide 20 mg oral once daily.
Conversion Ratio and Dosing
The established equivalence ratio is 40 mg furosemide = 10 mg torsemide, meaning your patient on 80 mg furosemide requires 20 mg torsemide 1. This 4:1 conversion ratio is consistently supported across guidelines and FDA labeling 1, 2.
The FDA-approved initial dose for heart failure is 10–20 mg torsemide once daily, making 20 mg an appropriate starting point for your patient 2. For chronic renal failure, the FDA recommends starting at 20 mg once daily 2.
Key Pharmacokinetic Advantages
Torsemide offers several practical benefits over furosemide:
- Torsemide has approximately 80–100% bioavailability compared to furosemide's 26–65%, eliminating concerns about variable absorption 3, 4, 5.
- The longer duration of action (12–16 hours) allows reliable once-daily dosing, whereas furosemide's 6–8 hour duration often necessitates split dosing 1, 3.
- Oral and IV torsemide doses are therapeutically equivalent due to high bioavailability, simplifying transitions between routes 3.
Critical Monitoring After Conversion
Within 1–2 weeks of switching, check:
- Serum creatinine, sodium, and potassium to detect electrolyte shifts or changes in renal function 1.
- Daily weights targeting 0.5–1.0 kg loss per day if actively diuresing 1.
- Signs of volume depletion (hypotension, tachycardia, decreased skin turgor) or inadequate diuresis (persistent edema, weight gain) 1.
Titration Strategy
If 20 mg torsemide provides inadequate diuresis after several days:
- Increase by approximately doubling the dose (to 40 mg, then 80 mg if needed) until desired response is achieved 2.
- The maximum studied dose is 200 mg daily for heart failure and chronic renal failure 2.
- For hepatic cirrhosis, combine with an aldosterone antagonist and do not exceed 40 mg daily 2.
Important Caveats
Recent mechanistic data challenge traditional assumptions about torsemide superiority 6. The TRANSFORM-Mechanism trial found that:
- Torsemide had lower kidney bioavailability (17% vs 25%) and shorter duration of tubular drug delivery compared to furosemide 6.
- When clinicians used the traditional 2:1 conversion (as you're doing with 80 mg furosemide → 40 mg torsemide would be), torsemide produced excessive natriuresis with greater neurohormonal activation and mild kidney dysfunction 6.
- A 4:1 ratio (80 mg furosemide = 20 mg torsemide) resulted in similar natriuresis without these adverse effects 6.
This recent evidence supports starting with 20 mg torsemide rather than 40 mg when converting from 80 mg furosemide 6.
Common Pitfalls to Avoid
- Do not combine torsemide with NSAIDs, which block diuretic effects and worsen renal function 1.
- Assess dietary sodium intake—patients consuming high sodium may appear resistant to the new regimen 1.
- If diuretic resistance develops, add a thiazide rather than exceeding maximum torsemide doses 1.
- Do not assume torsemide will automatically improve outcomes—the TRANSFORM trial showed no difference in clinical outcomes between torsemide and furosemide 6.