In a patient with an estimated glomerular filtration rate of approximately 44 mL/min/1.73 m², how should I choose between furosemide (Lasix) and torsemide?

How to Choose Between Furosemide (Lasix) and Torsemide

In a patient with eGFR ~44 mL/min/1.73 m² (CKD Stage 3b), either furosemide or torsemide can be used with equivalent clinical outcomes—choose based on practical considerations rather than expecting superior efficacy from either agent.

The Evidence-Based Reality

The 2025 TRANSFORM-Mechanism trial 1—the highest quality mechanistic study—definitively showed that torsemide offers no meaningful pharmacokinetic or pharmacodynamic advantages over furosemide. Despite theoretical benefits of higher bioavailability, torsemide actually had:

• Lower kidney bioavailability (17.1% vs 24.8%, p<0.001)
• Shorter duration of kidney drug delivery and natriuresis compared to furosemide
• Greater neurohormonal activation (increased renin, aldosterone, norepinephrine) when dosed equivalently
• No improvement in plasma volume or body weight versus furosemide

The 2026 meta-analysis 2 of 10 RCTs with 4,011 patients confirmed no significant differences in:

• All-cause mortality (OR 0.99, p=0.66)
• Heart failure hospitalization (OR 0.96, p=0.38)
• Weight change between agents

Practical Decision Algorithm

Start with Furosemide if:

• Cost is a consideration (furosemide is substantially cheaper)
• Patient is treatment-naïve to loop diuretics
• You want flexibility in dosing (wider dose range, more clinical experience)
• The 2022 ACC/AHA/HFSA guidelines 3 list furosemide as the most commonly used loop diuretic

Consider Torsemide if:

• Adherence is problematic (once-daily dosing vs twice-daily furosemide due to 12-16 hour duration of action) 3
• Patient has documented poor absorption with furosemide (though this theoretical advantage was not confirmed in TRANSFORM-Mechanism 1)
• Patient is already stable on torsemide—no reason to switch

Dosing Equivalence in Your CKD Stage 3b Patient

Use a 4:1 furosemide:torsemide ratio for equivalent natriuresis 1, not the commonly assumed 2:1 ratio:

• Furosemide 40 mg ≈ Torsemide 10 mg
• Furosemide 80 mg ≈ Torsemide 20 mg

The 2022 guidelines 3 suggest:

• Furosemide: Start 20-40 mg once or twice daily, max 600 mg/day
• Torsemide: Start 10-20 mg once daily, max 200 mg/day

Critical Considerations for eGFR 44 mL/min

At this level of renal function:

• Both drugs remain effective 4, 5
• Torsemide's half-life remains unchanged in CKD (unlike furosemide, whose half-life prolongs) 5
• Higher doses will be needed compared to normal renal function due to decreased tubular secretion
• Monitor for diuretic resistance—may need dose escalation or combination with thiazide-type diuretic 3

Common Pitfalls to Avoid

1. Don't assume torsemide is "better": The TRANSFORM trial and mechanistic substudy 1 disproved theoretical advantages
2. Don't use 2:1 dosing conversion: This results in excessive natriuresis with torsemide and compensatory neurohormonal activation 1
3. Don't use diuretics in isolation: Always combine with guideline-directed medical therapy (ARNI/ACEi/ARB, beta-blockers, MRAs) as diuretics alone don't reduce mortality 3
4. Watch for NSAIDs and high sodium intake: Both block diuretic effectiveness 3

The Bottom Line

Choose furosemide as first-line for cost-effectiveness and extensive clinical experience, or torsemide if once-daily dosing improves adherence—but don't expect different clinical outcomes. Focus instead on achieving euvolemia with the lowest effective dose while optimizing mortality-reducing HF therapies 3.