How should I convert a patient on furosemide (Lasix) 80 mg orally twice daily to an equivalent oral torsemide dose?

Converting Furosemide 80 mg PO BID to Oral Torsemide

Convert furosemide 80 mg PO twice daily (total 160 mg/day) to torsemide 40 mg PO once daily, using a 4:1 dose equivalence ratio based on the most recent mechanistic evidence.

Evidence-Based Dose Equivalence

The 2025 TRANSFORM-Mechanism trial definitively established that a 4:1 furosemide-to-torsemide dose equivalence produces similar natriuresis, contradicting the traditional 2:1 ratio 1. When clinicians used the conventional 2:1 conversion (as in the main TRANSFORM trial), torsemide produced substantially greater natriuresis but triggered compensatory neurohormonal activation (increased renin, aldosterone, norepinephrine) and mild kidney dysfunction, with no improvement in plasma volume or body weight 1.

• For furosemide 160 mg/day total (80 mg BID), convert to torsemide 40 mg once daily 1
• The 4:1 ratio accounts for torsemide's lower kidney bioavailability (17% vs. 25% for furosemide) but avoids excessive diuresis that triggers counterproductive neurohormonal responses 1

Pharmacokinetic Considerations

Torsemide's once-daily dosing is appropriate because its duration of action (6-8 hours) is similar to furosemide's, not longer as traditionally believed 2, 1. The TRANSFORM-Mechanism trial showed furosemide actually had a longer duration of kidney drug delivery and natriuresis than torsemide 1. However, torsemide's superior bioavailability (~80% vs. furosemide's variable absorption) makes once-daily dosing clinically effective 2.

• Torsemide reaches peak serum concentration within 1 hour and maintains diuresis for approximately 6-8 hours 2
• Furosemide 80 mg BID provides intermittent diuretic effect with 16-18 hours daily without active coverage 3
• Torsemide once daily is therapeutically equivalent to furosemide twice daily at the 4:1 dose ratio 2, 1

Practical Conversion Algorithm

Step 1: Calculate Total Daily Furosemide Dose

• Current regimen: 80 mg BID = 160 mg/day total

Step 2: Apply 4:1 Conversion Ratio

• 160 mg furosemide ÷ 4 = 40 mg torsemide once daily 1

Step 3: Timing and Administration

• Administer torsemide as a single morning dose 2
• Torsemide can be given without regard to meals due to minimal first-pass metabolism 2
• Oral and IV torsemide doses are therapeutically equivalent due to high bioavailability 2

Critical Monitoring After Conversion

Check electrolytes, renal function, and body weight within 3-7 days of conversion 4:

• Target daily weight loss: 0.5-1.0 kg until euvolemia achieved 4
• Monitor serum potassium (target 4.0-5.0 mEq/L), sodium, and creatinine 4
• Assess for signs of volume depletion: hypotension, tachycardia, rising creatinine 4
• Continue monitoring every 1-2 weeks until stable, then monthly for 3 months, then every 3-6 months 4

Common Pitfalls to Avoid

Do not use the traditional 2:1 conversion ratio (which would yield 80 mg torsemide daily for 160 mg furosemide). The TRANSFORM-Mechanism trial proved this overdoses patients, causing excessive natriuresis, neurohormonal activation, and kidney dysfunction without improving fluid status 1.

Do not expect superior efficacy from torsemide. The TRANSFORM trial showed no difference in all-cause mortality or hospitalization between torsemide and furosemide 1. The primary advantage of torsemide is consistent bioavailability and once-daily dosing convenience 2.

Do not discontinue potassium monitoring. Both loop diuretics cause significant potassium wasting; maintain potassium supplementation or potassium-sparing diuretics as previously prescribed 4.

Avoid combining with sodium-unrestricted diet. Furosemide and torsemide efficacy is enhanced by sodium restriction <2-3 g/day 4, 3. Without dietary sodium restriction, the kidney compensates for diuretic-induced natriuresis through increased sodium reabsorption during the post-diuretic period 3.

When to Escalate Torsemide Dose

If inadequate diuresis occurs after 48 hours on torsemide 40 mg daily:

• Increase to torsemide 80 mg once daily (equivalent to furosemide 320 mg/day) 4
• If still inadequate, add a thiazide (hydrochlorothiazide 25 mg) or aldosterone antagonist (spironolactone 25-50 mg) rather than further escalating torsemide alone 4
• Exceeding torsemide 80 mg/day (furosemide equivalent >320 mg/day) without combination therapy signals treatment failure 4

Special Populations

Elderly patients: No dosage adjustment necessary for torsemide 2. However, monitor more frequently (every 5-7 days initially) due to increased risk of volume depletion and electrolyte disturbances 4.

Renal impairment: Torsemide is eliminated 80% hepatically and 20% renally, making it suitable for patients with reduced GFR 2. However, higher doses may be required in advanced CKD due to reduced tubular secretion 4.

Hepatic disease: In cirrhosis with ascites, maintain the spironolactone:loop diuretic ratio of 100:40 mg. For torsemide conversion, use spironolactone 100 mg + torsemide 10 mg (equivalent to furosemide 40 mg) 4.