What is the equivalent dosing of Lasix (furosemide) for a patient taking 5 mg of torsemide?

Torsemide to Furosemide (Lasix) Dose Conversion

For a patient taking torsemide 5 mg, the equivalent furosemide (Lasix) dose is approximately 20 mg.

Conversion Ratio

The established conversion ratio between torsemide and furosemide is approximately 1:4, meaning 1 mg of torsemide is roughly equivalent to 4 mg of furosemide 1.

• Torsemide 5 mg = Furosemide 20 mg 1
• Torsemide 10 mg = Furosemide 40 mg 1
• Torsemide 20 mg = Furosemide 80 mg 1

Pharmacologic Basis for Conversion

Bioavailability Differences

• Torsemide has superior bioavailability (>80%) compared to furosemide, which has variable and lower bioavailability 2, 3, 4
• This higher bioavailability means torsemide requires lower doses to achieve equivalent diuretic effects 2, 4

Duration of Action

• Torsemide has a longer elimination half-life (3-4 hours) compared to furosemide, providing more prolonged diuresis 2, 3, 4, 5
• Torsemide produces diuresis lasting approximately 6-8 hours, allowing for once-daily dosing 4

Potassium-Sparing Properties

• Torsemide does not increase kaliuresis to the same extent as equipotent doses of furosemide, meaning it causes less potassium wasting 2
• At dosages below 5 mg/day, torsemide does not significantly affect serum potassium levels 2

Clinical Application

Initial Conversion

When switching from torsemide 5 mg to furosemide:

• Start with furosemide 20 mg once daily 1
• Monitor clinical response (urine output, weight, edema) within 24-48 hours 1

Monitoring Requirements

After conversion, check the following parameters:

• Serum potassium and renal function within 3-7 days 6
• Weight and volume status daily initially 1
• Blood pressure for orthostatic changes 3, 5

Dose Adjustments

• If inadequate diuretic response with furosemide 20 mg, increase to 40 mg rather than assuming exact 1:4 equivalence 1
• Maximum recommended doses: furosemide 160-240 mg/day vs torsemide 100-200 mg/day 1

Important Clinical Caveats

Potassium Supplementation

• Patients may require less potassium supplementation on torsemide compared to furosemide due to reduced kaliuresis 2
• When converting to furosemide, reassess potassium supplementation needs within 1 week 6

Renal Impairment

• Both agents require dose adjustment in renal failure, but torsemide has more predictable pharmacokinetics 2, 3
• In chronic renal failure, torsemide dosages up to 400 mg/day have been used effectively 2

Heart Failure Considerations

• For heart failure patients, maintain target potassium 4.0-5.0 mEq/L regardless of which loop diuretic is used 6
• Consider adding aldosterone antagonist (spironolactone 25-50 mg) to prevent hypokalemia with either agent 1, 6

Cost and Availability

• Furosemide is generally less expensive and more widely available than torsemide 3
• The pharmacokinetic advantages of torsemide may not translate to substantial clinical outcome differences in most patients 3