Converting 100mg PO Torsemide to IV Furosemide
For a patient taking 100mg oral torsemide, the equivalent IV furosemide dose is 400mg IV, based on the standard 40:10 loop diuretic equivalence ratio. 1
Dosing Equivalence Rationale
The established loop diuretic equivalence ratio is 40mg furosemide : 10mg torsemide : 1mg bumetanide. 1 This means 10mg of torsemide equals 40mg of furosemide in diuretic potency.
Using this 4:1 conversion ratio, 100mg oral torsemide converts to 400mg IV furosemide. 1
Recent mechanistic data from the TRANSFORM-Mechanism trial (2025) confirms that a dose equivalence of approximately 4:1 (furosemide:torsemide) results in similar natriuresis between the two agents. 2 This validates the traditional conversion ratio used in clinical practice.
Critical Considerations When Converting
Bioavailability Differences
Torsemide has superior oral bioavailability (>80%) compared to furosemide (approximately 50% with high variability). 3, 4, 5 This means oral torsemide is nearly equivalent to IV torsemide, while oral furosemide is substantially less potent than IV furosemide.
When converting from oral torsemide to IV furosemide, you are switching from a highly bioavailable oral agent to IV administration, which may result in more pronounced diuretic effect than expected. 5
Duration of Action Concerns
Torsemide has a significantly longer duration of action (12-16 hours) compared to furosemide (6-8 hours). 1, 5 A patient on once-daily torsemide 100mg has 24-hour diuretic coverage.
Converting to IV furosemide 400mg as a single bolus will provide only 6-8 hours of diuretic effect, leaving 16-18 hours without coverage. 1 This creates a substantial gap in diuretic therapy.
To maintain equivalent 24-hour diuretic coverage, consider splitting the IV furosemide dose to 200mg IV twice daily rather than 400mg once daily. 1 This prevents the rebound sodium retention that occurs during the off-diuretic period.
Practical Dosing Strategy
For acute situations requiring immediate IV diuresis, start with furosemide 200mg IV bolus, then reassess response within 1-2 hours. 6 This represents half the calculated equivalent dose and allows for titration based on response.
If inadequate diuresis occurs, administer an additional 200mg IV bolus rather than giving the full 400mg upfront. 6 This staged approach minimizes risk of excessive diuresis and electrolyte derangements.
For ongoing IV therapy, administer furosemide 200mg IV every 12 hours to maintain continuous diuretic effect. 1 This twice-daily dosing compensates for furosemide's shorter duration of action.
Monitoring Requirements After Conversion
Check electrolytes (sodium, potassium, magnesium) and renal function within 6-24 hours after conversion. 6, 1 The higher natriuretic load from IV furosemide increases risk of hypokalemia and hypomagnesemia.
Monitor urine output hourly in the acute setting, targeting 0.5-1.0 mL/kg/h. 6 Excessive diuresis (>1.5 mL/kg/h) suggests overdosing and requires dose reduction.
Assess blood pressure every 15-30 minutes for the first 2 hours after IV administration. 6 Watch for hypotension (SBP <90 mmHg), which indicates excessive volume depletion.
Monitor daily weights targeting 0.5-1.0 kg loss per day. 6, 1 Weight loss exceeding 1 kg/day increases risk of intravascular volume depletion and acute kidney injury.
Common Pitfalls to Avoid
Do not use a 2:1 conversion ratio (furosemide:torsemide), as this significantly underdoses the patient. 2 The TRANSFORM-Mechanism trial showed that clinicians commonly used 2:1 dosing, but this resulted in inadequate diuresis compared to the appropriate 4:1 ratio.
Avoid administering the full calculated 400mg dose as a rapid IV push. 6 Doses ≥250mg must be given by infusion over 4 hours to prevent ototoxicity.
Do not assume once-daily IV furosemide will provide equivalent coverage to once-daily torsemide. 1 The shorter duration of furosemide necessitates twice-daily dosing for continuous effect.
Recognize that 100mg daily torsemide represents a high diuretic requirement. 1 This patient likely has significant volume overload or diuretic resistance, and may require combination therapy with thiazides or aldosterone antagonists rather than loop diuretic monotherapy. 6
Alternative Approach: IV Torsemide
If available, IV torsemide 100mg once daily provides equivalent diuresis to oral torsemide 100mg due to torsemide's high bioavailability (>80%). 3, 4, 5 This eliminates the need for dose conversion and maintains the patient's established diuretic regimen.
The maximum recommended daily dose of torsemide is 200mg. 1 A patient already on 100mg daily is at 50% of maximum dosing, leaving room for escalation if needed.