What is the equivalent dose of intravenous (IV) furosemide for oral torsemide?

Equivalent Dosing of Oral Torsemide to IV Furosemide

When converting from oral torsemide to IV furosemide, use a ratio of 10 mg oral torsemide to 40 mg IV furosemide (1:4 ratio). 1

Pharmacokinetic Differences Between Torsemide and Furosemide

Torsemide and furosemide are both loop diuretics but have important pharmacokinetic differences that affect dosing conversion:

• Bioavailability: Torsemide has high oral bioavailability (>80%) compared to furosemide's lower and more variable bioavailability (40-60%) 2, 3
• Half-life: Torsemide has a longer elimination half-life (3-4 hours) compared to furosemide (0.6-0.8 hours) 2, 4
• Metabolism: Torsemide is eliminated primarily through hepatic metabolism (80%) with only 20% renal excretion, while furosemide is primarily excreted renally (62%) 3, 4

Dosing Conversion Algorithm

1. Standard conversion ratio: 10 mg oral torsemide ≈ 40 mg IV furosemide (1:4 ratio) 1
2. For patients on chronic diuretic therapy: When converting from oral torsemide to IV furosemide, the initial IV furosemide dose should be at least equivalent to the effective oral dose using the conversion ratio 5
3. For diuretic-naïve patients: Start with 20-40 mg IV furosemide regardless of prior torsemide dose 5

Administration Considerations

• Bolus vs. continuous infusion: IV furosemide can be given as intermittent boluses or continuous infusion, with the dose and duration adjusted according to the patient's clinical status 5
• Maximum dosing: Total furosemide dose should remain <100 mg in the first 6 hours and <240 mg during the first 24 hours 5
• Monitoring: Regularly monitor symptoms, urine output, renal function, and electrolytes during IV furosemide administration 5, 6

Special Considerations

• Renal impairment: In patients with renal dysfunction, higher doses of IV furosemide may be required when converting from torsemide, as torsemide's efficacy is less affected by renal impairment due to its hepatic metabolism 7
• Diuretic resistance: If diuretic response is inadequate, consider combination therapy with thiazide diuretics or aldosterone antagonists rather than excessive dose escalation 5
• Hemodynamic effects: Be aware that IV furosemide may transiently worsen hemodynamics for 1-2 hours after administration by increasing systemic vascular resistance and left ventricular filling pressures 6

Common Pitfalls to Avoid

• Underestimating equivalence: Using a 1:1 conversion ratio will result in underdosing of furosemide
• Excessive dosing: Overly aggressive furosemide dosing can lead to electrolyte abnormalities, dehydration, and hypotension
• Inadequate monitoring: Failure to monitor renal function, electrolytes, and clinical response may result in complications
• Ignoring concomitant medications: NSAIDs and certain antibiotics can reduce diuretic efficacy

By following this evidence-based conversion approach, you can effectively transition patients from oral torsemide to IV furosemide while minimizing risks and optimizing clinical outcomes.