What is the equivalent dosing of furosemide (Lasix) when converting from bumetanide (Bumex)?

Bumetanide to Furosemide Dosing Conversion

When converting from bumetanide to furosemide, use a ratio of 1:40, meaning 1 mg of bumetanide is equivalent to 40 mg of furosemide. 1, 2, 3, 4

Conversion Guidelines

The dosing equivalence between these loop diuretics is well-established in multiple guidelines:

• European Society of Cardiology guidelines explicitly state that 0.5-1 mg of bumetanide is equivalent to 20-40 mg of furosemide 1
• American College of Cardiology Foundation/American Heart Association guidelines provide a conversion table showing the same equivalence 1
• FDA drug information confirms this potency ratio 2
• Multiple clinical studies support the 1:40 potency ratio 3, 4

Practical Conversion Algorithm

1. Calculate the equivalent dose:

   • Multiply the bumetanide dose by 40 to get the equivalent furosemide dose
   • Example: 1 mg bumetanide = 40 mg furosemide
   • Example: 2 mg bumetanide = 80 mg furosemide

2. Route of administration considerations:

   • For oral conversion: maintain the 1:40 ratio
   • For IV conversion: maintain the same 1:40 ratio, but note that both drugs have higher bioavailability when given intravenously 5

3. Dosing frequency adjustments:

   • Consider the difference in duration of action:
     • Bumetanide: 4-6 hours 1
     • Furosemide: 6-8 hours 1
   • You may need to adjust dosing frequency accordingly

Special Considerations

• Renal function: Both drugs require dose adjustments in renal impairment, but the 1:40 ratio remains valid 6
• Heart failure patients: A retrospective study specifically in heart failure patients confirmed a potency ratio of 41:1 for intermittent IV dosing and 34:1 for all heart failure patients 4
• Monitoring: After conversion, closely monitor:
  • Urine output
  • Electrolytes (especially potassium)
  • Renal function
  • Clinical response

Potential Pitfalls

• Potassium loss: Bumetanide may cause slightly less potassium excretion than furosemide at equivalent natriuretic doses, but this difference is generally not clinically significant 7
• Bioavailability differences: Bumetanide has approximately 80% bioavailability compared to 40% for furosemide when given orally, which may affect the exact conversion in some patients 5
• Individual response variation: Some patients may require dose adjustments based on clinical response after the initial conversion

The 1:40 conversion ratio has been consistently demonstrated across multiple high-quality guidelines and research studies, making it the standard approach when switching between these loop diuretics.