What dose of bumetanide (Bumex) is equivalent to 80 mg of furosemide (Lasix)?

Bumetanide Equivalent to 80 mg Furosemide

2 mg of bumetanide (Bumex) is equivalent to 80 mg of furosemide (Lasix). 1, 2

Established Equivalence Ratio

• The standard conversion ratio is 1:40, meaning 1 mg of bumetanide equals 40 mg of furosemide. 1, 2
• Therefore, 80 mg of furosemide requires 2 mg of bumetanide (80 ÷ 40 = 2). 1
• This 1:40 potency ratio is consistently supported across FDA labeling, clinical guidelines, and pharmacological research. 1, 2, 3

Route-Specific Considerations

• For IV administration: 2 mg bumetanide IV equals 80 mg furosemide IV using the same 1:40 ratio. 1, 2
• For oral administration: The conversion remains 2 mg bumetanide PO equals 80 mg furosemide PO, though bumetanide has superior bioavailability (80% vs 40% for furosemide). 4, 5
• When converting from IV to oral routes, bumetanide's higher bioavailability means the oral dose can remain the same as the IV dose, whereas furosemide often requires dose increases. 4

Critical Pharmacokinetic Differences

• Duration of action: Bumetanide has a significantly shorter duration (4-6 hours) compared to furosemide (6-8 hours), often necessitating twice-daily dosing rather than once-daily. 1
• Onset of action: Both drugs produce diuresis within minutes IV and peak at 30-75 minutes orally, with virtually superimposable time-response curves. 6, 4
• Bioavailability advantage: Bumetanide's 80% oral bioavailability versus furosemide's 40% makes oral bumetanide more reliable, particularly in heart failure patients with gut edema. 4, 5

Practical Dosing Algorithm for Conversion

Step 1: Calculate equivalent dose using 1:40 ratio

• 80 mg furosemide ÷ 40 = 2 mg bumetanide 1, 2

Step 2: Adjust dosing frequency

• If patient was on furosemide 80 mg once daily, consider bumetanide 1 mg twice daily (morning and early afternoon) due to shorter duration. 1
• Alternatively, start with 2 mg once daily and monitor response over 24 hours. 1

Step 3: Monitor response within 24-48 hours

• Check daily weights targeting 0.5-1.0 kg loss per day. 1
• Assess urine output and clinical signs of congestion. 1
• Verify electrolytes (sodium, potassium) and renal function within 1-2 weeks. 1

Important Clinical Caveats

• Maximum daily dose: Bumetanide should not exceed 10 mg/day. 1
• Electrolyte monitoring: For every 200 mEq sodium excreted, bumetanide causes approximately 35 mEq potassium loss versus 50 mEq with furosemide, though this difference is not clinically significant. 6
• Diuretic resistance: If adequate diuresis is not achieved with bumetanide 2 mg twice daily (equivalent to furosemide 160 mg/day), add a thiazide diuretic or aldosterone antagonist rather than exceeding maximum loop diuretic doses. 1
• Heart failure patients: Delayed absorption in CHF reduces peak drug concentrations for both agents, potentially requiring higher doses or IV administration. 5
• Ototoxicity risk: Bumetanide may have a lower incidence of ototoxicity compared to furosemide, making it preferable in high-risk patients. 3, 7

Common Pitfalls to Avoid

• Underdosing due to short duration: Do not assume once-daily bumetanide 2 mg will provide 24-hour coverage equivalent to furosemide 80 mg once daily; consider split dosing. 1
• Ignoring bioavailability advantage: In patients with gut edema or malabsorption, bumetanide's superior oral bioavailability makes it more reliable than furosemide. 4, 5
• Combining with NSAIDs: Avoid concurrent NSAID use, which blocks diuretic effects and worsens renal function. 1
• Excessive sodium intake: High dietary sodium (>2-3 g/day) can create apparent diuretic resistance; counsel patients on sodium restriction. 1