Potency Comparison: Lasix (Furosemide) vs Bumex (Bumetanide)
No, Lasix and Bumex are not similar in potency—bumetanide is approximately 40 times more potent than furosemide on a milligram-per-milligram basis, meaning 1 mg of bumetanide equals approximately 40 mg of furosemide. 1, 2
Established Potency Ratio
- The FDA-approved drug label for bumetanide explicitly states that 1 mg bumetanide has diuretic potency equivalent to approximately 40 mg furosemide. 1
- Multiple clinical guidelines confirm this 1:40 potency ratio when discussing loop diuretic dosing 3
- Research studies consistently demonstrate bumetanide is 40-50 times more potent than furosemide on a weight basis 2, 4, 5
Clinical Dosing Implications
When converting between these medications, you must account for this dramatic potency difference:
- Initial furosemide dosing: 20-80 mg IV for acute heart failure 3, 6
- Initial bumetanide dosing: 1.0 mg IV (maximum single dose 4-8 mg) 3
- For chronic oral therapy in ascites: furosemide 40-160 mg/day versus bumetanide at proportionally lower doses 3
Pharmacologic Similarities Despite Potency Difference
Both drugs share the same mechanism and site of action:
- Both inhibit sodium reabsorption in the ascending limb of the loop of Henle 1, 2
- Both produce rapid diuresis with similar time courses of action 2, 7
- After IV administration, peak natriuresis occurs within 30 minutes for both drugs, returning to baseline by 3.5 hours 7
- After oral dosing, peak effect occurs at approximately 75 minutes for both, returning to baseline within 4 hours 7
Key Clinical Differences Beyond Potency
Bioavailability:
- Bumetanide is absorbed more quickly and has twice the bioavailability of furosemide 5
- For both drugs, IV dosing is approximately 3 times as potent as oral administration 7
Electrolyte effects:
- Bumetanide causes less potassium loss relative to sodium excretion compared to furosemide 7
- For every 200 mEq sodium excreted, bumetanide causes approximately 35 mEq potassium loss versus 50 mEq with furosemide 7
- However, this difference may not be clinically significant in most patients 7
Ototoxicity profile:
- Bumetanide may have lower incidence of ototoxicity compared to furosemide 2, 4
- This makes bumetanide potentially preferable in patients at increased risk for hearing complications 4
Critical Prescribing Caution
The most common prescribing error is failing to adjust doses when switching between these medications. A physician accustomed to prescribing furosemide 40 mg who inadvertently orders "40 mg" of bumetanide would be administering a dose equivalent to 1,600 mg of furosemide—a potentially dangerous overdose. 1, 2
Always verify the 1:40 conversion ratio when switching between furosemide and bumetanide to avoid profound volume depletion, electrolyte abnormalities, and circulatory collapse. 1