What is the ranking of Lasix (furosemide), Bumex (bumetanide), and torsemide in terms of diuretic potency?

Ranking of Loop Diuretics by Potency

Bumetanide (Bumex) is approximately 40 times more potent than furosemide (Lasix) on a milligram-to-milligram basis, while torsemide (Demadex) has similar potency to furosemide but with better bioavailability and longer duration of action. 1, 2

Comparative Potency and Equivalence

The relative potency of these three commonly used loop diuretics can be summarized as:

1. Bumetanide: Highest potency (40-60 times more potent than furosemide)

   • 1 mg bumetanide ≈ 40 mg furosemide
   • Maximum daily dose: 10 mg 1

2. Torsemide: Intermediate potency with better bioavailability

   • 10-20 mg torsemide ≈ 40 mg furosemide
   • Maximum daily dose: 200 mg 1

3. Furosemide: Lowest potency of the three

   • Standard reference (40 mg is the benchmark dose)
   • Maximum daily dose: 600 mg 1

Pharmacokinetic Differences

The diuretics differ significantly in their pharmacokinetic properties:

• Bumetanide:

  • Highest oral bioavailability (80-95%)
  • Rapid onset of action (30-60 minutes)
  • Short duration (4-6 hours) 2
  • Less variability in absorption compared to furosemide

• Torsemide:

  • High oral bioavailability (80-90%)
  • Longer duration of action (12-16 hours) 1
  • More consistent absorption than furosemide

• Furosemide:

  • Lower oral bioavailability (10-100%, highly variable)
  • Duration of action: 6-8 hours 1
  • Absorption can be significantly impaired in heart failure

Clinical Considerations

When selecting a loop diuretic, consider these important factors:

• Bioavailability: Torsemide and bumetanide have more predictable absorption than furosemide, particularly important in patients with heart failure who often have intestinal edema 1

• Duration of action: Torsemide's longer duration (12-16 hours) may allow for once-daily dosing and potentially less "rebound sodium retention" compared to shorter-acting agents 1

• Potency: Bumetanide's high potency makes it useful when high-dose diuresis is needed with volume constraints 2

• Ototoxicity risk: Bumetanide appears to have lower ototoxicity risk compared to furosemide at equipotent doses 3, 4

Special Populations

• Heart failure: Torsemide may offer advantages over furosemide in heart failure patients due to more consistent absorption and potentially improved outcomes 5

• Renal impairment: All three agents remain effective in renal impairment, but dose adjustments may be needed 2

• Diuretic resistance: When resistance develops to one loop diuretic, switching to another (particularly from furosemide to torsemide or bumetanide) may restore diuretic efficacy due to different pharmacokinetic properties 6

Pitfalls and Caveats

• Don't assume equivalent doses will produce identical effects in all patients due to individual variations in absorption and response
• Monitor for electrolyte abnormalities (especially hypokalemia) with all loop diuretics
• Be aware that bumetanide has a relatively stronger effect on potassium excretion compared to its sodium effects when compared to the other agents 2
• Avoid rapid high-dose administration of any loop diuretic due to risk of ototoxicity, particularly in patients with renal dysfunction

The selection of a specific loop diuretic should be based on the clinical scenario, with consideration of the pharmacokinetic differences that may provide advantages in specific patient populations.