What are the therapeutic equivalents of Lasix (furosemide), torsemide, and Bumex (bumetanide)?

Therapeutic Equivalence of Loop Diuretics: Furosemide (Lasix), Torsemide, and Bumetanide (Bumex)

The standard conversion ratio for loop diuretics is 40 mg furosemide = 1 mg bumetanide = 10-20 mg torsemide, which should be used when switching between different loop diuretics to maintain equivalent diuretic effect. 1

Pharmacological Properties and Differences

Furosemide (Lasix)

• Initial oral dose typically 20-40 mg daily 1
• Maximum single dose of 160-200 mg 1
• Typically requires twice-daily dosing due to shorter duration of action 2, 1
• Bioavailability is variable (10-100%) and can be affected by food intake 1
• Standard loop diuretic but has less predictable absorption compared to alternatives 2

Bumetanide (Bumex)

• Initial oral dose of 0.5-1.0 mg daily 3
• Maximum daily dose of 10 mg 1
• Duration of action is 4-6 hours 1
• 40-50 times more potent than furosemide on a weight basis 4
• Higher bioavailability (approximately twice that of furosemide) and more rapid absorption 4
• FDA-approved for treatment of edema associated with congestive heart failure, hepatic and renal disease, including nephrotic syndrome 3
• Can be considered in patients with allergic reactions to furosemide, as cross-sensitivity is uncommon 3

Torsemide

• Initial oral dose of 5-10 mg daily 2, 1
• Maximum single dose of 100-200 mg 1
• Longer duration of action allowing for once-daily dosing 1
• More consistent bioavailability (80-100%) compared to furosemide 1, 5
• May be preferred in patients with advanced chronic kidney disease who develop diuretic resistance to furosemide 1
• Recent research suggests no significant pharmacokinetic/pharmacodynamic advantages over furosemide in heart failure patients 6

Clinical Considerations for Loop Diuretic Selection

Conversion Between Loop Diuretics

• When switching from furosemide to bumetanide: divide furosemide dose by 40 1
• When switching from furosemide to torsemide: divide furosemide dose by 2-4 1
• When switching from torsemide to furosemide: multiply torsemide dose by 2-4 1
• Recent research suggests a dose equivalence of approximately 40 mg oral furosemide:10 mg oral torsemide results in similar natriuresis 6

Special Populations

• In heart failure patients:

  • All three loop diuretics are effective for managing fluid overload 2
  • Loop diuretics are preferred over thiazides in patients with moderate-to-severe chronic kidney disease (GFR <30 mL/min) 2
  • Torsemide has been suggested as potentially beneficial due to its more consistent absorption and longer duration of action, though recent research shows similar clinical outcomes compared to furosemide 5, 6, 7

• In patients with nephrotic syndrome or intestinal wall edema:

  • Orally administered torsemide or bumetanide may be more effective than oral furosemide due to greater bioavailability 2
  • Intravenously administered loop diuretics may be necessary in cases of significant intestinal edema 2

Monitoring After Conversion

• Assess clinical response (weight, edema, symptoms) within 1-2 days of conversion 1
• Monitor electrolytes (particularly potassium and magnesium) within 3-7 days 1
• Watch for signs of excessive diuresis (hypotension, azotemia) or inadequate diuresis (persistent edema) 1

Combination Therapy Considerations

• In resistant cases, loop diuretics can be combined with thiazide diuretics for synergistic effect 2
• Combination therapy with potassium-sparing diuretics may be considered in patients with hypokalemia on loop diuretic monotherapy 2
• Avoid combination of potassium-sparing diuretics with significant renal dysfunction (GFR <45 mL/min) 2

Pitfalls and Caveats

• Loop diuretics can cause electrolyte abnormalities, particularly hypokalemia and hypomagnesemia, requiring close monitoring 2
• Excessive diuresis can lead to dehydration, hypotension, and worsening renal function 2
• Torsemide may not provide the expected clinical advantages over furosemide despite theoretical pharmacokinetic benefits 6
• Higher doses of diuretics may lead to greater neurohormonal activation and kidney dysfunction, potentially offsetting benefits of increased natriuresis 6
• There is insufficient evidence to determine whether premedicating people undergoing blood transfusion with loop diuretics prevents transfusion-related morbidity 8