Converting IV Furosemide to Oral Bumetanide
The conversion from IV furosemide to oral bumetanide uses a 40:1 potency ratio, meaning 40 mg of IV furosemide equals approximately 1 mg of oral bumetanide. 1
Conversion Algorithm
For standard conversions:
- 20 mg IV furosemide = 0.5 mg oral bumetanide 1
- 40 mg IV furosemide = 1 mg oral bumetanide 1, 2
- 80 mg IV furosemide = 2 mg oral bumetanide 1
Starting dose range for oral bumetanide is 0.5-1.0 mg once or twice daily, with a maximum total daily dose of 10 mg. 3
Critical Pharmacokinetic Differences
Bumetanide has a significantly shorter duration of action (4-6 hours) compared to furosemide (6-8 hours), which often necessitates twice-daily dosing rather than once-daily. 3, 1
- Bumetanide is rapidly absorbed orally with peak effect within 30 minutes 2, 4
- Elimination half-life is 1.2-1.5 hours in adults 4, 5
- Bioavailability is excellent (>80%), making oral and IV formulations pharmacokinetically similar 4
Dosing Strategy by Clinical Context
For patients with heart failure:
- If previously on furosemide 40 mg IV daily → start bumetanide 1 mg oral once or twice daily 3, 1
- If previously on furosemide 80 mg IV daily → start bumetanide 2 mg oral once or twice daily 1
- Monitor response and adjust within 24-48 hours based on urine output and weight loss 3
For patients with renal impairment:
- Higher doses may be required (up to 10 mg/day) due to reduced drug delivery to the loop of Henle 2
- Bumetanide may be more effective than furosemide in patients with renal disease 2
- Half-life is prolonged in renal failure, requiring careful monitoring for drug accumulation 6
Monitoring Requirements After Conversion
Check within 1-2 weeks:
- Serum creatinine and estimated glomerular filtration rate 1
- Sodium and potassium levels 1
- Daily weights targeting 0.5-1.0 kg loss per day 3
- Urine output and signs of volume depletion 1
Bumetanide causes greater hypochloremia and hypokalemia compared to furosemide, requiring more vigilant electrolyte monitoring. 5, 7
Common Pitfalls and How to Avoid Them
Underdosing due to short duration of action:
- The 4-6 hour duration means once-daily dosing often fails 3, 1
- Start with twice-daily dosing (morning and early afternoon) to maintain 24-hour diuretic coverage 3
- Avoid evening doses to prevent nocturia 8
Electrolyte derangements:
- Hypokalemia and hyponatremia occur more frequently with bumetanide than furosemide 7
- Consider potassium supplementation or aldosterone antagonist (spironolactone 12.5-25 mg daily) from the start 3
- Magnesium depletion must be corrected before potassium repletion will be effective 1
Muscle cramps:
- More common with bumetanide, especially in renal failure patients receiving higher doses 2
- Consider adding potassium-sparing diuretic or reducing dose if cramps become incapacitating 3
Managing Inadequate Response
If diuresis is insufficient after 24-48 hours:
- Increase bumetanide dose by 0.5-1 mg increments up to maximum 10 mg/day 3
- Add thiazide diuretic (hydrochlorothiazide 25 mg or metolazone 2.5 mg) for sequential nephron blockade rather than exceeding maximum bumetanide dose 3, 1
- Combination therapy with furosemide plus metolazone or bumetanide produces greater urine output than furosemide alone 7
Contraindications to conversion:
- Systolic blood pressure <90 mmHg without circulatory support 8
- Severe hyponatremia (sodium <120-125 mmol/L) 8
- Anuria or marked hypovolemia 8
- Progressive acute kidney injury 8
Special Advantage of Bumetanide
Bumetanide has lower ototoxicity risk compared to furosemide, making it the preferred loop diuretic in patients at increased risk for hearing loss. 2, 5 This includes patients receiving concurrent aminoglycosides or requiring very high diuretic doses.