Choosing and comparing loop diuretics
Furosemide (Lasix) and bumetanide (Bumex) are loop diuretics that inhibit the Na-K-2Cl cotransporter in the thick ascending limb of the loop of Henle. They produce potent natriuresis and diuresis and are the preferred diuretics for patients with clinically significant volume overload/congestion, particularly acute decompensated heart failure.
Clinical questions for the ED
Does the IV dosage of Lasix equal the oral dosage?
What are the equivalent doses of Lasix and Bumex?
What might explain an inadequate response to Lasix?
When should Bumex be considered?
EM take-home points
Dose and response
Lasix got its name because it lasts six hours.
From The House of God: “Lasix Dose = Age + BUN.” In other words, a higher Lasix dose is needed in renal dysfunction.
Dosage equivalents: 40 mg Lasix = 1 mg Bumex. The comparison below specifies the equivalent oral doses and PO-to-IV conversions.
Consider lower doses for diuretic-naive patients.
May need to double the home diuretic dosage for decompensated patients who are compliant with their medication.
Absorption and electrolytes
Lasix has very variable oral absorption, averaging 50%.
Bumex has better oral bioavailability than Lasix.
Consider Bumex when a patient has an inadequate response to appropriate doses of Lasix.
Send a magnesium level in patients on loop diuretics. Potassium can also be lowered.
Tale of the tape
Potency, dose, and bioavailability
Relative potency: furosemide 1; bumetanide 40.
Equivalent oral dose (mg): furosemide 40; bumetanide 1.
PO to IV conversion: furosemide 2:1; bumetanide 1:1.
Bioavailability (%): furosemide range 10–100 (mean 50); bumetanide range 80–100.
Onset and peak concentration
Oral onset (min): furosemide 30–60; bumetanide 30–60.
IV onset (min): furosemide 5; bumetanide 5.
Time to peak serum concentration after PO administration (h): furosemide 1–2; bumetanide 1–2.
Binding, clearance, and half-life
Protein binding (%): furosemide 91–99; bumetanide 95.
Furosemide clearance: urine 50%–80%; minimal hepatic metabolism.
Bumetanide clearance: “Renal: 81% of total dose, 45% of which is unchanged drug. Hepatic: 50%.”
Half-life (h): furosemide 0.5–2; bumetanide 1–1.5.
Duration of action and maximum daily dose
Average duration of action, oral administration (h): furosemide 6–8; bumetanide 4–6.
Average duration of action, IV administration (h): furosemide 2; bumetanide 2–3.
Maximum daily dose (mg): furosemide 600; bumetanide 10.
