Loop Diuretics
Loop diuretics are furosemide, bumetanide, and torsemide—these agents act on the Na⁺-K⁺-2Cl⁻ cotransporter in the thick ascending limb of the loop of Henle. 1, 2
Specific Loop Diuretic Agents
The three primary loop diuretics used in clinical practice are:
Furosemide is the most commonly prescribed loop diuretic, with initial oral doses of 20-40 mg once or twice daily and a maximum daily dose of 600 mg, with a duration of action of 6-8 hours 1
Bumetanide has a diuretic potency where 1 mg is equivalent to approximately 40 mg of furosemide, with initial doses of 0.5-1.0 mg once or twice daily and a maximum daily dose of 10 mg, with a duration of action of 4-6 hours 1, 3
Torsemide is characterized by a longer half-life and longer duration of action (12-16 hours) compared to furosemide, and is used at approximately one-quarter the dose of furosemide, with initial doses of 10-20 mg once daily and a maximum daily dose of 200 mg 1, 4
Mechanism of Action
Loop diuretics work by inhibiting the Na⁺-K⁺-2Cl⁻ cotransporter located on the luminal membrane of cells in the thick ascending limb of Henle's loop, blocking the reabsorption of sodium, potassium, and chloride ions from the tubular lumen into the bloodstream 2, 3
This mechanism increases sodium excretion up to 20-25% of the filtered load, making loop diuretics the most potent class of diuretics available 2
Loop diuretics must be secreted into the tubular lumen via organic anion transporters in the proximal tubule to reach their site of action 2
Key Clinical Advantages
Loop diuretics maintain efficacy even when renal function is severely impaired, unlike thiazide diuretics which lose effectiveness when creatinine clearance falls below 40 mL/min 5, 2
Torsemide has higher oral bioavailability compared to furosemide, which may result in more predictable responses in some patients 1, 6
Important Distinctions from Other Diuretics
Loop diuretics should not be confused with: