Which of the following is NOT a loop diuretic?

Spironolactone is not classified as a loop diuretic; it is actually categorized as a potassium-sparing diuretic. Loop diuretics, including furosemide, bumetanide, and torsemide, work by inhibiting the sodium-potassium-chloride cotransporter in the thick ascending limb of the loop of Henle, which effectively increases the excretion of sodium, chloride, and water from the body, leading to diuresis.

In contrast, spironolactone operates primarily as an aldosterone antagonist in the distal convoluted tubule and collecting ducts of the nephron. It promotes the retention of potassium while facilitating the excretion of sodium and water. This mechanism differentiates it significantly from loop diuretics, thus clarifying why spironolactone is not a loop diuretic. Understanding these mechanisms is critical for healthcare professionals when selecting appropriate diuretics based on patient needs and potential side effects, such as hypokalemia with loop diuretics versus hyperkalemia with potassium-sparing ones.