loop diuretic

When a failing heart cannot keep up, fluid backs up into the lungs and legs, leaving people breathless and swollen. Loop diuretics are the most powerful “water pills,” telling the kidneys to dump extra salt and water so that this excess fluid drains away and breathing eases.

They act on a precise spot in the kidney — a salt transporter in the loop of Henle, which is how the class gets its name — and block it, so a large amount of sodium, and the water that follows it, is flushed out in the urine. The best-known example acts within an hour when given by vein.

Their main job is relieving congestion in heart failure and other fluid-overload states; they ease symptoms quickly but do not by themselves prolong life the way some other heart-failure drugs do. They are titrated to the lowest dose that keeps a person comfortable and dry.

Flushing out salt and water carries trade-offs: they can lower potassium, magnesium, and sodium, raise uric acid, and if overdone leave a person dehydrated with worsening kidney numbers, so electrolytes and weight are monitored.