Treating swelling due to congestive heart failure, liver problems, and severe kidney problems. It may also be used for other conditions as determined by your doctor. Ethacrynic acid is a loop diuretic. It works by making the kidneys eliminate larger amounts of electrolytes (especially sodium and potassium salts) and water than normal (diuretic effect). It is useful for treating many conditions in which salt and water retention (eg, edema, swelling) is a problem.