BRAND NAME: Lasix. DRUG CLASS AND MECHANISM: Furosemide is a potent diuretic (water pill) that is used to eliminate water and salt from the body.In the kidneys, salt (composed of sodium and chloride), water, and other small molecules normally are filtered out of the blood and into the tubules of the kidney.RUG CLASS AND MECHANISM: Furosemide is a potent diuretic (water pill) that is used to eliminate water and salt from the body.