Therefore, spironolactone is classified as a potassium-sparing diuretic, a drug that promotes the output of urine (diuretic) while allowing the kidneys to retain potassium. The FDA approved spironolactone in October 1985.PRESCRIBED FOR: Spironolactone removes excess fluid from the body in congestive heart failure, cirrhosis of the liver, and kidney disease.It can also be used in combination with other drugs to treat elevated blood pressure and for treating diuretic-induced low potassium (hypokalemia).At the same time, it also causes the kidneys to eliminate potassium.) The body then becomes overloaded with salt and water, and this worsens the heart failure. Spironolactone inhibits the action of aldosterone thereby causing the kidneys to excrete salt and fluid in the urine while retaining potassium.