ALDOSTERONE ANTAGONISTS are used mainly as DIURETICS to reduce fluid in the body by increasing the excretion of electrolytes and water by the kidney, so increasing urine production. They work by blocking the action of the endogenous MINERALOCORTICOID hormone aldosterone, and this makes them suitable for treating oedema associated with aldosteronism, liver failure, ascites caused by cirrhosis of the liver, hypertension and certain heart conditions. Examples of clinically used oral aldosterone antagonists are potassium canrenoate and spironolactone. They are relatively potassium-sparing’ diuretics which cause relative retention of potassium, and this makes them suitable for combination with some of the other diuretic classes that cause K+-loss, particularly the thiazides.