20,21-Dehydro Spironolactone (Spironolactone EP Impurity A) is an impurity of Spironolactone (S683000), a synthetic 17-lactone steroid which is a renal competitive aldosterone antagonist in a class of pharmaceuticals called potassium-sparing diuretics, used primarily to treat ascites in patients with liver disease, low-renin hypertension, hypokalemia, and Conn’s syndrome.