(7α,17α)- 9,17-Dihydroxy-3-oxo-pregn-4-ene-7,21-dicarboxylic Acid Di-γ-lactone is an eplerenone (E588775) impurity. Eplerenone is a selective aldosterone receptor antagonist (SARA), structurally similar to Spiranolactone. Eplerenone is used alone or in combination with other medications to treat high blood pressure. Eplerenone is in a class of medications called mineralocorticoid receptor antagonists. It works by blocking the action of aldosterone, a natural substance in the body that raises blood pressure.