Eplerenone drug substance having high phase purity

A novel crystalline form (Form L) of the aldosterone receptor antagonist drug eplerenone is provided having relatively high physical stability at normal temperatures of storage and use. Pharmaceutical compositions are also provided comprising Form L eplerenone, optionally accompanied by one or more other solid state forms of eplerenone, in a total unit dosage amount of eplerenone of about 10 to about 1000 mg, and further comprising one or more pharmaceutically acceptable excipients. Processes are provided for preparing Form L eplerenone and for preparing compositions comprising Form L eplerenone. A method for prophylaxis and/or treatment of an aldosterone-mediated condition or disorder is also provided, comprising administering to a subject a therapeutically effective amount of eplerenone, wherein at least a fraction of the eplerenone present is Form L eplerenone.