Spirorenone is an androstadienone derivative patented by Schering A.-G as a highly effective aldosterone antagonist. Spirorenone is 8.6 times as potent as spironolactone, but showed a lower affinity for the mineralocorticoid receptors. In phase I clinical trials Spirorenone was absorbed with a half-life of 20-30 min, achieving maximum concentrations of about 100 ng/ml (10 mg) and 260 ng/ml (40 mg) after 1-2 h. Disposition of the parent drug was biphasic with half-lives of 50-60 min (distribution) and 5-6 h (elimination). Neither significant accumulation nor enzyme induction was observed after prolonged treatment.