Indacrinone is an orally active, indanone-based loop diuretic patented by American pharmaceutical company Merck and Co as mixture of two enantiomers. In healthy volunteers, the racernic mixture of indacrinone exhibited greater natriuretic potency than furosemide, with a slower onset and longer duration of action. Furthermore, single doses of indacrinone decreased serum uric acid concentrations and increased uric acid clearance, while similar doses of furosemide generally had the opposite effects. Differences in the pharmacologic effects of the resolved enantiomers of indacrinone were initially studied in animals and confirmed in a series of studies we conducted in healthy human volunteer. The S( + ) form is a potent uricosuric agent that produces mild natriuresis only at higher doses, while the R( - ) form is a potent loop diuretic with only transient uricosuric effects. The (-) enantiomer and its active metabolite appear to be primarily responsible for the natriuretic effects of the racemic mixture; the ( + ) enantiomer is 20-40 times less potent a natriuretic agent.