Effect of spironolactone on excretion of 3H-digoxin and its metabolites in rats

Spironolactone increased the total excretion of radioactivity in female rats given specific labelled ³H-digoxin. This increase was due to enhanced fecal excretion while urinary elimination of radioactivity and blood tritium levels were reduced. The ratio of total excreted digoxin to its metabolites which was measured by paper and thin-layer chromatography was changed from 28%: 72% under control conditions to 2% : 98% during spironolactone treatment. This increased excretion of metabolites mainly concerned the aqueous soluble compounds, the digoxigenin monodigitoxoside and the digoxigenin. The excretion of the genin was enhanced in urine only.After metabolism of ³H-digoxin could still be observed 25 days after discontinuation of treatment with spironolactone. It is concluded that in rats spironolactone increased the metabolism of digoxin by induction of hepatic microsomal enzyme activity.