Influence of spironolactone and its metabolite canrenone on serum digoxin assays.

Although current immunoassay kits for digoxin supposedly have antibodies of high specificity, serum digoxin levels in patients taking spironolactone suggest that spironolactone interferes with the determination. In vitro determinations of digoxin performed on blank serum spiked with spironolactone and its metabolite canrenone showed that contrary to the belief gained from reading the manuals of some diagnostic immunoassay kits, spironolactone significantly influences digoxin determinations.