Digoxin × Spironolactone

Spironolactone reduces digoxin clearance and prolongs its half-life, so digoxin levels rise (spironolactone SmPC), by about 25% according to the digoxin label. Spironolactone and its metabolites can also distort digoxin assays that cross-react with them (spironolactone labels).

Nausea, vomiting, loss of appetite, confusion, altered colour vision with yellow-green halos around lights, and heart rhythm disturbances such as bigeminy and atrioventricular block.

Before starting spironolactone, measure the serum digoxin concentration with an assay that does not interact with spironolactone. Then reduce the digoxin dose by about 15–30% or give it less often and keep monitoring the concentration, as the FDA digoxin and spironolactone labels require. The Spanish spironolactone SmPC asks for caution with this combination (spironolactone SmPC). Spironolactone raises potassium, so check potassium and kidney function before starting and regularly during treatment (spironolactone SmPC).