Drug Interactions between Lanoxicaps and spironolactone

Consumer information for this interaction is not currently available.

ADJUST DOSE: Coadministration with spironolactone may increase the exposure and toxicity of digoxin, as well as interfere with some digoxin radioimmunoassays. The exact mechanism by which digoxin exposure is increased is unknown, but may involve reduced tubular secretion of digoxin due to inhibition of the P-glycoprotein (P-gp) efflux transporter by spironolactone. It has also been reported that some laboratory tests may falsely detect spironolactone as digoxin at levels up to 0.5 ng/mL, resulting in falsely elevated digoxin levels. In 6 healthy subjects, administration of digoxin (0.5 mg to 1 mg orally for 6 days followed by an intravenous dose 0.7 times the oral dose on day 7) in combination with spironolactone (200 mg daily) resulted in decreased renal and plasma clearance of digoxin by an average of 13% when compared to administration of digoxin alone. Another study reported that spironolactone increased the maximum plasma concentration (Cmax) and systemic exposure (AUC) of a single dose of digoxin by 55% and 18%, respectively, when compared to digoxin administered alone. This study reported that digoxin's renal clearance decreased by approximately 11%. Some studies have reported an increase in digoxin's AUC of up to 44% when used in combination with spironolactone. However, despite this interaction, the safe use of digoxin in combination with spironolactone in patients with heart failure has been described in the clinical trial setting.

MANAGEMENT: Serum digoxin concentrations should be measured prior to initiating spironolactone and digoxin's dose may need to be decreased by approximately 15% to 30% or the dosing frequency may need to be modified in order to maintain digoxin's concentration within the goal range. Caution and closer monitoring of digoxin levels, and signs and symptoms of digoxin toxicity are advised when this combination is used. As certain digoxin radioimmunoassays may be falsely elevated in the presence of spironolactone, it may be advisable to discuss which assay is being used to monitor digoxin and consider an alternative test if the patient's laboratory values do not seem to match the clinical state of the patient.