Drug Interactions between digoxin and solifenacin

Anticholinergic agents may increase the absorption and oral bioavailability of some digoxin formulations. The proposed mechanism involves increased gastrointestinal transit time due to reduction of stomach and intestinal motility by anticholinergic agents. In one study, coadministration with propantheline (15 mg three times a day for 10 days) led to a 30% mean increase in serum digoxin levels in 9 of 13 elderly women receiving a slow-dissolution formulation of digoxin. The interaction has also been reported with formulations containing large particle size digoxin. Other studies have found no significant effect of propantheline on digoxin elixir, solution in capsules, rapid-dissolution tablets, and micronized digoxin tablets. Therefore, the interaction is not expected to occur with most digoxin products used today in industrialized countries (e.g., Lanoxin). Due to the drug's narrow therapeutic index, however, clinicians may consider monitoring patients more closely for digoxin side effects and toxicity during coadministration with anticholinergic agents. Patients should be advised to notify their physician if they experience potential signs and symptoms of digoxin toxicity such as nausea, anorexia, visual disturbances, slow pulse, and irregular heartbeats.