Plasma digoxin levels are unaltered or only modestly increased bythe use of flecainide,but this is not likely to be important in mostpatients.
In contrast, a study in 15 healthy subjects found that flecainide 200mg twice daily increased trough and peak plasma levels of digoxin 250 micrograms by 24 % and 13%, respectively (See reference number 2). The changes observed in vital signs were not clinically significant. Based on results of a single-dose study steady-state digoxin levels were predicted to rise by about 15 % during use of flecainide 200mg twice daily (See reference number 3).
It is suggested that any changes may be due to alterations in volume of distribution (See reference number 3)
Documentation is limited but what is known suggests that either no interaction occurs,or any changes are small and unlikely to be clinically relevant in most patients. However, UK manufacturers of flecainide recommend that digoxin plasma levels should be measured not less than 6 hrs after any digoxin dose, before or after administration of flecainide (See reference number 4). The US manufacturers do not advise any additional monitoring (See reference number 5). The authors of one of reports(See reference number 2)suggest that patients with high drug levels, atrioventricular nodal dysfunction, or both, should be monitored during concurrent treatment.
McQuinn RL,Kvam DC, Parrish SL, Fox TL, Miller AM, Franciosa JA. Digoxin levels in patients with congestive heart failure are not altered by flecainide. Clin Pharmacol Ther (1988)43, 150.
Weeks CE,Conard GJ, Kvam DC, Fox JM, Chang SF, Paone RP, Lewis GP. The effect of flecainide acetate, a new antiarrhythmic, on plasma digoxin levels. J Clin Pharmacol (1986) 26, 27–31.
Tjandramaga TB,Verbesselt R, Van Hecken A, Mullie A, De Schepper PJ. Oral digoxin pharmacokinetics during multiple-dose flecainide treatment. Arch Int Pharmacodyn Ther (1982)260, 302–3.
Tambocor (Flecainide acetate). 3M Health Care Ltd. UK Summary of product characteristics,May 2006.
Tambocor (Flecainide acetate). 3M Pharmaceuticals. US Prescribing information,June 1998.