Digoxin-felodipine interaction in patients with congestive heart failure.

A possible interaction between felodipine and digoxin was studied in 23 patients with congestive heart failure before and after 8 weeks treatment with both drugs. A modest, non-significant increase in serum digoxin level 2 h postdose (+15%) was found in the felodipine group (n = 11) compared to placebo (n = 12), with no change in the trough and 6 h postdose levels. There was a bimodal distribution of the observed changes in serum digoxin level 2 h postdose: a significant increase (p less than 0.001) was observed only in patients with a high plasma felodipine level, which may have been caused by changes in the absorption rate in those patients. Changes in the elimination of digoxin after felodipine therapy appeared unlikely, since the trough and 6 h post-dose levels were unchanged. Analysis of the clinical characteristics, haemodynamics and laboratory values revealed no significant differences between the subgroups. The observed increase in serum digoxin warrants monitoring the trough and peak levels digoxin in patients with congestive heart failure who are also being treated with felodipine.