Dose-dependence of the nifedipine/digoxin interaction?

The dose-dependence of the nifedipine/digoxin interaction was investigated in seven healthy volunteers. After an adequate loading dose of digoxin for two weeks, 0.25 mg digoxin was given alone orally twice daily. Afterwards, 0.25 mg digoxin was administered twice daily for three one week periods combined with capsules of nifedipine 5 mg, 10 mg or 20 mg (ADA-LAT) respectively on a three times daily basis. Subsequently the study was completed with a digoxin monotherapy phase lasting seven days. All three doses of nifedipine administered led to a significant increase of the digoxin plasma concentrations and of the area under the plasma concentration-time curve (AUC) compared with digoxin monotherapy. In conclusion, nifedipine causes a slight but significant increase of digoxin plasma concentrations and of its AUC (15%). This effect was not dependent on the nifedipine dose administered.