Interaction Between Digoxin and Nifedipine at Steady State in Patients with Atrial Fibrillation

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Abstract
The possible kinetic and hemodynamic interactions between digoxin and nifedipine were evaluated in nine patients with atrial fibrillation who were receiving chronic digoxin. After 2 control weeks, nifedipine (20 mg b.i.d.), in a new formulation with sustained release characteristics, was added to the therapeutic regimen for 2 weeks. Trough serum digoxin concentrations and peak nifedipine concentrations were determined repeatedly. On the same days, resting blood pressure and heart rate were measured. During nifedipine administration, serum digoxin levels increased by 15% from 0.87 .+-. 0.38 to 1.04 .+-. 0.37 ng/ml (mean .+-. SD, p < 0.05). This was accompanied by a reduction in systolic and diastolic blood pressure of 16 .+-. 6 (p < 0.01) and 12 .+-. 5 mm Hg (p < 0.001), respectively. In two patients, noncardiac side effects were reported. In two other patients, nifedipine was discontinued because of skin rash and severe headache, respectively. In conclusion, plasma digoxin levels were revealed slightly in the presence of nifedipine, but this probably has little clinical relevance.

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