Digoxin and cimetidine: investigation of the potential for a drug interaction

The potential for a pharmacokinetic interaction between digoxin and cimetidine was investigated in a series of studies. In a single-dose cross-over study in healthy volunteer subjects cimetidine increased the area under the plasma digoxin concentration curve and the peak plasma digoxin concentration. In a repeated-dose study in healthy volunteer subjects taking digoxin 0.25 mg daily, co-administration of cimetidine resulted in an average increase in plasma digoxin concentration of 0.15 ng/ml. In a repeated-dose study in healthy volunteer subjects taking digoxin 0.5 mg daily, co-administration of cimetidine resulted in an average increase in plasma digoxin concentration of 0.19 ng/ml. In a repeated-dose study in patients receiving long-term digoxin therapy for atrial fibrillation co-administration of cimetidine had no significant effect on plasma digoxin concentrations. We have shown that co-administration of cimetidine and digoxin in volunteer subjects causes a statistically significant but small increase in plasma digoxin concentration but no such increase was found in patients. We conclude that it is doubtful that this interaction is of any clinical significance.