A prospective study of the clarithromycin-digoxin interaction in elderly patients.

The study was a prospective observational trial carried out to assess the clarithromycin-digoxin interaction in elderly patients chronically taking digoxin. Digoxin concentrations were determined before and after concomitant treatment with clarithromycin. A Bayesian approach was used to calculate digoxin pharmacokinetics. In the seven patients who were studied there was a significant increase in digoxin concentration after 4-7 days of clarithromycin treatment; digoxin clearance and elimination rate constant were 56-60% lower and elimination half-life was 82% longer. The pharmacokinetic clarithromycin-digoxin interaction in the elderly may be much more frequent than has been assumed up to now.