Digoxin Induced Dissolution of CTC Clusters

Patients will receive a daily maintenance dose of digoxin. The daily dose of digoxin will be calculated according to the renal function and the target serum digoxin concentration and applied in an adjusted regimen based on the availability of 0.125 mg and 0.25 mg pills in the morning (before 10 am). Blood samples for analyses of mean CTC cluster size will be drawn at screening, on day 0 (2 hrs after first oral intake), on day 3 and on day 7. Depending on the digoxin serum level maintenance therapy with digoxin will be continued up to 3 weeks if the digoxin serum level on day 7 or day 14 is below 0.70 ng/ml. For the third week of maintenance therapy individual dose adjustments will be carried out as needed.