Presentation of a case report and pharmacokinetic investigation in healthy volunteers on the potential interference between cardiac glycosides and glycosides of Uzara, a herbal antidiarrheal preparation.Pharmacokinetic pilot investigation of apparent digitoxin and digoxin serum concentrations in 4 healthy volunteers after single-dose administration of 30 drops Uzara (approximately 1.5 ml approximately = 22 mg glycosides).Maximal apparent serum concentrations of digitoxin between 198.0 microg/l and 919.8 microg/l (therapeutic range: 10-25 microg/l) occurred at 4-8 hours after administration. The terminal half-life of the glycosides was 8.87 +/- 2.20 hours. For digoxin, maximal apparent serum concentrations ranged between 1.4 microg/l and 6.34 microg/l (therapeutic range: 0.9-2.0 microg/l) at 6 hours post dosing.Administration of a single dose of an Uzara preparation, an over-the-counter product, results in false high serum concentrations of digitoxin and digoxin. As described in the manufacturers Summary of Product Characteristics, this preparation should not be given to patients with cardiac failure or arrhythmia who require treatment with cardiac glycosides because of the demonstrated pharmacological actions of uzara glycosides.