Approximately 24 patients will be entered into this study taking place in Canada. The aim of this study is to determine if an investigational drug is absorbed (taken up) in patients with C. difficile-associated diarrhea (CDAD). The investigational drug will be given in addition to current standard antibiotic treatment so that all patients will receive active medication. All study related care is provided including doctor visits, physical exams, laboratory tests, and study medication. The total length of participation is approximately 7 days.