A Study to Compare Safety and Efficacy of OPT-80(Fidaxomicin) With Vancomycin in Subjects With Clostridium Difficile-associated Diarrhea (CDAD)

Inclusion Criteria:

• Inpatients who have symptoms of CDAD as defined by;

• (1)Diarrhea: with ≥4 unformed bowel movements (or ≥200 mL unformed stool forsubjects having rectal collection devices) and

• (2)Presence of either toxin A and/or B of C. difficile in the stool

• Subjects who have not received antibacterials (vancomycin, metronidazole, et.al.)aiming at CDAD treatment before the study

Exclusion Criteria:

• Life-threatening or fulminant CDAD

• Ileus paralytic or toxic megacolon

• Likelihood of death before the completion of study from any cause

• Concurrent use of oral vancomycin, metronidazole, et.al. aiming at the treatment ofCDAD

• The anticipated need to continue other antibacterials for a period exceeding sevendays from providing the informed consent

• Subjects who in the opinion of the investigator require other drugs to controldiarrhea

• Need of change in dosage regimen of opiates during the study period

• Need of change in dosage regimen of probiotic products during the study period

• History/complications of ulcerative colitis or Crohn's disease

• Multiple occurrences of CDAD within the past three months

• Hypersensitivity to vancomycin

• Previous exposure to OPT-80 (fidaxomicin)

• Female patients who are pregnant, breastfeeding or possibly pregnant, or wishing tobecome pregnant during the course of study

• Participation in other clinical research studies or Post Marketing Clinical Trialsutilizing an investigational agent within one month prior to providing the informedconsent or within five half-lives of the investigational agent, whichever is longer