Safety and Efficacy of Fidaxomicin Versus Placebo for Prophylaxis Against Clostridium Difficile-Associated Diarrhea in Adults Undergoing Hematopoietic Stem Cell Transplantation

Inclusion Criteria:

- Male or female 18 years of age or older.

- Female subjects of childbearing potential must be using an adequate and reliable
method of contraception (e.g., abstinence, barrier with additional spermicide foam or
jelly, intrauterine device, hormonal contraception). Subjects (both male and female)
must agree to avoid conception during treatment and for four weeks following the end
of study treatment.

- Individuals undergoing HSCT with fluoroquinolone prophylaxis.

- Informed consent is provided.

Exclusion Criteria:

- Ongoing active CDAD infection (as evidenced by clinical signs of diarrhea along with
the presence of either toxin A and/or B [or their respective genes, tcdA and/or tcdB]
of C. difficile in the stool) or current treatment for CDAD.

- Undergoing cord blood transplants.

- Subject has fulminant colitis, toxic megacolon, or ileus.

- A history of inflammatory bowel disease (ulcerative colitis or Crohn's disease).

- Women who are pregnant or are actively breast feeding (all women of childbearing
potential must have a negative pregnancy test result prior to dosing study drug).

- Use of any drugs potentially useful in the treatment of CDAD (e.g. oral vancomycin,
metronidazole, oral bacitracin, fusidic acid, rifaximin, and nitazoxanide).

- Any other condition that, in the opinion of the investigator, would jeopardize the
safety or rights of the subject participating in the study, would make it unlikely
for the subject to complete the study, or would confound the results of the study.

- Participation in other clinical research studies utilizing an investigational agent
within one month prior to screening and during the study treatment period.