A Study of SYN-004 for the Prevention of C.Diff in Patients With a LRTI

This is a Phase 2b, randomized, double-blind, placebo controlled, parallel-group,
multi-center proof-of-concept study to assess the potential of SYN-004 in the prevention of
CDI and the unwanted side effects of IV antibiotic treatment in at risk patients who are
hospitalized for LRTI and receiving IV ceftriaxone alone or in combination with a macrolide.
Subjects will be 50 years or older. The entire duration of the study may be up to 59 days.
All patients will be evaluated for the occurrence of CDI and AAD by testing according to
local diagnostic standards and monitoring for diarrhea (3 or more unformed stools per 24 hour
period).

Inclusion Criteria:

- Expected minimum hospital stay of 5 days

- Expected ≥5 day course of intravenous (IV) ceftriaxone alone or in combination with a
macrolide

- Clinical diagnosis of moderate to severe lower respiratory tract infection consisting
of signs and symptoms of a lower respiratory tract infection and Pneumonia Severity
Index (PSI/PORT) score for CAP of 90-130, inclusive. Evidence of a new or progressive
infiltrate on chest x-ray is recommended.

Exclusion Criteria:

- Presence of a diarrheal illness within 72 hours prior to randomization

- Current treatment for CDAD or ongoing active CDI, as evidenced by clinical signs of
diarrhea along with the presence of toxin A and/or B (or their respective genes, tcdA
and/or tcdB) of C. difficile in the stool

- Number of previous CDAD episodes >1 within 12 weeks of randomization and no C.
difficile infection (CDI) within 4 weeks of randomization

- Use of antibiotics within 1 month of start of study drug except for the current
illness.