Rib-X Pharmaceuticals Initiates Two Phase 2 Studies For Novel Antibiotic Compound RX-1741

Rib-X Pharmaceuticals, Inc.
("Rib-X" or the "Company"), a biopharmaceutical company focused on the
development of novel antibiotics for the treatment of antibiotic-resistant
infections, announced the enrolment of the first patients in two
separate Phase 2 clinical trials. The studies will evaluate the safety and
efficacy of RX-1741 in the treatment of Community-Acquired Pneumonia (CAP),
and separately in the outpatient treatment of Uncomplicated Skin and Skin
Structure Infections (uSSSI). RX-1741 is the Company's first antibiotic
program developed using its proprietary technology platform.


RX-1741 is an oxazolidinone antibiotic that exhibits activity against
methicillin-resistant Staphylococcus aureus (MRSA) and other Gram-positive
organisms, and has demonstrated both greater spectrum and potency of
activity than the currently marketed product of the same class, Zyvox(R)
(linezolid). Discovered using proprietary knowledge of the three
dimensional structure of a key area of the ribosome, the 50S subunit, Rib-X
believes that RX-1741 will demonstrate a high level of effectiveness
against resistant microbes.



"These two studies represent important milestones for Rib-X," said Dr.
Susan Froshauer, President and CEO of Rib-X Pharmaceuticals. "RX-1741 is
the first of many compounds that Rib-X intends to design and develop in
response to the alarming growth of drug resistant microbial pathogens found
both in the hospital and in the community. This MRSA-active agent will
satisfy a critical need for physicians and their patients because current
treatment options are very limited, particularly for orally active agents,"
said Dr. Froshauer.



CAP Study Design



The CAP study is a Phase 2, multicenter, randomized, double-blind study
designed to evaluate the safety and efficacy of RX-1741 in the treatment of
adult patients with mild to moderate severity of Community-Acquired
Pneumonia (CAP). The study will assess the efficacy of three doses of
RX-1741, either once or twice a day, for seven to 10 days in the treatment
of adult patients with mild to moderate CAP. It will also evaluate the
safety and tolerability profile of the three doses.



The CAP study will enroll approximately 160 patients in 40 study
centers across the US, Canada, and Russia, and the Company expects to have
preliminary data available when approximately 80 patients (50% of the
planned patients) have completed the study. The Company intends to release
data from all patients during the first half of 2008.



uSSSI Study Design



The uSSSI study is a Phase 2, multicenter, randomized, open-label,
comparative study to evaluate the safety and efficacy of RX-1741 versus
linezolid in the outpatient treatment of adult patients with Uncomplicated
Skin and Skin Structure Infections (uSSSI). The study will assess the
efficacy of a single dose of RX-1741 given either once daily or twice daily
compared to linezolid given twice daily for five to ten days in the
treatment of ambulatory patients with uSSSI. It will also evaluate the
safety and tolerability profile of these two doses compared to linezolid.
















The uSSSI study will enroll approximately 150 patients in 25 study
centers across the US and the Company expects an interim analysis of the
data to be performed when approximately 75 patients (50% of the planned
patients) have completed the study. The Company intends to release data
from all patients during the first half of 2008.



About Rib-X Pharmaceuticals, Inc.



Rib-X Pharmaceuticals is a product-driven small molecule drug discovery
and development company focused on the structure-based design of new
classes of antibiotics. The Company's underlying drug discovery engine
capitalizes on its proprietary high-resolution crystal structure of the 50S
subunit of the ribosome, which performs an essential role in the
fundamental process of protein synthesis. Many known, commercially valuable
antibiotics bind to the 50S subunit, including those used to treat both
community-acquired and hospital-acquired pathogens. The Company's
integrated research strategy, which combines state of the art, proprietary
computational analysis, X-ray crystallography, medicinal chemistry,
microbiology and biochemistry, allows it to rapidly synthesize new agents
designed to avoid typical antibiotic resistance mechanisms. Rib-X's
iterative intelligent engine has yielded several distinctive new antibiotic
classes. The Company currently has two programs in human clinical trials,
the RX-1741 oxazolidinone program as an oral/IV agent to treat serious
hospital Gram-positive infections and the RX- 3341 program, a next
generation fluoroquinolone, active against a broad spectrum of bacteria,
including methicillin-resistant Staphylococcus aureus. Additionally, the
Company has two active drug discovery programs. The first of these
discovery programs is focused on developing an orally active agent, a
macrolide, for community use with activity against MRSA and other skin
infections. The second discovery program is directed towards identifying a
new chemical class of agents active against multi-drug resistant hospital
infections.



For more information on the ribosome and the Rib-X mission, please
visit the Company website at rib-x.


Rib-X Pharmaceuticals, Inc.

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