Rib-X Pharmaceuticals, Inc. Novel Antibiotic Delafloxacin Named One of R&D Directions 100 Great Investigational Drugs of 2009

NEW HAVEN, Conn., April 2 /PRNewswire/ -- Rib-X Pharmaceuticals, Inc. (“Rib-X” or the “Company”), a development-stage company focused on the discovery and development of novel antibiotics for the treatment of antibiotic-resistant infections, today announced that its lead compound, delafloxacin, has been selected by R&D Directions editors for the 8th annual report on “100 Great Investigational Drugs,” published in the March 2009 issue.

R&D Directions is a leading pharmaceutical industry magazine. Compounds selected by editors for the report, including delafloxacin, demonstrated “particular promise in a... growing therapeutic area of unmet medical need... and target disease pathways using a distinctly innovative mechanism of action."(1)

“We are honored to have our lead compound, delafloxacin, recognized by the editors of R&D Directions as one of the top 100 investigational drugs of 2009,” said Susan Froshauer, PhD, President and CEO of Rib-X Pharmaceuticals. “The broad spectrum activity demonstrated by delafloxacin against a wide range of highly-resistant bacteria may offer the medical community a much needed treatment alternative for a variety of serious hospital treated infections, including complicated skin, hospital acquired pneumonia, endocarditis and others. We are proud of the work we have done at Rib-X to further the development of this compound.”

A copy of the R&D Directions 100 Great Investigational Drugs of 2009 report can be viewed at http://www.rddirections.com/magazines/randd/.

About Delafloxacin

Delafloxacin, a novel, broad spectrum, next-generation fluoroquinolone, has demonstrated better activity than other quinolones against Gram-positive bacteria, including isolates of MRSA that are resistant to other quinolones. The Company recently announced positive results from a Phase 2 trial utilizing the IV formulation of delafloxacin in complicated skin and skin structure infections (cSSSI). Delafloxacin successfully completed two previous Phase 2 trials with the oral formulation. In large panel microbiological testing, the compound has been shown to be at least 32-fold more potent than levofloxacin, ciprofloxacin, gatifloxacin and moxifloxacin against quinolone-resistant MRSA (MIC90 of less than or equal to 0.5 ug/ml for delafloxacin versus > 16 ug/ml for all other quinolones) and twice as potent as daptomycin against MRSA. Delafloxacin has also been shown to be more potent than existing quinolones against a range of Gram-positive, anaerobic and Gram-negative organisms. Rib-X is currently developing both IV and oral formulations of delafloxacin for use in surgical prophylaxis and other therapeutic arenas within the over $9.9 billion hospital antibiotic market.(2)

About cSSSI

Complicated skin and skin structure infections (cSSSI) encompass a wide range of serious infections involving the deeper soft tissue, including severe cellulitis and major abscesses. These infections may occur in patients with skin ulcers or burns, as well as patients who have undergone surgery or experienced other kinds of trauma. These infections affect over one million patients in the U.S. annually and are most commonly caused by Gram-positive bacteria, specifically Staphylococcus aureus and methicillin-resistant S. aureus (MRSA).

About Rib-X Pharmaceuticals, Inc.

Rib-X Pharmaceuticals, Inc. 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 ribosome, which performs an essential role in protein synthesis. Many known, commercially valuable antibiotics exert their effects by binding to the bacterial ribosome. 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 antibiotics that can be used for the treatment of either community- or hospital-acquired infections. In addition to delafloxacin, Rib-X is currently in Phase 2 trials with radezolid (RX-1741), an oxazolidinone that was discovered at Rib-X, as an oral/IV agent for treatment of serious Gram-positive infections. The Rx-04 discovery program is developing novel classes of antibiotics active against multi-drug resistant Gram-negative bacteria and the Rx-02 discovery program is focused on developing an IV/oral macrolide active against methicillin-resistant S. aureus, multidrug-resistant Streptococcus pneumoniae and S. pyogenes. Both delafloxacin and radezolid are currently in Phase 2 clinical trials.

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

(1) 100 Great Investigational Drugs; R&D Directions; March 2009

(2) Commercial and Pipeline Insight: Hospital Antibacterials - A market beyond MRSA; Datamonitor; August 24, 2007

CONTACT: Media: Irma Gomez-Dib, FD Life Sciences, +1-212-850-5761,
irma.gomez-dib@fd.com, or Investors: John Capodanno, FD Life Sciences,
+1-212-850-5705, John.capodanno@fd.com

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