October 27, 2008

Rib-X’s Phase II Skin Structure Infections Study Meets End Point

Rib-X Pharmaceuticals, a developer of antibiotics for the treatment of antibiotic-resistant infections, has announced positive results from a Phase II clinical trial with the oral form of its compound, radezolid, for the treatment of uncomplicated skin and skin structure infections.

The open-label trial met both its primary (efficacy) and secondary (safety) endpoints. All doses of radezolid were as efficacious as linezolid and demonstrated a good safety profile.

The study also showed that radezolid was approximately four times more potent than linezolid against bacteria cultured from subjects in the study, including against methicillin-resistant Staphylococcus aureus (MRSA), with MIC90s of 0.5mg/l and 2mg/l respectively. MIC90s for other relevant bacterial isolates in the study were 0.5mg/l and 2mg/ for MRSA and 0.25mg/l and 1.0ug/ml for Streptococcus pyogenes for radezolid and linezolid, respectively. MIC90 is defined as the minimum inhibitory concentration necessary to inhibit the growth of 90% of the bacteria.

The study also showed clinical cure rates with a 95% confidence interval in clinically evaluable patients were 97.4% for patients treated with radezolid at a dosage of 450mg once a day (38/39); 94.4% for patients treated with radezolid 450mg twice a day (36/39); and 97.4% for patients treated with linezolid 600mg twice a day (37/38).

Clinical cure rates among clinically evaluable patients with confirmed MRSA infections with a 95% confidence interval were 100% and 92.9% for patients treated with radezolid once a day (8/8) and twice a day (13/14), respectively, and 93.3% for patients treated with linezolid 600mg twice a day (14/15). In microbiologically evaluable patients, eradication was achieved in 100% of the group treated with radezolid at 450mg once a day (20/20), and 87.5% in the group receiving radezolid 450mg twice daily (21/24), versus 91.3% in the group receiving linezolid 600mg twice daily (21/23).

Susan Froshauer, president and CEO of Rib-X Pharmaceuticals, said: "Additionally, these results further validate Rib-X's proprietary discovery and development approach which led to the identification of this compound as well as multiple other novel compounds in various classes which are able to circumvent bacterial resistance mechanisms."