Rib-X Pharmaceuticals, Inc., an antibiotics company with a broad development-stage pipeline, today announced the initiation of a Phase 2b clinical trial to evaluate delafloxacin, linezolid and vancomycin for the treatment of acute bacterial skin and skin structure infections (ABSSSI), including infections caused by methicillin-resistant Staphylococcus aureus (MRSA). The trial is designed to evaluate multiple objective efficacy measures based on the newly updated guidance from the US Food and Drug Administration (FDA) in order to support the design of the Phase 3 clinical studies. Delafloxacin is a novel fluoroquinolone antibiotic candidate that offers both IV and oral versatility. Delafloxacin has successfully completed three Phase 2 clinical studies and has been studied in approximately 1,000 subjects.