Rib-X Pharmaceuticals, Inc. an antibiotics company with a broad development-stage pipeline, announced the initiation of a phase II b 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 III clinical studies. Delafloxacin is a novel fluoroquinolone antibiotic candidate that offers both IV and oral versatility. Delafloxacin has successfully completed three phase II clinical studies and has been studied in approximately 1,000 subjects.

The phase II b study will be a randomized, double blind, comparison of delafloxacin, linezolid and vancomycin using objective efficacy measures to evaluate the relative clinical responses in subjects with ABSSSI, i.e., an infection involving subcutaneous tissues or requiring surgical intervention, of one of the following 4 types: cellulitis/erysipelas, wound infection, major cutaneous abscess, or burn infection.

The trial will enroll a total of 240 subjects across multiple centres in the United States. Subjects will be randomized into three equally sized treatment arms to receive either delafloxacin, 300 mg every 12 hours, or the recommended dosing for linezolid or vancomycin. The primary endpoints for the study are to assess the relative clinical response to delafloxacin, linezolid, and vancomycin and to assess the utility, variability, and measurement techniques of several objective measures of clinical efficacy for use in future clinical trials.

Efficacy will be evaluated at multiple time points during the study, with a focus on the first five days of administration, through assessments of objective signs and symptoms of infection (such as fever), measurement of the extent/size of infection, measurement of biochemical markers of inflammation, and culture and susceptibility testing of bacterial isolates.

“In prior clinical and preclinical studies, delafloxacin has been a well-tolerated, broad spectrum antibiotic candidate that effectively targets key resistant pathogens, such as MRSA, that cause life-threatening hospital-treated infections,” said Mark Leuchtenberger, president and CEO at Rib-X. “By choosing linezolid, the standard of care for IV to oral use, and vancomycin, the standard first-line treatment for MRSA infections, as comparator compounds, we believe this study will further strengthen the clinical profile for delafloxacin as an empiric first line, hospital-focused novel fluoroquinolone that offers both IV and oral versatility in the treatment of difficult to treat infections. We believe the results from this study could provide a roadmap for optimizing our phase III trial design in this indication. To complement this study, we plan to initiate a phase I study later in the year to assess the phase III oral formulation.”

Rib-X Pharmaceuticals is developing broad spectrum antibiotics with superior coverage, safety and convenience to deliver new standards of care for patients with serious infections.