Positive Phase IIb results position Synthetic Biologics’ Ribaxamase as serious contender for C. difficile Prophylaxis


During the 9th Annual Biotech Showcase Conference in San Francisco, Synthetic Biologics announced positive top-line numbers for the primary endpoint of its Phase IIb trial for ribaxamase, the company’s most advanced pipeline product for the prevention of hospital-acquired Clostridium difficile infections (CDIs). GlobalData believes these results could place the drug in a strong position within the CDI prophylaxis pipeline.

Ribaxamase, also known as SYN-004, is an orally administered synthetic beta-lactamase initially developed as an adjunctive therapy to intravenous (IV) beta-lactam antibiotics including cephalosporins and penicillins. This investigational drug utilizes an innovative approach, preventing beta-lactam antibiotics from accumulating in the gastrointestinal (GI) tract, thereby preserving the natural balance of the gut microbiome—the body’s symbiotic barrier against bacterial infections. Through this novel mode of action, ribaxamase could potentially reduce the risk of CDIs for patients who are prescribed beta-lactam antibiotics.

In the double-blind, placebo-controlled Phase IIb trial, 412 patients receiving IV ceftriaxone were co-administered either a course of placebo or ribaxamase, and monitored for the onset of CDIs and other healthcare-acquired infections for an additional six weeks.

Top-line results suggest that ribaxamase reached the primary endpoint by reducing the relative risk of developing CDIs by 71.4%

Top-line results suggest that ribaxamase reached the primary endpoint by reducing the relative risk of developing CDIs by 71.4%, as well as reducing the rates of vancomycin-resistant enterococci (VRE) colonization. A good safety profile was also observed, with ribaxamase exhibiting comparable adverse events to the placebo group. Although the analysis of the clinical trial is ongoing, the results encouraged Synthetic Biologics to announce its goal of initiating Phase III trials by the end of 2017.

As a prophylactic for CDIs, ribaxamase has potential access to a large patient population, with the company indicating a price allowing for maximum market penetration. GlobalData looks forward to seeing if the positive results for ribaxamase in conjunction with ceftriaxone will extend to other common beta-lactam antibiotics, which Synthetic Biologics intends to investigate during the upcoming Phase III trials.

Ribaxamase may face tough competition from several pipeline vaccines under development to protect against C. difficile. Sanofi Pasteur’s vaccine is the most advanced in the pipeline, and is currently being evaluated in Phase III clinical trials, with Pfizer and Valneva both having announced positive results from Phase II trials for their own candidates. These companies will all be looking to command their own share of the marketplace, although the Phase IIb results for ribaxamase position it to be a serious contender.