SAN DIEGO (FRONTLINE MEDICAL NEWS) Hospitalized patients who received the investigational oral agent ribaxamase had a 71% reduction in the development of new Clostridium difficile infection, results from a phase 2b study showed.

At an annual scientific meeting on infectious diseases, lead investigator John F. Kokai-Kun, PhD , said that the finding represents a paradigm shift in the use of intravenous beta-lactam antibiotics to prevent opportunistic infections. “We currently treat Clostridium difficile infection (CDI) with antibiotics, which attack the vegetative cells,” said Dr. Kokai-Kun, vice president of nonclinical affairs for Rockville, Md.–based Synthetic Biologics, which is developing ribaxamase. “Since C. diff. is primarily a toxin-mediated disease, certain products seem to neutralize the toxin. There’s also been work with probiotics and prebiotics to try to strengthen and repair the dysbiotic colon. Fecal replacement therapy has been shown to be fairly effective for treatment of recurrent C. diff. infection. What if we could simply block the initial insult that leads to this cascade? That’s the damage caused to the gut microbiome by the antibiotic that’s excreted to the intestine.”

That’s where ribaxamase comes in, he said at the combined annual meetings of the Infectious Diseases Society of America, the Society for Healthcare Epidemiology of America, the HIV Medicine Association, and the Pediatric Infectious Diseases Society. Ribaxamase is an orally administered beta-lactamase designed to degrade penicillin and cephalosporins in the intestinal lumen. It’s formulated for release in the proximal small intestine and is expected to be given during or a short time after administration of IV beta-lactam antibiotics such as ceftriaxone. “This is expected to degrade the excess antibiotics that are excreted into the small intestine via the bile,” Dr. Kokai-Kun explained. “It’s designed to prevent disruption of the gut microbiome and thus protect from opportunistic GI infections like CDI.” Early-stage clinical studies demonstrated that ribaxamase was well tolerated and that it is not systemically absorbed, while phase 2 studies showed that ribaxamase degrades ceftriaxone in the intestine to below the level of detection while not affecting the pharmacokinetics of ceftriaxone in the plasma.

For the current study, 412 patients were enrolled at 84 multinational clinical sites. These patients were admitted to the hospital for treatment of a lower respiratory tract infection and were randomized 1:1 to receive ceftriaxone plus 150 mg ribaxamase or ceftriaxone plus placebo. Patients in both groups could also receive an oral macrolide at the discretion of the clinical investigator. The researchers also obtained fecal samples at screening, 72 hours post antibiotic treatment, and at the end of a 4-week follow-up visit, to determine colonization by opportunistic pathogens and to examine changes in the gut microbiome. Patients were monitored for 6 weeks for diarrhea and CDI. Diarrhea was defined as three or more loose or watery stools in a 24-hour period. “If that occurred, then we collected a sample, which was sent to the local lab to determine the presence of C. difficile toxins,” Dr. Kokai-Kun said.

The average age of study participants was 70 years, and about one-third in each arm received oral macrolides. The number of adverse events and serious adverse events were similar between active and placebo arms, and there was no trend associated with ribaxamase use. The lower respiratory tract infection cure rate to the ceftriaxone treatment was about 99% in both arms at 72 hours post treatment and at 2 weeks post treatment.

To analyze changes in the gut microbiome, the researchers conducted 16S rRNA sequencing of DNA extracted from fecal samples. In all, 652 samples were sequenced from 229 patients. Results from that analysis suggests that ribaxamase “appears to protect the gut microbiome from the onslaught of the ceftriaxone,” he said.

Ribaxamase reduced the incidence of new-onset CDI by 71%, compared with placebo (P = .045). “It apparently did this by protecting the integrity of the gut microbiome,” Dr. Kokai-Kun said. “There was also a significant reduction of new colonization by vancomycin-resistant enterococci at 72 hours and 4 weeks (P = .0001 and P = .0002, respectively) which is an opportunistic pathogen that is known to be able to inhabit gut microbiome when there is dysbiosis.”

The study was sponsored by Synthetic Biologics. Dr. Kokai-Kun is an employee of the company.