Summit will take scenic route up FDA mountain after regulator recommends more trials for C. diff therapy

Summit Therapeutics’ troubled C. difficile medicine may have a path forward after the FDA cleared a section of trail—however, it’s going to be a steep climb.

The California biotech met with the agency last week (PDF) to discuss lead asset ridinilazole, which failed to outperform the common antibiotic vancomycin in a phase 3 clinical trial at the end of 2021. Summit has been looking for a way to advance the asset anyway, pitching potential partnerships or an acquisition as a way forward in March.

Neither of those have come to fruition as of yet, but now Summit says the FDA has opened a window by suggesting “at least one” more clinical trial could help secure a marketing authorization for ridinilazole. 

The brief update did not say what Summit will need to prove in the new trial or trials. But the latest Ri-CoDIFy trial readout showed that ridinilazole was not superior to vancomycin. Summit’s therapy is a “precision antibiotic” to treat infections with the common bacteria C. diff that can cause severe diarrhea and inflammation of the colon.

“This pathway would involve reasonable efforts that would likely involve at least one additional clinical trial,” Summit said in a Thursday press release. “We plan to explore this possibility.”

But the process of developing one or more clinical trials and seeing them through to clinical evidence could take years. The Ri-CoDIFy trials were posted in 2018, with a completion date of December 2021, according to the FDA’s clinical trials database. 

Summit will present results from the phase 3 Ri-CoDIFy program at IDWeek 2022 in Washington, D.C., in October.

The markets shrugged off the setback, with Summit’s shares trading up almost 2% around 97 cents Thursday morning.