Purified Firmicutes Spores Reduce Recurrent C. difficile Infections Over 24 Weeks

computer generated 3D illustration of a clostridium difficile bacteria
Researchers reported on the safety and efficacy of the investigational agent SER-109 at reducing rates of recurrent C. difficile infections over 24 weeks.

The following article is a part of conference coverage from the Digestive Disease Week 2021 Annual Meeting , held virtually from May 21 to 23, 2021. The team at Gastroenterology Advisor will be reporting on the latest news and research conducted by leading experts in gastroenterology. Check back for more from DDW 2021.


An investigational microbiome treatment consisting of purified Firmicutes spores reduced the rate of recurrent Clostridioides difficile (C. difficile) infections over 24 weeks compared with placebo, according to research presented at Digestive Disease Week 2021.

Treatment with the agent known as SER-109 previously helped patients achieve a 73% relative risk reduction in recurrence rates compared with placebo at 8 weeks in a phase 3 trial. In this longer-term efficacy and safety analysis of the double-blind trial, researchers examined the 24-week efficacy and safety of SER-109 vs placebo in 182 patients with recurrent C. difficile infection (rCDI) who had ≥3 infection episodes within 12 months of study entry.

At the start of the study, participants completed 10 to 21 days of fidaxomicin or vancomycin. Those who experienced resolution of symptoms were then randomly assigned to 4 capsules of SER-109 given for 3 days or a matching placebo. Randomization was stratified by age and antibiotics received.

A significantly lower proportion of patients in the SER-109 arm experienced rCDI at 24 weeks compared with participants in the placebo group (20.0% vs 49.9%, respectively; risk ratio [RR], 0.41; 95% CI, 0.26-0.65; P <.001).

Overall, SER-109 was considered well tolerated. The investigators noted the investigational therapy featured a safety profile similar to that of placebo. Frequently reported treatment-emergent adverse events (TEAEs) in the study were primarily gastrointestinal and mild to moderate in severity. There were no serious TEAEs, infections, deaths, or drug discontinuations related to SER-109.

The investigators suggest the durable efficacy seen with SER-109 in this study may lead to “a major paradigm shift in the clinical management of patients with recurrent CDI.” They wrote that the agent will soon be investigated in a currently enrolling open-label study.

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Korman L, Lashner B, Kraft C, et al. 24-week efficacy and safety data from ECOSPOR-III, a phase 3 double-blind, placebo-controlled randomized trial of SER-109, an investigational microbiome therapeutic for treatment of recurrent Clostridioides difficile infection. Poster presented at: Digestive Disease Week Annual Meeting; May 21-23, 2021. Abstract Fr572.