SER-109 Reduces Rate of Recurrent CDI


The treatment was well-tolerated, with all serious treatment emergent adverse events considered not related to the treatment.

SER-109 Reduces Rate of Recurrent CDI

Matthew D. Sims, MD, PhD

SER-109, an investigational live microbiota therapeutic, was well-tolerated, safe, and effective in a new trial of patients with recurrent clostridiodes difficile infections (CDI).1

A team, led by Matthew D. Sims, MD, PhD, Section of Infectious Diseases and International Medicine, Department of Internal Medicine, Beaumont Hospital, evaluated the safety and rate of CDI recurrence following SER-109 administration.

The Need

“A safe and effective treatment for recurrent Clostridioides difficile infection is urgently needed,” the authors wrote. “Antibiotics kill toxin-producing bacteria but do not repair the disrupted microbiome, which promotes spore germination and infection recurrence.”

In the phase 3, single-arm, open label ECOSPOR IV trial, the investigators examined patients at 72 US and Canadian outpatient sites between October 2017 and April 2022. Each patient was an adult with recurrent CDI.

The participants were divided into 2 cohorts—rollover patients from the ECOSPOR III trial who had CDI recurrence diagnosed by toxin enzyme immunoassay (n = 29) and patients with at least 1 CDI recurrence (diagnosed by polymerase chain reaction [PCR] or toxin EIA), inclusive of their acute infection at study entry (n = 234).

The Regimen

Each participant was treated with 4 capsules of SER-109 daily for 3 days following symptom resolution after antibiotic treatment for CDI.

The investigators sought main outcomes of safety, measured as the rate of treatment-emergent adverse events in patients treated with the study drug, as well as the cumulative rates of recurrent CDI through week 24 in the intent-to-treat population.

The team screened 351 total patients and included 263 participants with a mean age of 64 years in the final analysis.

The results show 29.3% (n = 77) of patients were enrolled at their first CDI recurrence and 53.6% (n = 141) of participants had treatment emergent adverse events.

However, while the majority of adverse events were mild to moderate and gastrointestinal in nature, there were 8 (3.0%) total deaths and 33 patients (12.5%) who developed serious treatment emergent adverse events, none of which were deemed treatment related.

The results also show 8.7% (n = 23; 95% confidence intervals [CI], 5.6-12.8%) had recurrent CDI at week 8 (n = 4; 13.8%; 95% CI, 3.9-31.7% in cohort 1 and n = 19; 8.1%; 95% CI, 5.0-12.4% in cohort 2).

The results were similar at week 8 (n = 5; 6.5%; 95% CI, 2.1%-14.5%) as in patients with 2 or more recurrences (n = 18; 9.7%; 95% CI, 5.8%-14.9%).

After further analysis of select baseline characteristics, the investigators found low recurrent CDI rates in the cohort of patients aged younger than 65 years, compared to those older than 65 years (n = 5; 4.0%; 95% CI, 1.3%-9.0% vs n = 18; 13.1%; 95% CI, 8.0%-20.0%).

The same was true for patients enrolled on positive PCR results compared to those with positive toxin EIA (n = 3; 4.3%; 95% CI, 0.9%-12.2% vs n = 20; 10.4%; 95% CI, 6.5%-15.6%).

“In this trial, oral SER-109 was well tolerated in a patient population with recurrent CDI and prevalent comorbidities,” the authors wrote. “The rate of recurrent CDI was low regardless of the number of prior recurrences, demographics, or diagnostic approach, supporting the beneficial impact of SER-109 for patients with CDI.”


Sims MD, Khanna S, Feuerstadt P, et al. Safety and Tolerability of SER-109 as an Investigational Microbiome Therapeutic in Adults With Recurrent Clostridioides difficile Infection: A Phase 3, Open-Label, Single-Arm Trial. JAMA Netw Open. 2023;6(2):e2255758. doi:10.1001/jamanetworkopen.2022.55758

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