Investigational Microbiome Therapeutic SER-109 Reduces Risk for CDI Recurrence

Recurrent Clostridioides difficile infection rates were low among patients who received SER-109, supporting its expanded use in community practice.

The investigational oral microbiome therapeutic SER-109 is safe and well-tolerated in patients with recurrent Clostridioides difficile infection (CDI), according to findings published in JAMA Network Open.

Researchers conducted a single-arm, open-label, multicenter phase 3 trial to evaluate the safety of SER-109 and its effect on CDI recurrence among adult patients. Assessed outcomes included the rate of treatment-emergent adverse events (TEAEs) and the rate of recurrent CDI through 24 weeks.

The final analysis included 263 patients with recurrent CDI, of whom the mean age was 64 years, 68.4% were women, and 92.4% were White. The most common comorbidities among the patients included cardiac disorders (31.2%), neoplasms (21.3%), type 2 diabetes (10.6%), chronic obstructive pulmonary disease (9.9%), chronic kidney disease (9.5%), and hepatobiliary disorders (8.7%).

A total of 141 (54%) patients had TEAEs, most of which were of mild to moderate severity. Fatigue and urinary tract infections (UTIs), including urosepsis, also were reported, but the researchers ruled out UTI occurrence as related to SER-109 treatment.

At week 8, CDI recurrence was observed in 23 patients (8.7%; 95% CI, 5.6%-12.8%), with recurrence confirmed in 16 patients and inferred in 7. Further analysis at week 24 showed CDI recurrence in 36 patients (13.7%; 95% CI, 9.8%-18.4%), with recurrence confirmed in 22 patients and inferred in 14.

These data support an important role for SER-109 as part of a paradigm shift in the clinical management of recurrent CDI.

Recurrent CDI rates remained low (range, 4.0%-13.1%) in analyses adjusted for patient age, sex, and antibiotic regimen and diagnostic test used for the qualifying CDI episode.

Further analysis showed lower recurrent CDI rates in patients younger than 65 years vs 65 years and older (4.0% vs 13.1%). In addition, recurrent CDI rates were lower in patients with polymerase chain reaction- vs toxin enzyme immunoassay-confirmed CDI (4% vs 10%).

Study limitations include the open-label design and the predominance of White patients.

“These data support an important role for SER-109 as part of a paradigm shift in the clinical management of recurrent CDI,” the researchers concluded.


Sims MD, Khanna S, Feuerstadt P, et al; for the ECOSPOR IV Investigators. 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