Positive topline results were announced from a pivotal phase 3 study investigating the oral microbiome therapeutic SER-109 (Seres Therapeutics) for the treatment of recurrent Clostridioides difficile infection (CDI).

SER-109 contains purified bacterial spores of multiple Firmicute species obtained from the stool of healthy human donors. The multicenter, placebo-controlled ECOSPOR III study evaluated the efficacy and safety of SER-109 in 182 adult patients with recurrent CDI (defined as a history of ≥3 CDI episodes within 9 months, including the current episode) who have received standard of care antibiotic treatment.

Patients were randomized 1:1 to receive either SER-109 or placebo orally for 3 consecutive days. The primary end point was the proportion of patients with recurrent CDI at up to 8 weeks.

Results showed the CDI recurrence rate was 11.1% in the SER-109 group compared with 41.3% for the placebo group (30.2% absolute reduction; P <.001); the SER-109 treatment arm relative risk was 0.27 (95% CI, 0.15-0.51) vs placebo. The Company plans to present additional results through 24 weeks (key secondary end point) at a future date. 

The safety profile of SER-109 was similar to that seen in the placebo arm. SER-109 was well tolerated with no treatment-related serious adverse events. The most common adverse events observed in both the SER-109 and placebo arms were flatulence, abdominal distention, and abdominal pain.

Patients in the ECOSPOR III study who experienced a recurrent CDI after treatment with SER-109 will be eligible to enroll in the ongoing open-label phase 3 ECOSPOR IV study to receive a second regimen of SER-109.

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“Based on these highly positive SER-109 ECOSPOR III results, we believe that this novel microbiome therapeutic candidate could potentially provide a much-needed effective oral treatment option for the approximately 170,000 patients in the US that suffer from recurrent CDI annually,” said Lisa von Moltke, MD, FCP, Chief Medical Officer of Seres.

The FDA previously granted Breakthrough Therapy and Orphan Drug designations to SER-109.

For more information visit serestherapeutics.com.


Seres Therapeutics announces positive topline results from SER-109 phase 3 ECOSPOR III study in recurrent C. difficile infection. https://www.businesswire.com/news/home/20200810005194/en/Seres-Therapeutics-Announces-Positive-Topline-Results-SER-109. Accessed August 10, 2020.