Time to Recurrence of Clostridioides Difficile Infection (rCDI) is Rapid Following Completion of Standard of Care Antibiotics: Results from ECOSPOR-III, a Phase 3 Double-Blind, Placebo-Controlled Randomized Trial of SER-109, an Investigational Microbiome Therapeutic

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Conference Proceeding

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Open Forum Infectious Diseases



The natural history of CDI recurrence after antibiotics may be helpful to understand the window of opportunity for microbiome repair. ECOSPOR III evaluated the efficacy of SER-109, an investigational microbiome therapeutic, compared to placebo with rates of rCDI as the primary endpoint. SER-109 was superior to placebo in reducing the rate of rCDI following standard-of-care antibiotics at 8 weeks (12.4% vs 39.8%, respectively; P < 0.001). Herein, we describe results from the secondary endpoint, time to recurrence, in this well-characterized study population. Methods

A total of 182 C. difficile toxin+ adults with ≥ 3 CDI episodes and symptom resolution on CDI antibiotics were randomly assigned to SER-109 (4 capsules orally x 3 days) or placebo. Recurrence for this analysis was defined as ≥ 3 unformed stools/day for ≥ 48 hours, ± C. difficile stool toxin test, and an investigator decision to treat. Time to CDI recurrence was analyzed using observed data and Kaplan-Meier methods. Data were not imputed for subjects lost to follow-up or discontinued from study. Subjects who did not have a CDI recurrence were censored on the date of study completion, study discontinuation or death. Results

Through 24 weeks, 11/89 (12.4%) SER-109 and 36/93 (38.7%) placebo subjects had rCDI (P < 0.001). Of all recurrence events in the study population, 16/47 (34.0%) were observed within 1 week; 30/47 (63.8%) within 2 weeks; and 34/47 (72.3%) within 4 weeks after randomization, highlighting the rapid onset of recurrence. On the other hand, 12/47 (25.5%) recurrences occurred between 4 and 12 weeks, highlighting late onset of recurrence in a subset of patients (Table). Significantly lower rates of recurrence in patients on SER-109 compared to placebo was maintained throughout the 24-week follow-up (Figure).

Time of rCDI


SER-109, an investigational oral microbiome therapeutic, maintained significant efficacy in reducing rCDI vs placebo through 24 weeks. About two-thirds of all recurrences occurred within 14 days of antibiotic completion highlighting the need for rapid repair of the disrupted microbiome. However, the significant number of late recurrences in the placebo arm also highlights that rCDI trials limited to 4 weeks of follow-up after treatment completion may underestimate recurrences.




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