Microbiome Therapy (SER-109) for Recurrent Clostrioides Difficile

P Feuerstadt et al. N Engl J Med 2022; 386:220-229. DOI: 10.1056/NEJMoa210651. SER-109, an Oral Microbiome Therapy for Recurrent Clostridioides difficile Infection

Background: “SER-109, an investigational oral microbiome therapeutic composed of live purified Firmicutes bacterial spores, was developed to reduce the risk of C. difficile infection recurrence.14 We hypothesized that these spore-forming bacteria would compete metabolically with C. difficile for essential nutrients, modulate bile-acid profiles to reestablish resistance to colonization, or have both of these effects. Here, we report the 8-week efficacy and safety results from a phase 3 [double-blind, randomized, placebo-controlled] trial involving patients with recurrent C. difficile infection, along with supportive microbiome engraftment and metabolomic analyses.”

Methods: N=182 enrolled in the “ECOSPOR III” trial; all patients had at least 3 infections in past year and positive toxin test. After standard-of-care antibiotic treatment, patients received SER-109 or placebo (four capsules daily for 3 days). The primary efficacy objective was to show superiority of SER-109 as compared with placebo in reducing the risk of C. difficile infection recurrence up to 8 weeks after treatment.

Key findings:

  • The percentage of patients with recurrence of C. difficile infection was 12% in the SER-109 group and 40% in the placebo group (relative risk, 0.32)
  • The recurrence risk following SER-109 was even lower after fidaxomicin than vancomycin: relative risk, 0.09 [95% CI, 0.01 to 0.63] with fidaxomicin and 0.41 [95% CI, 0.22 to 0.79] with vancomycin
  • SER-109 dose species were detected as early as week 1 and were associated with bile-acid profiles that are known to inhibit C. difficile spore germination.

My take: This study shows that clinical outcomes with C difficile may be improved by the addition of this microbiome therapeutic after standard therapy. Engraftment of Firmicutes bacteria as a dominant component of the microbiome is generally associated with a healthy state. This opens the door for treatment of other conditions that may benefit from microbiome modulation.

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