RBX2660 is Safe, Superior to Antibiotic-Treated Controls for Preventing Recurrent difficile, and May Rehabilitate Patient Microbiomes: Open Label Trial Results

Robert Orenstein DO, Erik Dubberke MD, MSPH, Sahil Khanna MBBS, Gail Hecht MD, Herbert Dupont MD, Christine H. Lee MD, Ken Blount PhD, Sharina Carter PhD

RBX2660 is Safe, Superior to Antibiotic-Treated Controls for Preventing Recurrent Clostridium difficile, and May Rehabilitate Patient Microbiomes: Open Label Trial Results Poster Image

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Infectious Diseases Week (ID Week)
October 4-8, 2017, San Diego, CA


  • Effective treatment options for recurrent C. difficile infection (rCDI) are limited
  • High recurrence rates are associated with the current standard of care
  • RBX2660, a standardized microbiota-based drug, was efficacious for preventing rCDI in a double-blinded Phase 2 clinical trial (PUNCH CD 2)
  • We report results from a subsequent open-label trial that evaluated:
    • safety and efficacy of RBX2660 for preventing rCDI relative to matched historical controls
    • microbiome altering-activity of RBX2660


  • Prospective, multicenter, open-label Phase 2 study (NCT02589847)
  • Inclusion criteria: >18 years old with documentation of either 2 recurrences after a primary episode and has completed at least two rounds of standardof-care oral antibiotic therapy, or at least 2 episodes of severe CDI resulting in hospitalization; a positive stool test for the presence of toxigenic C. dfficile within 60 days prior to enrollment
  • Exclusion criteria: History of irritable bowel inflammatory bowel disease (ulcerative colitis, Crohn’s disease or microscopic colitis), irritable bowel syndrome, chronic diarrhea; celiac disease; colostomy; evidence of active colitis; known exposure to antibiotics within 6 months after study enrollment; compromised immune system (white blood cell count <1000 cells/μL)
  • Antibiotics were discontinued 24-48 hours prior to the first enema
  • Participants received up to 2 doses of RBX2660 delivered via enema with doses 7 days apart
  • Safety was assessed via a patient diary: in clinic at 1, 4, and 8 weeks and via telephone at 2, 3, between 5-7 weeks, and at 3, 6, 12 and 24 months.
  • Success was defined as the absence of CDI at 8 weeks following completion of the last treatment. Patients were classified as a treatment failure if all four(4) of the following criteria were met: recurrence of diarrhea less than 8 weeks after administration of the last assigned study enema, a positive laboratory diagnosis of C. difficile as conducted and reported by the study investigator, a need for retreatment for CDI, and no other cause for diarrhea
  • Stool samples were collected at baseline and at 7, 30, and 60 days after treatment


  • Microbiota-based drug manufactured from live human-derived microbes using standardized processes and controls
  • Each unit of RBX2660 is identified by a unique batch number and is traceable to a specific donor and recipient

Historical Control Cohort

  • Subjects who matched key inclusion/exclusion criteria of the clinical study but who were only treated with standard of care antibiotics for powered efficacy
    analysis of RBX2660
  • Conducted by Loyola University, Mayo Clinic Arizona, Mayo Clinic Rochester, and Mid-Atlantic Permanente Research Institute
  • Applied published best practices in chart review methodology
    • Chart search methods and sampling criteria to avoid bias
    • Standardized, annotated abstraction forms
    • Pilot testing
    • Early and frequent site monitoring
  • Data collected from date of diagnosis of first CDI episode through six months after resolution of last episode or last encounter date, whichever is later

Microbiome Analysis

  • Patients in the RBX2660 treatment arm only submitted stool samples at baseline (pre-treatment) and at 7, 30, and 60 days after treatment
  • Stool samples were sequenced using BoosterShot (CoreBiome, Minneapolis, MN), an ultra-shallow shotgun sequencing that generates taxonomic profiles with species-level resolution
  • The variable region V4 was targeted to identify the operational taxonomic units (OTUs) in each sample
  • Relative abundance data from successful patient samples were grouped longitudinally and compared using a Bray-Curtis dissimilarity calculation with non-metric multi-dimensional scaling. Additional analyses were performed
    based on the Dirichlet-Multinomial distribution to compare group mean relative taxonomic abundances (pi) and within group over dispersion (theta)
  • Differentiation between sample communities was visualized using a Kullback-Leibler(KL) divergence analysis model (BioRankings, St. Louis, MO), a measure of the difference between microbial diversity at different time points or between different samples. A Wald-type test was used to assess the statistical significance of intergroup differences


  • 132 RBX2660 and 110 historical control subjects were enrolled at 29 centers and 4 centers, respectively (USA & Canada)
  • RBX2660’s efficacy in preventing rCDI (78.8%) was higher than CDI-free rates in the Historical Control group (51.8%, p<0.0001) (Figure 1)
  • A total of 482 adverse events (AEs) were reported by 99 RBX2660 subjects (73.5%) compared to 691 AEs among 69 historical controls (62.7%) (Tables 2,3)
  • Following treatment, RBX2660-treated subjects’ microbiomes were significantly altered compared to baseline and more closely resembled the RBX2660 microbiome profile than at baseline. Notably, the relative proportions of Bacteroidia and Clostridia increased after treatment, while the relative proportions of Gamma-proteobacteria decreased (Figures 2-4)


  • This open-label Phase 2 study demonstrates RBX2660’s efficacy in preventing rCDI compared to an antibiotic treated historical control group
  • The RBX2660 safety profile is consistent with results from previous clinical trials
  • Microbiota analysis suggests that RBX2660 may rehabilitate patient microbiota