Inclusion Criteria:  

• Signed informed consent obtained before any trial-related procedures at screening.
• Subject aged ≥ 18 years old at screening.
• Medical record documentation of recurrent Clostridioides difficile infection (rCDI) per the trial definition that includes ≥ 1 recurrence after a primary C. difficile infection (CDI) episode, at screening.
• Stool test positive for the presence of toxigenic C. difficile or C. difficile toxin for the qualifying rCDI episode, documented at the time of CDI diarrhea, at screening.
• Eligible for fecal microbiota transplantation (FMT) as judged by the investigator or current treatment guidelines for rCDI in the United States (US).
• Candidate for colonoscopy as judged by the investigator.
• Currently taking or have just received a prescription for a course of antibiotics to ensure control of CDI-related diarrhea, at screening. The antibiotic course should be for a minimum of 10 consecutive days, and a maximum of 30 days in total (including intermittent dosing/pulse) before the antibiotic washout period.
• Adherence to at least one of the following conditions throughout the trial period:
  • The subject, if female, must:
    • Be post-menopausal (women ≥ 45 years with no menstrual period for ≥ 12 months without an alternative medical cause); or
    • Have been surgically sterilized; or
    • Have had a hysterectomy prior to screening; or
    • Use an adequate method of contraception (i.e., implants, injectables, hormonal intrauterine devices, combined hormonal contraceptives, having a vasectomized sexual partner, or total abstinence from heterosexual relations with no plans of becoming pregnant through insemination or in vitro fertilization).
  • The subject, if male, must:
    • Use a non-hormonal single-barrier contraception (i.e., condom); and
    • Use an adequate method of contraception if his female partner is of childbearing potential (i.e., not post-menopausal) as defined above;
      • This is however not required if the male subject is documented surgically sterile, remains sexually abstinent, when this is in line with his preferred and usual lifestyle, or if he has a female partner who is surgically sterilized, had a hysterectomy, or is post-menopausal. 
• Willing to abstain from consuming probiotics (including over-the-counter and prescription) from screening through 8 weeks after RBX2660 treatment.
• Willing to comply with trial procedures, including attending scheduled visits, completion of the electronic stool diary, providing stool samples for future exploratory research, and adherence to treatment plan.

Exclusion Criteria: 

• Use or planned use of systemic antibiotics for an indication other than the qualifying rCDI episode.
• Current disease symptoms (e.g., diarrhea) caused by a confirmed intestinal pathogen other than C. difficile.
• Current uncontrolled chronic diarrhea not related to CDI.
• Current refractory CDI, i.e., CDI diarrhea not improving with antibiotics used to treat CDI.
• Fecal microbiota transplantation, treatment with other microbiota-based therapies, or treatment with RBX2660 other than the IMP:
  • Within 6 months before screening; or
  • Between screening and baseline.
• Receipt of CDI vaccine or treatment with CDI monoclonal antibodies:
  • Within 12 months before screening; or
  • Between screening and baseline.
• Compromised immune system including, but not limited to, inherited/primary and acquired immune disorders as judged by the investigator.
• Solid-organ transplant recipient.
• Initiation or escalation of systemic immunosuppressive agents, at the discretion of the investigator, for any condition:
  • During the 8 weeks before screening; or
  • Between screening and baseline.
    • Subjects on a stable dose of systemic immunosuppressants (e.g., ≤20 mg/day prednisone equivalent daily dose) may be considered eligible at the discretion of the investigator.
• Current or planned therapy that may cause diarrhea.
• Current or planned systemic cancer treatment (e.g., chemotherapy, radiotherapy, or other).
• Diagnosis of short bowel syndrome.
• Current uncontrolled gastrointestinal motility disorders.
• Evidence of active, severe, or fulminant colitis.
• Diagnosis of toxic megacolon.
• Have a current colostomy or ileostomy.
• Major gastrointestinal tract surgery (this does not include appendectomy or cholecystectomy):
  • Within 60 days before screening; or
  • Between screening and baseline.
• Planned surgery requiring perioperative antibiotics.
• Life expectancy of < 6 months, as judged by the investigator at screening.
• Current abuse of alcohol or drugs, as judged by the investigator at screening.
• Pregnant (as confirmed by a positive pregnancy test), breastfeeding, or intending to become pregnant, during trial participation.
• Participation in any interventional clinical trial during the past 12 weeks before screening.
• Known or suspected hypersensitivity to polyethylene glycol 3350.
• Inability to participate in the trial for other reasons, as judged by the investigator at screening.

Eligibility last updated 10/13/22. Questions regarding updates should be directed to the study team contact.