Summit is developing ridinilazole as a novel antimicrobial for Clostridium difficile Infection (CDI) with the goal of achieving comparable cure rates to standard of care, but reducing rates of recurrent disease. A phase 2 proof of concept study, with vancomycin as comparator, demonstrated these attributes with a comparable safety profile. A high fecal concentration of ridinilazole and little systemic exposure were noted. The rationale for this phase 3 study is to confirm the improvement in sustained clinical response of CDI over vancomycin and to compare the safety and tolerability of ridinilazole to that of vancomycin.



Eligible Ages
Over 18 Years
Eligible Genders
Accepts Healthy Volunteers

Inclusion Criteria

  1. At least 18 years of age, at the time of signing the informed consent.
  2. Signs and symptoms of CDI including diarrhea such that in the Investigator's opinion CDI antimicrobial therapy is required. Diarrhea is defined as a change in bowel habits, with ≥3 Unformed Bowel Movements (UBMs) (5, 6 or 7 on the Bristol Stool Chart) in the 24 h prior to randomization.
  3. The presence of either toxin A and/or B of C. difficile in the stool determined by a positive free toxin test, produced within 72 hours prior to randomization.
  4. Male or Female
  5. Male must agree to use contraception as detailed in the protocol during the treatment period and for at least 5 days after study treatment and refrain from donating sperm during this period.
  6. Female patient is eligible to participate if she is not pregnant, not breastfeeding, and either:

Not a woman of childbearing potential (WOCBP). A WOCBP who agrees to follow the contraceptive guidance per protocol during the treatment period and for at least 5 days after study treatment.

5. Documented signed informed consent and any authorizations required by local law (e.g. Protected Health Information [PHI]).

Exclusion Criteria

  1. More than one prior episode of CDI in the previous 3 months or more than 3 episodes in the past 12 months.
  2. A history of chronic diarrheal disease including inflammatory bowel disease (Crohn's disease or ulcerative colitis).
  3. Positive diagnostic test for other gastro intestinal (GI) pathogens within 2 weeks of randomization.
  4. Major gastrointestinal (GI) surgery (e.g. significant bowel resection) within 3 months of randomization (except appendectomy). Presence of a colostomy or ileostomy or likely requirement of an ostomy during the study.
  5. Life threatening or fulminant CDI with evidence of hypotension, septic shock, peritoneal signs or absence of bowel sounds, or toxic megacolon.
  6. Current history of significantly compromised immune system e.g.:
  7. HIV positive with a CD4<200 cells/mm3 within 6 months of randomization.
  8. Severe neutropenia with neutrophil count < 500 cells/mL.
  9. Concurrent immunosuppressive therapy for recent (within previous 6 months) or anticipated solid organ transplant or bone marrow transplant.
  10. Concurrent chemotherapy, radiotherapy or biologic for active malignancy. Or active malignancy with ablative chemotherapy within the past 3 months or anticipated during the study.
  11. More than one day (24 hours) of dosing of antimicrobial treatment active against CDI for the current episode of CDI prior to randomization.
  12. Prior or current use of anti-toxin antibodies including bezlotoxumab.
  13. Unable to discontinue products used to affect bowel movement or disease progression.
  14. Involved in a clinical trial and received an IMP for indications other than CDI within 1 month or five half-lives (whichever is longer) or within 3 months if the IMP was for CDI.
  15. Received an investigational vaccine against C.difficile.
  16. Patients that the Investigator feels are inappropriate for the study for any other reason e.g. have any conditions that would make the patient unsuitable for inclusion, patients not likely to complete the study for whatever reason, known hypersensitivity or intolerance to study IMPs, patients unwilling or unable to comply with protocol requirements

Study Design

Phase 3
Study Type
Intervention Model
Parallel Assignment
Primary Purpose
Quadruple (Participant, Care Provider, Investigator, Outcomes Assessor)
Masking Description
In both arms patients receive the same number of doses per day. Placebo tablets are included to maintain the same number and appearance of IP in both arms.

Arm Groups

ArmDescriptionAssigned Intervention
  • Drug: ridinilazole
    ridinilazole 200mg bid
Active Comparator
  • Drug: vancomycin
    vancomycin 125mg qid

Recruiting Locations

Montefiore Medical Center
Bronx, New York 10467

More Details

Summit Therapeutics

Study Contact

Lauren Kuhn
001 617 225 4464


Study information shown on this site is derived from ClinicalTrials.gov (a public registry operated by the National Institutes of Health). The listing of studies provided is not certain to be all studies for which you might be eligible. Furthermore, study eligibility requirements can be difficult to understand and may change over time, so it is wise to speak with your medical care provider and individual research study teams when making decisions related to participation.