Inclusion Criteria - Part A (Screening):

• Patient or legal representative voluntarily agreed to participate by signing and dating the written informed consent form after trial has been fully explained.
• Patient 18 years of age or older.
• History of recurrent CDI defined as:
  • ≥ 3 episodes of CDI, with 2 episodes occurring within the previous 6 months (inclusive of the current episode); OR
  • Patients with a history of 2 episodes of CDI occurring within the previous 6 months (inclusive of the current episode) may be eligible if 65 years of age or older.
• For the qualifying CDI episode, the following criteria must be satisfied:
  • History of diarrhea (> 3 unformed stools per day) for 2 or more consecutive days that is clinically consistent with CDI; AND
  • Documented positive stool test by local laboratory for toxigenic C. difficile (toxin EIA or polymerase chain reaction [PCR]-based testing) for the current CDI episode and within 45 days prior to Randomization; AND
  • Received a course of SOC CDI antibiotics for the most recent CDI episode (for 10 to 21 days, with exact duration, antibiotic type, and dose at the discretion of the Investigator); AND
  • Demonstrated an adequate clinical response, defined as ≤ 3 unformed stools in 24 hours for 2 or more consecutive days during SOC CDI antibiotics prior to Randomization.
    • NOTE: ALL Qualifying CDI episode requires CLINICAL and LABORATORY CONFIRMATION of eligibility by Medical Monitor.
• Females (assigned at birth) must fulfill at least 1 of the following criteria:
  • Postmenopausal, defined as amenorrhea ≥ 1 year; or
  • Surgically sterile: hysterectomy, bilateral oophorectomy, or tubal ligation; or 5.3 Abstinent or willing to use adequate contraception from Screening through the Week 24 visit.
• Males (as assigned at birth) must fulfill the following criteria:
  • Abstinent or willing to use adequate contraception from Screening through the Week 24 visit.

Exclusion Criteria - Part A (Screening):

• Known stool samples testing positive for enteric pathogens (e.g., Salmonella, Shigella, diarrhoeagenic E. coli, Campylobacter, Giardia) within 28 days prior to Screening.
• Inability to ingest capsules (e.g., severe nausea, vomiting, gastroparesis, gastric outlet obstruction, dysphagia and/or history of chronic aspiration).
• Active or suspected ileus, toxic megacolon, or bowel obstruction.
• Historical or current diagnosis of inflammatory bowel disease (e.g., Crohn’s disease, ulcerative colitis, indeterminate colitis, or microscopic colitis).
• Recent diagnosis (< 6 months prior to Screening) of diarrhea-predominant irritable bowel syndrome (post-infection or not related to an enteric infection). Patients with diarrhea-predominant irritable bowel syndrome ≥ 6 months prior to Screening may be randomized following confirmation of eligibility.
• Current diagnosis of chronic diarrheal illness with pre-CDI baseline diarrhea. This includes but is not limited to celiac disease, bile salt diarrhea, chronic pancreatitis, and short gut syndrome.
• Past administration of bezlotoxumab (Zinplava™), or past enrollment in a C. difficile vaccine trial within 12 months prior to Randomization.
• Participation in PRISM3 (CDI-001) or PRISM-EXT (CP101-CDI-E02) or received CP101 at any time in the past.
• Fecal transplant or other live microbiome therapeutics for any condition, regardless of route of administration within 12 months prior to Randomization.
• Initiation of any systemic cancer treatment (e.g., chemotherapy, radiotherapy, biologic, immunotherapy, others) for active malignancy that is planned 8 weeks prior to Randomization or during the 8 weeks following Randomization. Patients on maintenance treatment for malignancy may be randomized following confirmation of eligibility. NOTE: Patients on hormone therapy alone are eligible.
• Known primary or secondary immunodeficiency, including but not limited to, IgA deficiency, common variable immunodeficiency, severe combined immunodeficiency, or human immunodeficiency virus/acquired immune deficiency syndrome.
• History of solid organ transplantation or stem cell transplant.
• Initiation or dose escalation of systemic immunosuppressive agents, at the discretion of the Investigator, for any condition during the 8 weeks prior to Randomization or planned during the 8 weeks following Randomization. Examples may include but are not limited to corticosteroid agents given orally or intravenously, cyclosporine, tacrolimus, or tumor necrosis factor inhibitors. Patients on stable low dose of systemic immunosuppressive agents or short courses (< 2 weeks) may be randomized following confirmation of eligibility.
• Major intra-abdominal surgery (e.g., bowel resection) within the past 60 days prior to Screening (excluding appendectomy or cholecystectomy)and/or planned invasive surgery/hospitalization during the trial.
• History of total colectomy or ileostomy.
• Use of a systemic antibiotic for any condition (other than CDI) during the Screening period, or any anticipated use of a systemic antibiotic for any condition other than CDI during the trial for 8 weeks after Randomization. This includes patients who have a known medical procedure that requires antibiotic prophylaxis (e.g., elective surgical procedure or dental procedure requiring prophylactic antibiotics) scheduled during the trial.
• Active drug, chemical, or alcohol dependency as determined by the Investigator through history or optional toxicology screen.
• Enrollment in any other investigational drug, device, or observational trial within 30 days or 5 half-lives of the last dose, prior to Randomization (Day 1) or at any time during this trial.
• Pregnant, breast-feeding, or planning to become pregnant during the trial.
• Clinically significant abnormal laboratory values including, but not limited to, white blood cell count ≥ 15 × 10^9 /L, absolute neutrophil count of < 1 × 10^9 neutrophils/L, or laboratory evidence of acute kidney injury at Investigators discretion, at Screening.
• Screening nasopharyngeal PCR test is positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).
• Any acute, chronic, or unstable medical comorbidity, psychiatric, social, or other circumstances that, in the opinion of the Investigator, may interfere with trial compliance, completion, or accurate assessment of trial outcomes/safety. Examples include but not limited to acute myocardial infarction, acute stroke, uncompensated congestive heart failure, or decompensated liver disease.
  • NOTE: Trial patients may be screened while an inpatient in an acute care facility/hospital but must be discharged from inpatient medical admission prior to Randomization.
• Life expectancy < 24 weeks.
• Known hypersensitivity to CP101 or any component of its formulation or history of severe adverse reactions or other common drug class effects during prior exposure to similar compounds per the judgment of the investigator.

To be eligible for Randomization, the above listed Inclusion/Exclusion Criteria as well as the following additional Inclusion Criteria Part A - Randomization (Day 1) must be satisfied:

Inclusion Criteria - Part A Randomization (Day 1):

• An outpatient prior to Randomization. NOTE: Patient may be screened while an inpatient in an acute care facility/hospital but must be discharged from inpatient medical admission prior to Randomization. Patients residing in an assisted living center, long-term care facility, or rehabilitation ward/center may be randomized.
• Has received a course of SOC CDI antibiotics for the Qualifying CDI episode (for 10 to 21 days, with exact duration, antibiotic type, and dose at the discretion of the Investigator).
• Has an adequate clinical response, defined as ≤ 3 unformed stools in 24 hours for 2 or more consecutive days during SOC CDI antibiotics prior to Randomization.
• Patient has completed a CDI antibiotic washout (i.e., a minimum of 4 and a maximum of 7 days after cessation of SOC CDI antibiotics).
• Patient has had at least 1 bowel movement during the CDI antibiotic washout period and prior to Randomization.

Inclusion Criteria - Part B (Screening):

The following criteria must be satisfied for entry into Part B of the trial: 

• Previously enrolled in Part A:
  • Patients who have an on-trial, central laboratory-positive C. difficile-related diarrhea within 8 weeks after receiving CP101 or placebo in Part A defined as: a) Diarrhea (> 3 unformed stools in 24 hours for 2 or more consecutive days); AND
  • A stool specimen testing positive for C. difficile by central laboratory testing algorithm; AND
  • Patient has received a course of SOC CDI antibiotics for the most recent CDI event (for 10 to 21 days, with exact duration, antibiotic type, and dose at the discretion of the Investigator); AND
  • Patient has had an adequate clinical response, defined as ≤ 3 unformed stools in 24 hours for 2 or more consecutive days during SOC CDI antibiotics prior to IP administration.
  • NOTE: Confirmation of eligibility by Medical Monitor is required before entry into Part B.

Exclusion Criteria - Part B (Screening):

• New onset of any acute, chronic, or unstable medical comorbidity, psychiatric, social, or other circumstances that, in the opinion of the Investigator, may interfere with trial compliance, completion, or accurate assessment of trial outcomes/safety. Examples include but not limited to acute myocardial infarction, acute stroke, uncompensated congestive heart failure, and decompensated liver disease.
• Pregnant, breast-feeding, or planning to become pregnant during the trial.

Inclusion Criteria - Part B Open-Label Treatment (Day 1):

The following criteria must be satisfied prior to OLT in Part B of the trial:

• An outpatient prior to OLT.
  • NOTE: Patient may be screened while an inpatient in an acute care facility but must be discharged from inpatient medical admission prior to IP administration. Patients residing in an assisted living center, long-term care facility, or rehabilitation ward/center are eligible for Part B.
• Has received a course of SOC CDI antibiotics for the on-trial, central laboratory-positive C. difficile-related diarrhea (for 10 to 21 days, with exact duration, antibiotic type, and dose at the discretion of the Investigator).
• Has an adequate clinical response, defined as ≤ 3 unformed stools in 24 hours for 2 or more consecutive days during SOC CDI antibiotics prior to IP administration.
• Patient has completed a CDI antibiotic washout (i.e., a minimum of 4 and a maximum of 7 days after cessation of SOC CDI antibiotics).
• Patient has had at least 1 bowel movement during the CDI antibiotic washout period and prior to IP administration.

Eligibility last updated 11/17/21. Questions regarding updates should be directed to the study team contact.