Recurrent Clostridioides Difficile InfectionPhase 2ALDERNCT06536465

The Clostridioides Difficile Trial of REC-3964

A Phase 2 study testing REC-3964 in people with Recurrent Clostridioides Difficile Infection, run by Recursion Pharmaceuticals Inc. at 2 sites in United States.

Terminated

Stopped early. The study ended before it was planned to and will not resume.

Official record

Search all trials

Trial summary

This is a multi-center, open-label study to investigate the safety, tolerability, pharmacokinetics (PK) and efficacy of REC-3964 (doses of either 250 mg or 500 mg PO every 12 hours) for the reduction of Clostridioides difficile infection (CDI). Read more about this study

Who is it for?: Ages 18 to 115 years
Conditions the study is for: Recurrent Clostridioides Difficile Infection
What is being tested?: REC-3964
Type of treatment: Pill or oral medicine
Could I receive a placebo?: No, everyone receives an active treatment
How many people: 3 participants
Where: 2 sitesUnited States
Study dates: 14 Oct 2024to 6 May 2025
Phase: Phase 2
Are there results?: Yes, posted in the registrySummary in the doctors' view

Key requirements

Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.

Ages 18 to 115 years
All sexes
No healthy volunteers
Adult, Older adult

Who may be able to join

Be 18 years of age or older with Clostridioides difficile infection (CDI) diarrhea associated with a positive stool test for C. difficile toxin[s] prior to the preceding curative treatment.
The CDI episode, severe or otherwise, must have resolved after receiving vancomycin with a standard duration of treatment. The participant must be randomized within 2 days of completing the preceding curative treatment.
Have high risk for rCDI (a recurrent CDI episode within the last 6 months, age ≥65 years, immunocompromised state, or severe CDI with resolution prior to enrollment into the study).

Who cannot join

Have an active, symptomatic, chronic diarrheal illness from other causes, such as ulcerative colitis or Crohn's disease.
Diarrhea that requires on-study treatment with agents that would confound the interpretation of the study results.

Trial locations and contacts

2 sites in 1 country.

United States2 sites

Southern Star Research Institute, LLC
San Antonio, Texas, 78229
GANJ - Toms River - Ocean Family Gastroenterology
Toms River, New Jersey, 08755

Other trials in United States

About this study

Official title: A Phase 2 Clinical Study of REC-3964 in Adults for the Reduction of Recurrent Clostridioides Difficile Infection (CDI)

Read the detailed description

Study was terminated due to sponsor decision. This decision was not related to safety concerns.

Conditions: Recurrent Clostridioides Difficile Infection
Being tested: REC-3964
Keywords: Cdiff Infection, Clostridiodes difficile infection, Cdiff
Medical subject headings: Clostridium Infections

What participants receive

What participants receive. In a randomised study each person is assigned to one group by chance.

REC-3964Drug
REC-3964 given at a dose of either 500 mg q12h or 250 mg q12h

Study groups in NCT06536465
Study group	Role	What they receive
REC-3964 High-dose	Experimental	Participants will receive 500 mg REC-3964 q12h REC-3964 250 mg capsules Receives: Drug: REC-3964
REC-3964 Low-dose	Experimental	Participants will receive 250 mg REC-3964 q12h REC-3964 250 mg capsules Receives: Drug: REC-3964
Observation	No intervention	Participants will undergo watchful waiting

What is being measured

The primary outcome is the main question the study is designed to answer.

Number of Participants With Survival Without Recurrence or Requirement for Additional Clostridioides Difficile Infection (CDI) Treatment
Recurrent CDI was defined as a new episode of CDI associated with a new positive Clostridioides difficile stool toxin or requirement for additional CDI treatment during the 8-week Follow-up Period after cure of preceding CDI with initial curative treatment.
Measured: 8 weeks
Number of Participants With Treatment-emergent Adverse Events (TEAEs)
A TEAE was the development of an undesirable medical condition or the deterioration of a pre-existing medical condition following or during exposure to a pharmaceutical product, whether or not considered causally related to the product.
Measured: Up to 8 weeks
Number of Participants With Related TEAEs
A TEAE was the development of an undesirable medical condition or the deterioration of a pre-existing medical condition following or during exposure to a pharmaceutical product, whether or not considered causally related to the product. An Investigator who was qualified in medicine determined relationship to the study drug for each AE (unrelated or related). The Investigator decided whether, in his or her medical judgment, if there was a reasonable biological possibility that the event may have been caused by the study drug.
Measured: Up to 8 weeks
Number of Participants With Serious TEAEs
A TEAE was the development of an undesirable medical condition or the deterioration of a pre-existing medical condition following or during exposure to a pharmaceutical product, whether or not considered causally related to the product. A Serious TEAE was defined as results in death, immediately life-threatening, requires in-participant hospitalization or prolongation of existing hospitalization, results in persistent or significant disability or incapacity in conducting activities of daily living for at least 28 days, results in a congenital abnormality or birth defect, or an important medical event that may jeopardize the participant or may require medical intervention.
Measured: Up to 8 weeks
Number of Participants With TEAEs Leading to Study Drug Discontinuation
A TEAE was the development of an undesirable medical condition or the deterioration of a pre-existing medical condition following or during exposure to a pharmaceutical product, whether or not considered causally related to the product.
Measured: Up to 8 weeks

Secondary outcomes (7)

Rate of Recurrent Clostridioides Difficile Infection (rCDI)
Recurrent CDI was defined as a new episode of CDI associated with a new positive Clostridioides difficile stool toxin within 8 weeks of the cessation of initial curative treatment. The number of unformed [types 5-7 on the Bristol stool scale] bowel movements per day were recorded by the participant in the stool diary in order to identify a new episode of diarrhea. All new episodes of diarrhea were tested for toxigenic Clostridioides difficile to confirm CDI recurrence.
The rate of rCDI was defined as the proportion of participants who had the Clostridioides difficile recurrence among randomized participants.
Measured: 8 weeks
Time to Recurrence of rCDI
Recurrent CDI was defined as a new episode of CDI associated with a new positive Clostridioides difficile stool toxin within 8 weeks of the cessation of initial curative treatment. The number of unformed [types 5-7 on the Bristol stool scale] bowel movements per day were recorded by the participant in the stool diary in order to identify a new episode of diarrhea. All new episodes of diarrhea were tested for toxigenic Clostridioides difficile to confirm CDI recurrence. Time to recurrence of rCDI was to be assessed using Kaplan-Meier estimation.
Measured: Up to 8 weeks
Number of Participants With Severe rCDI
Recurrent CDI was defined as a new episode of CDI associated with a new positive Clostridioides difficile stool toxin within 8 weeks of the cessation of initial curative treatment. The number of unformed [types 5-7 on the Bristol stool scale] bowel movements per day were recorded by the participant in the stool diary in order to identify a new episode of diarrhea. All new episodes of diarrhea were tested for toxigenic Clostridioides difficile to confirm CDI recurrence. Severe CDI was defined as CDI with white blood cell count >15,000 cells/milliliter and/or serum creatinine ≥1.5 milligram/deciliter.
Measured: Up to 8 weeks
Number of Participants With rCDI Who Had Associated Hospital Admissions
Recurrent CDI was defined as a new episode of CDI associated with a new positive Clostridioides difficile stool toxin within 8 weeks of the cessation of initial curative treatment. The number of unformed [types 5-7 on the Bristol stool scale] bowel movements per day were recorded by the participant in the stool diary in order to identify a new episode of diarrhea. All new episodes of diarrhea were tested for toxigenic Clostridioides difficile to confirm CDI recurrence.
Measured: Up to 8 weeks
Maximum Observed Plasma Concentration (Cmax) of REC-3964
Measured: Pre-dose, 1 hour, 3 hours, and 6 hours post morning dose on Day 1 and Day 15
Time to Maximum Plasma Concentration (Tmax) of REC-3964
Measured: Pre-dose, 1 hour, 3 hours, and 6 hours post morning dose on the Day 1 and Day 15
Trough Plasma Concentration (Ctrough) of REC-3964
Measured: Pre-dose on Day 15

Timeline

From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.

14 Oct 20246 May 2025

First posted5 Aug 2024
Study start14 Oct 2024
Primary completion6 May 2025
Study completion6 May 2025

Why it stopped: Study was terminated due to sponsor decision. This decision was not related to safety concerns.

Resources

Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
Posted resultsParticipant flow, outcome measures and adverse events reported by the sponsor.
Other trials for Recurrent Clostridioides Difficile InfectionStudies of the same condition, open and under way.
What the trial phases meanHow a treatment moves from first tests in people to approval.

More details

For doctors and researchers: how the study is designed, who runs it, and its registry IDs.

Study design

Study type: Interventional
Phase: Phase 2
Primary purpose: Treatment
Allocation: Randomised
Intervention model: Parallel groups
Masking: None (open label)
Enrolment: 3 participants (actual)

IDs, dates and publications

ClinicalTrials.gov ID: NCT06536465
Sponsor's protocol ID: REC-3964-201
Acronym: ALDER
Status last verified: Nov 2025
First submitted: 15 Jul 2024
Last updated: 17 Nov 2025
Results posted: Yes, on ClinicalTrials.gov
FDA-regulated drug: Yes
FDA-regulated device: No
Individual data sharing: No

Want to know more?

The sponsor has not listed a contact. The official record may have more details.

Talk to your doctor first and take this page with you. Only the study team can confirm whether you can join.

Questions to ask the study team

What is the study trying to find out?
What would I need to do, and how often would I visit?
Could I receive a placebo instead of the treatment?
What are the possible risks and benefits for me?
Will it cost me anything? Are travel or time paid for?
Can I keep seeing my own doctor during the study?
What happens when the study ends?

See locations

Active, not recruitingObservational study
C. Difficile Toxin Levels in Stool From Healthy Individuals Following Standard of Care Antibiotic Treatment for CDI.
Clostridioides Difficile Infection Recurrence
RecruitingPhase 3
VE303 for Prevention of Recurrent Clostridioides Difficile Infection
Clostridium Difficile, Clostridium Difficile Infections
RecruitingEarly Phase 1
Prevention of Recurrence of Clostridioides Difficile Colitis With Ursodeoxycholic Acid (UCDA) as a Supplement to Standard Therapy
Clostridioides Difficile Infection
RecruitingPhase 1/2
Evaluation of EXL01, a New Live Biotherapeutic Product to Prevent Recurrence of Clostridioides Difficile Infection in High-risk Patients
Clostridioides Difficile Infection, Recurrent Infection
RecruitingPhase 2
ACX-362E [Ibezapolstat] for Oral Treatment of Recurrent Clostridioides Difficile Infection
Clostridium Difficile Infection Recurrence

All Recurrent Clostridioides Difficile Infection trials

Study at a glance

From the registry record, last updated by the sponsor on 17 Nov 2025. Recruitment status is as the sponsor reported it: confirm with the study team.

Official title: A Phase 2 Clinical Study of REC-3964 in Adults for the Reduction of Recurrent Clostridioides Difficile Infection (CDI)
ClinicalTrials.gov ID: NCT06536465
Acronym / sponsor ID: ALDER / REC-3964-201
Conditions: Recurrent Clostridioides Difficile Infection
Keywords: Cdiff Infection, Clostridiodes difficile infection, Cdiff
Phase: Phase 2
Study type: Interventional
Recruitment status: TerminatedReason stopped: Study was terminated due to sponsor decision. This decision was not related to safety concerns.
Enrolment: 3 participants (actual)
Lead sponsor: Recursion Pharmaceuticals Inc.Industry (pharma, biotech, devices)
Study start: 14 Oct 2024 (actual)
Primary completion: 6 May 2025 (actual)
Study completion: 6 May 2025 (actual)
First posted: 5 Aug 2024 (actual)
Results: Posted 17 Nov 2025

Clinical summary

The research question as the sponsor registered it. This describes what the study plans to test, not what it found.

Detailed description

Study was terminated due to sponsor decision. This decision was not related to safety concerns.

Study design

Primary purpose: Treatment
Allocation: Randomised
Intervention model: Parallel groups
Masking: None (open label)
Number of arms: 3

Arm	Type	Receives
REC-3964 High-dose	Experimental	Drug: REC-3964Participants will receive 500 mg REC-3964 q12h REC-3964 250 mg capsules
REC-3964 Low-dose	Experimental	Drug: REC-3964Participants will receive 250 mg REC-3964 q12h REC-3964 250 mg capsules
Observation	No intervention	–Participants will undergo watchful waiting

Who may qualify

Ages: 18 to 115 years
Sex: All
Healthy volunteers: Not accepted
Age groups: Adult, Older adult

Key inclusion criteria (3 listed)

Be 18 years of age or older with Clostridioides difficile infection (CDI) diarrhea associated with a positive stool test for C. difficile toxin[s] prior to the preceding curative treatment.
The CDI episode, severe or otherwise, must have resolved after receiving vancomycin with a standard duration of treatment. The participant must be randomized within 2 days of completing the preceding curative treatment.
Have high risk for rCDI (a recurrent CDI episode within the last 6 months, age ≥65 years, immunocompromised state, or severe CDI with resolution prior to enrollment into the study).

Key exclusion criteria (2 listed)

Have an active, symptomatic, chronic diarrheal illness from other causes, such as ulcerative colitis or Crohn's disease.
Diarrhea that requires on-study treatment with agents that would confound the interpretation of the study results.

Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.

Interventions

Intervention	Type	Arms
REC-3964REC-3964 given at a dose of either 500 mg q12h or 250 mg q12h	Drug	REC-3964 High-dose, REC-3964 Low-dose

Primary outcome

Number of Participants With Survival Without Recurrence or Requirement for Additional Clostridioides Difficile Infection (CDI) Treatment
Time frame: 8 weeks
Recurrent CDI was defined as a new episode of CDI associated with a new positive Clostridioides difficile stool toxin or requirement for additional CDI treatment during the 8-week Follow-up Period after cure of preceding CDI with initial curative treatment.
Number of Participants With Treatment-emergent Adverse Events (TEAEs)
Time frame: Up to 8 weeks
A TEAE was the development of an undesirable medical condition or the deterioration of a pre-existing medical condition following or during exposure to a pharmaceutical product, whether or not considered causally related to the product.
Number of Participants With Related TEAEs
Time frame: Up to 8 weeks
A TEAE was the development of an undesirable medical condition or the deterioration of a pre-existing medical condition following or during exposure to a pharmaceutical product, whether or not considered causally related to the product. An Investigator who was qualified in medicine determined relationship to the study drug for each AE (unrelated or related). The Investigator decided whether, in his or her medical judgment, if there was a reasonable biological possibility that the event may have been caused by the study drug.
Number of Participants With Serious TEAEs
Time frame: Up to 8 weeks
A TEAE was the development of an undesirable medical condition or the deterioration of a pre-existing medical condition following or during exposure to a pharmaceutical product, whether or not considered causally related to the product. A Serious TEAE was defined as results in death, immediately life-threatening, requires in-participant hospitalization or prolongation of existing hospitalization, results in persistent or significant disability or incapacity in conducting activities of daily living for at least 28 days, results in a congenital abnormality or birth defect, or an important medical event that may jeopardize the participant or may require medical intervention.
Number of Participants With TEAEs Leading to Study Drug Discontinuation
Time frame: Up to 8 weeks
A TEAE was the development of an undesirable medical condition or the deterioration of a pre-existing medical condition following or during exposure to a pharmaceutical product, whether or not considered causally related to the product.

7 secondary outcomes

Rate of Recurrent Clostridioides Difficile Infection (rCDI)
Time frame: 8 weeks
Time to Recurrence of rCDI
Time frame: Up to 8 weeks
Number of Participants With Severe rCDI
Time frame: Up to 8 weeks
Number of Participants With rCDI Who Had Associated Hospital Admissions
Time frame: Up to 8 weeks
Maximum Observed Plasma Concentration (Cmax) of REC-3964
Time frame: Pre-dose, 1 hour, 3 hours, and 6 hours post morning dose on Day 1 and Day 15
Time to Maximum Plasma Concentration (Tmax) of REC-3964
Time frame: Pre-dose, 1 hour, 3 hours, and 6 hours post morning dose on the Day 1 and Day 15
Trough Plasma Concentration (Ctrough) of REC-3964
Time frame: Pre-dose on Day 15

Results and safety

Results posted to the registry on 17 Nov 2025, as reported by the sponsor. Figures are copied from the record, not re-analysed. Full results on ClinicalTrials.gov.

Participant flow

Group	Started	Completed
REC-3964 250 mg	1	1
REC-3964 500 mg	1	1
Observation	1	1

Primary outcome: Number of Participants With Survival Without Recurrence or Requirement for Additional Clostridioides Difficile Infection (CDI) Treatment

Time frame: 8 weeks. Count of participants. Unit: Participants

Measure	REC-3964 250 mg n = 1	REC-3964 500 mg n = 1	Observation n = 1
Value	1	1	1

Population analysed: All randomized participants who received at least 1 dose of REC-3964 intervention or who were followed-up on in the Observational arm.

Primary outcome: Number of Participants With Treatment-emergent Adverse Events (TEAEs)

Time frame: Up to 8 weeks. Count of participants. Unit: Participants

Measure	REC-3964 250 mg n = 1	REC-3964 500 mg n = 1	Observation n = 1
Value	0	0	1

Population analysed: All randomized participants who received at least 1 dose of REC-3964 intervention or who were followed-up on in the Observation arm.

Primary outcome: Number of Participants With Related TEAEs

Time frame: Up to 8 weeks. Count of participants. Unit: Participants

Measure	REC-3964 250 mg n = 1	REC-3964 500 mg n = 1	Observation n = 1
Value	0	0	0

Population analysed: All randomized participants who received at least 1 dose of REC-3964 intervention or who were followed-up on in the Observation arm.

Primary outcome: Number of Participants With Serious TEAEs

Time frame: Up to 8 weeks. Count of participants. Unit: Participants

Measure	REC-3964 250 mg n = 1	REC-3964 500 mg n = 1	Observation n = 1
Value	0	0	0

Population analysed: All randomized participants who received at least 1 dose of REC-3964 intervention or who were followed-up on in the Observation arm.

7 secondary outcomes are reported in the full results.

Adverse events

Time frame: Up to 8 weeks. Other adverse events reported at 0% frequency or more

Group	Serious adverse events	Other adverse events	Deaths
REC-3964 250 mg	0 of 1 (0%)	0 of 1 (0%)	0 of 1
REC-3964 500 mg	0 of 1 (0%)	0 of 1 (0%)	0 of 1
Observation	0 of 1 (0%)	1 of 1 (100%)	0 of 1

Limitations and caveats (from the sponsor): Due to the early termination of the study, only 3 participants were enrolled. Data are limited due to the small sample size.

Loading the posted results from ClinicalTrials.gov…

Research links

Official record on ClinicalTrials.govLast updated by the sponsor 17 Nov 2025.
Posted resultsParticipant flow, baseline, all outcome measures and adverse events.
Individual participant dataSharing planned: No

Related trials for Recurrent Clostridioides Difficile Infection

Active, not recruitingObservational study
C. Difficile Toxin Levels in Stool From Healthy Individuals Following Standard of Care Antibiotic Treatment for CDI.
Clostridioides Difficile Infection Recurrence
RecruitingPhase 3
VE303 for Prevention of Recurrent Clostridioides Difficile Infection
Clostridium Difficile, Clostridium Difficile Infections
RecruitingEarly Phase 1
Prevention of Recurrence of Clostridioides Difficile Colitis With Ursodeoxycholic Acid (UCDA) as a Supplement to Standard Therapy
Clostridioides Difficile Infection
RecruitingPhase 1/2
Evaluation of EXL01, a New Live Biotherapeutic Product to Prevent Recurrence of Clostridioides Difficile Infection in High-risk Patients
Clostridioides Difficile Infection, Recurrent Infection
RecruitingPhase 2
ACX-362E [Ibezapolstat] for Oral Treatment of Recurrent Clostridioides Difficile Infection
Clostridium Difficile Infection Recurrence

Referral and contact

AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part. This study is not recruiting at the moment.

The record lists no contact. Use the official record to reach the sponsor.

2 sites in 1 country: see every site and its status.

Questions about this trial

What is this clinical trial studying?

A Phase 2 study testing REC-3964 in people with Recurrent Clostridioides Difficile Infection, run by Recursion Pharmaceuticals Inc. at 2 sites in United States.

The full registered description is in the About this study section and the official record.

Who may be eligible to take part?

The sponsor lists 3 inclusion and 2 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.

Is this clinical trial currently recruiting?

The record says: stopped early, as of the sponsor's last update on 17 Nov 2025. Status can change between updates, so confirm with the study contact before making plans.

Where is the study taking place?

The record lists 2 sites in United States. Whether a site is taking part right now should be confirmed with that site. See every site.

What are the possible benefits and risks?

They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.

What does this phase mean?

Phase 2 studies give the treatment to a larger group to see whether it has the intended effect and to keep checking safety.

Not every study follows the same path, and some studies (observational studies, device studies) have no phase.

Are results available for this study?

Yes. Results are posted in the registry (first posted 17 Nov 2025). A summary is in the For doctors view, and the full results are on ClinicalTrials.gov.

How can a doctor refer a patient or contact the research team?

The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.

What does the primary outcome measure?

Number of Participants With Survival Without Recurrence or Requirement for Additional Clostridioides Difficile Infection (CDI) Treatment (time frame: 8 weeks). The study lists 5 primary outcomes in all. It is what the study was designed to measure, not a finding.

Where can I read the original study information?

On the ClinicalTrials.gov record for NCT06536465.

Does a listing mean the treatment is approved or proven to work?

No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.

How often is this information updated?

AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 17 Nov 2025.