IBS (Irritable Bowel Syndrome)Phase 2NCT06727422
Efficacy of Rifaximin With NAC in IBS-D
A Phase 2 study testing rifaximin 66mg + N-acetylcysteine 560mg three times daily and RNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times daily in people with IBS (Irritable Bowel Syndrome) and IBS-D (Diarrhea-predominant), run by Mark Pimentel, MD at 1 site in United States.
Trial summary
The purpose of this study is to examine the effectiveness of using a combination of a drug, rifaximin and a dietary supplement, N-acetyl-L-cysteine (NAC), to treat patients with irritable bowel syndrome with diarrhea (IBS-D). Rifaximin is one of the standard treatments for IBS-D and is FDA approved. Read more about this study
- Who is it for?
- Ages 18 years and older
- Conditions the study is for
- IBS (Irritable Bowel Syndrome), IBS-D (Diarrhea-predominant)
- What is being tested?
- rifaximin 66mg + N-acetylcysteine 560mg three times daily and RNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times daily
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 225 participants
- Where
- 1 siteUnited States
- Study dates
- 4 Feb 2026to 1 Jan 2027
- Phase
- Phase 2
- Are there results?
- Not yet: the study is under way
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 years and older
- All sexes
- No healthy volunteers
- Adult, Older adult
Who may be able to join
- Male or non-pregnant, non-lactating female patients ≥ 18 years of age
- Diagnosed with IBS confirmed by the Rome IV criteria, with associated symptoms of diarrhea as noted below in 4(b).
- Do not have adequate relief of IBS symptoms of abdominal pain, stool consistency or stool frequency
- Have daily IBS symptom scores during screening as below:
- Weekly average score of worst daily abdominal pain >3.0 on a 0-10 point scale
- At least one stool with a consistency of Type 6 or 7 on the Bristol
Who cannot join
- Present with the following symptoms of IBS with constipation:
- Less than 3 bowel movements a week,
- Hard or lumpy stools, and
- Excessive straining during a bowel movement.
- History of inflammatory bowel disease, celiac disease, GI surgery (except cholecystectomy and/or appendectomy)
- Evidence of active duodenal ulcer, gastric ulcer, diverticulitis, or active infectious gastroenteritis
Show all 11Show fewer
- Current diagnosis of asthma
- Current user of NAC and/or rifaximin
- Systemic antibiotic use in the last month
- Not currently on a prokinetic drug
- A significant medical condition including but not limited to hepatic, uncontrolled diabetes, renal, cardiovascular, pulmonary, uncontrolled thyroid disease. or psychiatric disease, which in the opinion of investigator precludes study participation
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
United States1 site, 1 recruiting
- Recruiting
Cedars-Sinai Medical Center
Los Angeles, California, 90048
Ava Hosseini, 3104230617, ava.hosseini@cshs.org
About this study
Official title: A Phase 2b, Randomized, Double-Blind, Placebo- Controlled, Multicenter Study to Assess the Safety, Efficacy and Pharmacokinetics of RNIB21 in the Treatment of Patients With Irritable Bowel Syndrome With Diarrhea (IBS-D)
The purpose of this study is to examine the effectiveness of using a combination of a drug, rifaximin and a dietary supplement, N-acetyl-L-cysteine (NAC), to treat patients with irritable bowel syndrome with diarrhea (IBS-D). Rifaximin is one of the standard treatments for IBS-D and is FDA approved. While rifaximin is safe and effective for treating symptoms in patients with IBS-D, many patients find that their symptoms may not completely resolve, or may come back after a period of time.
This research study is designed to test the investigational use of a combination of rifaximin and NAC. The combination of rifaximin and NAC is not approved by the U.S. Food and Drug Administration (FDA) for the treatment of IBS-D, and the effects of taking both medications together are unknown. However, the two medications are approved for use separately, as detailed below.
Read more
Rifaximin is the only antibiotic approved by the FDA for the treatment of IBS-D. Rifaximin (at a dose of 550 mg by mouth three times daily for 14 days) is approved by the FDA for the treatment of IBS-D. Rifaximin (at a dose of 200 mg per mouth three times daily for 3 days) is FDA approved for the treatment of traveler's diarrhea. Rifaximin at a dose of 200 mg per mouth three times daily is not approved by the FDA for the treatment of IBS-D.
NAC is approved by the FDA to treat acetaminophen overdose (72-hour oral and 21-hour intravenous (IV) regimens), and for use in breaking up mucus in the lungs in patients with chronic obstructive pulmonary disease (COPD) and other lung conditions such as bronchitis. NAC is also available over-the-counter in 600 mg and 900 mg capsules as a dietary supplement, although over-the-counter use is not regulated by the FDA. This study will utilize the 600 mg dietary supplement capsules.
The Investigators want to know if using a combination of rifaximin and NAC will give better results in decreasing IBS-D symptoms than using rifaximin alone. As NAC is used to break up mucus in the lungs, and the Investigators want to see if this can also break up the mucus layer in the small intestine, and therefore potentially increase the effectiveness of rifaximin. The Investigators will be testing 2 doses to determine which dose is most effective.
participants are being asked to take part in this research study because participants were diagnosed with IBS-D.
Read the detailed description
This is a phase 2b, multi-center, randomized, double-blind, placebocontrolled study of rifaximin in patients with IBS-D. Eligible patients will be randomized (1:1:1) to receive RNIB21 containing rifaximin 66mg + NAC 560mg TID; RNIB21 containing rifaximin 132mg + NAC 560mg TID; or placebo TID. The study will consist of the following phases: Screening Phase; Treatment Phase (Days 1 to 14) which includes the Randomization Visit (Day 1) and visits at Week 1 (Day 7 ± 2) and Week 2 (Day 14 ± 2); and a Follow-up Phase including an End of Study visit at Week 14 (Day 98 ± 3). REDCap, a web-based reporting system will be utilized to capture daily patient reported outcomes as regards abdominal pain and stool consistency. A subset of participating sites will be designated as Pharmacokinetics sites. In a blinded fashion 24 patients (8 from each treatment arm) will participate in PK sampling in order to establish a PK profile and PK parameters for both rifaximin and NAC. Serial blood samples will be collected following first dose and last dose to establish the PK profiles after a single dose, and multiple doses. The primary evaluation period (PEP) will be the 28 days following the completion of therapy. The primary outcome for the study will be adequate relief of IBS symptoms based on FDA guidance during this period, specifically: the proportion of patients who are responders to treatment in both IBS-related abdominal pain AND stool consistency during the 4-week PEP. A patient will be considered a weekly responder if there is adequate relief in their IBS-related symptoms, which is defined as a 30% or greater improvement from their baseline in the weekly average of worst abdominal pain in past 24 hours score AND at least 50% reduction in the number of days in a week with at least one stool that has a consistency of type 6 or 7 compared with their baseline. Responders have to meet both abdominal pain and stool consistency criteria for at least 2 of 4 weeks of the PEP. Abdominal pain will be self-reported on a daily basis using an 11-point (0-10) pain scale. Stool consistency will be self-reported daily by patients based on the Bristol Stool Scale. A smartphone app which captures stool image will be used as an seondary endpoint, and compared to the patients' self-reports of stool consistency recorded on the BSS.
- Being tested
- rifaximin 66mg + N-acetylcysteine 560mg three times daily, RNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times daily, Placebo
- Keywords
- IBS-D
- Medical subject headings
- Irritable Bowel Syndrome
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
rifaximin 66mg + N-acetylcysteine 560mg three times dailyDrug
RNIB21 containing rifaximin 66mg + N-acetylcysteine 560mg three times daily
RNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times dailyDrug
RNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times daily
PlaceboDrug
placebo three times daily
| Study group | Role | What they receive |
|---|---|---|
| low dose for IBS-D | Experimental | RNIB21 containing rifaximin 66mg + NAC 560mg three times a day Receives: Drug: rifaximin 66mg + N-acetylcysteine 560mg three times daily |
| high dose for IBS-D | Experimental | RNIB21 containing rifaximin 132mg + NAC 560mg three times a day Receives: Drug: RNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times daily |
| placebo | Placebo comparator | placebo three times a day Receives: Drug: Placebo |
What is being measured
The primary outcome is the main question the study is designed to answer.
stool consistency
A 50% reduction in the number of days per week with at least one stool consistency of Type 6 or 7 on the BSS compared to baseline, for at least 2 of the 4 weeks of the PEP
Measured: 2 weeks
Abdominal pain
Abdominal pain will be self-reported on a daily basis using an 11-point (0-10) pain scale, where 10 represent the highest pain.;A 30% improvement compared to baseline on the weekly average score of worst daily abdominal pain for at least 2 of the 4 weeks of the primary evaluation period .
Measured: 2 weeks
Secondary outcomes (2)
overall response
Overall response: Proportion of patients that achieve a weekly response during at least 50% of the weeks of treatment and follow up (i.e. 7 of 14 weeks
Measured: up to 7 weeks of 14 weeks
stool frequency
Stool frequency as number of bowel movements per day averaged on a weekly basis, versus baseline determined during the PEP
Measured: 2 weeks
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted10 Dec 2024
- Study start4 Feb 2026
- Primary completion1 Aug 2026 (estimated)
- Study completion1 Jan 2027 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (21)Papers the sponsor has linked to this study.
- Other trials for IBS (Irritable Bowel Syndrome)Studies 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
- Quadruple blind
- Who is masked
- Participant, Care provider, Investigator, Outcomes assessor
- Enrolment
- 225 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Mark Pimentel, MD
- Sponsor type
- University, hospital or other
- Responsible party
- Sponsor-investigator, Mark Pimentel, MD, Cedars-Sinai Medical Center
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06727422
- Sponsor's protocol ID
- RNIB21-201
- Status last verified
- Apr 2026
- First submitted
- 5 Dec 2024
- Last updated
- 20 Apr 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
- Individual data sharing
- No
Publications
Lauritano EC, Gabrielli M, Lupascu A, Santoliquido A, Nucera G, Scarpellini E, Vincenti F, Cammarota G, Flore R, Pola P, Gasbarrini G, Gasbarrini A. Rifaximin dose-finding study for the treatment of small intestinal bacterial overgrowth. Aliment Pharmacol Ther. 2005 Jul 1;22(1):31-5. doi: 10.1111/j.1365-2036.2005.02516.x.
PubMed 15963077Scarpellini E, Gabrielli M, Lauritano CE, Lupascu A, Merra G, Cammarota G, Cazzato IA, Gasbarrini G, Gasbarrini A. High dosage rifaximin for the treatment of small intestinal bacterial overgrowth. Aliment Pharmacol Ther. 2007 Apr 1;25(7):781-6. doi: 10.1111/j.1365-2036.2007.03259.x.
PubMed 17373916O'Brien PC. Procedures for comparing samples with multiple endpoints. Biometrics. 1984 Dec;40(4):1079-87.
PubMed 6534410Pimentel M, Park S, Mirocha J, Kane SV, Kong Y. The effect of a nonabsorbed oral antibiotic (rifaximin) on the symptoms of the irritable bowel syndrome: a randomized trial. Ann Intern Med. 2006 Oct 17;145(8):557-63. doi: 10.7326/0003-4819-145-8-200610170-00004.
PubMed 17043337Sharara AI, Aoun E, Abdul-Baki H, Mounzer R, Sidani S, Elhajj I. A randomized double-blind placebo-controlled trial of rifaximin in patients with abdominal bloating and flatulence. Am J Gastroenterol. 2006 Feb;101(2):326-33. doi: 10.1111/j.1572-0241.2006.00458.x.
PubMed 16454838Trespi E, Ferrieri A. Intestinal bacterial overgrowth during chronic pancreatitis. Curr Med Res Opin. 1999;15(1):47-52. doi: 10.1185/03007999909115173.
PubMed 10216811Di Stefano M, Malservisi S, Veneto G, Ferrieri A, Corazza GR. Rifaximin versus chlortetracycline in the short-term treatment of small intestinal bacterial overgrowth. Aliment Pharmacol Ther. 2000 May;14(5):551-6. doi: 10.1046/j.1365-2036.2000.00751.x.
PubMed 10792117Corazza GR, Ventrucci M, Strocchi A, Sorge M, Pranzo L, Pezzilli R, Gasbarrini G. Treatment of small intestine bacterial overgrowth with rifaximin, a non-absorbable rifamycin. J Int Med Res. 1988 Jul-Aug;16(4):312-6. doi: 10.1177/030006058801600410.
PubMed 3169375Miglio F, Valpiani D, Rossellini SR, Ferrieri A. Rifaximin, a non-absorbable rifamycin, for the treatment of hepatic encephalopathy. A double-blind, randomised trial. Curr Med Res Opin. 1997;13(10):593-601. doi: 10.1185/03007999709113333.
PubMed 9327194Gillis JC, Brogden RN. Rifaximin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic potential in conditions mediated by gastrointestinal bacteria. Drugs. 1995 Mar;49(3):467-84. doi: 10.2165/00003495-199549030-00009.
PubMed 7774516Attar A, Flourie B, Rambaud JC, Franchisseur C, Ruszniewski P, Bouhnik Y. Antibiotic efficacy in small intestinal bacterial overgrowth-related chronic diarrhea: a crossover, randomized trial. Gastroenterology. 1999 Oct;117(4):794-7. doi: 10.1016/s0016-5085(99)70336-7.
PubMed 10500060Nayak AK, Karnad DR, Abraham P, Mistry FP. Metronidazole relieves symptoms in irritable bowel syndrome: the confusion with so-called 'chronic amebiasis'. Indian J Gastroenterol. 1997 Oct;16(4):137-9.
PubMed 9357184Pimentel M, Chow EJ, Lin HC. Normalization of lactulose breath testing correlates with symptom improvement in irritable bowel syndrome. a double-blind, randomized, placebo-controlled study. Am J Gastroenterol. 2003 Feb;98(2):412-9. doi: 10.1111/j.1572-0241.2003.07234.x.
PubMed 12591062Drossman DA, McKee DC, Sandler RS, Mitchell CM, Cramer EM, Lowman BC, Burger AL. Psychosocial factors in the irritable bowel syndrome. A multivariate study of patients and nonpatients with irritable bowel syndrome. Gastroenterology. 1988 Sep;95(3):701-8. doi: 10.1016/s0016-5085(88)80017-9.
PubMed 3396817Agreus L, Svardsudd K, Nyren O, Tibblin G. Irritable bowel syndrome and dyspepsia in the general population: overlap and lack of stability over time. Gastroenterology. 1995 Sep;109(3):671-80. doi: 10.1016/0016-5085(95)90373-9.
PubMed 7657095
Study at a glance
From the registry record, last updated by the sponsor on 20 Apr 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- A Phase 2b, Randomized, Double-Blind, Placebo- Controlled, Multicenter Study to Assess the Safety, Efficacy and Pharmacokinetics of RNIB21 in the Treatment of Patients With Irritable Bowel Syndrome With Diarrhea (IBS-D)
- ClinicalTrials.gov ID
- NCT06727422
- Acronym / sponsor ID
- RNIB21-201
- Keywords
- IBS-D
- Phase
- Phase 2
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 225 participants (estimated)
- Lead sponsor
- Mark Pimentel, MDUniversity, hospital or other
- Study start
- 4 Feb 2026 (actual)
- Primary completion
- 1 Aug 2026 (estimated)
- Study completion
- 1 Jan 2027 (estimated)
- First posted
- 10 Dec 2024 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
The purpose of this study is to examine the effectiveness of using a combination of a drug, rifaximin and a dietary supplement, N-acetyl-L-cysteine (NAC), to treat patients with irritable bowel syndrome with diarrhea (IBS-D). Rifaximin is one of the standard treatments for IBS-D and is FDA approved. While rifaximin is safe and effective for treating symptoms in patients with IBS-D, many patients find that their symptoms may not completely resolve, or may come back after a period of time.
This research study is designed to test the investigational use of a combination of rifaximin and NAC. The combination of rifaximin and NAC is not approved by the U.S. Food and Drug Administration (FDA) for the treatment of IBS-D, and the effects of taking both medications together are unknown. However, the two medications are approved for use separately, as detailed below.
Rifaximin is the only antibiotic approved by the FDA for the treatment of IBS-D. Rifaximin (at a dose of 550 mg by mouth three times daily for 14 days) is approved by the FDA for the treatment of IBS-D. Rifaximin (at a dose of 200 mg per mouth three times daily for 3 days) is FDA approved for the treatment of traveler's diarrhea. Rifaximin at a dose of 200 mg per mouth three times daily is not approved by the FDA for the treatment of IBS-D.
NAC is approved by the FDA to treat acetaminophen overdose (72-hour oral and 21-hour intravenous (IV) regimens), and for use in breaking up mucus in the lungs in patients with chronic obstructive pulmonary disease (COPD) and other lung conditions such as bronchitis. NAC is also available over-the-counter in 600 mg and 900 mg capsules as a dietary supplement, although over-the-counter use is not regulated by the FDA. This study will utilize the 600 mg dietary supplement capsules.
The Investigators want to know if using a combination of rifaximin and NAC will give better results in decreasing IBS-D symptoms than using rifaximin alone. As NAC is used to break up mucus in the lungs, and the Investigators want to see if this can also break up the mucus layer in the small intestine, and therefore potentially increase the effectiveness of rifaximin. The Investigators will be testing 2 doses to determine which dose is most effective.
participants are being asked to take part in this research study because participants were diagnosed with IBS-D.
Detailed description
This is a phase 2b, multi-center, randomized, double-blind, placebocontrolled study of rifaximin in patients with IBS-D. Eligible patients will be randomized (1:1:1) to receive RNIB21 containing rifaximin 66mg + NAC 560mg TID; RNIB21 containing rifaximin 132mg + NAC 560mg TID; or placebo TID. The study will consist of the following phases: Screening Phase; Treatment Phase (Days 1 to 14) which includes the Randomization Visit (Day 1) and visits at Week 1 (Day 7 ± 2) and Week 2 (Day 14 ± 2); and a Follow-up Phase including an End of Study visit at Week 14 (Day 98 ± 3). REDCap, a web-based reporting system will be utilized to capture daily patient reported outcomes as regards abdominal pain and stool consistency. A subset of participating sites will be designated as Pharmacokinetics sites. In a blinded fashion 24 patients (8 from each treatment arm) will participate in PK sampling in order to establish a PK profile and PK parameters for both rifaximin and NAC. Serial blood samples will be collected following first dose and last dose to establish the PK profiles after a single dose, and multiple doses. The primary evaluation period (PEP) will be the 28 days following the completion of therapy. The primary outcome for the study will be adequate relief of IBS symptoms based on FDA guidance during this period, specifically: the proportion of patients who are responders to treatment in both IBS-related abdominal pain AND stool consistency during the 4-week PEP. A patient will be considered a weekly responder if there is adequate relief in their IBS-related symptoms, which is defined as a 30% or greater improvement from their baseline in the weekly average of worst abdominal pain in past 24 hours score AND at least 50% reduction in the number of days in a week with at least one stool that has a consistency of type 6 or 7 compared with their baseline. Responders have to meet both abdominal pain and stool consistency criteria for at least 2 of 4 weeks of the PEP. Abdominal pain will be self-reported on a daily basis using an 11-point (0-10) pain scale. Stool consistency will be self-reported daily by patients based on the Bristol Stool Scale. A smartphone app which captures stool image will be used as an seondary endpoint, and compared to the patients' self-reports of stool consistency recorded on the BSS.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind (participant, care provider, investigator, outcomes assessor)
- Number of arms
- 3
| Arm | Type | Receives |
|---|---|---|
| low dose for IBS-D | Experimental | Drug: rifaximin 66mg + N-acetylcysteine 560mg three times dailyRNIB21 containing rifaximin 66mg + NAC 560mg three times a day |
| high dose for IBS-D | Experimental | Drug: RNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times dailyRNIB21 containing rifaximin 132mg + NAC 560mg three times a day |
| placebo | Placebo comparator | Drug: Placeboplacebo three times a day |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (6 listed)
- Male or non-pregnant, non-lactating female patients ≥ 18 years of age
- Diagnosed with IBS confirmed by the Rome IV criteria, with associated symptoms of diarrhea as noted below in 4(b).
- Do not have adequate relief of IBS symptoms of abdominal pain, stool consistency or stool frequency
- Have daily IBS symptom scores during screening as below:
Key exclusion criteria (11 listed)
- Present with the following symptoms of IBS with constipation:
- History of inflammatory bowel disease, celiac disease, GI surgery (except cholecystectomy and/or appendectomy)
- Evidence of active duodenal ulcer, gastric ulcer, diverticulitis, or active infectious gastroenteritis
- Current diagnosis of asthma
- Current user of NAC and/or rifaximin
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 |
|---|---|---|
| rifaximin 66mg + N-acetylcysteine 560mg three times dailyRNIB21 containing rifaximin 66mg + N-acetylcysteine 560mg three times daily | Drug | low dose for IBS-D |
| RNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times dailyRNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times daily | Drug | high dose for IBS-D |
| Placeboplacebo three times daily | Drug | placebo |
Primary outcome
stool consistency
Time frame: 2 weeks
A 50% reduction in the number of days per week with at least one stool consistency of Type 6 or 7 on the BSS compared to baseline, for at least 2 of the 4 weeks of the PEP
Abdominal pain
Time frame: 2 weeks
Abdominal pain will be self-reported on a daily basis using an 11-point (0-10) pain scale, where 10 represent the highest pain.;A 30% improvement compared to baseline on the weekly average score of worst daily abdominal pain for at least 2 of the 4 weeks of the primary evaluation period .
2 secondary outcomes
overall response
Time frame: up to 7 weeks of 14 weeks
stool frequency
Time frame: 2 weeks
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 20 Apr 2026.
- Background: PubMed 15963077Lauritano EC, Gabrielli M, Lupascu A, Santoliquido A, Nucera G, Scarpellini E, Vincenti F, Cammarota G, Flore R, Pola P, Gasbarrini G, Gasbarrini A. Rifaximin dose-finding study for the treatment of small intestinal bacterial overgrowth. Aliment Pharmacol Ther. 2005 Jul 1;22(1):31-5. doi: 10.1111/j.1365-2036.2005.02516.x.
- Background: PubMed 17373916Scarpellini E, Gabrielli M, Lauritano CE, Lupascu A, Merra G, Cammarota G, Cazzato IA, Gasbarrini G, Gasbarrini A. High dosage rifaximin for the treatment of small intestinal bacterial overgrowth. Aliment Pharmacol Ther. 2007 Apr 1;25(7):781-6. doi: 10.1111/j.1365-2036.2007.03259.x.
- Background: PubMed 6534410O'Brien PC. Procedures for comparing samples with multiple endpoints. Biometrics. 1984 Dec;40(4):1079-87.
- Background: PubMed 17043337Pimentel M, Park S, Mirocha J, Kane SV, Kong Y. The effect of a nonabsorbed oral antibiotic (rifaximin) on the symptoms of the irritable bowel syndrome: a randomized trial. Ann Intern Med. 2006 Oct 17;145(8):557-63. doi: 10.7326/0003-4819-145-8-200610170-00004.
- Background: PubMed 16454838Sharara AI, Aoun E, Abdul-Baki H, Mounzer R, Sidani S, Elhajj I. A randomized double-blind placebo-controlled trial of rifaximin in patients with abdominal bloating and flatulence. Am J Gastroenterol. 2006 Feb;101(2):326-33. doi: 10.1111/j.1572-0241.2006.00458.x.
- Background: PubMed 10216811Trespi E, Ferrieri A. Intestinal bacterial overgrowth during chronic pancreatitis. Curr Med Res Opin. 1999;15(1):47-52. doi: 10.1185/03007999909115173.
- Background: PubMed 10792117Di Stefano M, Malservisi S, Veneto G, Ferrieri A, Corazza GR. Rifaximin versus chlortetracycline in the short-term treatment of small intestinal bacterial overgrowth. Aliment Pharmacol Ther. 2000 May;14(5):551-6. doi: 10.1046/j.1365-2036.2000.00751.x.
- Background: PubMed 3169375Corazza GR, Ventrucci M, Strocchi A, Sorge M, Pranzo L, Pezzilli R, Gasbarrini G. Treatment of small intestine bacterial overgrowth with rifaximin, a non-absorbable rifamycin. J Int Med Res. 1988 Jul-Aug;16(4):312-6. doi: 10.1177/030006058801600410.
- Background: PubMed 9327194Miglio F, Valpiani D, Rossellini SR, Ferrieri A. Rifaximin, a non-absorbable rifamycin, for the treatment of hepatic encephalopathy. A double-blind, randomised trial. Curr Med Res Opin. 1997;13(10):593-601. doi: 10.1185/03007999709113333.
- Background: PubMed 7774516Gillis JC, Brogden RN. Rifaximin. A review of its antibacterial activity, pharmacokinetic properties and therapeutic potential in conditions mediated by gastrointestinal bacteria. Drugs. 1995 Mar;49(3):467-84. doi: 10.2165/00003495-199549030-00009.
- Background: PubMed 10500060Attar A, Flourie B, Rambaud JC, Franchisseur C, Ruszniewski P, Bouhnik Y. Antibiotic efficacy in small intestinal bacterial overgrowth-related chronic diarrhea: a crossover, randomized trial. Gastroenterology. 1999 Oct;117(4):794-7. doi: 10.1016/s0016-5085(99)70336-7.
- Background: PubMed 9357184Nayak AK, Karnad DR, Abraham P, Mistry FP. Metronidazole relieves symptoms in irritable bowel syndrome: the confusion with so-called 'chronic amebiasis'. Indian J Gastroenterol. 1997 Oct;16(4):137-9.
- Read NW. Irritable Bowel Syndrome. In: Feldman J, Friedman LS, Sleisenger MH, eds. Sleisenger and Fordtran's Gastrointestinal and Liver Disease: Pathophysiology/Diagnosis/Management. 7th ed. Philadelphia, PA: Saunders; 2002: 1794-1806.Link provided by the sponsor.
- Pimentel M. A New IBS Solution: Bacteria - The missing link in treating irritable bowel syndrome. Sherman Oaks, CA: Health Point Press; 2006.Link provided by the sponsor.
- Individual participant dataSharing planned: No
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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.
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 2 study testing rifaximin 66mg + N-acetylcysteine 560mg three times daily and RNIB21 containing rifaximin 132mg + N-acetylcysteine 560mg three times daily in people with IBS (Irritable Bowel Syndrome) and IBS-D (Diarrhea-predominant), run by Mark Pimentel, MD at 1 site 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 6 inclusion and 11 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: looking for participants now, as of the sponsor's last update on 20 Apr 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site 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. Some participants in this study may receive a placebo. 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?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Mark Pimentel, MD (310.423.0617, mastprogrram@cshs.org), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
stool consistency (time frame: 2 weeks). The study lists 2 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 NCT06727422, which also lists 21 linked publications.
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 20 Apr 2026.