Clarification on nonresponder follow-up and end-of-study assessments was added. Key secondary endpoints were added as components of the primary endpoint. The weekly diary subject global assessment (SGA) questions were added as a requirement with details about how responsiveness and validity of the SGA would be evaluated. The following secondary endpoints were added: - Responsiveness of the weekly SGA question in detecting daily IBS symptom changes each week. - Validity of the weekly SGA question in correlating with daily IBS symptoms each week. - Proportion of subjects who are monthly responders by month during the DBR Treatment Phase, the Maintenance Phase 2, and the SRT Phase. - Proportion of subjects who are weekly responders by week during Treatment 2 Phase, Maintenance Phase 1, DBR Treatment Phase, Maintenance Phase 2 and SRT Phase - Proportion of subjects who are responders during PEP in the DBR Treatment Phase for the complete recurrence subjects during the Maintenance Phase 1. “Treatment Success” was replaced with “Weekly Responder” and both terms were clarified. Recurrence was redefined. Additional information was added regarding potential substudies. Exclusion criterion #6 was modified. “Prohibited medications” were redefined as “restricted medications” with clarification on handling the latter. Additional instructions and explanation for the requirement for stool samples was added. Weekly nonresponder was redefined. Subjects who were responders during the 4-week follow-up period in the DBR Treatment Phase (PEP) and experienced recurrence during the Maintenance Phase 2 were considered having “recurrence at the first non-responding week” within a 4-week assessment period during which the recurrence occurs, as opposed to “no treatment success” as defined in the original protocol. Worst case analysis method was added to the methods of handling dropouts and missing data. Subgroup analyses were added to Section 8.3.3

The skin swab sub-study was added, noting instruction for collection of samples and that further details would be provided in a separate protocol. The 14 day window after signing the informed consent form (ICF) for colonoscopy was removed. Exclusion criterion #16 was removed as creatinine clearance was not a concern while using rifaximin in this study population. The window for taking antibiotics was reduced from 60 to 14 days prior to signing the ICF. Simethicone was added as a restricted therapy. Visit windows were defined for colonoscopy requirements.

Added a standard of care approach to endoscopic examination and removed the 7 day waiting period between colonoscopy and Screening Phase.

Added European Union investigative sites to the study design and incorporated required statements for submission of the protocol in Europe.

The DBR population was clarified as the ITT population. DBR phase noted as the randomization phase and is the basis for analysis of ITT population. Key secondary endpoints were re-ranked to reflect the study design objectives and clarification for the analysis thereof was added. Decreased the sample size from 800 to 600 based on a change in the PEP in DBR Treatment phase. The new assumption accounts for the enrichment aspects of the study design and is supported by literature regarding a repeat treatment study. Post-marketing experience information, prohibited medications, and updates to birth control methods was added per country specific requests made by the German Competent Authority (BfArM). “Recurrence” definition was clarified for partial recurrence and definition of “durability” of response was added.