Irritable Bowel Syndrome With Diarrhea (IBS-D) Rifaximin Re-Treatment Study

It is important in chronic conditions to have information about how a product that is intended for short course administration in order to confer prolonged benefit should be administered beyond the first cycle of use once symptoms reappear. This Phase 3 study will evaluate the efficacy and safety of repeat treatment with rifaximin 550 mg three times daily (TID) for 14 days in subjects with IBS-D who respond to an initial treatment course with rifaximin 550 mg TID for 14 days. This study consists of several treatment phases outlined below: Screening/Treatment 1 Phase. Subjects will receive single-blind placebo TID for 7-13 days and answer daily IBS symptom-related questions. Treatment 2 Phase. Eligible subjects will receive open-label rifaximin 550 mg TID for 2 weeks with a 4-week treatment-free follow-up. Responders will continue into Maintenance Phase 1. Nonresponders will withdraw from the study. Maintenance Phase 1. Subjects will continue the treatment-free follow-up period for up to 18 weeks until either: 1) they experience recurrence or 2) enrollment is met in the Treatment 3 Phase (Double Blind Repeat Treatment Phase). Subjects who do not meet recurrence criteria by the end of the Maintenance Phase 1 will withdraw from the study. Treatment 3 Phase/ Double Blind Repeat Treatment Phase. Subjects who meet criteria for recurrence will be randomized 1:1 to receive either rifaximin 550 mg TID or placebo TID for 2 weeks with a 4-week treatment-free follow-up. Primary efficacy analysis will be performed at the end of the Treatment 3 Phase (at Week 6 of the double-blind period). Maintenance Phase 2. All subjects continued into an additional treatment-free follow-up period of up to 6 weeks (Maintenance Phase 2). Treatment 4 Phase/Second Repeat Treatment Phase. Subjects will receive the same double-blind treatment as previously assigned in the Treatment 3 Phase for 2 weeks with a 4-week treatment-free follow-up. A lactulose breath test sub-study will be conducted at select sites.