Hydrogen Breath Test an Instrument to Predict Rifaximin-Response in Irritable Bowel Syndrome Predominant Diarrhea

Inclusion Criteria: * IBS-D (Rome IV Diagnostic Criteria) * Diary compliance for at least 5 days and no rescue medications during baseline * Appropriate levels of abdominal pain and diarrhea Exclusion Criteria: * Pregnant women or planning on becoming pregnant while in the study, or lactating women while in the study * Inflammatory bowel disease, diabetes mellitus, systemic sclerosis, or celiac disease * Active gastrointestinal or hematological malignancy which requires ongoing treatment * Surgery to the GI tract in the past 3 months * Gastrointestinal infection or diverticulitis in the past 3 months * Severe hepatic impairment * Any use of antibiotics in the past month * Current use of probiotics * Any history of allergies to rifaximin or its derivatives * Any comitant use of P-glycoprotein inhibitors (for example. Cyclosporine) * Known allergies to glucose or lactulose