Small intestinal bacterial overgrowth (SIBO) is a common condition associated with gastrointestinal symptoms such as bloating, abdominal pain, diarrhea, and constipation, particularly in patients with irritable bowel syndrome. Antibiotic therapy with rifaximin is commonly used, but relapse rates remain high.

This randomized, placebo-controlled clinical trial aims to evaluate whether supplementation with a multispecies probiotic containing Enterococcus faecium and Bacillus subtilis improves the effectiveness of rifaximin therapy in adult patients with SIBO.

Participants will be randomly assigned to receive either rifaximin plus the probiotic or rifaximin plus placebo. Clinical assessments will include hydrogen breath testing and evaluation of gastrointestinal symptoms using standardized questionnaires at baseline and during follow-up visits.

The study is being conducted at a single academic medical center in Poland and is sponsored by Państwowy Instytut Medyczny MSWiA. The probiotic and rifaximin are provided by Urgo.

The results of this study may help determine whether probiotic supplementation can improve treatment outcomes and reduce recurrence of SIBO.

Inclusion Criteria:

• Age ≥18 years.
• Meets Rome IV criteria for irritable bowel syndrome.
• Written informed consent to participate in the study.

Exclusion Criteria:

• Lack of cooperation with investigators.
• Age >75 years.
• Need for modification of gastrointestinal treatment during the study.
• Use of antibiotics within 4 weeks before screening.
• Use of probiotics within 7 days before screening.
• Endoscopic examination within 6 weeks before screening or during the study without investigator approval.
• History of abdominal surgery.
• Crohn's disease, ulcerative colitis, microscopic colitis, celiac disease, cystic fibrosis, chronic pancreatitis, liver cirrhosis, or end-stage renal disease.
• Low FODMAP diet within 4 weeks before screening.
• Pregnancy or breastfeeding.
• Lactulose intolerance.