The goal of this clinical trial is to determine efficacy of FMT via rectal enema and encapsulated FMT in patients with IBS in Thailand. The main question it aims to answer is:

• Does FMT provide better efficacy than placebo in IBS patients?

Participants will be randomized into 3 groups:

• In placebo group, patients will receive placebo capsules and placebo via enema.
• In enema group, patients will receive placebo capsules and FMT via rectal enema.
• In capsule group, patients will receive FMT capsules and placebo via rectal enema.

Researchers will compare FMT and placebo group to see if using FMT provides better efficacy for IBS patients than placebo. Moreover, researchers will compare efficacy of FMT capsules and FMT via rectal enema in IBS patients.

Irritable bowel syndrome (IBS) is a common functional bowel disorder defined by recurrent abdominal pain related to defecation or a change in bowel habit (1). Pathogenic mechanisms of IBS include gut microbial dysbiosis, low-grade mucosal inflammation, increased gut permeability, and altered gut-brain interaction (2). Dysbiosis is an imbalance of gut microbiota which can contribute to IBS. Emerging treatment approach for IBS aims to correct dysbiosis by modulation of intestinal microbiota (3).

Fecal microbiota transplantation (FMT) is an administration of feces from a healthy donor to the gastrointestinal tract of a recipient in order to restore balanced microbial flora (4). Correcting gut dysbiosis might be another target to improve IBS symptoms. Some previous randomized controlled trials demonstrated that FMT could provide clinical response in patients with IBS (5-7), whereas others reported no different outcome from placebo (8, 9). Most trials delivered FMT via more invasive routes such as colonoscopy or gastroscopy. There were few studies using less invasive methods, e.g., oral FMT capsules and FMT via rectal enema. Less invasive routes of FMT administration are needed to be evaluated so as to reduce risk and cost of endoscopy.

This study aimed to determine efficacy of FMT via rectal enema and encapsulated FMT compared with placebo in IBS patients in Thailand.

Inclusion Criteria:

• Patients aged 18-70 years with IBS diagnosed by Rome IV criteria
• Patients who can provide written informed consent.

Exclusion Criteria:

• Pregnant or breastfeeding women
• Severe comorbidities: chronic kidney disease (GFR<15 ml/min), cirrhosis, cancer, etc.
• Fecal incontinence
• Immunocompromised patients
• Taking probiotic, or fermented food
• Discontinue medication for IBS <1 month prior to study inclusion