Intervention: Rifaximin
Trial phase: Phase 2
ATC code: A07AA11 | D06AX11
SMILES: COC1C=COC2(C)Oc3c(C)c(O)c4c(O)c(c5c(nc6cc(C)ccn65)c4c3C2=O)NC(=O)C(C)=CC=CC(C)C(O)C(C)C(O)C(C)C(OC(C)=O)C1C
Sex: All
Age groups: Adult | Older Adult
Healthy volunteers: No
Participants at risk: 4
Group description: 4 subjects with diarrhea-predominant IBS (IBS-D) or mixed IBS (IBS-M) enrolled in the study. At the first clinic visit, subjects did rectal sensitivity testing, as well as lactulose breath testing. Subjects were asked to record their symptoms and bowel habits in a diary over the next 7 days. During the second clinic visit, subjects will receive a 14-day course of rifaximin (550 mg PO TID). During these 14 days, subjects will record their symptoms and bowel habits. Subjects will return to the clinic after completion of the medication and did repeat evaluation via rectal sensitivity testing to assess for change in rectal sensitivity.

Rifaximin: Rifaximin will be administered to patients diagnosed with IBS-D or IBS-M to evaluate whether the medication is effective in decreasing rectal hypersensitivity. The secondary objective of the study is to assess the role of SIBO in rectal sensitivity.
Eligibility criteria:
Inclusion Criteria:

Male or female subjects aged 18-75 years old inclusive
Meet Rome IV criteria for IBS-D or IBS-M
Subjects should report urgency with bowel movement at least once a week
If subjects are ≥50 years old, a colonoscopy must have been completed within the past 5 years
Subjects are capable of understanding the requirements of the study, are willing to comply with all the study procedures, and are willing to attend all study visits.
Agree to use an acceptable method of contraception throughout their participation in the study. Acceptable methods of contraception include: double barrier methods (condom with spermicidal jelly or a diaphragm with spermicide); hormonal methods (e. g. oral contraceptives, patches or medroxyprogesterone acetate); or an intrauterine device (IUD) with a documented failure rate of less than 1% per year. Abstinence or partner(s) with a vasectomy may be considered an acceptable method of contraception at the discretion of the investigator.
All subjects will provide Institutional Review Board (IRB)-approved informed written consent prior to beginning any study-related activities

NOTE: Female subjects who have been surgically sterilized (e.g. hysterectomy or bilateral tubal ligation) or who are postmenopausal (total cessation of menses for >1 year) will not be considered "females of childbearing potential".

Exclusion Criteria:

Treatment with antibiotics or Xifaxan in the last two months
Subjects with history of intestinal surgery (except appendectomy or cholecystectomy)
Subjects with known pelvic floor dysfunction
Pregnancy
Nursing mothers
Poorly controlled/uncontrolled significant medical condition that would interfere with study procedures
History of bowel obstruction
History of celiac disease
History of inflammatory bowel disease
Cirrhosis
IBS-C/chronic idiopathic constipation
Diabetes
History of anorectal radiation/surgery
History of prostatitis
Known allergy or hypersensitivity to rifaximin or rifamycin
Current treatment with eluxadoline or opiates

NOTE: Development of any of the exclusion criteria during the study will be considered a basis for subject discontinuation.