Rifaximin on Visceral Hypersensitivity

Irritable bowel syndrome (IBS) is one of the most common gastrointestinal disorders, with a global prevalence of 11% according to a recent meta-analysis. The total cost of managing IBS in the United States is in excess of $30 billion per year, including indirect costs relating to loss of productivity of more than $20 billion. Abdominal pain/discomfort (i.e. visceral hypersensitivity) is present in all patients with IBS and remains the most therapy-resistant symptom. Apart from abdominal pain, which is measured subjectively using visual scales, several studies have shown a significant increase in rectal sensitivity, which is measured objectively using an inflatable balloon. Drugs which are shown to have objective effects on visceral hypersensitivity are crucial in the management of IBS.

While certain drugs have shown to decrease abdominal pain, there is very little data to substantiate objective changes in visceral hypersensitivity. Rifaximin is a poorly absorbed antibiotic and the exact underlying mechanism of action for rifaximin in reducing the pain component of IBS remains unknown. However, rifaximin has been shown in randomized controlled trials to decrease abdominal discomfort in all subtypes of IBS.

The investigators hypothesize that rifaximin is effective in decreasing rectal visceral hypersensitivity in IBS patients. In this study, the investigators propose to test this hypothesis by measuring visceral hypersensitivity using the graded balloon distention test, before and after a course of rifaximin. To test whether this effect is accompanied by treating SIBO, the investigators will also perform lactulose breath tests before and after rifaximin therapy.


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.