Efficacy and Safety of Oral Rifaximin in Patients With Active Microscopic Colitis

This is an open-label single-arm trial to evaluate the efficacy of Rifaximin in patients with active microscopic colitis (MC). 10 subjects will be asked to take 500mg Rifaximin three times per day for 4 weeks. The primary endpoints will be histologic response and clinical remission (less than 3 stools per day and less than 1 watery stool per day within the prior 7 days. The secondary endpoint will be change of the MC Disease Activity Index (MCDAI).

• Rifaximin 550mg (Drug): Rifaximin 550mg

Primary outcomes

• Number of Subject Experiencing Remission of MC Symptoms [6 weeks]: Remission, which will be define as less than 3 stools per day and less than 1 watery stool per day within the prior 7 days as per Hjortswang criteria, which has been used as the standard definition of remission in most all randomized clinical trials evaluating budesonide and MC. Investigators will also look at number of bowel movements, abdominal pain, incontinence, and nocturnal bowel movements. Symptoms will be compared at Week 0 and Week 6.
• Histologic Response for Indications of Disease Severity [6 weeks]: Our institution has identified histologic parameters associated with more severe disease activity. In collaboration with pathologists, investigators will compare histologic inflammation on patients before and after treatment. Histology will be assessed via standard H\&E staining, specifically looking at surface epithelial changes associated with disease severity.

Secondary outcomes

• Change of the MC Disease Activity Index (MCDAI) [6 weeks]: The MCDAI scale was developed to best predict a patient's quality of life as well as approximate a physician's global assessment. In multivariate analysis, the MCDAI demonstrated four independent clinical features associated with the physician global assessment including the number of unformed stools daily, number of nocturnal stools, abdominal pain, and number of episodes of fecal incontinence. These factors were used to develop estimated regression coefficients as weights produced the MCDAI formula: 1.1+0.31 (average number of unformed stools daily over the past week; continuous variable)+0.78 (nocturnal stools over past week, 0=absent, 1=present)+0.22 (maximum abdominal pain over past week, score 1-10)+0.11 (average weight loss per month (lbs))+0.93 (fecal urgency over past week, 0=absent, 1=present)+0.01 (number of episodes of fecal incontinence over past month; continuous variable). This will be assessed at Week 0 and at Week 6.

Sex: All, ages: 18 Years to any

Inclusion Criteria:

* Collagenous colitis (CC) or lymphocytic colitis (LC) diagnosed on colon biopsies reviewed by 2 separate pathologists
* CC will be defined histologically to be the following: thickness of the collagenous subepithelial table >10 micrometer using an ocular micrometer, inflammation in the lamina propria consisting of mainly lymphocytes and plasma cells, lack of crypt architectural distortion, and regenerative-appearing changes in the surface and/or crypt epithelium
* LC will be defined histologically to be the following: intraepithelial lymphocytes >20 per 100 epithelial cells in the subjective area of highest lymphocyte density, inflammation in the lamina propria consisting of mainly lymphocytes and plasma cells, and regenerative-appearing changes in the surface and/or crypt epithelium
* Subjects in active flare, defined as >3 watery/loose stools per day on >4 / 7 days over >4 weeks in the past 3 months.

Exclusion Criteria:

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• Eugene Yen, MD, Principal investigator, Endeavor Health