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

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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