Rifaximin, an antibiotic, fights bacterial infections only in the intestines. Rifagut 550 mg is different than any other antibiotic in that it passes through your stomach into your intestines and does not enter your bloodstream. Rifaximin only treats the intestinal tract. It won't treat any other infections. Rifaximin is used to treat travelers' diarrhea due to E.coli in children and adults who are at least 12 years of age. This infection is most commonly contracted by people who ingest or drink E.coli bacteria-contaminated food and fluids. Rifaximin can also be used to treat diarrhea in adults with irritable bowel syndrome.