Rifaximin 200-mg tablets are used to treat traveler’s diarrhea caused by certain bacteria in adults and children at least 12 years of age. Rifaximin 550-mg tablets are used to prevent episodes of hepatic encephalopathy (changes in thinking, behavior, and personality caused by a build-up of toxins in the brain in people who have liver disease) in adults who have liver disease and to treat irritable bowel syndrome (with diarrhea) in adults. Rifaximin is in a class of medications called antibiotics.