Rifaximin is a semisynthetic, rifamycin-based non-systematic antibiotic, meaning that the drug will not pass the gastrointestinal wall into the circulation as is common for other types of orally administered antibiotics. It is primarily used to treat diarrhea caused by E. coli, but recent studies published in the American Journal of Gastroenterology suggest its efficacy in relieving chronic functional symptoms of bloating and flatulence that are common in gastrointestinal disorders, such as Irritable Bowel Syndrome.
It is currently sold under the brand name Xifaxan® by Salix Pharmaceuticals.

Xifaxan - Consumer information sheet provided by the U.S. Food and Drug Administration Center for Drug Evaluation and Research.