Xifaxan (Rifaximin) is an antibiotic that fights bacterial infection only in the intestines. Because rifaximin treats only the intestinal tract, it will not treat infections of other parts of the body. Xifaxan is used to treat travelers’ diarrhea caused by E. coli in adults and children who are at least 12 years old. Most people get this infection by eating food or drinking fluids that have been contaminated with the E. coli bacteria.