Refexan is a medication that contains rifaximin, an antibiotic primarily used to treat gastrointestinal conditions such as traveler's diarrhea and irritable bowel syndrome with diarrhea (IBS-D). It works by targeting specific bacteria in the gut without significantly affecting the rest of the body's microbiome. Rifaximin is often favored for its localized action and low systemic absorption, which minimizes side effects. Always consult a healthcare professional for personalized advice and treatment options.