<p>Rifaximin is a semisynthetic, rifamycin-based non-systemic antibiotic. Very little of the drug will pass the gastrointestinal wall into the circulation as is common for other types of orally administered antibiotics. Rifaximin inhibits bacterial RNA synthesis by its action on the beta-subunit of the DNA-dependent RNA polymerase. It shows the same broad spectrum activity as rifamycin which exerts bactericidal action against many species of Gram-positive and Gram-negative, aerobic and anaerobic bacteria.</p>