Application Rifamycin SV is a broad-spectrum semisynthetic antimicrobial agent of the rifamycin group. It is used to study potential genes, such as rif15 and rif16, which may be involved in the conversion of rifamycin SV into rifamycin B1. It is a potential treatment for traveler’s diarrhea (TD), Clostridium difficile-associated disease (CDAD) and rheumatoid knee synovitis2,3. It is used in electron spin resonance studies4. Biochem/physiol Actions Rifamycin SV inhibits selective (E. coli, B. subtilis) bacterial DNA-dependent RNA polymerase by binding to the polymerase β-subunit, a mechanism similar to rifabutin. It acts as a selective cytochrome P450 3A4 inducer. It has limited oral absorption that is active against Gram-positive bacteria and is moderately active against Gram-negative organisms2.