Rifampicin is an antibiotic used to treat several types of bacterial infections, including tuberculosis, Mycobacterium avium complex, leprosy, and Legionnaires’disease. It inhibits bacterial DNA-dependent RNA synthesis by inhibiting bacterial DNA-dependent RNA polymerase. It prevents RNA synthesis by physically blocking elongation, and thus preventing synthesis of host bacterial proteins. By this “steric-occlusion” mechanism, rifampicin blocks synthesis of the second or third phosphodiester bond between the nucleotides in the RNA backbone, preventing elongation of the 5′ end of the RNA transcript past more than 2 or 3 nucleotides.