Rifampicin is a semi synthetic member of the rifamycins. It inhibits DNA dependent RNA polymerase, probably by interfering with the initiation of RNA synthesis, after the attachment of the polymerase but before nucleotide bond formation. The antibacterial action of rifampicin is due to the fact that it inhibits bacterial RNA synthesis without affecting RNA synthesis in the host.
Rifampicin has also been found to inhibit the multiplication of several mammalian viruses, e. g. vaccinia, cowpox, adenovirus and the trachoma virus. The concentration required for antiviral activity is, however, much higher than for antibacterial activity. It does not appear to inhibit viral RNA polymerase.
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