ABSTRACT
An exciting discovery was made in 1969 by investigators working independently in Israel and Scotland. It found that a rifamycin antibiotic, known to be effective in the treatment of diseases of bacterial etiology, also inhibited the growth of certain mammalian viruses. In the presence of mild reducing agents, rifamycin S was converted to rifamycin SV, a substance with high antibiotic activity and relatively low toxicity. Several rifamycin derivatives, including some that are known to inhibit reverse transcriptase activity and others that are relatively inactive in this respect, have been tested for their effects on replication and cell transformation by ribonucleic acid (RNA) tumor viruses. Rifamycins are clinically useful antibacterial agents that act by specifically inhibiting RNA polymerase activity. Although rifamycins do not appear to be broad spectrum antiviral agents, certain derivatives possess selective antiviral properties. The relatively high concentration of rifampin needed for inhibition and the ease of reversibility are features that distinguish the antipoxviral from the antibacterial effects.
