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The results of the study on the inhibitory effect of a number of rifamycin derivatives, such as rifamycin B, rifamycin O, rifamycin, rifamycin A, 25-desacetylrifampicin and rifampicin are presented. It was shown that rifampicin had the highest inhibitory effect on the synthesis of RNA in the cells of E. coli and Staph. aureus. It inhibited the above process by 93.0 and 98.8 per cent respectively. The data on the cells of Staph. aureus, as well as the data on comparison of the inhibitory effect of rifampicin derivatives with respect to the RNA-polymerase reaction in acellular systems are presented.

The study on distribution of 14C-rifampicin and 14C-rifamycin S in experimental animals after intramuscular administration of the drugs showed that concentrations of rifampicin in the organs and blood were higher than those of rifamycin S. Biotransformation products of both antibiotics, such as 25-deacetylrifampicin, N-oxide of rifampicin, 3-phormylrifamycin SV, rifamycin SV and others were found in the liver, kidneys, bile and urine. No products of the antibiotic metabolism were found in the blood, lungs and spleen.

The results of studying the effectiveness of incorporation of the label from different 14C- and 3H-precursors into the molecule of rifamicin B during its biosynthesis are presented. The regularities of the label incorporation into the antibiotic composition as dependent on the time of the precursor addition were investigated. A radiochemically pure preparation of 14C-rifamicin B with specific radioactivity of 3 mcurie/mg was obtained.