Effect of some rifamycin derivatives on chemically-induced mammary tumors in rats.

Five rifamycin derivatives have been compared for their effectiveness in inhibiting chemically-induced mammary tumours in rats. Daily oral administration of DMB (dimethylbenzyl-desmethylrifampicin), starting 2 weeks before the carcinogen challenge, was the most effective, both in inhibiting or delaying the onset of tumours and in slowing the growth of those that occurred. The inhibitory effects of rifampin, dirifampin, RC-16(rifazacyclo16) and R-82) were less than those of DMB when administered by the same route at the same dose level.