LM 427, a new spiropiperidylrifamycin: in vitro and in vivo studies.

The spiropiperidylrifamycin LM 427 (4-deoxo-3,4-[2-spiro-N-isobutyl-4-piperidyl]-(1H)-imidazo-(2,5-dihydro) rifamycin S) displays a broad spectrum of potent antibacterial activity in vitro. In vivo it is particularly effective in the therapy of experimental tubercular infections of mice. Three schedules of treatment were employed and the best results were obtained when intermittent administrations were used (ED50 of LM 427; 7 times lower than rifampicin). LM 427 is well distributed in tissues of mice and rats, with lung concentrations 10 to 20 times higher than plasma levels.