Dynamic aspects of the in vitro chemotherapeutic activity of ansamycin (rifabutine) on mycobacterium intracellulare.

The in vitro action of ansamycin against Mycobacterium intracellulare was studied using continuous, dynamic (a rapidly falling off concentration simulating that existing in vivo in humans), and pulsed exposures. Ansamycin at a concentration of 5 micrograms/ml showed bactericidal activity starting from as early as 3 days after constant exposure. In the dynamic model with the drug present in bactericidal concentration for only 2 h a day, bactericidal activity was demonstrated. With pulsed exposure, a minimal period of 72 to 96 h is necessary for effective inhibitory action.