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Appl Environ Microbiol. 1969 June; 17(6): 861-865
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Antimycobacterial Activity of Rifampin Under In Vitro and Simulated In Vivo Conditions

Mycobacteriology Unit, National Communicable Disease Center, Atlanta, Georgia 30333

ABSTRACT

Minimal inhibitory concentrations of rifampin for different species of mycobacteria were determined in 7H-10 agar medium and Lowenstein-Jensen egg medium. When rifampin was incorporated into egg medium, approximately 90% of its activity was lost. The stability of rifampin was tested during storage at different temperatures and concentrations. When tested in agar medium, a combination of isoniazid (INH) and rifampin inhibited multiple drug-resistant strains of Mycobacterium intracellulare, but under simulated in vivo conditions the drugs did not eliminate these same organisms. Drug-resistant mutants of M. intracellulare multiplied during an 8-day period when exposed 10 hr daily to the INH-rifampin regimen. However, combinations of rifampin and INH reduced drug-resistant mycobacterial populations by 99%, an effect which could not be enhanced by the addition of either erythromycin, ethionamide, or cycloserine.