The Effects of Exposure Time, Drug Concentration, and Temperature on the Activity of Ethambutol versus Mycobacterium tuberculosis

In a series of dynamic in vitro studies designed to assess the activity of ethambutol (EMB) against Mycobacterium tuberculosis, we made the following observations. Ethambutol showed bactericidal action with 10 µg/ml concentration when in constant contact with M. tuberculosis. At a lower concentration, bactericidal action was evident up to 6 days; after that time, this effect was lost owing to the development of drug-resistant mutants. The bactericidal action of ethambutol in this model was similar to that of rifampin and isoniazid. Pulsed exposure for 96 h caused a four-log reduction in cfu counts, but the growth resumed rapidly. The bactericidal action of ethambutol was maximal at 37° C and less at low temperatures. Ethambutol showed little activity against cultures growing at 8° C continuously that were incubated for only 1 h at 37° C. Against cultures growing at 8° C that were brought to 37° C for 6 h, its action was similar to that of rifampin. Ethambutol combined with other drugs showed bactericidal ...