Combinations of Rifampin or Rifabutine plus Ethambutol againstMycobacterium aviumComplex: Bactericidal Synergistic, and Bacteriostatic Additive or Synergistic Effects

Abstract

Ethambutol, when combined with rifampin or rifabutine (ansamycin, LM427), produced an additive inhibitory effect against most of the tested M. avium complex strains (12 of 16 with rifampin, 13 of 16 with rifabutine). The inhibitory effect was synergistic for the remaining of 4 of 16 and 3 of 16 strains. This relationship reduced the minimal inhibitory concentrations for each drug in combination. In addition, the minimal bactericidal concentrations of all 3 drugs were reduced because of synergistic bactericidal activity in 6 of 6 strains tested.