Bacteriostatic and bactericidal activities of gentamicin alone and in combination with clarithromycin against Mycobacterium avium.

The inhibitory activity of gentamicin against Mycobacterium avium depended on the pH of the medium, and the broth-determined MICs for 90% of strains were 5.0 micrograms/ml at pH 7.4, 9.5 micrograms/ml at pH 6.8, and greater than 16.0 micrograms/ml at pH 5.0. The MBCs were two- to eightfold higher than the MICs. The combined effect of gentamicin and clarithromycin was additive, and the MICs and MBCs of each drug were either the same as those in the single-drug tests or reduced twofold.