Amikacin, ethambutol, and rifampin for treatment of disseminated Mycobacterium avium-intracellulare infections in patients with acquired immune deficiency syndrome.

Synergistic combinations of achievable serum levels of amikacin, rifampin, and ethambutol were tested for their ability to inhibit growth of Mycobacterium avium-intracellulare strains isolated from seven patients with acquired immune deficiency syndrome. Even when the isolates were very resistant to the individual antimicrobial agents in vitro, growth was completely inhibited by all combinations of the three agents tested. Four of the patients treated with a combined regimen of amikacin, rifampin, and ethambutol showed clinical improvement. Synergistic antimicrobial susceptibility tests seem to more accurately represent the efficacy of combined regimens used to treat these extremely resistant mycobacteria than do conventional susceptibility determinations with individual antimicrobial agents.