Activity of rifabutin, clarithromycin, ethambutol, sparfloxacin and amikacin, alone and in combination, against Mycobacterium avium complex in human macrophages.

Disseminated infection with Microbacterium avium complex (MAC) in patients with AIDS is currently treated with a combination of antimycobacterial agents in order to prevent the selection of resistant mutant strains. Although clinical and microbiological responses can generally be achieved within a few weeks, relapses are common and require modification of the combination regimen or identification of effective alternate therapies. In this study we investigated the activities of rifabutin 0.5 mg/L, sparfloxacin 1 mg/L, clarithromycin 4 mg/L, amikacin 16 mg/L and ethambutol 2 mg/L, alone and in combination, against nine strains of M. avium isolated from the blood of patients with AIDS in order to identify regimens with the greatest therapeutic potential. Macrophages derived from human monocytes were infected with M. avium and inoculated with a single drug or a combination of drugs; cfu counts were performed at 0, 4 and 7 days after infection. At day 4 and at day 7, the combination of rifabutin, clarithromycin, amikacin and sparfloxacin displayed the highest degree of activity. However, the activity did not differ significantly from that of the combination of rifabutin, clarithromycin and ethambutol. The results of this study confirm the activity of combinations including rifabutin and clarithromycin (+/- ethambutol) in human monocyte-derived macrophages and suggest potentially useful associations in incorporating sparfloxacin and amikacin.