In vitro and in vivo activities of clarithromycin against the Mycobacterium avium complex

Clarithromycin (CAM) was assessed for in vitro antimicrobial activity against various mycobacterial species. Except for Mycobacterium tuberculosis, CAM displayed MICs for test mycobacteria comparable to those of sparfloxacin (SPFX) but lower than those of rifampicin (RMP) and ofloxacin (OFLX). CAM at 0.25 mug/ml (1 MIC) exhibited bactericidal action against M. intracellulare growing in 7H9 medium and at 1 or 10 mug/ml (4 and 40 MIC, respectively) CAM displayed antimicrobial activity against the organism phagocytosed in murine macrophages, while RMP failed to manifest such an effect. When CAM was given s.c. or by gavage to mice infected i.v. with M. intracellulare at doses of 0.2 to 2 mg/mouse once daily, six times per week, it exhibited significant therapeutic efficacy in terms of decreased incidence of gross lung lesions and reduced bacterial loads in the lungs and spleen.