Evidence that antituberculosis drugs are really effective in the treatment of pulmonary infection caused by Mycobacterium avium complex.

Successful chemotherapy of pulmonary disease caused by Mycobacterium avium complex by antituberculosis drugs has been reported by a number of investigators. However, no certain evidence of the efficacy has yet been demonstrated in a controlled clinical trial. The present study has approached this problem in 2 ways: serial analysis of minimal inhibitory concentrations (MIC) during treatment and correlation of response to therapy with initial MIC. It was observed that after administration of antituberculosis drugs (rifampin, isoniazid, kanamycin, enviomycin, and minocycline), MIC values for the M. avium complex strain increased significantly. This change may be considered a result of suppression of relatively susceptible bacteria and as evidence of the efficacy of drugs. Furthermore, a correlation between the MIC values determined before chemotherapy with the conversion of sputum to negative was shown. The M. avium complex strains varied markedly in their susceptibility to antituberculosis drugs, and these susceptibilities were correlated with the chemotherapeutic effect. The fate of patients seemed to be greatly influenced by the susceptibilities of the strains that caused infection.