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Treatment of nontuberculous mycobacterial infection should be carried out by the chemotherapeutic regimens most suitable for each species. We performed in-vitro susceptibility tests for various species and determined the probability in which the mycobacteria of each species are inhibited by blood concentrations attainable by the dosages usually used. From such determinations, the following regimens have been recommended: 1) M. avium-M. intracellulare complex, Rifampicin + Enviomycin + Ethambutol; 2) M. kansasii, Ofloxacin + Enviomycin + Rifampicin; 3) M. szulgai, Enviomycin - Ethambutol + Isoniazid; 4) M. fortuitum, Ofloxacin. The effectiveness of the treatment of the infection caused by M. avium complex is less than 15% even using the above regimen, while it is high in the treatment of infections caused by M. kansasii and M. szulgai. There are no effective regimens for the treatment of infection caused by M. chelonae or M. simiae. The above recommendations are useful in practice, because, at present, reliable susceptibility testing of nontuberculous mycobacteria is not yet done commonly.

The rate of sputum conversion (continuously negative cultures for six months or more) was compared among four regimens given to 83 patients with moderately advanced, cavitary lung disease caused by Mycobacterium avium complex untreated previously. The regimens of rifampin + isoniazid + enviomycin and rifampin + isoniazid + streptomycin appeared to be superior to the regimen of rifampin + isoniazid + ethambutol. No statistically significant difference was observed between the regimens rifampin + isoniazid + enviomycin and rifampin + isoniazid + streptomycin.