Patients with chronic cavitary pulmonary tuberculosis who were treated previously with antituberculous agents for more than two years were treated with a regimen composed of an agent previously unused and two agents to which tubercle bacilli were already resistant, and the time of resistance development was observed. The time that required for resistance develop ment to a single agent was as follows: rifampicin resistance (25μg/m
l) (0.45g per day, daily, per os) 2.27 months; rifampicin resistance (25μg/m
l) (0.45g per day, twice weekly, per os) 2.50 months; kanamycin low level resistance (100μg/m
l) (1g per day, three times weekly, intramuscularly) 3.07 months; ethionamide resistance (30μg/m
l) (0.5g per day, daily, per os) 3.33 months; kanamycin high level resistance (500μg/m
l) (1g per day, three times weekly, intramuscularly) 5.07 months; lividomycin resistance (200μg/m
l) (1g per day, three times weekly, intramuscularly) 4.68 months; enviomycin resistance (100μg/m
l) (1g per day, daily, intramuscularly) 4.80 months.
From the results obtained, the generation time of tubercle bacilli growing in cavities was estimated theoretically as 54 hours. This value is much longer than the generation time of 12 hours estimated in in vitro experiments (Ogawa egg medium).
From theoretical considerations based on the above results, the ranking of
in vivo effec tiveness of antituberculous drugs was summarized as follows: rifampicin (daily or intermittent) >kanamycin=lividomycin>enviomycin.
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