STUDIES ON THE ANTITUBERCULOUS ACTIVITIES OF RIFAMPICIN (RFP) AND THE PERIOD OF EXPOSURE IN VITRO

この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました。A new antituberculous drug, rifampicin (RFP) is a semisynthetic compound belonging to the group of rifamycins that were isolated from the fermentation broth of Streptomyces mediterranei. In this report, the antituberculous activities of RFP and the period of exposure were evaluated in vitro. The experiments were practiced by using the silicone-coated slide culture method (SSC-method), H_Rv strain of Mycobacterium tuberculosis, Kirchner's medium, 1% Ogawa medium, silicone-coated slides, rifampicin (RFP), streptomycin (SM), and isoniazid (INH). To obtain the microbial cell units, four week cultures of the H_Rv strain of M. tuberculosis cultivated in a 1% Ogawa medium were adjusted to a density equivalent to ca. 0.1 mg/ml in petroleum benzine. Then, silicone-coated slides were dipped and attached to the petroleum benzine containing microbial cell units. These slides with tubercle bacilli were put in test tubes containing Kirchner's media with serial concentrations of drugs. They were incubated at 37℃ for four weeks. The concentrations of drugs were compounded by serial double dilution method. Test tube No. 1 contains RFP 100 mcg/ml, SM 1000 mcg/ml and INH 1000 mcg/ml, respectively. Test tube No. 20 is a controlled culture. Types of drug regimen are the following. Experiment 1 (1) Continuous contact with 3 drugs, RFP, SM, INH, respectively (2) Intermittent contact with 3 drugs, 24 hours a week, respectively (3) Intermittent contact with 3 drugs 24 hours twice a week, respectively Experiment 2 (1) Continuous contact with RFP (2) Intermittent contact with RFP, 3 hours twice a week (3) Intermittent contact with RFP, 1 hour a week (4) Intermittent contact with RFP, 1 hour twice a week The evaluation of bacteriostatic effect was macroscopically performed at the end of three-week incubation. The evaluation of bactericidal effect was macroscopically performed at furthermore four-week incubation after stopped contact with drugs. Experimental findings were the following. Experiment 1 (1) The bacteriostatic effects of SM and INH were remarkably weakened as the duration of contact period with drugs were shortened; on the other hand those of RFP were not and the difference of continuous and intermittent contact with RFP was very slight. (2) RFP was also the most effective drug in bactericidal action among three drugs. And the difference of continuous and intermittent contact with it was very slight in comparison with SM and INH. Experiment 2 Minimal inhibitory concentrations (MIC) of intermittent contact with RFP, 3 hours twice a week; 1 hour twice a week; 1 hour a week were 1.56, 3.13, 12.5 mcg/ml, respectively, and MIC of continuous contact with RFP was 0.049 mcg/ml. In the finding of bactericidal action of RFP, slight difference of continuous and intermittent contact was still maintained. These findings suggest that RFP has very strong bactericidal action and may be particularly suitable for intermittent administration. In this report, the development of drug (RFP) resistance was also evaluated. The development of drug resistance were not observed in both strains of continuous and intermittent contact with RFP