Abstract
Microbiologically active isoniazid (INH) concentration in the sensitivity test medium was assayed to the lower limit of 0.08μg/ml, by the thin-agar cylinder-plate method using INH highly sensitive rapid grower i. e., Mycobacterium H-7 as a test organism.
INH potency in the sensitivity test medium during storage or incubation was investigated as follows:
1) In the solid egg medium (Ogawa's 1 % KH2PO4), no remarkable decrease of INH activity was observed under the conditions of heating at 90°C for 60 minutes or storage at 4°C for 3 months. Whereas, deterioration of INH potency was observed after storage at 4°C for more than 3 months and within 2 months incubation at 37°C.
2) In Dubos' liquid medium, all of INH and its derivatives i. e., IHMS, INHG, IP, which proved to be microbiologically active, decreased in their potencies and were inactivated within 2 weeks incubation at 37°C.
