The semicarbazide hydrochloride in concentrations at least 6.0, 10.0 and 4.0 mg./ml. could inhibit the microbiological test organisms of Sarcina lutea ATCC 9341, Staphylococcus aureus ATCC 6538P and Bacillus subtilis ATCC 6633 respectively. In the microbiological assay of antibiotics must be added semicarbazide hydrochloride in concentrations less than these according to the interference. Streptomycin in concentration of 100 mcg./ml. was antagonistic with semicarbazide hydrochloride in concentration at least 1.5 mg./ml. (equal volume) against B. subtilis at 37 ?C in 180 min. and in concentration of 2.0 mg./ml. in at least 30 min. whereas at 37?C the lowest concentration was 3.0 mg./ml. in 60 min. and 4.0 mg./ml. in at least 30 min. The maximal concentration of semicarbazide hydrochloride to neutralize the activity of streptomycin against the test organism at 30?C and 37?C were 4.0 and 6.0 mg./ml. respectively. The experiments suggested that in case of incubation at 30?C was used in lower concentration ofsemicarbazide hydrochloride and less time than at 37?C. The suitable concentration to neutralize the activity of streptomycin wa 2.0 mg./ml. at 30?C in 30 min. For the semicarbazide hydrochloride effects on the other aminoglycoside antibiotics, the concentrations of 0.5 to 2.0 mg./ml. either 30?C or 37?C was no effect to dihydrostreptomycin against B. subtilus but 1.0 to 1.5 mg./ml. or more was antagonist the activity of kanamycin against S.aureus In penicillin group, the semicarbazide hydrochloride in concentrations of 0.5 to 10.0 mg./ml. at 30?C were no effect to neutralize the activity of penicillin G against S. sureus. Rifampin, the rifamycin group, was the same as the aminoglycoside antibiotics that 0.5 to 2.0 mg./ml. at 30?C and 0.5 to 1.5 mg./ml. at 37?C were no effect to rifampin against S. lutea. The most of incubation time to neutralize activity should be less than 120 min. The microbiological assay of the combination with streptomycin must be consideration of the concentration of semicarbazidehydrochloride, temperature and time for preventing the influence of antibiotic to be assayed. In this study the assay of penicillin in the combination of penicillin and streptomycin by the use of selective inactivation was compared to the specific strain of test organism. The potency of penicillin G (% labeled amount) in the assay with semicarbazide hydrochloride was 112.56+- 6.86 % closed to 112.02 +- 4.99% in the assay with S. lutea. The rifampin concentration in cerebrospinal fluid (CSF) and serum of five tuberculous meningitis patients treated with rifamin, streptomycin and other drugs were assays by using semicarbazide hydrochloride. The levels of rifampin in CSF were 0.10-0.57 mcg./ml./ which ensure therapeutic concentration to MIC against Mycobacterium tuberculosis (0.1 mcg./ml). The average concentration of rifampin in CSF in a week was 4.52% of the corresponding serum levels. From this study, the determination of the potency and concentration of drug in combined with streptomycin by the use of semicarbazide hydrochloride are valuable to the quality control, the treatment and other researches.
