[Effect of norfloxacin on bacterial flora in human feces].

Norfloxacin (NFLX), a synthetic oral antibacterial agent of quinolone carboxylic acid, was given orally for 5 full days at a dose of 200 mg, three times daily after each meal to healthy normal men with ages between 22 and 25 years weighing 53.0 to 84.0 kg (average 67.0 kg). The actual regimen followed was that the drug was administered twice after lunch and supper on the first day of dosing, and once after breakfast on the last day of dosing. On the 5th day before the start of dosing, on the first, 3rd and 5th days (last dosing day) of dosing, and on the 3rd, 5th, 10th and 20th days after the end of dosing, effects of the drug on the fecal flora were examined and its fecal levels were determined. Susceptibilities against NFLX and nalidixic acid (NA) of various fecal isolates from 7 men were determined. Adverse effects and influences on clinical laboratory tests were also examined. The results obtained are summarized below. 1. Following the drug administration, a transient decrease or disappearance of Escherichia coli, Klebsiella sp., Citrobacter sp. and Enterobacter sp. of Enterobacteriaceae was noted. The 3 strains other than E. coli were isolated from increasing number of cases after the end of dosing. No constant trend was observed in the isolation of Proteus sp. Organisms belong to Enterobacteriaceae were isolated only in 4 and 2 cases after 3 and 5 days of the start of dosing, respectively, but then gradually increased to the predose level. Among other Gram-negative bacteria, no constant trend was noted in the isolation frequency of Plesiomonas sp. Pseudomonas sp. was isolated from 6 and 5 cases on the 3rd day after dosing and on the 3rd day after the end of dosing, respectively; the frequency of isolation increased after dosing. Gram-positive bacteria such as Staphylococcus sp. were isolated with a reduced frequency on the 3rd day of dosing. However, the number of isolates increased in all cases both on the 5th day of dosing and on the 3rd day after the end of dosing, and then decreased. No change was noticed in the number of isolates of Enterococcus sp., and no constant trend was observed for Micrococcus sp. and YLO. The average count of the whole aerobic bacteria did not change. Some strains decreased significantly after the start of dosing. 2. Among anaerobes, Bacteroides fragilis and other Bacteroides were isolated on every test day.(ABSTRACT TRUNCATED AT 400 WORDS)