In vitro activity of norfloxacin against Neisseria gonorrhoeae.

Norfloxacin, an analogue of nalidixic acid, is a novel antibacterial compound active against both gram-negative and gram-positive pathogens. 142 Neisseria gonorrhoeae isolates proved to be remarkably sensitive to it; the MIC50 and MIC90 values for norfloxacin were 0.03 microgram/ml and 0.06 microgram/ml, respectively, for the strains resistant to the penicillins; for the strains susceptible to the penicillins, the same value of 0.03 microgram/ml was found both for the MIC50 and MIC90. 100% of the strains were inhibited by 0.125 microgram/ml of the drug: this concentration is far below the serum levels (1.5 micrograms/ml) achievable following normal dosage. Clinical trials should be performed to establish whether the activity in vivo corresponds to that found in vitro.