Comparative In Vitro Studies of Cinoxacin, Nalidixic Acid, and Oxolinic Acid

Cinoxacin and nalidixic acid were found to be similar in in vitro activity against 138 Shigella isolates and somewhat less active than oxolinic acid on a weight basis. Cross-resistance developed when 10 shigellae were transferred on increasing amounts of the respective agent contained in Mueller-Hinton agar. Plate dilution studies of the effect of changes in agar pH on the minimum inhibitory concentration revealed that the antibacterial activity increased with decreasing pH. Protein binding investigations revealed a high degree of binding, with nalidixic acid > oxolinic acid > cinoxacin.