1. Nalidixic acid is effective primarily against gram-negative bacteria, with minor anti-gram-positive activity. 2. For example, WIN 18, 320 was nalidixic acid, the first quinolone antibiotic. 3. Quinolones ( including nalidixic acid and ciprofloxacin ) have this function. 4. They are very sensitive to ampicillin and resistant to kanamycin and nalidixic acid. 5. Most of the strains studied are resistant to ampicillin, kanamycin and nalidixic acid. 6. Other drugs can also be used, significant ones being chloramphenicol, streptomycin, and nalidixic acid. 7. They proved to be only marginal improvements over nalidixic acid. 8. The subunit A is selectively inactivated by antibiotics such as oxolinic and nalidixic acids. 9. It is resistant to cephalothin and nalidixic acid. 10. The first quinolone was nalidixic acid-introduced in 1962 for treatment of urinary tract infections in humans.