Nalidixic acid is a monocarboxylic acid comprising 1,8-naphthyridin-4-one substituted by carboxylic acid, ethyl and methyl groups at positions 3, 1, and 7, respectively. An orally administered antibacterial, it is used in the treatment of lower urinary-tract infections due to Gram-negative bacteria, including the majority of E. coli, Enterobacter, Klebsiella, and Proteus species. It has a role as an antibacterial drug, a DNA synthesis inhibitor and an antimicrobial agent. It is a monocarboxylic acid, a 1,8-naphthyridine derivative and a quinolone antibiotic. It is a conjugate acid of a nalidixic acid anion.