Nalidixic acid

Nalidixic acid is the basis for quinolone antibiotics.

Nalidixic acid is effective against both gram-positive and gram-negative bacteria. In lower concentrations, it acts bacteriostatically (that is, it inhibits growth and reproduction). In higher concentrations, it is bactericidal, meaning that it kills bacteria instead of merely inhibiting their growth.

It is especially used in treating urinary tract infections, caused for example by Escherichia coli, Proteus, Shigella, Enterobacter and Klebsiella.