Nalidixic acid, the first of the synthetic quinolone antibiotics
With much of the literature on the synthesis of quinolines, there is some discrepancy on whether a substituted 4-hydroxyquinoline or a substituted 4-quinolone is the final product of the Conrad-Limpach synthesis.
XDR-TB is defined as TB that has developed resistance to at least rifampicin and isoniazid (resistance to these first line anti-TB drugs defines Multi-drug-resistant tuberculosis, or MDR-TB), as well as to any member of the quinolone family and at least one of the following second-line anti-TB injectable drugs: kanamycin, capreomycin, or amikacin.