Classification and structure-activity relationships of fluoroquinolones

Fluoroquinolones are potent broad spectrum antibacterial agents. Two classifications have been described: chemical and biological. Quinolones can be classified into 4 groups according to their chemical structures: monocyclic, bicyclic, tricyclic and tetracyclic derivatives. Each group can be subdivided into subgroups if a fluorine atom is fixed at the 6-position. The biological classification recognised 4 groups. Groups 1 and 2 are composed of compounds showing limited spectra (Enterobacteriaceae) and groups 3 and 4 contain compounds displaying broad antibacterial spectra. Compounds that are highly metabolised fall into groups 1 and 3 and those poorly metabolised (< 5%) into groups 2 and 4. The structure of fluoroquinolones may help to predict antibacterial activity, pharmacokinetics, physicochemical properties, toxicity and adverse events.