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The quinolones are a family of broad-spectrum antibiotics. The parent of the group is nalidixic acid. The majority of quinolones in clinical use belong to the subset of fluoroquinolones, which have a fluoro group attached the central ring system, typically at the 6-position.
Additional recommended knowledge
Quinolones and fluoroquinolones are bactericidal drugs, actively killing bacteria. Quinolones inhibit the bacterial DNA gyrase or the topoisomerase IV enzyme, thereby inhibiting DNA replication and transcription. Quinolones can enter cells easily and therefore are often used to treat intracellular pathogens such as Legionella pneumophila and Mycoplasma pneumoniae. For many gram-negative bacteria DNA gyrase is the target, whereas topoisomerase IV is the target for many gram-positive bacteria. Eukaryotic cells do not contain DNA gyrase or topoisomerase IV.
Quinolone antibiotics were once considered relatively safe, but several side effects have become evident with experience. For example, numerous case reports have implicated their use since 1965 in spontaneous tendon ruptures or damage, especially with the concurrent use of a systemic corticosteroid. In the fall of 2004, the Food and Drug Administration upgraded the warnings found within the package inserts for all drugs within this class regarding such serious adverse reactions. It is important to note, though, that the incidence of this is quite rare, with occurrences at less than one per ten thousand person-years.
Other problems include:
Resistance to quinolones can develop rapidly, even during a course of treatment. Numerous pathogens, including Staphylococcus aureus, enterococci, and Streptococcus pyogenes now exhibit resistance worldwide. Widespread veterinary usage of quinolones, particularly in Europe, has been implicated.
There are three known mechanisms of resistance. Efflux pumps can be used to decrease intracellular drug concentration. In gram-negative bacteria, plasmid-mediated resistance genes produce proteins that can bind to DNA gyrase, protecting it from the action of quinolones. Finally, mutations at key sites in DNA gyrase or topoisomerase IV can decrease their binding affinity to quinolones, decreasing the drug effectiveness.
The quinolones are divided into generations based on their antibacterial spectrum. The earlier generation agents are generally more narrow spectrum than the later ones.
The quinolones have been widely used in agriculture and several agents exist which have veterinary but not human use.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Quinolone". A list of authors is available in Wikipedia.|