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Essential structure of all quinolone antibiotics: the blue drawn remainder of R is usually piperazine; if the connection contains fluorine (red), it is a fluoroquinolone.
The quinolones are a family of synthetic 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.
MechanismQuinolones 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 via porins 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. Adverse effectsIn the fall of 2004, the Food and Drug Administration upgraded the warnings found within the package inserts for quinolones regarding potentially serious adverse reactions. It is important to note that pharmaceutical companies claim that the incidence of the following is quite rare, with occurrences at less than one per ten thousand person-years. However, many people that have been adversely effected dispute that the adverse reactions are rare, and contend that they may, in fact, be much more widespread than previously thought. 1 Side-effects from fluoroquinolones can be mild and short-lived or they can be severe and long-lasting after therapy has been discontinued. If side-effects affecting the central nervous system, peripheral nervous system, or muscular system occur, the patient should discontinue therapy and consult with his/her doctor. The side-effects from fluoroquinolones include tingling, anxiety, numbness, twitching, joint pain, muscle pain, tendinitis, fear, blurred vision, memory loss, diarrhea, severe panic attacks, insomnia, tear of achilles tendon, confusion, impaired concentration, burning pain, carpal tunnel syndrome, nightmares, confusion, tachycardia, nausea, palpitations, hyperesthesia, fatigue, depersonalisation, pins and needles sensation, muscular spasms, tremors, headaches, agitation, hallucinations, psychosis, tinnitus, skin rash, hair loss, abdominal pain, visual disturbances.2
InteractionsCaffeine, nonsteroidal antiinflamatory drugs, Theophylline, and corticosteroids enhance the toxicity of fluoroquinolones.627 Other drugs that interact with fluoroquinolones include Antacids, Sucralfate, Probenecid, Cimetidine, Probenecid, Warfarin, Antiviral agents, phenytoin, cyclosporine, rifampin, pyrazinamide, and cycloserine.8 ResistanceResistance to quinolones can evolve rapidly, even during a course of treatment. Numerous pathogens, including Staphylococcus aureus, enterococci, and Streptococcus pyogenes now exhibit resistance worldwide.9 Widespread veterinary usage of quinolones, in particular in Europe, has been implicated.citation needed There are three known mechanisms of resistance.10 Some types of efflux pumps can act to decrease intracellular quinolone 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's effectiveness. GenerationsThe quinolones are divided into generations based on their antibacterial spectrum.1112 The earlier generation agents are, in general, more narrow spectrum than the later ones. 1st generation
2nd generation
3rd generation
4th generation
In developmentVeterinary useThe quinolones have been widely used in agriculture and several agents exist which have veterinary but not human use.
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