Quinolones represent a separate class of antibiotics. They all have the same basic chemical structure, which is derived from quinoline. A variety of different quinolones can be produced by exchanging substituents on the nitrogen-containing ring system.
What are quinolones?
Quinolones represent a separate class of antibiotics. They have a wide range of applications against many types of bacteria. Quinolones have as their basic structure a nitrogen-containing ring system derived from quinoline. The ring system is composed of a benzene ring and a pyridine ring. In the quinolones, there is also a carboxylic acid group and a carbonyl group on the nitrogen-containing pyridine ring. Different substituents are attached to the benzene ring and the nitrogen atom of the pyridine ring. Basically, the quinolones act by inhibiting the bacterial enzyme gyrase. The fluoroquinolones also inhibit bacterial growth via another biochemical pathway, although this has not yet been fully elucidated. Due to the extended action of fluoroquinolones, they have a wide range of applications against many types of bacteria. The active ingredient nalidixic acid, which is no longer used, serves as the starting substance for the synthesis of the quinolones. Nalidixic acid, in turn, is also produced synthetically. Alternatively, the non-fluorine-containing quinolones have a piperazine ring at the appropriate site. The spectrum of action of quinolones is very broad. There are both limited-acting and broadly and intensively acting representatives of this class of active ingredients. The basic mechanism of antibacterial action is the same for all quinolones. Only the substituents determine the intensity and selectivity of their influence.
Pharmacologic action
The antibacterial action of quinolones is based on inhibition of bacterial gyrase. Gyrase is an enzyme found only in bacteria. It ensures the despiralization and the restoration of the spiral structure of DNA. Only in the despiralized state can the genetic code of bacterial DNA be read and translated into proteins. However, when gyrase is blocked, the process of DNA untwisting is no longer active. The DNA can no longer be read properly, with the result that bacterial growth is inhibited. Existing bacteria then slowly die. In the case of fluoroquinolones, there is an additional mechanism that leads to the growth inhibition of many bacterial strains. However, this process has not yet been fully elucidated. The substituents determine the strength of the effect and at the same time which bacteria are combated. Some quinolones exert their effect mainly on Gram-positive bacteria, others on Gram-negative bacteria. In addition to quinolones that have a broad spectrum of activity against many types of bacteria, there are also quinolones with a very limited spectrum of activity. Since the gyrase is only found in bacteria, quinolones can only treat bacterial infections. They have no effect against fungi and viruses.
Medical application and use
Quinolones are used to fight bacterial infections. To determine which antibiotics in this class of agents promise the best chances of cure, the type of bacteria must first be determined. This is because not every quinolone is effective against every bacterium. This fact gives rise to the different areas of application. The drugs can be applied in various ways. They can be taken orally as tablets, capsules or in the form of juices, or they can be injected as an infusion solution. All quinolones are effective in urinary tract and kidney infections. The drugs norfloxacin or pipemidic acid can be used for urinary tract infections. Norfloxacin is also effective against the sexually transmitted disease gonorrhea (gonorrhea). Drugs such as enoxacin can also be used for respiratory, lung or skin infections. The drug levofloxacin has an even wider range of applications. In addition to urinary tract and respiratory infections, it can also be used for infections of the skin, soft tissues and eyes. The two drugs ofloxacin and ciprofloxacin cover the widest range of applications.Applications here include kidney, urinary tract, respiratory tract or skin infections, as well as application in bone and joint infections, infections of the digestive tract, gall bladder, ear, nose and throat, and eyes. In addition, ciprofloxacin can also be used in sepsis (blood poisoning), anthrax or cystic fibrosis (cystic fibrosis) in children. Fluoroquinolones are very well absorbed by the tissues of the body, so they are quickly found everywhere in the organism. Therefore, fluoroquinolones can be used to fight infections that are difficult to reach with other drugs, such as bone or prostate infections.
Risks and side effects
Quinolones interact with other drugs, either reducing their effectiveness or leading to side effects. For example, the effectiveness of quinolones is reduced by divalent calcium or magnesium salts and by antacids because they form complexes together. When used with antirheumatic agents and steroids, agitation may occur. Furthermore, various side effects may occur with the use of the drugs. Nausea and vomiting are observed. Diarrhea and abdominal pain are less common. Neurological disorders such as increased excitability, restlessness, insomnia, dizziness or even hallucinations may also occur in rare cases. During treatment with quinolones, there is an increased sensitivity to solar radiation. Sunbathing or high-altitude sun are contraindicated during quinolone therapy. Studies also indicate cartilage damaging properties of quinolones. Cardiac arrhythmias are also possible due to disturbances in the conduction of excitation. Very rare side effects include alteration of the blood count and allergic reactions. Quinolones must not be used during pregnancy and breastfeeding. The same applies to the application in children and adolescents. A contraindication is also present in cerebral spasms, severe renal insufficiency, or cardiac arrhythmias.
