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 Antibiotics are classified as anti-infectious drugs. They are chemicals produced by microorganisms, such as bacteria and fungi, that can kill or inhibit other microorganisms at low concentrations. The discovery of antibiotics was one of the most important advances in medicine in the twentieth century. Penicillin, the first antibiotic, was first released in the United States in 1942.
Around the same time, new antibiotics, including streptomycin, were discovered in a mixture of microbial substances from soil sticks. Many of these drugs found had narrow effects, but in 1947 chloramphenicol, the first broad-spectrum antibiotic, was introduced. Chloramphenicol is a nitrobenzene derivative of dichloroacetic acid, produced synthetically and used to treat typhoid fever and severe infections caused by penicillin-resistant microorganisms.
As antibiotics wiped out more common pathogens, the highly resistant strains that survived began to pose problems and new antibiotics were needed to eradicate them. By the end of the twentieth century, more than ten thousand antibiotics were already known, among which there are both simple and very complex substances. This expansion in the number of new antibiotics has been achieved through successful synthetic modifications, and many antibiotics are now being produced in large quantities. This approach has been particularly successful with antibiotics whose molecular structure contains four-unit lactam rings, including penicillins and cephalosporins, which now account for over 60 percent of the world's antibiotic production.
Penicillin is the safest of all antibiotics, although some patients are hypersensitive to it and this leads to adverse reactions. In addition, some microorganisms, in particular, staphylococci, develop resistance to natural penicillins, and this has led to the production of new synthetic modifications. Thus, there are two groups of penicillins, those that occur naturally and semi-synthetic penicillins obtained by growing Penicillium in the presence of certain chemicals. This produces broad-spectrum penicillins that have been developed to treat typhoid fever and certain urinary tract infections. However, natural penicillins are still the best treatment for many bacterial infections.
Cephalosporins, discovered in the 1950s by Sir Edward Abraham, are relatively non-toxic antibiotics. Like penicillin, they were first isolated from fungi, but later modified lactam rings made it possible to reproduce the antibiotic in more than 20 variations. First generation cephalosporins have been used in patients who develop penicillin sensitivity. They were active against many bacteria, including E. coli, but soon they had to be replaced with drugs of the second and third generation, as the microorganisms lost their sensitivity to them. They have been used to treat lung infections, gonorrhea, and meningitis.
Aminoglycosides, including streptomycin (discovered in 1944), inhibit protein biosynthesis. They are poorly absorbed from the gastrointestinal tract and are administered intramuscularly. Streptomycin was one of the first aminoglycosides discovered and is still used with penicillin to treat infections. Other aminoglycosides are used to treat meningitis, sepsis, and urinary tract infections. But the narrow spacing between therapeutic and toxic doses presents complex problems, with risks increasing with age. The antimicrobial activity of tetracyclines, belonging to another group of synthetic antibiotics, depends on the fact that, although they inhibit protein biosynthesis in bacterial and animal cells, they are able to penetrate only into bacterial cells. Tetracyclines are absorbed from the gastrointestinal tract and can be taken orally.
In addition to their medicinal uses, antibiotics have also been of great veterinary importance and are used as animal feed or as an additive to stimulate growth in animal husbandry. Tetracyclines account for about half of antibiotic sales as such supplements, but many other antibiotics are also used for this purpose. Feed antibiotics are believed to promote growth by preventing disease. Another important use of antibiotics in agriculture is their use as antiparasitic agents against worms and other parasites present in the gastrointestinal tract and against ectoparasites such as ticks.
In addition to biochemical antibiotics, sulfonamides, synthetic chemotherapeutic agents also used in the treatment of bacterial diseases, are used. The first sulfonamide, prontosil, was used in 1932 to fight streptococcal infections. Broad spectrum sulfonamides were widely used before antibiotics were introduced. They work by preventing the production of folic acid, which is essential for the synthesis of nucleic acids. The use of sulfonamides has decreased due to the availability of more effective and safer antibiotics, but they are still used effectively to treat urinary tract infections and malaria, and to prevent possible infection after burns. Related to sulfonamides, sulfones are also inhibitors of folic acid biosynthesis. They tend to accumulate in the skin and inflamed tissues, making them indispensable in the treatment of leprosy. There are also some chemical synthesized drugs that have antibacterial properties and have specific clinical uses.
Andreev S.
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