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tufailAntibiotics are substances that inhibit the growth of or destroy bacteria that cause infection. Antibiotics do not work against viral diseases such as the common cold or influenza. The word â€œantibioticsâ€ comes from the Greek anti(â€œagainstâ€) and bios(â€œlifeâ€). Antibiotics have been used since the 1930s to prevent or treat a wide variety of infections in plants, animals,and humans. Before that time, there were few effective ways of combating microbial infections (infections caused by microorganisms). Illnesses such as pneumonia, tuberculosis, and typhoid fever were essentially untreatable. Even minor infections could be deadly.

The years between 1928 and 1940 were the most productive in the discovery and development of antimicrobial drugs. In 1928 Sir Alexander Fleming, a Scottish physician, was working on ways to kill bacteria isolated from infected wounds. He observed that a mold growing in a laboratory culture was able to destroy that cultureâ€™s bacteria. Since the mold that produced the bacteria-killing substance was a species of Penicillium, Fleming named the substance penicillin.

It is not known when the first antibiotic was used; folk medicine has used various molds to fight infections for centuries. In 1935 a German chemist named Gerhard Domagk discovered the first class of antibacterial agents, the sulfonamides. Sulfanilamide (the parent compound of the sulfonamides) was originally part of a leather dye compound that was being screened for its potential ability to kill bacteria. It was found to be relatively nontoxic and when the dye was broken down in the body, it was converted to the compound sulfanilamide.

By 1941 penicillin had been tested in humans and was being used to treat serious infections. The results were dramatic; patients who received the drug made rapid and complete recoveries. Bacitracin, chlortetracycline, and streptomycin, naturally occurring antibiotics, were discovered by 1948. The penicillin ring (chemical structure) was finally isolated in 1959 by scientists from Britain and the United States, and the door was open for the development of made-made (synthetic) antibiotics. Since 1948, a wide variety of substances that inhibit or kill bacteria have been discovered.

How Antibiotics Are Made

The overwhelming majority of antibiotics are made from living organisms such as bacteria about 90% of antibiotics are isolated from bacteria fungi, and molds. Others are produced synthetically, either in whole or in part.



Pharmaceutical companies use computer-generated images of the rings and experiment with a countless variety of possible chains. Researchers have developed antibiotics with long half-lives (period of effectiveness), which means that the medication can be taken every 24 hours instead of every few hours. The newer antibiotics are also more effective against a wider range of infections than were earlier drugs.

How Antibiotics Work



In most infections, including certain types of pneumonia (pneumococcal) and urinary tract infections, there seems to be no advantage of bactericidal over bacteriostatic drugs. However, bactericidal activity seems to be necessary in infections in which host (the organism from which the bacteria obtains its nourishment) defense mechanisms are at least partially lacking locally or systemically (in the whole system), for example, endocarditis (inflammation of the lining membrane of the heart), meningitis (inflammation of the membranes of the spinal cord or brain), or serious staphylococcal infections.

Each of the various types of antibiotics kill microorganisms in a unique way.Some disturb the structure of the bacterial cell wall; others interfere with the production of essential proteins; and still others interfere with the transformation (metabolism) of nucleic acid (substances found in the cells of all living things).

It is believed that antibiotics interfere with the surface of bacteria cells,causing a change in their ability to reproduce. Testing the action of an antibiotic in the laboratory shows how much exposure to the drug is necessary to decrease reproduction or to kill the bacteria. Although a large dose of an antibiotic taken at one time might kill the bacteria causing an illness, the dose would most likely cause severe side effects. Therefore, antibiotics are given in a series of smaller doses. This method assures that the bacteria are either killed or reduced enough in number so that the body can repel them. On the other hand, when too little antibiotic is taken, bacteria can develop methods to protect themselves against it. Thus the next time the antibiotic is needed against these bacteria, it will not be effective.

Classes of Antibiotics



â€¢    penicillins
â€¢    cephalosporins
â€¢    fluoroquinolones
â€¢    aminoglycosides
â€¢    tetracyclines
â€¢    macrolides
â€¢    polypeptides

Penicillins encompass a large group of bactericidal agents. They include:

â€¢    penicillin G
â€¢    penicillin V
â€¢    cloxacillin
â€¢    nafcillin
â€¢    oxacillin
â€¢    ampicillin
â€¢    amoxicillin
â€¢    ticarcillin



Broad-spectrum penicillins, such as ampicillin and amoxicillin, are used on infections caused by what are called gram-negative organisms. In Gramâ€™s method(named after Hans C.J. Gram, a Danish physician), bacteria are identified by staining them with dye and placed them on slides. Gram-negative bacteria take up a red color; gram-positive bacteria retain the gentian violet stain.


Cephalosporins are broad-spectrum antibiotics. They include:

â€¢    cefadroxil
â€¢    cefazolin
â€¢    cephalexin
â€¢    cephalothin
â€¢    cephapirin
â€¢    cephradine


Fluoroquinolones are the newest class of antibiotics. They include:

â€¢    ciprofloxacin
â€¢    enoxacin
â€¢    levofloxacin
â€¢    norfloxacin
â€¢    ofloxacin

The fluoroquinolones are well absorbed, have a broad spectrum of attack, and are considered relatively safe. These antibiotics interfere with bacterial enzymes and are most often used for treating urinary tract infections. Since fluoroquinolones may affect bone growth, however, the use of this class of antibiotics is not recommended in children or pregnant women.


â€¢    gentamicin
â€¢    streptomycin
â€¢    neomycin


Tetracyclines include:

â€¢    tetracyline
â€¢    doxycycline
â€¢    minocycline


The macrolides include:

â€¢    azithromycin
â€¢    clarithromycin
â€¢    erythromycin


â€¢    bacitracin
â€¢    colistin
â€¢    polymyxin B

Choosing an Antibiotic

Physicians are usually able to determine the type of organism responsible for causing the most commonly seen infections and know which class of antibiotic will be the most effective in combating it. If the agent causing illness isnot known, a culture from the infection is usually examined under a microscope to identify the invading organism. However, even when the bacteria have been identified and their sensitivity to antibiotics have been determined, the choice of antibiotic is not always an easy one.


Administering Antibiotics

To work against infecting organisms, an antibiotic can be applied externally,such as to a cut on the skinâ€™s surface, or administered internally, throughthe bloodstream. Antibiotics are manufactured in several forms and are administered in a variety of ways: topically, orally, or parenterally.

Topical application means â€œto a local areaâ€ such as on the skin, in the eyes,or on the mucous membrane. Antibiotics for topical use are available in theform of powders, ointments, drops, or creams.



Read more: http://www.faqs.org/health/topics/59/Antibiotics.html#ixzz2Kk3vSJoI


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