Antibiotics

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An antibiotic is a drug that kills or slows the growth of bacteria. They have no effect against viruses, fungi, or parasites. Antibiotics are one class of antimicrobials, a larger group which also includes anti-viral, anti-fungal, and anti-parasitic drugs. They are relatively harmless to the host, and therefore can be used to treat infections. The term, coined by Selman Waksman, originally described only those formulations derived from living organisms, in contrast to "chemotherapeutic agents", which are purely synthetic. Nowadays the term "antibiotic" is also applied to synthetic antimicrobials, such as the sulfa drugs. Antibiotics are generally small molecules with a molecular weight less than 2000. They are not enzymes. Some antibiotics have been derived from mold, for example the penicillin class.
Unlike previous treatments for infections, which included poisons such as strychnine and arsenic, antibiotics were labelled "magic bullets": drugs which targeted disease without harming the host. Conventional antibiotics are not effective in viral, fungal and other nonbacterial infections, and individual antibiotics vary widely in their effectiveness on various types of bacteria. Antibiotics can be categorised based on their target specificity: 'narrow-spectrum' antibiotics target particular types of bacteria, such as Gram-negative or Gram-positive bacteria, while 'wide-spectrum' antibiotics affect a larger range of bacteria.
The effectiveness of individual antibiotics varies with the location of the infection, the ability of the antibiotic to reach the site of infection, and the ability of the bacteria to resist or inactivate the antibiotic. Some antibiotics actually kill the bacteria (bactericidal), whereas others merely prevent the bacteria from multiplying (bacteriostatic) so that the host's immune system can overcome them.
Oral antibiotics are the simplest approach when effective, with intravenous antibiotics reserved for more serious cases. Antibiotics may sometimes be administered topically, as with eyedrops or ointments.
Antibiotics can also be classified by the organisms against which they are effective, and by the type of infection in which they are useful, which depends on the sensitivities of the organisms that most commonly cause the infection and the concentration of antibiotic obtainable in the affected tissue
History



Many ancient cultures, including the ancient Egyptians, ancient Greeks and ancient Chinese, already used moulds and plants to treat infections. This worked because some moulds produce antibiotic substances. However, they couldn't distinguish or distil the active component in the moulds.
Modern research on antibiotics began with the discovery of Penicillin in 1928 by Alexander Fleming. More than ten years later, Ernst Chain and Howard Florey became interested in his work, and came up with the purified form of penicillin. The three shared the 1945 Nobel Prize in Medicine. "Antibiotic" was originally used to refer only to substances extracted from a fungus or other microorganism, but has come to include also the many synthetic and semi-synthetic drugs that have antibacterial effects.
Classes of antibiotics
At the highest level, antibiotics can be classified as either bactericidal or bacteriostatic. Bactericidals kill bacteria directly where bacteriostatics prevent them dividing. However, these classifications are based on laboratory behaviour; in practice, both of these will end a bacterial infection.
Production

Since the first pioneering efforts of Florey and Chain in 1939, the importance of antibiotics to medicine has led to much research into discovering and producing them. The process of production usually involves screening of wide ranges of microorganisms, testing and modification. Production is carried out using fermentation; a process that is important in anaerobic conditions when there is no oxidative phosphorylation to maintain the production of ATP (Adenosine triphosphate) by glycolysis.
Side effects
Possible side effects are varied, and range from fever and nausea to major allergic reactions. One of the more common side effects is diarrhoea, which results from the antibiotic disrupting the normal balance of intestinal flora. Other side effects can result from interaction with other drugs, such as elevated risk of tendon damage from administration of a quinolone antibiotic with a systemic corticosteroid.
It is a common assertion that some antibiotics can interfere with the efficiency of birth control pills. Although there remain few known cases of complication, the majority of antibiotics do not interfere with oral contraception, despite widespread misinformation to the contrary.
Antibiotic misuse
Common forms of antibiotic misuse include failure to take the entire prescribed course of the antibiotic, usually because the patient feels better, but before the infecting organism is completely eradicated. In addition to treatment failure, these practices can result in antibiotic resistance in the bacteria that survive the abbreviated treatment. Taking antibiotics in inappropriate situations is another common form of antibiotic misuse. Common examples of this would be the use of antibacterials for viral infections such as the common cold.
In the United States, vast quantities of certain antibiotics are routinely included as low doses in the diet of some kinds of healthy farm animals, where this practice has been shown to make animals grow faster. Opponents of this practice, however, point out the likelihood that it also leads to an environment conducive to the evolution of antibiotic resistance, frequently in bacteria that are known to also infect humans. There has been no convincing evidence yet that the evolution of antibiotic resistance in such bacteria is actually occurring. As the majority of bacteria is killed in the pasteurization process applied to the milk, and the cooking of the meat, of such animals, any possible resistance may go unnoticed until the bacteria survives it. Theoretically, though, there is a significant possibility that such resistances could be transferred through bacterial plasmids, and the aforementioned conditions of continuous, low-dose antibiotics are ideal for the development of antibiotic resistance.
Excessive use of prophylactic antibiotics in travelers may also be classified as misuse References
1. ^ The Merck Manual of Medical Information - Home Edition, Robert Berkow (Ed.), Pocket (September, 1999), ISBN 0-671-02727-1.
2. ^ Planned Parenthood: Does taking antibiotics make the pill less effective?, July 15, 2004
3. ^ Purdue University "Biologists build better software, beat path to viral knowledge", see Imaging of Epsilon 15, a virus that infects the bacterium Salmonella News report