Antibiotics have played a major role in our society thanks to Sir Alexander Fleming’s careful observations in 1928. Without it, many lives would be in danger due to infectious diseases.
Antibiotics are chemical substances produced by various species of microorganisms and other living systems that are capable in small concentrations of inhibiting the growth of or killing bacteria and other microorganisms. These organisms can be bacteria, viruses, fungi, or animals called protozoa. A particular group of these agents is made up of drugs called antibiotics, from the Greek word anti (“against”) and bios (“life”). Some antibiotics are produced from living organisms such as bacteria, fungi, and molds. Others are wholly or in part synthetic – that is, produced artificially.
Penicillin is perhaps the best known antibiotic. Its discovery and later development is among mankind’s greatest achievements. Antibiotics have enabled the medical profession to treat effectively many infectious diseases, including some that were once life-threatening.
How Antibiotics Work?
Antibiotics can be bacteriostatic (bacteria stopped from multiplying) or bactericidal (bacteria killed). To perform either of these functions, antibiotics must be brought into contact with the bacteria.
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 halt reproduction or to kill the bacteria. Although a large amount of an antibiotic taken at one time might kill the bacteria causing an illness, such a dose usually would make the person suffer from illness caused by the drug. Therefore, antibiotics are given in a series of smaller amounts. This assures that the bacteria are either killed or reduced enough in numbers so that the body can repel them. When too little antibiotic is taken, bacteria can often develop methods to protect themselves against it . The next time the antibiotic is needed against these bacteria, it will not be effective.
Taking in Antibiotics.
To work against infecting organisms, an antibiotic can be applied externally, such as to a cut on the skin’s surface, or internally, reaching the bloodstream within the body. Antibiotics are made in several forms and given in different ways.
Topical. Topical application means “to a local area” such as on the skin, in the eyes, or on the mucous membrane. Antibiotics for topical use are available in the form of powders, ointments, or creams.
Oral. Tablets, liquids, and capsules are swallowed. The antibiotic is released in the small intestine to be absorbed into the bloodstream. Troches, or lozenges, are allowed to dissolve in the mouth, where the antibiotic is absorbed through the mucous membrane.
Parenteral. Applications outside the intestine are called parenteral. One form is an injection, which can be subcutaneous (under the skin), intramuscular (into a muscle), or intravenous (into a vein). Parenteral administration of an antibiotic is used when a physician requires a strong, quick concentration of the antibiotic in the bloodstream.
Natural. At one time all antibiotics were made from living organisms. This process, known as biosynthesis, is still used in the manufacture of some antibiotics. It is actually the organisms that manufacture the antibiotic. The people involved merely provide favorable conditions for the organisms to do the work and then they collect the drug. For example, mold organisms are placed in a medium (a substance used for the growth of microorganisms) such as corn steep liquor to which milk sugar has been added. This forms a broth that is put into a tank, which is kept at a temperature of 25C and shaken for more than 100 hours. The mold organisms grow rapidly in this warm soup, producing penicillin as they do so. The penicillin is later extracted.
Synthetic. All penicillin types have an identical chemical nucleus called a ring. The chemical chain that is attached to the ring is different in each type. By changing the molecules of the chain, scientists devise drugs with potentially different effects on different organisms. Some of these drugs are useful in treating infections, some are not.
Pharmaceutical manufacturers now use computer-generated images of the rings and experiment with an endless variety of possible chains. Researchers have developed antibiotics with long half- lives (period of effectiveness), which allow taking the medication once in 24 hours instead of every few hours. The newer antibiotics are also more effective against a wider range of infections than were earlier drugs.
Varieties of Antibiotics.
There are dozens of antibiotics. The following are in common use:
Penicillins. The various types of penicillins make up a large group of antibacterial antibiotics of which only those from benzyl penicillin are naturally produced from molds. Penicillin G and ampicillin are in this class. Another penicillin, called piperacillin, has been shown to be effective against 92 percent of infections without causing serious side effects. Penicillins are often given in combination with some of the following categories of drugs.
Cephalosporins. Similar to the penicillins, cephalosporins are often given when a sensitivity (allergic reaction) to the former is known or suspected in a patient. Cefotaxime sodium is a kind of cephalosporin that is very effective in combating deep infections such as those that occur in bones and those resulting from surgery.
Aminoglycoside. Aminoglycosides include streptomycin and neomycin. These drugs are used to treat tuberculosis, bubonic plague, and other infections. Because of potentially serious side effects, such as interference with hearing and their ability to make one sensitive to sunlight, these drugs are given with caution.
Tetracyclines. Tetracyclines are effective against pneumonia, typhus, and other bacteria-caused illness but can harm the function of the liver and kidneys. Tetracycline in a special gel base is used to treat many eye infections.
Macrolides. Macrolides are often used in patients who appear to be sensitive to penicillin. Erythromycin is the best known medicine in this group.
Polypeptides. The class of antibiotics called polypeptides is quite toxic (poisonous) and is used mostly on the surface of the skin (topically). Bacitracin is in this category.
Resistance and Side Effects.
An antibiotic acts by limiting or stopping (and therefore killing) the growth of a specific microorganism. It probably accomplishes this by interfering with the wall of the bacteria cell at which it is targeted while at the same time having little effect on the body’s normal cells.
When one is exposed continually to an antibiotic for an illness of long duration (such as rheumatic fever), the targeted bacteria may develop its own defense against the drug. An enzyme that can destroy the drug may be produced by the bacteria, or the cell wall can become resistant to being broken by the action of the antibiotic. When this happens, and it does most frequently in response to long or frequent treatment with penicillin or streptomycin, the patient is said to be “fast” against the drug. For example, one may be penicillin-fast, meaning penicillin is no longer able to help fight the infection and another type of antibiotic must be given.
Allergic reactions to antibiotics are usually seen as rashes on the skin, but severe anemia (too few red blood cells), stomach disorders, and deafness can occasionally result. It was once thought that allergic reactions to antibiotics – penicillin in particular – were frequent and permanent. Recent studies suggest, however, that many people outgrow their sensitivity or never were allergic. The large number of antibiotics that are now available offers a choice of treatment that can, in most instances, avoid allergy-causing drugs.
It is well to remember that all drugs can cause both wanted and unwanted effects on the body. The unwanted ones are called side effects, and these must be balanced against the effects desired in determining if a particular drug will do more harm than good. It is a fact that all drugs have the potential to be both beneficial and harmful.
History and Future.
The years between 1928 and 1940 were the most fruitful in the discovery and development of antimicrobial drugs. In 1928 Sir Alexander Fleming, a British bacteriologist, noticed that a mold growing in one of his laboratory cultures was able to destroy that culture’s bacteria. Since the mold that produced the substance that killed the bacteria was a species of Penicillium, he named the germ-killing substance penicillin. The first use of an antibiotic, however , is not known, as folk medicine has used various molds to fight infections throughout history. In 1935 a German chemist, Gerhard Domagk, discovered the first sulfa drug, prontosil. In 1941 penicillin was used to treat serious infections. The results were dramatic because patients who received the drug made rapid and complete recoveries. Bacitracin, chlortetracycline, and streptomycin, naturally occurring antibiotics, were discovered by 1948. The penicillin ring was finally isolated in 1959 by british and united States scientists, and the way was open for the development of penicillin was the beginning of an era that has been called the golden age of chemotherapy. Since 1948, a large number of substances that inhibit or kill bacteria have been discovered.
Another use of antibiotics is as additives to the feed of animals. Chickens and beef cattle, for example, can be fed with these additives for better weight gains and to speed their growth.
Current work in antibiotics is largely in the area of viruses. Although some antivirals are available, most have toxic effects so severe that they can be used only in life-threatening diseases where the negative effects are the lesser danger. Preliminary studies, however, are reporting success in the development of safer antiviral drugs, and their use should be possible within the near future.
Pharmaceutical Preparations, Except Biologicals, 1978, Current Industrial Reports, Series MA28(78)-1, U.S. Department of Commerce, Bureau of the Census, Washington, D.C.
Synthetic Organic Chemicals, United States Production and Sales of Medicinal Chemicals, U.S. Tariff Commission (1972-73) United States International Trade Commission (1974-75), U.S. Government Printing Office, Washington, D.C.
L.S. Goodman and A. Gilman, The Pharmacological Basis of Therapeutics, 5th ed., Macmillan Publishing Co., New York, 1975.