Antibiotics

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. 

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.
 
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, it could also cause the
patient to suffer a reaction to 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. 

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. 

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. 

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 25øC 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. 

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.
 
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. 

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. 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. 

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. 
 
Bibliography
 
"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.