Transcript Antibiotics

Antibiotics
What
How
Why
What
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Antibiotics are drugs derived wholly or
partially from certain microorganisms
Are used to treat bacterial or fungal
infections.
They are ineffective against viruses
Antibiotics either kill microorganisms or stop
them from reproducing, allowing the body's
natural defenses to eliminate them.
Selecting an Antibiotic
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Each antibiotic is effective only against
certain bacteria
In selecting an antibiotic to treat a
person with an infection, a doctor
makes a best guess as to which
bacterium is responsible.
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For some infections, doctors know that
only certain types of bacteria may be
responsible.
If there is one antibiotic that is
predictably effective against all of these
bacteria, further testing is not needed.
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For infections that may be caused by many
different types of bacteria or by bacteria
whose susceptibility to antibiotics is not
predictable, a laboratory will be asked to
identify the infecting bacterium from
samples of blood, urine, or tissue taken
from the person
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The infecting bacterium is then tested
for susceptibility to a variety of
antibiotics. These tests generally take a
day or two to yield results and thus
cannot guide the initial choice of which
antibiotic is given
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The effectiveness of the treatment
depends on how well the drug is
absorbed into the bloodstream, how
much of the drug reaches the sites of
infection in the body, and how quickly
the body eliminates the drug.
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In selecting which antibiotic to use, a
doctor also considers the nature and
seriousness of the infection, the drug's
possible side effects, the possibility of
allergies or other serious reactions to
the drug, and the cost of the drug.
How
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For severe bacterial infections,
antibiotics are usually first given by
injection. When the infection is under
control, antibiotics can then be taken by
mouth. Less severe infections can be
treated from the start with oral
antibiotics.
Taking Antibiotics
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Antibiotics need to be taken until the
infecting organism is eliminated from
the body, which may be days after the
symptoms disappear.
Antibiotics are rarely given for fewer
than 5 days (an exception is certain
uncomplicated urinary tract infections).
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A doctor, nurse, or pharmacist can
explain how the prescribed antibiotic
should be taken.
Some antibiotics must be taken on an
empty stomach, whereas others may be
taken with food.
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Also, some antibiotics can interact with
other drugs a person may be taking,
possibly reducing the effectiveness or
increasing the side effects of the
antibiotic or the other drugs. Some
antibiotics make the skin sensitive to
sunlight.
Prophylaxis
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In addition to treating existing infections, antibiotics
are sometimes used to prevent infections
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Antibiotics may be used to prevent meningitis in people who
have been exposed to someone with meningitis.
Some people with abnormal or artificial heart valves take
antibiotics before dental and surgical procedures to prevent
bacteria from infecting the damaged valves.
Prophylactic antibiotics may also be given to people who
have a weakened immune system, such as people with
leukemia, people receiving chemotherapy for cancer, or
people with AIDS.
Side Effects and Allergies
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Common side effects of antibiotics include
upset stomach, diarrhea, and, in women,
vaginal yeast infections.
Some side effects are more severe and,
depending on the antibiotic, may disrupt the
function of the kidneys, liver, bone marrow, or
other organs.
Blood tests are used to monitor such adverse
reactions.
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Some people who receive antibiotics
develop colitis, an inflammation of the
large intestine.
The colitis results from a toxin produced
by the bacterium Clostridium difficile,
which grows unchecked when other
antibacteria are killed by the antibiotics.
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Antibiotics can also cause allergic
reactions.
Mild allergic reactions consist of an itchy
rash or slight wheezing.
Severe allergic reactions (anaphylaxis)
can be life threatening and usually
include swelling of the throat, inability
to breathe, and low blood pressure.
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Many people tell their doctor that they
are allergic to an antibiotic when in fact
they have only experienced side effects
from it that are not allergy-related.
The distinction is important because
people who are allergic to an antibiotic
should not be given that drug or one
closely related to it.
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However, people who have experienced
minor side effects can usually take
related drugs or even continue taking
the same one. The doctor can
determine the significance of any
unpleasant reaction a person has to an
antibiotic
Antibiotic Resistance
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Antibiotic resistance is a worldwide
public health problem that continues to
grow. It occurs when strains of bacteria
in the human body become resistant to
antibiotics due to improper use and
abuse of antibiotics.
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In hospitals, 190 million doses of antibiotics
are administered each day.
Among non-hospitalized patients, more than
133 million courses of antibiotics are
prescribed by doctors each year.
It is estimated that 50 percent of these latter
prescriptions are unnecessary since they are
being prescribed for colds, coughs and other
viral infections.
Common causes
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Many individuals either expect or ask
their physicians to prescribe antibiotics
when they feel sick or have a common
cold.
Patients should understand, though,
that antibiotics are intended to treat
bacterial infections, not viral infections.
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The only true way to know if your cold or
sickness is a bacterial infection and whether it
should be treated with antibiotics is for your
physician to test it.
If you have a sore throat your physician
should take a throat culture test. If the the
test results indicate that a bacterial infection
is present, then antibiotics should be
prescribed to treat the infection.
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The improper use and abuse of antibiotics
has led to the development of antibiotic
resistance. The most common misuse and
abuse of antibiotics are:
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Physicians prescribing antibiotics for viral
infections
Not finishing the full dosage of the antibiotic.
When an antibiotic prescription is not finished
(even leaving one or two pills), it leaves some
bacteria alive and "resistant" to future antibiotic
treatment.
Prevention
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Both physicians and patients have a role to play in
decreasing the misuse of antibiotics. Antibiotics
should only be prescribed when a test (such as a
throat culture) shows that there is a bacterial
infection present. Antibiotics are not effective in
fighting a viral infection. Even so, patients often
demand that their physicians prescribe antibiotics
when they are not needed. Taking antibiotics when
you have a viral infection not only wastes your time
and money, but also contributes to increasing
antibiotic resistance.
What Can You Do
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Patients should ask their doctor if they
have a viral or bacterial infection and
which tests have been done to prove
this. Physicians too, must change their
prescribing practices and only prescribe
antibiotics for their patients when a
bacterial infection is present
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Doctors, pharmacists, and researchers
knew that some medicines caused serious
side effects or reacted dangerously with
other drugs. But there were few tests to
predict these problems before drugs went
into clinical studies or were used by many
people.
Copyright © 1995-2006 Merck & Co., Inc., Whitehouse Station, NJ, USA. .
Understanding How Drugs Work
In the Body
Thirty Years Ago
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Most studies on drug-metabolizing enzymes
were done in rats or mice, so scientists didn’t
know much about these enzymes in humans.
To infer if a drug candidate would be toxic to
humans, scientists evaluated whether the
molecule caused organ damage in animals.
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Drug makers lacked the ability to
customize the packaging and delivery of
a drug to ensure that it would be well
absorbed and available to the body.
Today
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As recently as 10 to 15 years ago, up to
40 percent of drugs failed to work
properly because they were poorly
absorbed, were destroyed by the body,
failed to get to the right place, or were
excreted from the body too quickly.
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Fewer than 10 percent of medicines fail
for these reasons. In part, that’s
because scientists are able to identify
which enzymes metabolize a candidate
drug and what the end products will be.
The Food and Drug Administration now
requires this information before it
considers approving a new drug.
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Researchers have characterized dozens
of human drug-metabolizing enzymes
and transport proteins that regulate the
activity and levels of drugs in the body.
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Scientists also have identified certain medicines,
vitamins, herbal remedies, nutritional supplements,
and other compounds that interact with these
enzymes and transporters, possibly causing adverse
cross-reactions. To minimize dangerous interactions,
doctors and pharmacists maintain lists of such
substances. Pharmaceutical scientists are able to
detect potentially troublesome compounds early in
drug discovery so they can prevent these compounds
from moving forward in development.
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By analyzing the genetic sequences of drugmetabolizing enzymes from many people, researchers
have identified more than 100 slightly different
versions of the enzymes. Although most of these
genetic variations are rare, some of them can
markedly alter the activity and side effects of drugs.
As scientists learn more about drug-metabolizing
enzymes, particularly those called P450s, they are
able to design and develop drugs that influence the
activity of the enzymes.
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Scientists are now able to use human,
rather than animal, enzymes to predict
whether a drug candidate or any of its
byproducts will be toxic to humans.
However, rare, serious drug reactions
remain difficult to predict before testing
experimental medicines in humans.
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Patient instructions routinely indicate
whether a drug should be taken at a
particular time of day and whether oral
medications should be consumed with a
meal or on an empty stomach.
National Institute of General Medical Sciences