An antibiotic is a drug that kills or slows the growth of bacteria.
Antibiotics are one class of antimicrobials, a larger group which also
includes anti-viral, anti-fungal, and anti-parasitic drugs. Antibiotics
are chemicals produced by or derived from microorganisms (i.e. bugs or
germs such as bacteria and fungi). The first antibiotic was discovered
by Alexander Fleming in 1928 in a significant breakthrough for medical
science. Antibiotics are among the most frequently prescribed
medications in modern medicine.
Some antibiotics are 'bactericidal', meaning that they work by killing
bacteria. Other antibiotics are 'bacteriostatic', meaning that they
work by stopping bacteria multiplying.
Each different type of antibiotic affects different bacteria in
different ways. For example, an antibiotic might inhibit a bacterium's
ability to turn glucose into energy, or its ability to construct its
cell wall. When this happens, the bacterium dies instead of reproducing.
Some antibiotics can be used to treat a wide range of infections and
are known as 'broad-spectrum' antibiotics. Others are only effective
against a few types of bacteria and are called 'narrow-spectrum'
antibiotics.
Side effects of antibiotics
Antibiotics can literally save lives and are effective in treating
illnesses caused by bacterial infections. However, like all drugs, they
have the potential to cause unwanted side effects. Many of these side
effects are not dangerous, although they can make life miserable while
the drug is being taken.
In general, antibiotics rarely cause serious side effects. The most
common side effects from antibiotics are diarrhea, nausea, vomiting.
Fungal infections of the mouth, digestive tract and vagina can also
occur with antibiotics because they destroy the protective 'good'
bacteria in the body (which help prevent overgrowth of any one
organism), as well as the 'bad' ones, responsible for the infection
being treated.
Some people are allergic to antibiotics, particularly penicillins.
Allergic reactions cause swelling of the face, itching and a skin rash
and, in severe cases, breathing difficulties. Allergic reactions
require prompt treatment.
Types of antibiotics
There are many different kinds of antibiotics. The type of antibiotics
you take depends on the type of infection you have and what kind of
antibiotics are known to be effective.
The main classes of antibiotics:
- Aminoglycosides
- Cephalosporins
- Fluoroquinolones
- Macrolides
- Penicillins
- Tetracyclines
Macrolides
There are a couple of new relatives of erythromycin (azithromycin and
clarithromycin) that work the same way, but kill more bugs and have
slightly fewer side effects. The erythromycin-like antibiotics are also
known as macrolides. Macrolides belong to the polyketide class of
natural products. Macrolide antibiotics are used to treat respiratory
tract infections, genital, gastrointestinal tract, soft tissue
infections caused by susceptible strains of specific bacteria.
Macrolides bind with ribosomes from susceptible bacteria to prevent
protein production. This action is mainly bacteriostatic, but can also
be bactericidal in high concentrations.
Macrolides cause very little allergy problems compared to the
penicillins and cephalosporins, the biggest concern with these
medicines is that they can irritate the stomach.
The most commonly-prescribed macrolides:
- erythromycin
- clarithromycin
- azithromycin
- roxithromycin
Aminoglycosides
Aminoglycoside antibiotics are used to treat infections caused by
gram-negative bacteria. Aminoglycosides may be used along with
penicillins or cephalosporins to give a two-pronged attack on the
bacteria. Aminoglycosides work quite well, but bacteria can become
resistant to them. Since aminoglycosides are broken down easily in the
stomach, they can't be given by mouth and must be injected. When
injected, their side effects include possible damage to the ears and to
the kidneys. This can be minimized by checking the amount of the drug
in the blood and adjusting the dose so that there is enough drug to
kill bacteria but not too much of it. Generally, aminoglycosides are
given for short time periods.
The aminoglycosides are drugs which stop bacteria from making proteins. This effect is bactericidal.
The most commonly-prescribed aminoglycosides:
- amikacin
- gentamicin
- kanamycin
- neomycin
- streptomycin
- tobramycin
Cephalosporins
Cephalosporins are grouped into "generations" by their antimicrobial
properties. Cephalosporins are categorized chronically, and are
therefore divided into first, second, and third generations. Currently,
three generations of cephalosporins are recognized and a fourth has
been proposed. Each newer generation of cephalosporins has greater gram
negative antimicrobial properties than the preceding generation. The
later-generation cephalosporins have greater effect against resistant
bacteria.
Cephalosporins are used to treat pneumonia, strep throat, staph
infections, tonsillitis, bronchitis, otitis media, various types of
skin infections, gonorrhea. Cephalosporin antibiotics are also commonly
used for surgical prophylaxis. Cephalosporins are closely related to
the penicillins.
Cephalosporins have a bacteriocidal effect by inhibiting the synthesis of the bacteria cell wall.
The most commonly-prescribed cephalosporins:
- cephazolin
- cefadroxil
- cephalexin
- cephradine
- cefaclor
- cefuroxime
- cefprozil
- loracarbef
- cefotaxime
- cefixime
- cefpodoxime
- ceftazidime
- cefdinir
Fluoroquinolones
Fluoroquinolones are known as broad-spectrum antibiotics, meaning they
are effective against many bacteria. Fluoroquinolones are used to treat
most common urinary tract infections, skin infections, and respiratory
infections (such as sinusitis, pneumonia, bronchitis). Common side
effects of fluoroquinolones include mainly the digestive system: mild
stomach pain or upset, nausea, vomiting, and diarrhea. These are
usually mild and go away over time. Fluoroquinolones should not be
given during pregnancy.
Fluoroquinolones inhibit bacteria by interfering with their ability to
make DNA. This activity makes it difficult for bacteria to multiply.
This effect is bacteriocidal.
The most commonly-prescribed fluoroquinolones:
- ciprofloxacin
- gatifloxacin
- gemifloxacin
- levofloxacin
- moxifloxacin
- norfloxacin
- ofloxacintrovafloxacin
Penicillins
Penicillin was the first antibiotic discovered by Alexander Fleming in
1929. Penicillins are used to treat skin infections, dental infections,
ear infections, respiratory tract infections, urinary tract infections,
gonorrhea. Penicillins are sometimes combined with other ingredients
called beta-lactamase inhibitors, which protect the penicillin from
bacterial enzymes that may destroy it before it can do its work.
Penicillins are usually very safe. The greatest risk is an allergic
reaction, which can be severe. People who have been allergic to
cephalosporins are likely to be allergic to penicillins.
Penicillins block the construction of bacteria cell walls, causing the walls to break down, and eventually killing the bacteria.
The most commonly-prescribed penicillins:
- amoxicillin
- ampicillin
- bacampicillin
- oxacillin
- penicillin
Tetracyclines
Tetracyclines are a family of antibiotics used to treat a broad
spectrum of bacterial infections. Tetracyclines were discovered in the
late 1940s and were extremely popular when they were first discovered.
The tetracycline antibiotics have a very broad spectrum of action.
Tetracyclines are used to treat mild acne, Rocky Mountain spotted
fever, Lyme Disease, upper respiratory tract infections, urinary tract
infections, sexually transmitted diseases, typhus.
The most commonly-prescribed tetracyclines:
- tetracycline
- doxycycline
- minocycline
Antibiotic resistance
Antibiotics are extremely important in medicine, but unfortunately
bacteria are capable of developing resistance to them.
Antibiotic-resistant bacteria are germs that are not killed by commonly
used antibiotics. When bacteria are exposed to the same antibiotics
over and over, the bacteria can change and are no longer affected by
the drug.
Bacteria have number of ways how they become antibiotic-resistant. For
example, they possess an internal mechanism of changing their structure
so the antibiotic no longer works, they develop ways to inactivate or
neutralize the antibiotic. Also bacteria can transfer the genes coding
for antibiotic resistance between them, making it possible for bacteria
never exposed to an antibiotic to acquire resistance from those which
have. The problem of antibiotic resistance is worsened when antibiotics
are used to treat disorders in which they have no efficacy (e.g.
antibiotics are not effective against infections caused by viruses),
and when they are used widely as prophylaxis rather than treatment.
Resistance to antibiotics poses a serious and growing problem, because
some infectious diseases are becoming more difficult to treat.
Resistant bacteria do not respond to the antibiotics and continue to
cause infection. Some of these resistant bacteria can be treated with
more powerful medicines, but there some infections that are difficult
to cure even with new or experimental drugs.
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