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Antibiotics Classification And Side Effects What
are Antibiotics?
The word "antibiotics" comes from the
Greek anti ("against") and bios ("life").
Antibiotics are drugs that either destroy bacteria
or prevent their reproduction. Antibiotics that kill
bacteria are called "bactericidal" and
the ones that stop the growth of bacteria are called "bacteriostatic".
Since penicillin's introduction during the 1940s,
scientists developed numerous other antibiotics.
Today, over 100 different antibiotics are available.
About 90% of antibiotics are made from living organisms
such as bacteria, others are produced synthetically,
either in whole or in part.
Antibiotics classification
Although there are several classification schemes
for antibiotics, based on bacterial spectrum (broad,
narrow) or route of administration (injectable, oral,
topical), or type of activity (bactericidal, bacteriostatic),
the most useful is based on chemical structure. Antibiotics
within a structural class will generally have similar
patterns of effectiveness, toxicity, and allergic
potential.
Most commonly used types of antibiotics are: Penicillins,
Fluoroquinolones, Cephalosporins, Macrolides, and
Tetracyclines. While each class is composed of multiple
drugs, each drug is unique in some way.
Penicillins
The penicillins are the oldest class of antibiotics.
Penicillins have a common chemical structure which
they share with the cephalopsorins. Penicillins are
generally bactericidal, inhibiting formation of the
cell wall.
There are four types of penicillins:
* The natural pencillins are based on the original
penicillin-G structure. Penicillin-G types are effective
against gram-positive strains of streptococci, staphylococci,
and some gram-negative bacteria such as meningococcus.
* Penicillinase-resistant penicillins are active
even in the presence of the bacterial enzyme that
inactivates most natural penicillins.
* Extended spectrum penicillins which are effective
against a wider range of bacteria.
* Aminopenicillins such as ampicillin and amoxicillin
have an extended spectrum of action compared with
the natural penicillins.
Penicillins side effects
Penicillins are among the least toxic drugs known.
The most common side effect of penicillin is diarrhea.
Nausea, vomiting, and upset stomach are also common.
In rare cases penicillins can cause immediate and
delayed allergic reactions - specifically, skin rashes,
fever, and anaphylactic shock. Penicillins are classed
as category B during pregnancy.
Cephalosporins
Cephalosporins have a mechanism of action identical
to that of the penicillins. However, the basic chemical
structure of the penicillins and cephalosporins differs
in other respects, resulting in some difference in
the spectrum of antibacterial activity. Like the
penicillins, cephalosporins interfere with synthesis
of the bacterial cell wall and so are bactericidal.
Cephalosporins are among the most diverse classes
of antibiotics, they are grouped into "generations" by
their antimicrobial properties. Each generation has
a broader spectrum of activity than the one before.
The first generation cephalosporins include: cephalothin,
cefazolin, cephapirin, cephradine, cephalexin, cefadroxil.
Their spectrums of activity are quite similar. They
possess generally excellent coverage against most
gram-positive pathogens and variable to poor coverage
against most gram negative pathogens.
The second generation cephalosporins include: cefaclor,
cefamandole, cefonicid, ceforanide, cefuroxime. In
addition to the gram-positive spectrum of the first
generation cephalosporins, these agents have expanded
gram-negative spectrum. Cefoxitin and cefotetan also
have good activity against Bacteroides fragilis.
The third generation cephalosporins have much expanded
gram-negative activity. However, some members of
this group have decreased activity against gram-positive
organisms. The third generation cephalosporins include:
cefcapene, cefdaloxime, cefditoren, cefetamet, cefixime,
cefmenoxime, cefodizime, cefoperazone, cefotaxime,
cefpimizole, cefpodoxime, ceftibuten, ceftriaxone.
They have the advantage of convenient dosing schedules,
but they are expensive.
The fourth generation cephalosporins are extended-spectrum
agents with similar activity against gram-positive
organisms as first-generation cephalosporins. They
also have a greater resistance to beta-lactamases
(bacterial enzymes that may destroy antibiotic before
it can do its work) than the third generation cephalosporins.
Many fourth generation cephalosporins can cross blood
brain barrier and are effective in meningitis. The
fourth generation cephalosporins include: cefclidine,
cefepime, cefluprenam, cefozopran, cefpirome, cefquinome.
Cephalosporin side effects
Cephalosporins generally cause few side effects.
Common side effects associated these drugs include:
diarrhoea, nausea, mild stomach cramps or upset.
Approximately 5?10% of patients with allergic hypersensitivity
to penicillins will also have cross-reactivity with
cephalosporins. Thus, cephalosporin antibiotics are
contraindicated in people with a history of allergic
reactions (urticaria, anaphylaxis, interstitial nephritis,
etc) to penicillins or cephalosporins. Cephalosporin
antibiotics are classed as pregnancy category B.
Fluoroquinolones
Fluoroquinolones are the newest class of antibiotics.
Their generic name often contains the root "floxacin".
They are synthetic antibiotics that belong to the
family of antibiotics called quinolones. The older
quinolones are not well absorbed and are used to
treat mostly urinary tract infections. The newer
fluoroquinolones are broad-spectrum bacteriocidal
drugs that are chemically unrelated to the penicillins
or the cephaloprosins. Because of their excellent
absorption fluoroquinolones can be administered not
only by intravenous but orally as well.
Commonly used fluoroquinolones include ciprofloxacin,
levofloxacin, lomefloxacin, norfloxacin, sparfloxacin,
clinafloxacin, gatifloxacin, ofloxacin, trovafloxacin.
Fluoroquinolones side effects
Fluoroquinolones are well tolerated and relatively
safe. The most common side effects include nausea,
vomiting, diarrhea, abdominal pain. Other more serious
but less common side effects are central nervous
system effects (headache, confusion and dizziness),
phototoxicity (more common with lomefloxacin and
sparfloxacin). All drugs in this class have been
associated with convulsions. Fluoroquinolones are
classed as pregnancy category C.
Tetracyclines
Tetracyclines got their name because they share
a chemical structure that has four rings. They are
derived from a species of Streptomyces bacteria.
Tetracycline antibiotics are broad-spectrum bacteriostatic
agents, that inhibit bacterial protein synthesis.
Tetracyclines may be effective against a wide variety
of microorganisms, including rickettsia and amebic
parasites.
Tetracyclines are used in the treatment of infections
of the respiratory tract, sinuses, middle ear, urinary
tract, skin, intestines. Tetracyclines also are used
to treat Gonorrhoea. Their most common current use
is in the treatment of moderately severe acne and
rosacea.
The most commonly prescribed tetracycline antibiotics
are: tetracycline, doxycycline, minocycline, oxytetracycline.
Tetracycline side effects
Drugs in the tetracycline class become toxic over
time. Expired drugs can cause a dangerous syndrome
resulting in damage to the kidneys.
Common side effects associated with tetracyclines
include cramps or burning of the stomach, diarrhea,
sore mouth or tongue. Tetracyclines can cause skin
photosensitivity, which increases the risk of sunburn
under exposure to UV light. This may be of particular
importance for those intending to take on holidays
long-term doxycyline as a malaria prophylaxis. Rarely,
tetracyclines may cause allergic reactions. Very
rarely severe headache and vision problems may be
signs of dangerous secondary intracranial hypertension.
Tetracycline antibiotics should not be used in children
under the age of 8, and specifically during periods
of tooth development. Tetracyclines are classed as
pregnancy category D. Use during pregnancy may cause
alterations in bone development.
Macrolides
The macrolide antibiotics are derived from Streptomyces
bacteria, and got their name because they all have
a macrocyclic lactone chemical structure. The macrolides
are bacteriostatic, binding with bacterial ribosomes
to inhibit protein synthesis. Erythromycin, the prototype
of this class, has a spectrum and use similar to
penicillin. Macrolide antibiotics are used to treat
respiratory tract infections (such as pharyngitis,
sinusitis, and bronchitis), genital, gastrointestinal
tract, and skin infections.
The most commonly prescribed macrolide antibiotics
are: erythromycin, clarithromycin, azithromycin,
roxithromycin, troleandomycin.
Macrolides side effects
Side effects associated with macrolides include
nausea, vomiting, and diarrhea; infrequently, there
may be temporary auditory impairment. Azithromycin
has been rarely associated with allergic reactions,
including angioedema, anaphylaxis, and dermatologic
reactions. Oral erythromycin may be highly irritating
to the stomach and when given by injection may cause
severe phlebitis. Macrolide antibiotics should be
used with caution in patients with liver dysfunction.
Pregnancy category B: Azithromycin, erythromycin.
Pregnancy category C: Clarithromycin, dirithromycin,
troleandomycin. |
