Topic: AntibioticsDefinition
Antibiotics may be informally defined as the subgroup of anti-infectives that are derived from
bacterial sources and are used to treat bacterial infections.
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Antibiotics Classifications
Although there are several classification schemes for antibiotics, based on bacterial spectrum (broad versus
narrow) or route of administration (injectable versus oral versus topical), or type of activity (bactericidal
vs. bacteriostatic), the most useful is based on chemical structure.
PENICILLINS
The penicillins are the oldest class of antibiotics, and have a common chemical structure which they share with
the cephalosporins. The two groups are classed as the beta-lactam antibiotics, and are generally bacteriocidal
-that is, they kill bacteria rather than inhibiting growth.
CEPHALOSPORINS
Cephalopsorins are the usually preferred agents for surgical prophylaxis. Cefotaxime, ceftizoxime, ceftriaxone
and others, cross the blood-brain barrier and may be used to treat meningitis and encephalitis.
FLUROQUINOLONES
The fluroquinolones are synthetic antibacterial agents, and not derived from bacteria. They are included
here because they can be readily interchanged with traditional antibiotics.
TETRACYCLINES
Tetracyclines got their name because they share a chemical structure that has four rings.
The tetracyclines may be effective against a wide variety of microorganisms, including rickettsia
and amebic parasites.
MACROLIDES
Erythromycin, the prototype of this class, has a spectrum and use similar to penicillin. Newer members
of the group, azithromycin and clarithyromycin, are particularly useful for their high level of lung
penetration. Clarithromycin has been widely used to treat Helicobacter pylori infections, the cause
of stomach ulcers.
OTHERS
Other classes of
antibiotics include the aminoglycosides, which are particularly useful for their effectiveness
in treating Pseudomonas aeruginosa infections; the lincosamindes, clindamycin and lincomycin, which are
highly active against anaerobic pathogens.
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