Antibiotic





In common usage, an antibiotic is a drug that kills certain kinds of
bacteria, but which is generally harmless to the host and is used to treat
infection. The term was originally used to describe only antibacterial
formulations derived from living organisms but is now used in reference to
synthetic antimicrobials such as the Sulfonamides.

In general, the term can also apply to substances that affect prions,
viruses, fungi, worms or any other intracellular or extracellular parasite,
but the antibacterial kind are the most common. Generally, the antibiotics
are not effective in viral infections.

History

The first antibiotic to be discovered was penicillin. Alexander Fleming had
been culturing bacteria on an agar plate with an accidental fungal
contamination, and noticed that the culture medium around the mould was free
of bacteria. He had previously worked on the antibacterial properties of
lysozyme, and so was predisposed to make the correct interpretation of what
he saw: that the mold was secreting something that stopped bacterial growth.
Though he was unable to produce the pure material (the beta-lactam ring in
the penicillin molecule was not stable under the purification methods he
tried), he reported it in the scientific literature. Since the mold was of
the genus Penicillium, he named this compound penicillin. With the increased
need for treating wound infections in World War II, resources were poured
into investigating and purifying this compound, and a team led by Howard
Florey succeeded in producing large quantities of the purified active
ingredient. Antibiotics soon came into widespread use.

The discovery of antibiotics, along with anesthesia and the adoption of
hygienic practices by physicians (for example, washing hands and using
sterilized instruments) revolutionized medicine - it has been said that this
is the greatest advance in health since modern sanitation. They are often
called "magic bullets": drugs which target bugs without greatly harming the host.

Classes

There are many way to classify antibiotics.

One such classification is by chemical structure:

   * Aminoglycosides
        o Gentamicin
   * Beta-lactam ring antibiotics
        o Carbapenems
             + Ertapenem
             + Imipenem
        o Cephalosporins and Cephamycins
        o Monocyclic beta-lactams
        o Penicillins
   * Glycopeptide Antibiotics
        o Vancomycin
        o Teicoplanin
   * Macrolides
   * Oxazolidinones
   * Polymyxins
   * Quinolones
   * Streptogramins
   * Sulfonamides
   * Tetracyclines
   * Other important antibiotics:
        o Chloramphenicol
        o Clindamycin
        o Fusidic acid
        o Trimethoprim

Another such classification is by their mechanism of action (that is, the
mechanism by which they selectively poison bacterial cells:

   * antibiotics which interfere with cell-wall synthesis'
        o beta-lactams, including penicillins and cephalosporins;
          mono-lactams, such as Imipenem; vancomycin, bacitracin
   * antibiotics which interfere with bacerial protein synthesis
        o antibiotics which bind to the 50S ribosomal unit'
             + Lincosamides/lincosides including clindamycin and lincomycin;
               chloramphenicol
        o antibiotics which interfere the 30S ribosomal unit
             + tetracyclines; aminoglycosides including gentamicin
   * drugs with inhibit folate sytheisis
        o sulfonamides and tirmethoprim
   * drugs which interfere with DNA synthesis
        o rifampin, metronidazole, quinolines, novobiocin
   * drugs which interfere with cell membrane function
        o polymyxin B, Gramicidin

Antibiotics can also be classified by the organisms against which they are
effective, and by the type of infection in which they are useful, which
depends on the sensitivities of the organisms that most commonly cause the
infection and the concentration of antibiotic obtainable in the affected
tissue.

Antibiotic misuse

Common forms of antibiotic misuse include taking an antibiotic for an
inappropriate condition, in particular the use of antibiotics for viral
infections; and not taking the entire course of the antibiotic, usually
because the patient feels better before the infection is cured.

There is debate over the appropriateness of including antibiotics in the
diet of healthy farm animals. Opponents of this practice point out that it
leads to antibiotic resistance, including in bacteria that infect humans.
The practice continues in many places, however, because feeding livestock
antibiotics promotes weight gain, and thus makes economic sense for the
individual farm or ranch.

Antibiotic resistance

One side effect of misusing antibiotics is the development of antibiotic
resistance by bacteria. By 1984 half the people with active tuberculosis in
the United States had a strain that resisted at least one antibiotic.
Between 1985 and 1991 tuberculosis increased 12 per cent in the US and 300
per cent in Africa where HIV and TB are often found together.