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Antibiotics were the first antimicrobials. These were substances that were derived from living microorganisms which could inhibit the growth or kill other types of microorganisms. We now also have synthetic and semisynthetic agents that can exert the same effects. The organisms affected by antimicrobials are bacteria, parasites, fungi, and a few selected viruses.

In order for antimicrobials to work they must first gain access to the target in order to exert their effect. Once at the site they can have either a bactericidal or a bacteriostatic effect, and can act in the following ways: by inhibiting cell wall synthesis (primarily a bactericidal action), alter or disrupt membrane permeability (as with both bactericidal or bacteriostatic), or inhibit protein synthesis (accomplished by the use of bacteriostatics).

Some antimicrobial agents can have either effect (as noted above) based on dose level. An example is tetracycline: it is generally bacteriostatic but at high concentrations may be bactericidal.

Since most antimicrobial agents have a specific effect on certain types of microorganisims, it is most helpful if specimens from the infected area can be sent to a lab for culture and sensitivity reports. In this way the most effective drug can be prescribed. However, this may not be practical when treatment needs to be immediate. In these cases or when it is difficult to identify the specific microorganism, then broad-spectrum antibiotics are initiated.

There are some infections that can be treated effectively with only one antibiotic, but in other situations, like that above, more than one antimicrobial agent may be used simultaneously. It is important to remember that agents which exert a bactericidal effect may be impaired when mixed in with bacteriostatic agents. It is, therefore, wise, when administering two different types of antibiotics simultaneously, to give them on different schedules.

Sometimes microorganisms will develop resistance either suddenly or over time to previously sensitive antimicrobial agents. This may be due to high concentrations of an antibiotic or genetic events that lead to the microorganism mutating. Microorganisms that become resistant to an antibiotic will also be resistant to those antibiotics that are chemically related.

Because antibiotics can disturb the normal microbial flora in the gut, unless specifically contraindicated, give yogurt, Lactobacillus capsules/granules, or Bene-Bac to replenish. This is just a very brief statement of what antibiotics do.

Hopefully it will help with understanding why I have listed the drugs by categories.

Antimicrobial Agents


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