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Use and Abuse of Anitbiotic Drugs
graphic showing unnecessary prescriptions for antibiotics
More than 50 million unnecessary antibiotic prescriptions are written each year in the United States for patients outside of hospitals, according the the Centers for Disease Control and Prevention
Graphic: Erik Dunham, NPR/U.S. Food and Drug Administration

What are antibiotics?

Antibiotics are chemicals usually derived from molds, bacteria or other organisms that inhibit the growth of bacteria or kill the bacteria completely.

The first effective antibiotic, penicillin, kills bacteria by interfering with the bacteria's ability to create cell walls. It was derived from a common mold.

But the drugs are not invincible -- for example, some bacteria avoid the effect of penicillin by creating an enzyme that destroys penicillin. Natural defenses and resistant strains prompt researchers to continually look for new antibiotic chemicals, also called antimicrobials.

How are they used?

About one-half of the antibiotics produced in the United States are used to treat bacterial infections in humans. Most of the rest is added to animal feed, especially to feed given to pigs and chickens.

Some farmers use the antibiotics to help prevent mass infections among animals. This is particularly true in "factory farms," where the animals are packed tightly together and infections can spread rapidly. With some animals, the antibiotics also promote faster growth -- an effect that is still not fully understood.

Antibiotics are also sprayed on apple orchards, added to water to treat fish diseases and even used to stop bacteria from growing inside oil pipelines.

How can antibiotics be misused?

Antibiotics can "speed up" the process of natural selection, which is a driving factor in evolution. A single antibiotic, for example, can kill off nearly all of a particular strain of bacteria. But a small amount of bacteria that have a natural degree of immunity can survive.

Experts emphasize the importance of completing the entire course of medication when a patient is prescribed antibiotics. If the medication is stoppended too early, not all the bacteria may be killed off, and those that remain may develop resistance to the drug.

Sources: World Health Organization, Food and Drug Administration, Centers for Disease Control and Prevention