Antibiotics are chemicals designed specifically to kill or prevent the growth of some specific types of infections. A wide variety of things can cause infection, such as bacteria, parasites, viruses, and fungi, so we need a variety of antibiotics. Many infectious agents, such as E. coli, can be killed by a variety of antibiotics. Some agents, such as HIV, the virus which causes AIDS, cannot be wiped out completely by any antibiotic we have so far. No antibiotics can treat the common cold, which is unfortunate since the common cold is so common!

In order to correctly treat an infection with antibiotics, we first need to have a good idea which agent is causing the infection. Otherwise we won't be able to select the right antibiotic. And as we saw above, some infections, like a cold, simply don't improve no matter what antibiotic we give. Second, we need to be sure that taking the antibiotic won't cause more problems than it solves. Some antibiotics have only been tested in adults, or are known to cause problems when given to children. And any antibiotic has the potential of causing unwanted side effects in some people.

Some antibiotics kill the bacteria which live in our large intestines. This can cause diarrhea and may affect other drugs also being taken. Some antibiotics cause nausea. For any antibiotic, an allergic rash can will develop in a small percentage of patients. Also, the more we take any particular antibiotic, the more resistant infections can become to that antibiotic over time. These are all good reasons to be cautious about giving antibiotics unless we believe they will help.

• Symptoms of infection in the nose, such as congestion, runny nose, and cough, which last less than two weeks are probably caused by one of the many viruses which we don't have useful antibiotics against. Our bodies can usually take care of those infections within two weeks, so if symptoms last longer than that, we may consider another cause, such as allergies or bacterial infection. In that case, antibiotics and other medicines may help treat the problem.
• Children frequently contract viral infections which cause fever, nausea, vomiting, diarrhea, decreased appetite, and crankiness. The fever from a virus should last three days or less. If the fever lasts longer than this, a bacterial infection may have occurred, and antibiotics may be appropriate. As always, you should call us if you have any doubt about your child's condition. See our fever page for more on this topic.