Antibiotics are medications that kill bacteria. Bacteria are organisms that cause infections.

A health professional will choose an antibiotic to treat an illness based on:

• Whether taking an antibiotic will reduce the length or severity of the illness.
• The person's age. (For example, some antibiotics are not safe for children.)
• The symptoms.
• Other medical problems that the person may have.
• The severity of the illness.
• How likely it is that a certain antibiotic will kill the bacteria believed to be causing the symptoms.
• Whether the person is allergic to any antibiotics.
• Whether a woman is pregnant.