Antibiotics are medicines used to kill bacteria that cause infections.

A doctor will choose an antibiotic to treat an illness based on:

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