Antibiotics are usually prescribed to treat bacterial infections. Such infections can cause many different types of illnesses, including:

• Pneumonia
  
  
• Strep throat
  
  
• Urinary tract infections
  
  
• Wound and skin infections (caused by Staph bacteria)
  
  
• Certain sexually transmitted diseases (e.g., chlamydia, gonorrhea, syphilis)
  
  
• Certain types of ear infections

In some cases, antibiotics are prescribed as a prophylactic measure to prevent infection. For example, people with artificial or abnormal heart valves often are required to take antibiotics before dental procedures. Antibiotics may also be used as a prophylactic in people with weakened immune systems. This may include patients with leukemia, AIDS and those undergoing chemotherapy treatment for cancer.

Antibiotics only treat infections caused by bacteria. They are not effective against any other type of infection, such as viral or fungal infections. In some cases, a physician may not know whether a virusvirus or bacteria is causing the infection, and may only prescribe antibiotics if the infection persists.