Bacteria are tiny, single-cell organisms. Illnesses caused by bacteria are usually localized at a single point in the body. However, these antibiotics do nothing to combat viral infections. A virus is an infectious agent, smaller than a bacteria, which requires the cells of a living organism to grow or reproduce. Viruses are responsible for a number of infectious diseases which usually involve several parts of the body.
Viruses are responsible for all colds and the flu, most coughs, and most sore throats.
Taking a standard antibiotic such as penicillin or amoxicillin for a viral infection does not work. In numerous studies across the United States, researchers have noted that antibiotics are often prescribed in situations such as the common cold or viral bronchitis where antibiotics cannot do any good and may even cause harm. This misuse of antibiotics creates problems in two ways. First, it fails to treat the viral infection that is causing the patient to suffer. Second, increased exposure to antibiotics can result in resistant bacteria.