Antivirals are medications that keep viruses from reproducing inside the body. It is difficult to produce effective antivirals because they have to target viruses that are small and that use a host cell’s metabolic pathways to replicate. Thus, an antiviral has difficulty targeting such a virus without damaging the host cell as well.

Antiviral medications are used to treat some diseases, including hepatitis, genital herpes, and HIV and associated AIDS infections. Antivirals are also used to both prevent infection with influenza and to shorten the duration of the illness in people who are already infected. The four antiviral medications used to treat people with influenza are:

• amantadine (Symmetrel)
• rimantadine (Flumadine)
• oseltamivir (Tamiflu)
• zanamivir (Relenza)

Antiviral medications typically are prescribed to control outbreaks of influenza in institutions with large numbers of people at high risk for complications associated with the flu, such as nursing homes or hospital wards. The effectiveness of these drugs depends on many factors, including how soon after infection the drugs are administered and the nature of the flu virus that has caused the infection.

People with certain health conditions, such as underlying respiratory disease, may be prohibited from using antiviral medications. In addition, the newer flu medications called neuraminidase inhibitors are less likely to cause side effects than the older flu drugs.