Antiviral agent: An agent that kills viruses or suppresses their replication and, hence, inhibits their capability to multiply and reproduce.

For example, amantadine (BRAND name: SYMMETREL) is a synthetic (man- made) drug that inhibits the multiplication of the influenza A virus and has therefore been used to prevent the flu and (given within 24- 48 hours of the onset of symptoms) to lessen the severity of the disease, particularly in individuals at high-risk such as those who are immunosuppressed or in a nursing home. Rimantadine (BRAND name: FLUMADINE) is related in structure and anti-influenza A action to amantadine (SYMMETREL) but has fewer side effects. (Neither drug is a substitute for flu shots).