Influenza (commonly known as the flu) is a severe infectious respiratory disease which has as main symptoms fever, chills, muscle aches, headache, coughing and pharyngitis. The oldest flu drug known is amantadine (Symmetrel), a drug that is given as prevention and affects the replication of the virus. Rimantadine (Flumadine) has the same effect as amantadine but has the advantage of far less side effects. However, its effectiveness is limited to only one type of flu, the influenza A. Zanamavir (Relenza) is a newer flu drug, which has proven to shorten the duration of influenza illness if taken within 30 hours of the onset. It helps against the most common strains of flu, the influenza A and influenza B.