Two classes of antiviral agents have been developed for prevention and treatment of influenza: the M2 channel inhibitors (amantadine and rimantadine), and the neuraminidase inhibitors (zanamivir and oseltamivir). Amantadine and rimantadine were the first generation of influenza antiviral agents. These compounds specifically block the ion channel function of the M2 protein of influenza A virus, thus interfering with the corresponding specific steps in the viral life cycle. The use of these agents is limited, since viral resistance can emerge rapidly during treatment. Zanamivir and oseltamivir are analogues of sialic acid, which specifically inhibit all nine NA subtypes. The inhibition of neuraminidase has three important consequences. First, it hinders the passage of the virus through the mucus of the respiratory tract and thus slows down initial infection of epithelial cells. Second, it inhibits the release of new viral particles from the surface of infected cells and thus slows the spreading of the virus. Third, it inhibits transmission of the virus from one infected individual to another.