What is the best antiviral agent for influenza infection?

Four antiviral agents have been approved by the U.S. Food and Drug Administration for the treatment of influenza infection: amantadine (Symmetrel), oseltamivir (Tamiflu), rimantadine (Flumadine), and zanamivir (Relenza). No head-to-head trials have compared the effectiveness of these agents, and no direct evidence exists regarding their relative efficacy. In the absence of specific contraindications, amantadine and rimantadine are preferred for use in most patients because these two agents cost less than the other two. Patients with renal insufficiency or a seizure disorder should not take amantadine, and patients with chronic obstructive pulmonary disease or asthma should not take zanamivir. [Strength of recommendation: C]