Antiviral therapy of influenza.

The prevention of influenza virus infections by the use of vaccines remains the most cost-effective and practical method of influenza virus control, but the use of antiviral prophylaxis and treatment in certain populations or high-risk individuals is also possible. Four antiviral drugs are currently licensed in the United States for the treatment and/or prevention of influenza virus infection in children. The M2 blockers, (amantadine and rimantadine) have been licensed for the prophylaxis and treatment of influenza in diverse high-risk populations, including children, for years. Advantages of these agents include the low cost, high oral bioavailability, and relative tolerability of one of these agents (rimantadine) in children. Disadvantages include efficacy against influenza A viruses only (not type B), the relative rapid development of resistance, and adverse effects associated with amantadine in particular (especially in the elderly and those with decreased renal function). Two agents in a new antiviral class, the neuraminidase inhibitors, have been licensed recently for the treatment and prophylaxis of influenza in the United States. Oseltamivir is licensed for the treatment of influenza in children older than 1 year and for the prophylaxis in children older than 13 years. This drug is safe and well-tolerated, and is available in capsules or a liquid suspension. Another neuraminidase inhibitor, zanamivir, is administered as an inhaled powder via a special inhaler device and is licensed for the treatment of influenza in children older than 7 years. Both neuraminidase inhibitors appear to be similarly effective and are not associated with the development of antiviral resistance. No direct comparisons of any of these antiviral agents has been performed; all result in clinical improvement approximately 1 to 2 days earlier in otherwise healthy children when therapy is initiated within 48 hours of onset of symptoms.