Medications

Four influenza antiviral drugs are currently licensed in the United States. If given within the first 48 hours, antiviral agents decrease the severity and duration of symptoms, but their ability to prevent complications of influenza A has not been established. The primary drawback of these types of medications is that resistant viruses can slow recovery.

• M2 inhibitors include the drugs amantadine (Symmetrel and Symadine) and rimantadine (Flumadine). Either can be used in the prevention and treatment of influenza type A. Antiviral agents are not effective against influenza B and are not approved for use in children younger than 1 year. Rimantadine has not been approved for treatment of children younger than 13 years. Amantadine and rimantadine are not recommended by the Centers for Disease Control and Prevention (CDC) for the 2005-2006 influenza season. Laboratory testing by the CDC on the predominant strain of influenza (H3N2) currently circulating in the United States shows that it is resistant to amantadine and rimantadine.
  
  
• Neuraminidase inhibitors (NAIs) are FDA approved for uncomplicated influenza when the symptoms have been present for fewer than 48 hours. The main advantages of the NAIs are their activity against both influenza A and B. Zanamivir (Relenza) is approved for treatment in children older than 7 years, but it is not approved for prevention. The drug is available as topical powder administered by a breath-activated inhalation device. Oseltamivir (Tamiflu) is licensed for children older than 1 year. It is available as a tablet and suspension and is usually taken for 5 days.
  
  
• Side effects: The use of amantadine has been associated with central nervous system side effects including headache, insomnia, confusion, and failure to concentrate. In addition, the risk of seizure activity during therapy with amantadine in people with known seizure disorders is increased, even if they use medications to counteract that side effect. These side effects go away when a person stops taking the drug. Gastrointestinal side effects, such as nausea and loss of appetite, occur in 3% of people taking them.
  
  
• Currently, no antiviral agents exist for use against influenza C infections.
  
  
• The broad-spectrum antiviral agent ribavirin (Rebetol, Virazole Aerosol), given in aerosol form like nebulization, has benefited adults with influenza A and B infections. Ribavirin is not approved for treatment of influenza in children.