Adamantanes: Amantadine and rimantadine have activity against influenza A but not B viruses.

  • Both are approved for use as chemoprophylaxis to prevent influenza. They are 70-90% effective in limiting the infection to subclinical levels so that the body still has a protective immune response and develops antibodies for circulating influenza viruses. However, the use of chemoprophylaxis is limited. Those who should consider it include:
    • People at high risk for serious influenza disease who were not vaccinated before a local outbreak.
    • Health care providers for people at high risk
    • Severely immunocompromised persons (including HIV disease, transplant patients, and cancer therapy recipients).
    • The elderly

Neuraminidase inhibitors: Zanamivir (Relenza) and oseltamivir (Tamiflu)

  • Relenza is the brand name for the drug zanamivir, developed by GlaxoSmithKline (
  • It is an antiviral medication that works by inhibiting the neuraminidase protein of Influenza A and B viruses, effectively blocking the release of virus from infected cells, and therefore limiting viral spread from one cell to another.
  • The FDA has approved Relenza for the treatment of uncomplicated influenza virus infection for persons of 7 years and older.
  • It is effective against both type A and B influenza provided that patients begin treatment within 48 hours of the onset of symptoms.
  • Relenza is administered as a powder, inhaled through a Diskhaler device twice a day for five days after illness onset.
  • The most common side effect is bronchospasm (wheezing). Relenza is therefore not typically recommended for people with chronic respiratory disease.
  • The FDA has not yet approved Relenza for chemoprophylactic use, though studies done in nursing homes indicate that it is 84% effective in prevention of influenza disease.
  • Treatment with Relenza does not appear to antagonize immune response to influenza vaccine, but should not be used as a substitute for the vaccine.
  • Please refer to the U.S. Food and Drug Administration’s Center for Drug Evaluation and Research for more information:"


  • Tamiflu is the brand name for the drug Oseltamivir phosphate (
  • Like Relenza it is able to block the release of virus progeny by binding to the neuraminidase protein.
  • It was FDA approved in October 27, 1999.
  • It is effective against Influenza A and B.
  • Tamiflu is taken orally in a grey/light yellow capsule or in Powder for Oral Suspension.
  • Tamiflu's safety and effectiveness on immunocompromised individuals has not been tested.
  • For more information please refer to U.S. Food and Drug Administration’s Center for Drug Evaluation and Research:


For more information on drug therapy for influenza virus, please visit the CDC’s website:


Contact Us | Created: November 2005