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Back To Vidyya More Information On Flu Drugs: Antivirals

The Antivirals

Influenza viruses are divided into three types, designated A, B, and C. Influenza types A and B are responsible for epidemics that occur almost every winter, and are associated with increased rates for hospitalization and death. Epidemics of influenza occur during the winter months nearly every year and are responsible for an average of approximately 20,000 deaths per year in the United States. (Influenza type C usually causes either a very mild respiratory illness or no symptoms at all, and it does not cause epidemics.)

This year’s flu vaccine contains the following strains: A/Panama, A/New Caledonia, and B/Yamanashi. Although flu shots are the primary way to prevent infection with influenza, antiviral drugs can play an important role, along with the vaccine, in controlling and preventing illness as follows:

  • Four different antiviral drugs (amantadine, rimantadine, zanamivir and oseltamivir) have been approved for treating influenza illness. All four must be prescribed by a physician. On January 12, 2000, the Food and Drug Administration issued an advisory letter emphasizing that physicians should 1) always consider the possibility of primary or secondary bacterial infection when making treatment decisions for patients with suspected influenza, and to 2) use special caution if prescribing zanamivir to patients with underlying asthma or chronic obstructive pulmonary disease.
  • At this time, only amantadine and rimantadine are approved for the prevention (prophylaxis) of influenza A.
  • Amantadine (available in the U.S. since 1976) and rimantadine (available in the U.S. since 1993) can reduce the severity and shorten the duration of type A influenza, and are very useful in controlling outbreaks (e.g., nursing homes). However, the use of these drugs has been associated with adverse reactions that can affect the central nervous system. Amantadine and rimantadine are not generally recommended for widespread use in healthy persons.
  • The newer influenza antiviral drugs, zanamivir (Relenza® ) and oseltamivir (Tamiflu™), both became available in 1999. Both drugs can reduce the severity and shorten the duration of types A and B influenza, but have not been approved for the prevention of influenza.
  • Comparison of antiviral drugs for influenza*
Comparison of antiviral drugs for influenza*
Description Amantadine Rimantadine Zanamivir Oseltamivir
Flu virus affected influenza A influenza A influenza A & B influenza A & B
Administration oral oral oral inhalation oral
Ages approved for treatment >1 year >14 years >12 years >18 years
Ages approved for prevention >1 year
>1 year not approved not approved
* For more information see Prevention and Control of Influenza: Recommendations of the Advisory Committee on Immunization Practices (ACIP), April 14, 2000 / 49(RR-3). This report is available online at

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Editor: Susan K. Boyer, RN
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