October 21, 2005 Page 1 of 2

Antiviral Drugs and Influenza

Four antiviral drugs (amantadine, rimantadine, zanamavir and oseltamivir) have been approved by the U.S. Food and Drug 

Administration (FDA) for treatment of influenza. However, you will need to begin taking an antiviral drug within 2 days after 

becoming sick. When used in this manner, these drugs can reduce influenza symptoms and may shorten the time you are sick 

by 1 or 2 days. The drugs also may make you less contagious. All of these drugs must be prescribed by a doctor and taken for 

3-5 consecutive days (5 days for oseltamivir and zanamivir). The 4 antiviral drugs are effective only against influenza viruses. 

They will not help symptoms associated with the common cold or many other influenza-like illnesses caused by viruses that 

circulate in the winter. 

Three antiviral drugs (amantadine, rimantadine, and oseltamivir) are approved by the FDA and are commercially available for 

use in the United States to prevent influenza. All of these medications are prescription drugs, and a doctor should be consulted 

before the drugs are used. When used for prevention, they are about 70% to 90% effective in preventing illness in healthy 

adults. 

All of the antiviral drugs may be effective for influenza A viruses. However, only oseltamivir and zanamivir are effective for 

influenza B viruses. 

All of the antiviral drugs are different in terms of who can take them, how they are given, any dosing changes based on age or 

medical conditions, and side effects (http://www.cdc.gov/flu/protect/antiviral/sideeffects.htm). Your doctor can help decide 

whether you should take an antiviral drug and which one you should use. 

Use of Antiviral Drugs 

Antiviral drugs are most often used to help control influenza outbreaks in institutions, for example in nursing homes or in hospital 

wards, where people at high risk for complications from influenza are in close contact with each other. Antivirals also have been

used on cruise ships or similar settings to help control influenza outbreaks. 

In the event of an outbreak, public health practice is to combine the use of influenza vaccine and antivirals. For example, nursing 

home residents and staff are given vaccine during an outbreak and also are given antivirals to prevent influenza until the vaccine 

takes effect (about 2 weeks). This practice continues as long as influenza is occurring in that setting. 

Doctors also can prescribe influenza antivirals to people not living in institutional settings, but treatment must begin within 2 days 

of the onset of symptoms for the drugs to be effective. Although all antivirals lessen symptoms and shorten the duration of 

illness, only one (oseltamivir) has been shown in a study to reduce lower respiratory tract complications requiring antibiotics. 

They do not cure influenza outright. 

When considering the use of antivirals it is important to remember that most healthy people recover from influenza without 

complications.

Who Should Get Antiviral Drugs 

People who are at high risk of serious complications from influenza may benefit most from antiviral medications. This includes:

people 65 years of age and older, children 12-23 months of age, people with chronic medical conditions (for example, heart or 

lung disease, diabetes), and pregnant women. (Note that none of the antivirals are approved for use in children less than 1 year 

of age.) Although CDC has provided guidelines for health-care professionals on the use of antiviral drugs, your doctor will decide 

whether you should receive antiviral drugs this season. The guidelines for use of influenza anitivirals are not intended as 

recommendations for use of these medications in other situations, such as outbreaks of new strains of avian influenza. 
Antiviral Drugs and Influenza 

(continued from previous page) 

October 21, 2005 Page 2 of 2

For Treatment: If you become sick with influenza-like symptoms this season, your doctor first may give you a test to find out 

whether you have influenza. (Symptoms include fever (usually high), headache, tiredness, a sore throat and dry cough, nasal 

congestion, and body aches.) Your doctor also will consider a number of factors before making a treatment decision, such as 

your risk for complications from influenza.

For Prevention: In the event of an influenza outbreak in a home, institution, or community, your doctor may choose to prescribe 

antivirals to you as a preventive measure, especially if you are at high risk for complications from influenza. Also, if you are in 

close contact with someone who is considered at high risk for complications, you may be given antiviral drugs to reduce the 

chances of passing influenza to the high-risk person. 

For more information, see the following: 

• Antiviral Drugs: Summary of Side Effects 

http://www.cdc.gov/flu/protect/antiviral/sideeffects.htm 

• Background Information for Clinicians: Antiviral Agents for Influenza 

http://www.cdc.gov/flu/professionals/antiviralback.htm

For more information, visit www.cdc.gov/flu, 

or call CDC at 800-CDC-INFO (English and Spanish) or 888-232-6348 (TTY).