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Key Facts About Antiviral Drugs and Influenza (Flu)

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Background

While getting a flu vaccine each year is the best way to protect you from the flu, there also are drugs that can fight against influenza viruses, offering a second line of defense against the flu. These are called “influenza antiviral drugs” and they must be prescribed by a health care professional. These drugs can be used to treat the flu or to prevent infection with flu viruses. Influenza antiviral drugs only work against influenza viruses -- they will not help treat or prevent symptoms caused by infection from other viruses that can cause symptoms similar to the flu.  
Antiviral drugs are used in different settings and circumstances to treat the flu and to prevent people from getting the flu:

While most healthy people recover from the flu and don’t have serious complications, some people—such as older people, young children, and people with certain health conditions (such as asthma, diabetes, or heart disease)—are at higher risk for serious flu-related complications. It’s especially important that these people are protected from the flu.

Remember, a flu vaccine is the first and best defense against the flu, but antiviral drugs can be an important second line of defense to treat the flu or prevent flu infection.

Antiviral Drugs for the 2008-09 Flu Season

Two flu antiviral drugs are recommended for use in the United States during the 2008-09 flu season: oseltamivir and zanamivir. Oseltamivir and zanamivir are effective against both influenza A and B viruses.

Antiviral drugs differ in terms of who can take them, how they are given, their dose (which can vary depending on a person’s age or medical conditions), and side effects.

For more information, see “Information for Health Care Professionals: Using Antiviral Agents for Seasonal Influenza” or consult the package insert for each drug. Your doctor can help decide whether you should take an antiviral drug this flu season and which one you should use.

Use of Antiviral Drugs for Treatment

For treatment, influenza antiviral drugs should be started within 2 days after becoming sick and taken for 5 days.  When used this way, these drugs can reduce flu symptoms and shorten the time you are sick by 1 or 2 days. They also may make you less contagious to other people. 

If you become sick with flu-like symptoms this season, your doctor will consider the likelihood of influenza being the cause of your illness, the number of days you have been sick, side effects of the medication, etc. before making a recommendation about using antivirals.  He or she may test you for influenza, but testing is not required in order for a physician to recommend influenza antiviral medications for you.

Use of Antiviral Drugs for Prevention 

Influenza antiviral drugs can also be used to prevent influenza when they are given to a person who is not ill, but who has been or may be near a person with influenza. When used to prevent the flu, antiviral drugs are about 70% to 90% effective. It’s important to remember that flu antiviral drugs are not a substitute for getting a flu vaccine. When used for prevention, the number of days that they should be used will vary depending on a person’s particular situation.

In some instances, your doctor may choose to prescribe antiviral drugs to you as a preventive measure, especially if you are at high risk for serious flu complications and either did not get the flu vaccine or may still be at risk of illness even after vaccination.  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 catching the flu and passing it on to the high-risk person.

Who Should Get Antiviral Drugs?

CDC has provided guidelines for health care professionals on the use of antiviral drugs (see: Information for Health Care Professionals: Using Antiviral Agents for Seasonal Influenza).

In general, antiviral drugs can be offered to anyone 1 year of age or older who wants to avoid and/or treat the flu.  People who are at high risk of serious complications from the flu may benefit most from these drugs.

Antiviral drugs can also be used to prevent influenza among people with weak immune systems who may not be protected after getting a flu vaccine or who haven’t been vaccinated. 

Remember, a flu vaccine is the first and best defense against seasonal flu, but antiviral drugs can be an important second line of defense to treat the flu or prevent flu infection.

Notes

This information is summarized from Prevention & Control of Influenza - Recommendations of the Advisory Committee on Immunization Practices (ACIP) 2008. MMWR 2008 Jul 17; Early Release:1-60. (Also available as PDF, 586K).

There are other antiviral drugs (amantadine and rimantadine), but they are not recommended for use in the United States during the 2008-09 flu season because many flu viruses are resistant to these drugs. When viruses are resistant to drugs, the drugs don’t work or don’t work as well.

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