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Content on this page was developed during the 2009-2010 H1N1 pandemic and has not been updated.

  • The H1N1 virus that caused that pandemic is now a regular human flu virus and continues to circulate seasonally worldwide.
  • The English language content on this website is being archived for historic and reference purposes only.
  • For current, updated information on seasonal flu, including information about H1N1, see the CDC Seasonal Flu website.

2009 H1N1 and Seasonal Flu: What You Should Know About Flu Antiviral Drugs

The Public Health Emergency determination for 2009 H1N1 Influenza expired on June 23, 2010, terminating Emergency Use Authorizations issued during the pandemic, including some related to antiviral medications.

October 8, 2009, 2:00 PM ET

What are antiviral drugs?

Antiviral drugs are prescription medicines (pills, liquid or an inhaled powder) that fight against the flu in your body. While CDC recommends flu vaccine as the first and most important step in preventing flu, antiviral drugs are a second line of defense against the flu. Antiviral drugs are not sold over-the-counter and are different from antibiotics. You can only get them if you have a prescription from your doctor or health care provider.

What antiviral drugs are recommended this flu season?

There are two antiviral drugs recommended by CDC this season. The brand names for these are Tamiflu® and Relenza® (The generic names for these drugs are oseltamivir and zanamivir). Tamiflu® is available as a pill or liquid and Relenza® is a powder that is inhaled.

Who should take antiviral drugs?

It’s very important that antiviral drugs be used early to treat flu in people who are very sick (for example people who are in the hospital) and people who are sick with flu and have a greater chance of getting serious flu complications (see box). Other people may also be treated with antiviral drugs by their doctor this season. Most healthy people with flu, however, do not need to be treated with antiviral drugs.

What are the benefits of antiviral drugs?

When used for treatment, these drugs can make you feel better and shorten the time you are sick by 1 or 2 days. They can also prevent serious flu complications.

When should antiviral drugs be taken for treatment?

Studies have shown that flu antiviral drugs work best for treatment if they are started within 2 days of getting sick. There may still be benefit in treating people with antiviral drugs even after two days have gone by, especially if the sick person has a greater change of serious flu complications (see box) or if the person has certain symptoms (such as shortness of breath, chest pain/pressure, dizziness, or confusion) or is in the hospital because of the flu.

How long should antiviral drugs be taken?

To treat flu, Tamiflu® and Relenza® are usually taken for 5 days, although people hospitalized with flu may need the medicine for longer than 5 days.

Can children take antiviral drugs?

Yes. Children can take antiviral drugs.

  • Tamiflu® is FDA-approved for use in children 1 year of age or older. For the 2009 H1N1 flu emergency, FDA has authorized Tamiflu® to be used for treatment or prevention of 2009 H1N1 influenza infections in children younger than 1 year old. Tamiflu® can come in liquid for children or in capsules. If your doctor prescribes Tamiflu® capsules for your child and they cannot swallow capsules, you can open the capsule and mix the contents with regular or sugar-free chocolate syrup and give that mixture to your child.
  • Relenza® is FDA-approved for treatment in children 7 years of age and older, but only for people without breathing problems (such as asthma) or heart disease. It is an inhaled powder that comes in a disk inhaler.

Can pregnant women take antiviral drugs?

Yes. At this time, there are no studies suggesting harm to a pregnant woman or her developing baby if she takes antiviral medicine.  The flu can cause severe illness and even death in pregnant women. Taking antiviral medicine can help prevent these complications. At this time, Tamiflu® is the best medicine to treat pregnant women who have 2009 H1N1 flu.

What are the side effects of antiviral drugs?

Side effects differ for each antiviral drug.

Tamiflu® has been in use since 1999. The most common side effects are nausea or vomiting which usually happen in the first 2 days of treatment. Taking Tamiflu® with food can reduce the chance of getting these side effects.

Relenza® has been in use since 1999. The most common side effects are dizziness, sinusitis, runny or stuffy nose, cough, diarrhea, nausea, or headache. Relenza® may also cause wheezing and trouble breathing in people with lung disease.

Confusion and abnormal behavior leading to injury has been observed rarely in people with the flu, mostly children, who were treated with Tamiflu® or Relenza®.  Flu can also cause these behaviors. But persons taking these drugs should be closely monitored for signs of unusual behavior or problems thinking clearly. This behavior should be immediately reported to a health care provider.

If an antiviral drug has been prescribed for you, ask your doctor to explain how to use the drug and any possible side effects.

People who have a greater chance of serious flu complications can include:

  • Children younger than 2 years old*
  • Adults 65 years and older
  • Pregnant women and women up to 2 weeks from end of pregnancy
  • People with certain chronic medical conditions (such as asthma, heart failure, chronic lung disease) and people with a weak immune system (such as diabetes, HIV)
  • People younger than 19 years of age who are receiving long-term aspirin therapy

*It is also important to know that children who are 2 years though 4 years of age also have a higher rate of complications compared to older children, although the risk for these children is lower than the risk for children younger than 2 years.

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