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Questions & Answers

Antiviral Drugs for Seasonal Flu

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Antiviral Drugs General Information

What are flu antiviral drugs?

Flu antiviral drugs are prescription drugs (pills, liquid, or inhaler) that decrease the ability of flu viruses to reproduce. While getting a flu vaccine each year is the first and most important step in protecting against flu, antiviral drugs are a second line of defense in the prevention and treatment of flu.

What are the treatment benefits of flu antiviral drugs?

For treatment, antiviral drugs should be started within 2 days after becoming sick. When used this way, these drugs can reduce the severity of flu symptoms and shorten the time you are sick by 1 or 2 days.

How effective are antiviral drugs at preventing the flu?

When used to prevent the flu, antiviral drugs are about 70% to 90% effective against susceptible viruses (i.e. viruses that are not resistant to the antiviral medication). It’s important to remember that flu antiviral drugs are not a substitute for getting a flu vaccine.

Antiviral Drugs for the 2008-09 Season

What flu antiviral drugs does CDC recommend for use in the United States for the 2008-09 season?

There are four flu antiviral drugs approved for use in the United States. The four antiviral drugs are oseltamivir (brand name Tamiflu ®); zanamivir (brand name Relenza ®); amantadine (Symmetrel®, generic); and rimantadine (Flumadine®, generic). CDC has issued interim guidance for health care providers on which antiviral drugs to use during the 2008-09 flu season.

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. 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

Who should take antiviral drugs for flu?

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 who wants to avoid and/or treat the flu. People who are at high risk of serious flu-related complications may benefit most from these drugs. Also, close contacts of people with the flu who are at high risk of serious flu-related complications may benefit from antiviral drugs to protect them from getting sick.

How can I get an antiviral drug for flu?

Antiviral drugs must be prescribed by a health care professional.

How long should antiviral drugs be taken?

The length of time antiviral drugs should be taken depends on how they are being used. To prevent flu, antiviral drugs should be taken for as long as flu viruses are circulating in a given setting. To treat flu, oseltamivir and zanamivir are taken for 5 days. Treatment for flu with amantadine and rimantadine should be stopped 3-5 days after beginning treatment or within 24-48 hours after the disappearance of signs and symptoms. See Treatment & Prevention: Influenza Antiviral Drugs for more information.

What side effects can occur with flu antiviral drugs?

Side effects differ for each drug. If an antiviral drug has been prescribed for you, ask your doctor to explain how to use the drug and any possible side effects. Health care professionals prescribing flu antiviral drugs should alert patients about adverse events that can occur. For more information about side effects, see Antiviral Drugs: Summary of Side Effects.

Can flu antiviral drugs help with other illnesses such as the common cold?

No. Flu antiviral drugs only work against flu viruses. They will not help reduce symptoms from the common cold or any other flu-like illnesses caused by viruses other than flu viruses. Many other viruses cause winter illnesses besides the flu.

Can people who are not in a high-risk group receive antiviral drugs?

Yes. Consult with your doctor if you are ill or have been exposed to influenza to determine if you should take antiviral drugs.

Can antiviral drugs be helpful for people unable to take the flu vaccine?

Yes. CDC and ACIP recommend use of antiviral drugs for people allergic to eggs (which can cause them to have an allergic reaction to the vaccine) or for people who previously have encountered complications from Guillain-Barre syndrome (GBS) associated with influenza vaccination. In addition, taking antiviral drugs may be recommended among persons that may not have a good immune response to the flu vaccine.

Should people use antiviral drugs before or after receiving the live attenuated influenza vaccine (LAIV) called FluMist®?

LAIV is one of two types of flu vaccine. It is given as a nasal spray and contains weakened, live virus. Flu antiviral drugs taken from 48 hours before through 2 weeks after getting LAIV can lower or prevent the vaccinated person from responding to the vaccine and the person may not get immune protection from the vaccine.

Antiviral drugs can be taken with the inactivated (i.e. killed) flu vaccine.

Can antiviral drugs be given even if a person is not tested for flu or if a flu test does not indicate that they have influenza?

Yes. For individual patients, influenza testing is not required for antiviral drugs to be prescribed. Testing is done based on health care provider recommendations.

Tests are available that can test for flu viruses in as little as 30 minutes or less. Flu testing can be used to rapidly confirm the flu as the cause of outbreaks. However, results from these rapid tests are not 100% accurate; the test may indicate that a person does not have influenza even though they really do have the flu. So, other information in addition to influenza test results, if done, need to be factored into decisions about using antiviral drugs. One consideration will be information about influenza circulating in the community in general.

Can influenza antiviral drugs be used in pregnant women?

Antiviral drugs are "Pregnancy Category C" medications, indicating that no studies have been conducted to assess the safety of these drugs for pregnant women. No safety problems have been identified for use of these medications for pregnant women However, because of the unknown effects of these drugs on pregnant women and infants who were exposed before birth, these drugs should be used during pregnancy only if the potential benefit justifies the potential risk to the unborn child. Physicians considering using one of these drugs in a pregnant woman should consult that drug package insert.

Oseltamivir (Tamiflu®) & Zanamivir (Relenza®)

What are oseltamivir (Tamiflu®) and zanamivir (Relenza®)?

Tamiflu® and Relenza® are antiviral drugs known as neuraminidase inhibitors that fight against both influenza A and B viruses.

Oseltamivir (brand name Tamiflu ®)is approved to both treat and prevent flu in people one year of age and older.

Zanamivir (brand name Relenza ®) is approved to treat flu in people 7 years and older and to prevent flu in people 5 years and older.

What are the possible side effects of oseltamivir (Tamiflu®)?

Tamiflu® has been in use since 1999. The most common side effects are nausea and vomiting which usually happen in the first 2 days of treatment. Taking Tamiflu® with food can reduce the chance of getting these side effects. The FDA now requires that neuraminidase inhibitors have information in the package labeling that warns that people with the flu, mostly children, may be at an increased risk of self-injury and confusion shortly after taking and should be closely monitored for signs of unusual behavior. This precaution was added after the FDA received post marketing reports (mostly from Japan) about persons (primarily among children and adolescents) who had purposefully injured themselves or been delirious while using neuraminidase inhibitors to treat influenza. Most reports were among persons using Tamiflu. The reports appear to be uncommon. For more information, visit the Food & Drug Administration's MedWatch page.

What should be done if complications while taking oseltamivir (Tamiflu®) occur?

Contact a health care professional immediately if someone taking Tamiflu® shows any signs of unusual behavior.

What are the possible side effects of zanamivir (Relenza®)?

Relenza® has been in use since 1999. The most common side effects are diarrhea, nausea, sinusitis, runny or stuffy nose, bronchitis, cough, headache, dizziness, and ear, nose and throat infections. Some persons, mostly those who already had a chronic lung disease such as asthma, have reported serious breathing problems such as wheezing or shortness of breath after taking Relenza® (zanamivir). In rare cases, people have had an allergic reaction to the drug, including rashes and edema (a build up of fluid in body-tissue) of the face and throat.

The FDA now requires that neuraminidase inhibitors have information in the package labeling that warns that people with the flu, mostly children, may be at an increased risk of self-injury and confusion shortly after taking and should be closely monitored for signs of unusual behavior. This precaution was added after the FDA received post marketing reports (mostly from Japan) about persons (primarily among children and adolescents) who had purposefully injured themselves or been delirious while using neuraminidase inhibitors to treat influenza. For more information, visit the Food & Drug Administration's MedWatch page.

Who is at risk for complications from zanamivir (Relenza®)?

Persons with chronic lung diseases such as asthma or chronic obstructive pulmonary disease are not recommended to use Relenza® (zanamivir), as some patients have reported difficulty breathing after inhaling the drug.

What should be done if complications while taking zanamivir (Relenza®) occur?

If you have side effects while taking Relenza® talk to your health care provider immediately.

Amantadine (Symmetrel®) & Rimantadine (Flumadine®)

What are amantadine (Symmetrel®) and rimantadine (Flumadine®)?

Amantadine (Symmetrel®) and rimantadine (Flumadine®) are antiviral drugs known as adamantanes that fight against influenza A viruses, but not influenza B viruses.

Amantadine (Symmetrel®) is approved to treat and prevent flu in people older than 1 year.
Rimantadine (Flumadine®) is approved to prevent flu among people older than 1 year. It is approved to treat flu infections in people 13 and older.

What are the possible side effects of amantadine (Symmetrel®) and rimantadine (Flumadine®)?

Side effects of amantadine and rimantadine can include central nervous system (CNS) side effects such as nervousness, anxiety, difficulty concentrating, and lightheadedness, and gastrointestinal side effects like nausea and loss of appetite. CNS side effects happen more often among persons taking amantadine than among persons taking rimantadine. Among some other persons with long-term illnesses, more serious side effects, such as delirium, hallucinations, agitation, and seizures, can occur. Side effects usually diminish and disappear after 1 week.

What should be done if possible complications while taking amantadine (Symmetrel®) or rimantadine (Flumadine®) occur?

If you experience side effects, talk to your health care provider immediately.

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