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Antiviral Drugs & The Flu

By the Center for Disease Control
October 7, 2004

• Use of Antiviral Drugs for Flu
• Antiviral Drugs for High Risk People
• Who Should Get Antivirals?
• Antiviral Drugs: Summary of Side Effects
• Links, Information, & Resources
• Questions & Answers: Breastfeeding and the Flu
• Download PDF version formatted for print (95 KB/2 pages)

Three antiviral drugs (amantadine, rimantadine, and oseltamivir) are approved and commercially available for use in preventing flu. 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 for preventing illness in healthy adults.

Four antiviral drugs (amantadine, rimantadine, zanamavir and oseltamivir) have been approved for treatment of the flu. If taken within 2 days of getting sick, these drugs can reduce the symptoms of the flu and shorten the time you are sick by 1 or 2 days. They also can make you less contagious to others. All of these drugs must be prescribed by a doctor and taken for 5 days. Antiviral drugs are effective only against influenza viruses. They will not help the symptoms associated with the common cold or many other flu-like illnesses caused by viruses that circulate in the winter.

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. Your doctors will help decide whether you should get antivirals and which one you should get.

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Use of Antiviral Drugs

Antiviral drugs are most often used to control flu outbreaks in institutions, for example in nursing homes, or in hospital wards, where people at high risk (see below) for complications from flu are in close contact with each other. Antivirals also have been used on cruise ships or similar settings to control outbreaks of the flu.

In the event of an outbreak, public health practice is to combine the use of flu vaccine and antivirals. In a nursing home during an outbreak, for example, residents and staff are given the flu vaccine and antivirals to prevent flu until the vaccine takes effect (about 2 weeks). This practice continues as long as influenza is occurring in that setting.

Doctors also can prescribe antivirals for flu to people not living in institutional settings, but treatment must begin within 2 days of the onset of symptoms for it to be effective. Also, while all antivirals lessen the symptoms of illness and shorten the duration of illness, only 1 (oseltamivir) has been shown in a study to reduce some complications requiring antibiotics.

When considering antivirals, it’s important to remember that most healthy people recover from the flu without complications.

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Antiviral Drugs for People at High Risk for Complications

Some people are considered to be at high risk from complications of flu. This includes

• People 65 years of age and older
• Children 6-23 months of age*
• People of any age with chronic medical conditions (for example, heart or lung disease, diabetes)
• Pregnant women

Note that none of the antivirals are approved for use in children less than 1 year of age.

*Children 6-23 months of age are at increased risk for influenza-related hospitalization.

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Who Should Get Antiviral Drugs

For Treatment: If you get sick with flu-like symptoms this season, your doctor first may give you a test to find out whether you have influenza. (Symptoms of flu 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 things before making a treatment decision, such as your risk for complications from flu.

For Prevention: In the event of a flu outbreak in a home, institution, or community, your doctor may choose to give antivirals to you as a preventive measure, especially if you are at high risk for complications from the flu. Also, if you are in close contact with someone who is considered at high risk for complications from flu, you may be given antiviral drugs to prevent passing flu to the high-risk person.

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Antiviral Drugs: Summary of Side Effects - Amantadinean d Rimantadine

Among some healthy adults and children, side effects 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.

Zanamivir

This drug is inhaled and can cause side effects, especially in those with asthma or other chronic lung disease. Decreased respiratory function and bronchospasm have been reported with use of zanamivir. Zanamivir is generally not recommended for use in persons with underlying lung disease such as asthma and chronic obstructive pulmonary disease. Other side effects reported by less than 5% of those who have used this drug are diarrhea, nausea, sinusitis, nasal infections, bronchitis, cough, headache, and dizziness.

Oseltamivir

The side effects reported most often in those people who took this drug were gastrointestinal (i.e., nausea and vomiting). Nausea and vomiting may be less severe if oseltamivir is taken with food.
Click on the link below for more detailed information about antiviral drugs for influenza:
Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP) Morbidity and Mortality Weekly Report (MMWR), April 25, 2003 / Vol. 52 / No. RR-08.

Click on the link below for more detailed information about antiviral drugs for influenza:
Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP) Morbidity and Mortality Weekly Report (MMWR), April 25, 2003 / Vol. 52 / No. RR-08.

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Antiviral Drug Links

U.S. Food and Drug Administration (FDA) website, antiviral drugs for influenza pages:

• Oseltamivir*
• Zanamivir*

Antiviral Information

• Information for Healthcare Providers (exit site)
• "Prevention and Control of Influenza, Recommendations of the Advisory Committee on Immunization Practices (ACIP),"
      Morbidity and Mortality Weekly Report (MMWR), April 25, 2003/ Vol. 52 / No. RR-08

Resources

Influenza Information by Telephone and U.S. Mail
If you do not have access to the Internet, you may call the toll-free number 888-CDC-FACTS (888-232-3228). Once the system has answered, you may bypass other disease information not specific to influenza by pressing options 2, then 2, then 1, then 3, then 4, then 3, and then 3. At the prompt that asks if you want a current copy of the ACIP recommendations, please leave your name and address, and the document will be mailed to you.

*Note: This link leads outside the CDC site to another federal agency or CDC partner site. Any links from these sites to nonfederal organizations' links do not constitute an endorsement of these organizations or their programs by CDC or the federal government, and none should be inferred. CDC is not responsible for the content of the individual organization Web pages found at these links. The link will open the page in a new browser window.

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Questions & Answers: Breastfeeding and the Flu

January 12, 2004

What precautions should I take to protect my baby if I have the flu and am breastfeeding?

Nursing mothers who have the flu should take the following steps before every breastfeeding and when handling their infants:

•  Put on a surgical mask. (You can purchase surgical masks in most drugstores.)

•  Wash your hands thoroughly, and dry them with a clean towel or paper towels. (Information about hand hygiene can be found at: www.cdc.gov/od/oc/media
/pressrel/fs021025.htm.)

•  Leave your breasts covered until you have put on a surgical mask and washed your hands. You can then begin breastfeeding.

•  Do not remove your surgical mask until you are done breastfeeding and you have put your baby down.

How long should I continue to take these precautions?

Continue to take these precautions at every feeding for 7 days following the first day of your illness (when you first noticed flu symptoms).

Influenza Antiviral Drugs and Related Information

• Introduction
• Influenza Vaccine Information   
• Drug Information  
• Influenza Information from Other Web Sites
• Contacts For More Information

Introduction

The term "influenza" refers to illness caused by influenza virus. This is commonly also called "flu", but many different illnesses cause "flu-like" systemic and respiratory symptoms such as fever, chills, aches and pains, cough, and sore throat. In addition, influenza itself can cause many different illness patterns, ranging from mild common cold symptoms to typical "flu" to life-threatening pneumonia and other complications, including secondary bacterial infections.

This article contains links to several sources of general information about influenza. Because vaccination is the primary means of preventing and controlling influenza, links related to influenza vaccine are listed first, followed by links related to antiviral drugs that have been approved in the United States for influenza. After the vaccine and antiviral drug links, there is a list of web sites that provide additional influenza information from United States government agencies and the World Health Organization, and a list of contacts for further inquiries.

Information provided in this article may change frequently, and should not be used as a substitute for individual evaluation by a health care provider, or as the primary means of diagnosing influenza or determining treatment.

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Influenza Vaccine Information

Influenza vaccine is the principal method of preventing and controlling influenza. The following links provide information on general uses of vaccines and on current supply issues.

• Center for Biologics Evaluation and Research (CBER). This web page links to information on influenza virus vaccine.
• Influenza (Flu): Protect Yourself and Your Loved Ones. Comprehensive flu information from the Centers for Disease Control.
• Centers for Disease Control and Prevention:  Prevention and Control of Influenza:  Recommendations of the Advisory Committee on Immunization Practices  (Issued May 28, 2004). 
• Centers for Disease Control and Prevention - National Immunization Program.  Influenza Vaccine: What you need to know.   This consumer pamphlet contains basic vaccine questions and answers.

Drug Information

Uncomplicated influenza gets better with or without treatment, but may cause substantial discomfort and limitation of activity before getting better. Complications of influenza can include bacterial infections, viral pneumonia, and cardiac and other organ system abnormalities. People with chronic medical conditions may have increased risk of complications when they get influenza. Many other diseases, including serious infections such as rapidly progressive bacteremias, may start with symptoms that resemble influenza and may need to be considered in treatment decisions.

Many people with uncomplicated influenza use over-the-counter medicines to help lessen their symptoms. Antiviral drugs can also help to reduce the time it takes for symptoms to improve in uncomplicated illness caused by influenza virus. Recent increases in the number and promotion of antiviral drugs for influenza have increased interest in the role of specific antiviral drugs for this condition.

Complications of influenza, and other illnesses that resemble influenza, may require different treatment and may need urgent medical attention. Use of antiviral drugs does not eliminate the risk of complications, and some complications (as well as other medical conditions that could be confused with influenza) can be life-threatening. In addition, influenza viruses can become resistant to specific anti-influenza antiviral drugs, and all of the drugs have side effects. Therefore, if you have new symptoms during treatment, or your symptoms persist or get worse during treatment, you should see your health care provider.

The following links lead to information such as trade names, package inserts, and other material related to the four antiviral drugs currently approved by FDA to treat acute, uncomplicated influenza. Two related drugs, amantadine (approved 1966; Trade Name Symmetrel, also available as generic Amantadine Hydrochloride) and rimantadine (approved 1993; Trade Name Flumadine, also available as generic Rimantadine Hydrochloride), are approved for treatment and prevention of influenza A.  Two newer drugs, zanamivir (approved 1999; Trade Name Relenza) and oseltamivir phosphate (approved 1999; Trade Name Tamiflu), are approved for treatment of acute uncomplicated illness due to influenza A and B.  Oseltamivir has been approved also for preventive use, while zanamivir is approved only for treatment.  Approved ages, doses, and uses in children are different for each drug, so the individual package inserts should be checked for this information. The anti-influenza antiviral drugs are not a substitute for vaccine and are used only as an adjunct to vaccine in the control of influenza.

The antiviral drug information covers the side effects of each drug. Because some side effects can be serious and because viruses may become resistant when antiviral drugs are used indiscriminately, decisions on the use of these drugs should be based on individual evaluations of risk and benefit.

• Symmetrel (amantadine). Approval, review, and labeling information from Drugs@FDA.
• Flumadine (rimantadine). Approval, review, and labeling information from Drugs@FDA.
• Relenza (zanamivir). Approval, review, and labeling information from Drugs@FDA, plus consumer information, and Dear Health Professional letter regarding updated safety information. 
• Tamiflu (oseltamivir phosphate). Approval, review, and labeling information from Drugs@FDA, plus consumer information.
• Electronic Orange Book  This resource can be searched for holders of approved or discontinued marketing applications, especially for drugs that may have more than one source of generic preparations.
• Centers for Disease Control and Prevention:  Prevention and Control of Influenza:  Recommendations of the Advisory Committee on Immunization Practices  (Issued May 28, 2004). 
• Public Health Advisory: Safe and Appropriate Use of Influenza Drugs. (Issued 1/12/2000).  Health professionals, especially prescribers, are reminded of important clinical decisions that need to be made when considering use of anti-viral drugs for signs and symptoms of influenza.
• Talk Paper: FDA Reminds Prescribers of Important Considerations before Prescribing Flu Drugs (Issued 1/12/00).
• Letter from the Glaxo Wellcome, Inc.on Relenza (zanamivir for inhalation). (Issued 7/2000). Optional format: PDF.  This letter notifies health professionals of important revisions to the safety labeling for Relenza. The labeling has been revised to more clearly reflect that serious respiratory adverse events have been reported in patients with or without known underlying respiratory disease, and to incorporate additional updated safety information.
• A Look at the 2003-2004 Flu Season.   March-April, 2004 FDA Consumer magazine article on influenza prevention and treatment. 

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Influenza Information from Other Web Sites

• World Health Organization (WHO) Influenza Information.  This web page provides links to WHO fact sheets, plus global surveillance and outbreak information.
• National Institute of Allergy and Infectious Diseases. NIAID's flu and cold publications page.
• National Vaccine Program Office  Influenza pandemics can occur when a novel strain of virus causes an epidemic that spreads over a wide geographic area and affects an exceptionally high proportion of the population. This web site contains information about influenza, pandemics, and the Draft Pandemic Influenza Preparedness and Response Plan.

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Contacts for More Information

Information on availability of influenza vaccine:
Food and Drug Administration
Center for Biologics Evaluation and Research
Office of Communication, Training & Manufacturers Assistance
301-827-1800.  Fax: 301-827-3843
octma@cber.fda.gov

Information on drugs used to treat influenza:
Food and Drug Administration
Center for Drug Evaluation and Research
Drug Information Line
888-info-FDA or 301-827-4573.  Fax: 301-827-4577
druginfo@cder.fda.gov

Information on influenza prevention and control:
Centers for Disease Control and Prevention
Public Inquiries Office
800-311-3435 or 404-639-3311.  Fax: 770-488-4995
inquiry@cdc.gov

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Influenza virus is responsible for acute upper respiratory disease, usually accompanied by fever and myalgia. Virions are usually roughly spherical and about 200nm in diameter. The envelope contains rigid "spikes" of haemagglutinin and neuraminidase which form a characteristic halo of projections around negatively stained virus particles. Flu virus photos - University of Cape Town