New Flu Drugs Neuraminidase Inhibitors, NIAID Fact Sheet: NIAID


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Article title: New Flu Drugs Neuraminidase Inhibitors, NIAID Fact Sheet: NIAID
Conditions: Flu
Source: NIAID
December 2000

The New Flu Drugs: Neuraminidase Inhibitors

In 1999, the Food and Drug Administration (FDA) approved two new drugs to fight the flu: zanamivir (Relenza®) and oseltamivir (Tamiflu®), the first of a new class of antiviral drugs called neuraminidase inhibitors.

How do they work?

The surfaces of influenza viruses are dotted with neuraminidase proteins. Neuraminidase, an enzyme, breaks the bonds that hold new virus particles to the outside of an infected cell. Once the enzyme breaks these bonds, this sets free new viruses that can infect other cells and spread infection. Neuraminidase inhibitors block the enzyme's activity and prevent new virus particles from being released, thereby limiting the spread of infection.

Are they effective against any kind of influenza virus?

Although zanamivir and oseltamivir inhibit both influenza A and B viruses, more information is available on the effectiveness of these drugs against influenza A viruses. (Note - the previously approved antiviral flu drugs, rimantadine and amantidine, are effective only against type A influenza - see below.)

Who should consider using these drugs?

Zanamivir is approved only for treating uncomplicated influenza virus infection in people 7 years of age and older who have not had symptoms for more than two days.

Oseltamivir is approved for treating uncomplicated influenza virus infection in people 18 years of age or older who have not had symptoms for more than two days. A liquid suspension of oseltamivir is approved for treating acute illness in children who are 1 year of age and older who have been symptomatic for no more than two days. Oseltamivir also is approved for preventing influenza A and B in people 13 years and older.

Currently, oseltamivir is the only neuraminidase inhibitor approved to prevent the flu.

How are these drugs administered?

You orally inhale zanamivir, available as a dry powder, using a device known as a "Diskhaler." The recommended dosage is two inhalations twice a day, morning and night, for five days. Oseltamivir, available as a pill, is taken twice daily for five days. A liquid suspension of oseltamivir can be taken by children or adults who cannot swallow a capsule.

How much do they help?

Studies have shown that both oseltamivir and zanamivir can reduce the duration of flu symptoms by one day if taken within two days of the onset of the illness. There is no information about how effective these drugs are if treatment is started more than two days after onset of flu symptoms. When taken as directed to prevent the flu, oseltamivir can significantly reduce your chance of getting the disease if there is a flu outbreak in your family or community.

What other benefits might they have?

Neither zanamivir nor oseltamivir has been shown to effectively prevent serious influenza-related complications such as bacterial or viral pneumonia. However, studies of the use of zanamivir in families and in nursing homes at risk for influenza infection resulted in the reduced use of antibiotics, which are frequently prescribed to treat these serious complications.

What about side effects?

The neuraminidase inhibitors generally cause fewer side effects than the older flu drugs. The most common side effects seen with oseltamivir are nausea and vomiting. In some people, zanamivir can cause wheezing or serious breathing problems that need prompt treatment (see below). The other most common side effects seen with zanamivir include headache and diarrhea. Your health care provider or pharmacist can discuss with you a more complete list of possible side effects.

Should certain people not take these drugs?

People allergic to these drugs or their ingredients should not take them.

Zanamivir generally is not recommended for people with chronic respiratory diseases such as asthma or chronic obstructive pulmonary disease. In clinical studies, some patients with mild or moderate asthma or chronic obstructive pulmonary disease had bronchospasm (wheezing) after taking zanamivir. If you have an underlying respiratory disease and have been prescribed zanamivir, your health care provider should instruct you to have a fast-acting inhaled bronchodilator available for use when taking the drug.

The dosage of oseltamivir may need to be adjusted if you have any type of kidney disease.

Neither drug is generally recommended for use during pregnancy or nursing, as no information is available about the effects of these drugs on the unborn child because these drugs have not been evaluated in pregnant women.

In laboratory and in limited clinical studies, there have been no reported interactions of the neuraminidase inhibitors with other drugs.

For complete safety information about these drugs, talk with your pharmacist or health care provider.

Can influenza viruses develop resistance to these drugs?

Laboratory studies have shown that influenza A and B viruses can develop resistance to zanamivir and oseltamivir. Surveillance for neuraminidase inhibitor-resistance has been initiated.

What other neuraminidase inhibitors are in the pipeline?

A third neuramindase inhibitor, known only as RWJ-270201, is being developed by R.W. Johnson Pharmaceutical Research Institute (a Johnson and Johnson company) and BioCryst Pharmaceuticals (Birmingham, Alabama). It is currently being evaluated in Phase I and II clinical trials.

What other drugs are approved for influenza?

In 1976, amantadine was approved by the FDA to both treat and prevent influenza type A in adults. Rimantadine–a derivative of amantadine–was similarly approved in 1993. These two drugs are active against influenza A viruses but not against influenza B viruses. These compounds inhibit the activity of the influenza virus M2 protein, which forms a channel in the virus membrane. As a result, the virus cannot replicate after it enters a cell. The FDA does recommended daily doses for amantadine and rimantadine treatment and prophylaxis in different age groups; however, the use of amantadine and rimantadine among children younger than one year old has not been adequately evaluated.

So which anti-flu drug should I take?

No study to date has directly compared the effectiveness of zanamivir, oseltamivir, amantadine, and rimantadine for the treatment of influenza A. The available information suggests that these four drugs are similarly effective in reducing the duration of uncomplicated acute illness due to influenza A. Zanamivir and oseltamivir differ from amantadine and rimantadine in terms of their side effects and cost. Use of amantadine, and to a lesser extent rimantadine, has been associated with side effects including tremors, excitability, insomnia, dizziness, mood change, muscle movement problems, psychosis, and fatigue. These side effects have not been associated with zanamivir or oseltamivir. On the other hand, zanamivir and oseltamivir are currently significantly more expensive than either rimantadine or amantadine. All four drugs are available by prescription only, and it is best to consult with your health care provider to determine what drug might be best for you.

Since these drugs are available, do I still need a flu shot?

Neither the neuraminidase inhibitors nor the older flu drugs are a substitute for the flu shot. The flu shot can provide season-long protection against influenza A and B and more effectively prevent you from spreading the virus to others.



NIAID is a component of the National Institutes of Health (NIH). NIAID supports basic and applied research to prevent, diagnose, and treat infectious and immune-mediated illnesses, including HIV/AIDS and other sexually transmitted diseases, tuberculosis, malaria, autoimmune disorders, asthma and allergies.

Prepared by:
Office of Communications and Public Liaison
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892

Public Health Service
U.S. Department of Health and Human Services



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