What is zanamivir, and how does it work (mechanism of action)?

Zanamivir is an inhaled drug that is used for treating and preventing influenza (the "flu"). Zanamivir decreases the spread of influenza A and B viruses, the viruses responsible for the flu. It does this by blocking the action of neuraminidase, an enzyme produced by the viruses that enables the viruses to spread from infected cells to healthy cells. By preventing the spread of virus from cell to cell, the symptoms and duration of influenza infection are reduced. On average, zanamivir reduces the duration of symptoms by one day if treatment is started within forty-eight hours after symptoms begin.

  • The FDA approved zanamivir in July 1999.
  • The brand name for Zanamivir is Relenza.
  • Zanamivir is available over-the-counter (OTC).

What are the side effects of zanamivir?

The most frequent side effects are:

Other important side effects include:

Patients with respiratory diseases may experience breathing problems when treated with zanamivir due to irritation of the breathing tubes by the particles from the inhaler. If breathing problems occur, zanamivir should be discontinued. Patients who have asthma or other breathing problems that make them sensitive to inhaled particles should have a fast acting, inhaled bronchodilator available to treat any breathing problem that may occur when zanamivir is used.


Which illness is known as a viral upper respiratory tract infection? See Answer

What is the dosage for zanamivir?

Zanamivir is administered by oral inhalation. The recommended dose is two inhalations (5 mg per inhalation) twice daily (approximately 12 hours apart) for five days. Two doses (separated by at least two hours) should be administered on the first day of treatment. For best results, treatment should begin as soon as symptoms develop. The recommended dose for prevention of influenza in a household setting is 10 mg once daily for 10 days. The recommended dose for preventing influenza in a community setting is 10 mg once daily for 28 days.

Which drugs or supplements interact with zanamivir?

Zanamivir potentially may interfere with the action of injections of live attenuated flu vaccine because zanamivir prevents viral replication. Therefore, live attenuated flu vaccine should not be administered from 2 weeks before to 48 hours after administration of zanamivir. Trivalent inactivated influenza vaccine can be administered while using zanamivir.

Is zanamivir safe to take if I'm pregnant or breastfeeding?

The Centers for Disease Control (CDC) states that pregnancy is not a contraindication for use of zanamivir in pregnant women because the benefits outweigh the risks.

It is not known whether zanamivir is excreted in breast milk. However, the CDC recommends that nursing women who develop flu after child birth should be treated with antiviral drugs.

What else should I know about zanamivir?

What preparations of zanamivir are available?

Inhalation Powder: 5 mg per inhalation

How should I keep zanamivir stored?

Zanamivir should be stored at room temperature, 15 C to 30 C (59 F to 86 F)


Zanamivir (Relenza) is a prescription inhaled medication used to treat and prevent the flu (influenza)including H1N1 (swine flu). Zanamivir (Relenza) decreases and suppresses the spread of influenza A and B viruses (to include H1N1 or swine flu. Side effects, drug interactions, warnings and precautions, and patient information should be reviewed prior to taking any medication.

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See more info: zanamivir on RxList
Medically reviewed by John P. Cunha, DO, FACOEP

Relenza FDA Prescribing Information. What You Should Know About Flu Antiviral Drugs. September 17, 2013.