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Generic name: zanamivir (zan AM i vir)
Brand name: Relenza
Dosage forms: inhalation powder (5 mg)
Drug class: Inhaled anti-infectives, Neuraminidase inhibitors

Medically reviewed by on Sep 15, 2021. Written by Cerner Multum.

What is zanamivir?

Zanamivir is an antiviral medicine that blocks the actions of viruses in your body.

Zanamivir is used to treat flu symptoms caused by influenza virus in people who have had symptoms for less than 2 days. Zanamivir may also be given to prevent influenza in people who may be exposed but do not yet have symptoms. Zanamivir will not treat the common cold.

Zanamivir should not be used in place of getting a yearly flu shot. The Centers for Disease Control recommends an annual flu shot to help protect you each year from new strains of influenza virus.

Zanamivir may also be used for purposes not listed in this medication guide.


Some people using zanamivir have had sudden unusual changes in mood or behavior, most often in children. It is not certain that zanamivir is the exact cause. Even without using zanamivir, anyone with influenza can have neurologic or behavioral effects that may lead to confusion or hallucinations. Call your doctor right away if the person using zanamivir has any signs of unusual thoughts or behavior.

Before taking this medicine

You should not use this medicine if you are allergic to zanamivir or to lactose (milk sugar).

Do not use zanamivir to treat flu symptoms in a child younger than 7 years old. Children as young as 5 years old may use zanamivir to prevent flu symptoms.

Tell your doctor if you have ever had:

It is not known whether this medicine will harm an unborn baby. However, getting sick with influenza during pregnancy can cause complications leading to birth defects, low birth weight, preterm delivery, or stillbirth. Your doctor will decide whether you should use zanamivir if you are pregnant.

The Centers for Disease Control and Prevention (CDC) recommends that pregnant women may receive a yearly flu vaccine to prevent influenza. Zanamivir is not to be used in place of the yearly flu shot.

It may not be safe to breast-feed while using this medicine. Ask your doctor about any risk.

How should I use zanamivir?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Use the medicine exactly as directed.

Start taking zanamivir as soon as possible after flu symptoms appear, such as fever, chills, muscle aches, sore throat, and runny or stuffy nose.

Read and carefully follow any Instructions for Use provided with your medicine. Ask your doctor or pharmacist if you do not understand these instructions.

Zanamivir is packaged in disk-shaped foil packs that contain 4 blisters of medicine. These disks are placed into a device called a DISKHALER that you will use to inhale the medicine. The device opens and loads a blister of zanamivir each time you use the inhaler.

To treat flu symptoms: Use 2 inhalations twice per day for 5 days. On the first day of treatment, space your doses at least 2 hours apart. On the following days, space your doses at least 12 hours apart.

To prevent flu symptoms: Use 2 inhalations every 24 hours for 10 to 28 days. Follow your doctor's instructions.

Do not use a nebulizer or ventilator to give zanamivir. Zanamivir inhalation powder should never be mixed with a liquid.

If you are scheduled to use a bronchodilator at the same time as zanamivir, use the bronchodilator first.

Use zanamivir for the full prescribed length of time, even if your symptoms quickly improve. Call your doctor if your symptoms do not improve, or if they get worse.

Store at room temperature away from moisture and heat. Throw away the DISKHALER after your treatment ends.

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What happens if I miss a dose?

Use the medicine as soon as you can, but skip the missed dose if your next dose is due in less than 2 hours. Do not use two doses at one time.

Call your doctor if you miss several doses.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What should I avoid while using zanamivir?

Do not use a nasal flu vaccine (FluMist) within 48 hours after taking zanamivir. zanamivir may interfere with the drug action of FluMist, making the vaccine less effective. Follow your doctor's instructions.

Zanamivir side effects

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Some people using zanamivir (especially children) have had sudden unusual changes in mood or behavior. It is not certain that zanamivir is the exact cause of these symptoms. Even without using zanamivir, anyone with influenza can have neurologic or behavioral symptoms. Call your doctor right away if the person using this medicine has:

  • sudden confusion;

  • trouble speaking;

  • tremors or shaking;

  • a seizure; or

  • hallucinations (hearing or seeing things that are not there).

Stop using zanamivir and call your doctor at once if you have wheezing or severe breathing problems, or if you feel like you might pass out.

Common side effects may include:

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What other drugs will affect zanamivir?

Other drugs may affect zanamivir, including prescription and over-the-counter medicines, vitamins, and herbal products. Tell your doctor about all your current medicines and any medicine you start or stop using.

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.