Sounds like 'za-NAM-i-vir'. Also known as Relenza®

Easy-to-read medicine information about zanamivir – what it is, how to take zanamivir safely and possible side effects.

Type of medicine Also called
  • Belongs to a group of medicines called anti-viral medicines
  • Relenza®

What is zanamivir?

  • Zanamivir is used to treat and prevent symptoms caused by the influenza (flu) virus.
  • It works by attacking the influenza virus and stopping it from multiplying in your body.
  • If you already have signs and symptoms of the flu, zanamivir helps to reduce symptoms such as fever, chills, stuffy nose, cough, sore throat, aches, and tiredness. It shortens the time to recover from the flu by 12 to 24 hours.
  • Zanamivir is most effective when it is started within an hour or two of the first symptoms of the flu, but it can still be effective after this time, as long as it is started within 48 hours of the first symptoms or within 36 hours for children.
  • Zanamivir may also be used to prevent the flu if you have been exposed to someone who already has the flu (such as a sick household member) or if there is a flu outbreak in the community.
  • To prevent influenza, zanamivir is most effective when it is started within 36 hours of exposure.
  • Zanamivir is not a substitute for the flu vaccine. Getting the flu vaccine is the best way to protect against getting the flu and to control the spread of the flu.
  • Zanamivir is available as an inhalation powder, to be used with a special disk inhaler device.
  • In New Zealand, zanamivir is not funded by the government, which means the patient has to meet the full cost. It is not free on prescription.


  • The dose of zanamivir is different depending on whether it is used to treat influenza or prevent influenza.
  • To treat influenza:
    • The usual dose of zanamivir is 2 inhalations twice daily for 5 days.
  • To prevent influenza:
    • The usual dose of zanamivir is 2 inhalations once daily for 10 days.
    • In some cases zanamivir can be continued for up to 28 days during an influenza epidemic.
  • Always take your zanamivir exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much zanamivir  to take, how often to take it, and any special instructions.

How to take zanamivir

  • Zanamivir is available as an inhalation powder, to be used with a special disk inhaler device. The powder is contained in blisters in a foil disc which you load into a disk inhaler.
  • Your doctor or pharmacist will show you how to use the disk inhaler. The following is a guide:
    • Remove the cover on the disk inhaler.
    • Before use, check the mouthpiece to be sure it is clean and free of particles.
    • Load the medication disk into the disk inhaler.
    • Puncture one medication blister.
    • Keep the disk inhaler level so that the medication will not spill out.
    • Breathe out all the way through your mouth, put the mouthpiece into your mouth, and breathe in through your mouth as deeply as you can. This will draw the medication into your lungs.
    • Hold your breath for a few seconds.
    • To take another inhalation, advance to the next medication blister and repeat the process. Replace the cover of the disk inhaler.
  • If you are taking zanamivir twice a day, space your doses evenly throughout the day. So, for example, take one dose in the morning and the other in the evening.
  • If you forget your dose, take it as soon as you remember that day. But, if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
  • Continue to take zanamivir for the full time it has been prescribed. Stopping the medication too early may result in a return of the infection or failure to protect you from the flu.

Possible side effects

Like all medicines, zanamivir can cause unwanted side effects, although not everyone gets them. Often unwanted side effects improve as your body gets used to the new medicine.

Side effects What should I do?
  • Itchy skin rash
  • This is quite common when you first start taking zanamivir. 
  • Tell your doctor if troublesome or if the rash gets worse.
  • Feeling faint and lightheaded 
  • Dizziness
  • Sit down in a relaxed position before inhaling the dose of zanamivir, and only hold your breath for as long as is comfortable after inhaling the dose.
  • Tell your doctor if troublesome.
  • Signs of an allergic reaction such as severe itchy skin rash (hives), swelling of the lips, face, and mouth or difficulty breathing
  • Tell your doctor immediately or ring HealthLine 0800 611 116

Learn more

Relenza Medsafe Consumer Information Sheet (NZ)
Relenza (UK)

Credits: Sandra Ponen, Pharmacist.