Sounds like 'za-NAM-i-vir'.

Key points about zanamivir

  • Zanamivir is a medicine used to treat influenza, or 'flu', which is caused by a virus.
  • Zanamivir is also known as Relenza®.
  • Find out how to take it safely and possible side effects.
blue unaunahi tile generic
Print this page

Zanamivir is used to treat and prevent symptoms caused by the influenza (flu) virus. It works by stopping the influenza virus from multiplying in your body and reduces the symptoms of the flu. It also reduces the risk of other problems that can sometimes occur with the flu, such as pneumonia. In New Zealand, zanamivir is only funded for some people in hospital with a weakened immune system who are at higher risk of getting the complications of the flu. Others will need to pay the full cost. It is not free on prescription. Zanamivir is available as an inhalation powder to be used with a special disk inhaler device. 

To treat influenza 

  • 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 best 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.

To prevent influenza

  • Zanamivir may also be used to prevent the flu in some high-risk people who 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 best started within 36 hours of coming into contact with someone with the flu.
  • Getting the flu vaccine is the best way to protect against getting the flu and to control the spread of the flu. Zanamivir is not a substitute for the flu vaccine.

The dose of zanamivir is different depending on whether it is used to treat influenza or prevent influenza.

  Dose of zanamivir
To treat influenza 2 inhalations two times a day for 5 days.
To prevent influenza 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.

Zanamivir is a powder to be used with a special disk inhaler. The powder is in blisters in a foil disc to put into the disk inhaler. Your doctor or pharmacist will show you how to use the disk inhaler. The following is a guide:

  • Remove the cover on your inhaler.
  • Check the inhaler to be sure it is clean.
  • Load the medication foil into the inhaler.
  • Puncture one foil blister.
  • Keep the 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 dose, move to the next blister and repeat. Replace the cover of the inhaler to keep it clean.

If you are taking zanamivir two times a day, space your doses evenly, so 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.
  • Keep taking zanamivir for the full time it has been prescribed. Stopping the medication too early may cause a return of the infection or may not protect you from the flu. 

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

Side effects What should I do?
  • 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 your lips, face and mouth, or difficulty breathing
  • Tell your doctor immediately or ring HealthLine 0800 611 116
Did you know that you can report a side effect to a medicine to CARM (Centre for Adverse Reactions Monitoring)? Report a side effect to a product(external link)

The following link gives more information on zanamivir. 

Relenza(external link) Medsafe Consumer Information Sheet, NZ


5 questions to ask about your medications(external link) Health Quality and Safety Commission, NZ, 2019 English(external link), te reo Māori(external link)


  1. Zanamivir(external link) New Zealand Formulary

Free helplines

Healthline logo

Text 1737 Helpline logo

Logo with link to Māori Pharmacists website

Credits: Sandra Ponen, Pharmacist, Healthify He Puna Waiora. Healthify is brought to you by Health Navigator Charitable Trust.

Reviewed by: Angela Lambie, Pharmacist, Auckland

Last reviewed:

Page last updated: