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Zanamivir is prescribed for influenza virus A and B infections.

You can help to prevent the flu virus from spreading to others by using clean tissues to cover your mouth and nose when you cough or sneeze, and by washing your hands regularly.

Remember to keep warm, drink plenty of fluids and stay away from crowds.

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About zanamivir

Type of medicine

An antiviral medicine

Used for

Treating or preventing flu (influenza).

Also called


Available as

Blisters of powder with a Diskhaler® (inhaler) and injections

Zanamivir treats flu (influenza) by preventing the viruses causing the infection from spreading once they are inside your body. This reduces the symptoms of the influenza infection. It also reduces the risk of other problems which can sometimes occur alongside flu, such as pneumonia. It is most effective when it is started within an hour or two of the first symptoms of infection, but it can still be effective after this time, as long as it is started within 48 hours of the first symptoms for adults, or within 36 hours for children.

Zanamivir is also used to prevent flu when there is a flu outbreak in the community, such as in epidemics and pandemics. It is used for those who have been in close contact with people with flu and for those who would be at particular risk if they developed flu (such as children, people with long-term medical conditions, and the elderly). It is most effective when treatment begins as soon as possible after the contact, but it can still be effective when started up to 36 hours afterwards.

Another antiviral medicine called oseltamivir is often prescribed in preference to zanamivir, so you will have been prescribed zanamivir because oseltamivir is not suitable for you for some reason. Zanamivir is not a substitute for seasonal flu vaccination.

Before taking zanamivir

Some medicines are not suitable for people with certain conditions, and sometimes a medicine can only be used if extra care is taken. For these reasons, before you start taking zanamivir it is important that your doctor knows:

  • If you are pregnant, trying for a baby or breastfeeding. Although you can take zanamivir if you are expecting or feeding a baby, it is important that your doctor knows about this so that you can be made aware of the benefits and any risks of treatment.

  • If you have any breathing problems (such as asthma or chronic bronchitis), or if you are using other inhalers.

  • If you have ever had an allergic reaction to cow's milk protein. This is different to dairy or lactose intolerance.

  • If you are taking or using any other medicines. This includes any medicines you are taking which are available to buy without a prescription, as well as herbal and complementary medicines.

  • If you have ever had an allergic reaction to a medicine.

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How to take zanamivir

  • Before you start the treatment, read the manufacturer's printed information leaflet from inside the pack. It will give you more information about zanamivir and provide you with full instructions for using the Diskhaler® with the powder blisters.

  • Take zanamivir exactly as your doctor tells you to. It is a powder which is inhaled. The powder is contained in blisters in a foil disc which you load into a Diskhaler®. Your doctor or pharmacist will show you how to use the Diskhaler®.

  • Zanamivir is a course of treatment which usually lasts 5-10 days, although it can sometimes be prescribed for up to 28 days during an epidemic. Use the Diskhaler® for as long as your doctor has advised, even if you do not feel unwell. If you have been prescribed it because you already have flu symptoms, you will need to use two inhalations (two blisters) twice-daily for five days, preferably morning and evening. Start using it as soon as possible. If you are taking it because you have been in contact with someone with flu but you do not have any symptoms yourself, then you will need to use two inhalations (two blisters) once a day for at least ten days.

  • Try to use the Diskhaler® at the same times each day, as this will help you to take zanamivir regularly.

  • If you forget to take a dose, take it as soon as you remember (unless it is nearly time for your next dose, in which case leave out the missed dose). Do not take two doses together to make up for a forgotten dose.

Getting the most from your treatment

  • Try to help stop the spread of flu to others. You can do this by remembering to use clean tissues to cover your mouth and nose when you cough and sneeze, binning the tissues after use, and washing your hands regularly with soap and hot water.

  • Remember to keep warm, drink plenty of fluids and stay away from crowds. If your symptoms do not improve or they get worse, phone your doctor for further advice.

  • If you regularly use other inhalers and these are due at the same time as zanamivir, use your usual inhalers first and then wait a few minutes before you use zanamivir. If you use a reliever inhaler (such as salbutamol) keep this with you while you are using zanamivir, just in case you feel breathless and you need to use it.

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Can zanamivir cause problems?

Along with their useful effects, most medicines can cause unwanted side-effects although not everyone experiences them. The table below contains the most common ones associated with zanamivir. You will find a full list in the manufacturer's information leaflet supplied with your medicine. The unwanted effects often improve as your body adjusts to the new medicine, but speak with your doctor or pharmacist if any continue or become troublesome.

Common zanamivir side-effects (these affect fewer than 1 in 10 people)

What can I do if I experience this?

Itchy skin rash

If this becomes troublesome, speak with your doctor

Less common zanamivir side-effects

What can I do if I experience this?

Feeling short of breath, throat tightness, allergic-type reactions

Let your doctor know about this

If you experience any other symptoms which you think may be due to the medicine, speak with your doctor or pharmacist for further advice.

How to store zanamivir

  • Keep all medicines out of the reach and sight of children.

  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines

Important information about all medicines

If you are due to have an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.

If you buy any medicines, check with a pharmacist that they are suitable to take with your other medicines.

Never take more than the prescribed dose. If you suspect that you or someone else might have taken an overdose of this medicine, go to the accident and emergency department of your local hospital at once. Take the container with you, even if it is empty.

This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.

Do not keep out-of-date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.

If you have any questions about this medicine ask your pharmacist.

Report side effects to a medicine or vaccine

If you experience side effects, you can report them online through the Yellow Card website.

Further reading and references

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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