Influenza (flu) is an infection of the breathing system, caused by a flu virus. Most people recover from flu without the need for medicines. However, people at risk of complications may be prescribed antiviral flu medicines.
 
Why would I take antiviral flu medicines?
What are the main types of antiviral flu medicine?
How do antiviral flu medicines work?
How to take antiviral flu medicines
Special care
Side-effects of antiviral flu medicines
Resistance to antiviral flu medicines
Names of common antiviral flu medicines
 
 

Why would I take antiviral flu medicines?

 
For healthy people, flu is usually an unpleasant illness with symptoms that include:
 

  • fever
  • headache
  • coughing
  • joint pains
  • sore throat

 
Over the course of a few days, your body's immune system usually fights off the flu virus. However, if you’re over 65 or have a weakened immune system (for example, if you have HIV/AIDS or a chronic disease such as diabetes) a bout of flu can become much more serious. There is a risk that you may develop pneumonia (inflammation of your lungs) or other complications.
 
If you’re at an increased risk of developing complications, your doctor may prescribe antiviral flu medicines. In the UK, the National Institute for Health and Clinical Excellence (NICE) has issued advice on the specific groups of people who are eligible to receive these medicines. These include people who:
 

  • are 65 or older
  • have a long-term lung condition such as asthma
  • have heart disease
  • have long-term kidney disease
  • have diabetes
  • have a weakened immune system

 
If you fall into one of these categories, have been in close contact with someone who has flu (for example, if you live with them) and aren’t protected by the flu vaccine, your GP may prescribe you antiviral flu medicines.
 
Antiviral flu medicines stop the flu virus spreading inside your body, so can reduce, or sometimes prevent, the symptoms of flu. These medicines can also reduce the length of time you’re ill and make you less likely to develop any complications. However, you need to start taking them within 48 hours of being exposed to the virus or of your symptoms starting, for them to be effective.
 
A flu pandemic happens when a new version of a flu virus emerges and spreads easily and quickly across the world.  Antiviral medicines are sometimes used to treat pandemic flu. However, until a flu pandemic starts, doctors can't be sure that antiviral medicines will work for that particular flu virus.
 

What are the main types of antiviral flu medicine?

 
There are two medicines currently recommended for preventing and treating flu. These are zanamivir and oseltamivir. They work to treat both influenza A and B (the two main types of seasonal flu virus).
 
Another medicine, called amantadine, is licensed to prevent and treat influenza A, but its use is no longer recommended.
 

How do antiviral flu medicines work?

 
Zanamivir and oseltamivir belong to a group of antiviral medicines called neuraminidase inhibitors. When a virus infects your body, it multiplies inside your cells. These medicines inhibit a protein called neuraminidase. This stops the virus being released from infected cells and therefore reduces multiplication of the virus inside your body.
 

How to take antiviral flu medicines

 
Zanamivir comes as an inhaler ('puffer'), similar to the type used to treat asthma. Each puff contains a small amount of the medicine. To treat flu (if you have symptoms), you need to use the puffer twice a day for five days. To prevent flu after you have been exposed to someone with the illness, you will need to use it once a day for 10 days. If there is an epidemic of flu, you may be prescribed zanamivir for up to 28 days.
 
Oseltamivir comes as capsules or a syrup. You will need to take one capsule twice a day for five days to treat flu. Doctors prescribe lower doses for children aged over one year, depending on how much they weigh. To prevent flu, you will need to take a capsule once a day for 10 days after exposure to the virus or for up to six weeks during an epidemic.
 
For oseltamivir and zanamivir to be effective, you need to start taking them within 48 hours of your symptoms first appearing.

 
Special care

 
Zanamivir is the preferred antiviral flu medicine for pregnant women and oseltamivir is usually recommended for women who are breastfeeding.
 
If you have advanced kidney disease, you may not be able to take oseltamivir.
 
Always ask your GP for advice and read the patient information leaflet that comes with your medicine.
 

Side-effects of antiviral flu medicines

 
Side-effects of oseltamivir include:
 

  • feeling sick
  • vomiting
  • abdominal (tummy) pain
  • diarrhoea
  • headache
  • conjunctivitis

 
These side-effects usually happen after you have taken the first dose of your medicine and will usually stop as you continue to take your medicine. The likelihood of you having these side-effects is reduced if you take oseltamivir with food.
 
Side-effects of zanamivir are very rare, but include:  
 

  • swelling of your face, mouth or throat
  • rashes
  • difficulty breathing

 
Because zanamivir can cause breathing difficulties, it isn't usually recommended if you have an underlying medical condition that affects your breathing system. Examples of such conditions include asthma or chronic obstructive pulmonary disease (COPD). Ask your GP for more advice.

 
Resistance to antiviral flu medicines

 
Because the flu virus is continually changing, strains can develop that aren't controlled by antiviral medicines. This is called resistance. Since early 2008, there have been reports from several countries in Europe, including the UK, of strains of influenza A that are resistant to oseltamivir. These resistant strains can still be treated with zanamivir.
 

Names of common antiviral flu medicines

 
Antiviral flu medicines and their brand names are shown in the table.
 

Generic name Brand name
zanamivir Relenza
oseltamivir Tamiflu

See our answers to common questions about antiviral flu medicines, including:
 
Can antiviral flu medicines be used as an alternative to the flu vaccine?
Can I take antiviral flu medicines if I’m not part of an ‘at risk’ group?
Can I buy antiviral flu medicines online?
 

Answers to questions about antiviral flu medicines

 
This section contains answers to common questions about this topic. Questions have been suggested by health professionals, website feedback and requests via email.
 

  • Can antiviral flu medicines be used as an alternative to the flu vaccine?
  • Can I take antiviral flu medicines if I’m not part of an ‘at risk’ group?
  • Can I buy antiviral flu medicines online?

 
 

Can antiviral flu medicines be used as an alternative to the flu vaccine?

 
No, these medicines aren’t a substitute for the vaccination.
 

Explanation

The flu vaccine is the most effective way of preventing flu. Antiviral flu medicines can’t be used instead of having the vaccination.
The flu vaccine is freely available to everyone over 65 and is recommended for people at risk from the complications of flu. This includes adults and children (over six months) who have:

  • long-term lung disease such as asthma
  • long-term heart, liver or kidney disease
  • diabetes
  • a weakened immune system

 
If you fall into one of these categories, speak to your GP about having the flu vaccine. The usual time to have a flu vaccination is between September and early November, which is generally before the flu season starts.
 

Can I take antiviral flu medicines if I’m not part of an ‘at risk’ group?

 
No, you’re unlikely to be prescribed an antiviral medicine for flu if you’re under 65 and are otherwise healthy.
 

Explanation

Only certain groups of people are usually prescribed antiviral flu medicines. These are people who are most at risk of the complications of flu. This includes people who:
 

  • are 65 or older
  • have a long-term lung disease such as asthma
  • have long-term heart, liver or kidney disease
  • have diabetes
  • have a weakened immune system

 
If you fall into this at risk category, have been in close contact with someone who has flu (for example, if you live with them) and aren’t protected by the flu vaccine, you may be prescribed antiviral flu medicines.
 
Sometimes, otherwise healthy people may be prescribed antiviral flu medicines during a flu pandemic. A flu pandemic happens when a new version of the flu virus emerges and spreads easily and quickly across the world. For example, pandemic H1N1 (‘swine’) flu affected the UK in 2009 and oseltamivir and zanamivir were used to treat it in otherwise healthy people. However, until a flu pandemic starts, doctors can't be sure that antiviral medicines will work with that particular flu virus.
 

Can I buy antiviral flu medicines online?

 
It's possible to buy the antiviral flu medicines zanamivir and oseltamivir over the internet, often from overseas. However, be careful if you’re considering buying medicines this way. If you buy medicines over the internet, there is a risk that they are from unregulated or illegal websites. If they are, there will be no guarantee of safety, quality or effectiveness of the medicines provided.
 

Explanation

If you choose to buy medicines online, look for pharmacies in the UK that are registered with the Royal Pharmaceutical Society of Great Britain (RPSGB) – they can display a logo on their website.
 
However, it’s important to remember that if you buy medicines online, you won’t have the benefit of a face-to-face consultation with a healthcare professional and you risk buying medicines that aren’t suitable for you. If you do wish to buy medicines online, speak to your GP first.
 

Further information

 
Health Protection Agency
www.hpa.org.uk
 
 

Sources

 

  • Amantadine, oseltamivir and zanamivir for the treatment of influenza. National Institute for Health and Clinical Excellence (NICE), February 2009. www.nice.org.uk
  • Influenza. The Merck Manuals Online Medical Library. www.merck.com/mmhe, published November 2009
  • Influenza – seasonal – Management: People at risk from influenza. Clinical Knowledge Summaries. www.cks.nhs.uk, accessed 16 April 2010
  • Influenza – seasonal – Background information: What is it? Clinical Knowledge Summaries. www.cks.nhs.uk, accessed 16 April 2010
  • Chapter 19: Influenza. Immunisation against infectious disease – ‘The Green Book’. Department of Health, 29 October 2009. www.dh.gov.uk
  • Joint Formulary Committee, British National Formulary. 59th ed. London: British Medical Association and Royal Pharmaceutical Society of Great Britain, March 2010: 350–51, 385–86
  • Weekly update on oseltamivir resistance to pandemic influenza A (H1N1) 2009 viruses. World Health Organization. www.who.int, accessed 7 April 2010
  • Clinical management of human infection with pandemic (H1N1) 2009: revised guidance. World Health Organization, November 2009. www.who.int
  • Public warned against online swine flu medicines. Directgov. www.direct.gov.uk, published 7 May 2009
  • Immunizations – seasonal influenza – Management: Who should be immunized with the influenza vaccine? Clinical Knowledge Summaries. www.cks.nhs.uk, accessed 16 April 2010
  • Immunizations – seasonal influenza – Management: When should influenza vaccines be given? Clinical Knowledge Summaries. www.cks.nhs.uk, accessed 16 April 2010
  • Simon C, Everitt H, van Dorp F. Oxford Handbook of General Practice. 3rd ed. Oxford: Oxford University Press, 2010: 330–31
  • Summary of prescribing guidance for the treatment and prophylaxis of influenza-like illness. Health Protection Agency. www.hpa.org.uk, published 18 December 2009
  • Swine flu: antiviral medicines. Medicines and Healthcare products Regulatory Agency (MRHA). www.mhra.gov.uk, published March 2010

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