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
  • muscle pains
  • sore throat
  • extreme tiredness

Over the course of a few days, your body's immune system usually fights off the flu virus. However, if you're over 65, have a weakened immune system (for example, if you have HIV/AIDS or are taking medicines that suppress your immune system), or an underlying medical condition, a bout of flu can become much more serious. There is a risk that you may develop pneumonia (inflammation of your lungs), bronchitis or other complications.

If you're at an increased risk of developing complications, your GP may prescribe you 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 or chronic obstructive pulmonary disease (COPD)
  • have heart disease
  • have long-term kidney disease
  • have long-term liver disease
  • have a long-term neurological (brain or spinal) condition
  • 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. They are only usually prescribed when it has been shown that influenza cases are occurring at sufficient numbers in the population.

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 are 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 oseltamivir and zanamivir. 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?

Oseltamivir and zanamivir 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 then stops the virus being released from infected cells and therefore reduces multiplication of the virus inside your body.

How to take antiviral flu medicines

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, 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.

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 (once you have symptoms), you need to use the puffer twice a day for five days. To prevent flu after you’ve been exposed to someone with the illness, you will need to use it once a day for 10 days. If there is a flu epidemic, you may be prescribed zanamivir for up to 28 days.

For oseltamivir and zanamivir to be effective, you need to start taking them within 48 hours of your symptoms first appearing. In children, zanamivir needs to be taken within 36 hours.

Special care

If you’re a woman and are pregnant or breastfeeding, your doctor may advise you to take either oseltamivir or zanamivir during a flu pandemic. Oseltamivir is the preferred medicine 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 the course.

Side-effects of zanamivir are uncommon, but include:

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

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
oseltamivir Tamiflu
zanamivir Relenza

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

Answer

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

Explanation

Having the flu vaccine is the most effective way of preventing flu. Antiviral flu medicines can't be used instead of having the vaccination.

In the UK, 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 a long-term lung disease, such as asthma
  • have long-term heart, liver or kidney disease
  • have diabetes
  • have a weakened immune system
  • have a long-term neurological condition, for example, have had a stroke
  • are pregnant

If you fall into one of these categories, speak to your GP about having the flu vaccine. It’s also usually recommended for residents in long-stay residential care homes and for carers of older, disabled people. The usual time to have a flu vaccination is October or 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?

Answer

No, you're unlikely to be prescribed an antiviral flu medicine 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 a long-term neurological condition, for example, have had a stroke
  • 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?

Answer

It's possible to buy the antiviral flu medicines oseltamivir and zanamivir over the internet, often from overseas. However, you must be careful if you're considering buying medicines this way.

Explanation

In the UK, both oseltamivir and zanamivir are prescription-only medicines, which mean they may only legally be dispensed with a prescription. You should never buy medicines such as these online without a prescription.

If you buy medicines over the internet, there is a risk that they are from unregulated or illegal websites. There may be no guarantee of safety, quality or effectiveness of the medicines provided and potentially could result in serious harm.

If you do choose to buy medicines online, look for pharmacies in the UK that are registered with the Royal Pharmaceutical Society of Great Britain (RPSGB) – they will 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.