Antiviral flu medicines

Published by Bupa's Health Information Team, July 2010.

This factsheet is for anyone taking antiviral flu medicines, or who would like information about them.

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?

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.

For answers to frequently asked questions on this topic, see Common questions.

For sources and links to further information, see Resources.