Zanamivir is a drug for the treatment of flu (influenza), developed by GlaxoSmithKline and marketed as Relenza. It is taken as an inhalation of powder into the lungs, and reduces the severity and duration of flu symptoms.

The treatment is for use by people over the age of seven, who have Influenza A or Influenza B, and who have not had the symptoms for more than two days.

It is impossible to be absolutely sure someone has influenza without doing laboratory tests, but these take too long for them to be of any practical value. Therefore, the way in which it is suggested zanamivir is used, is that it be given to people who develop symptoms of 'flu when influenza is known to be circulating.

Zanamivir acts by inhibiting an enzyme known as neuraminidase, which results in the virus not being able to reproduce itself.

Unfortunately zanamivir has the drawback that it can cause tightness of the tubes in the lungs (bronchospasm) in some patients, and it is not recommended for people with airways disease, eg asthma or chronic obstructive pulmonary disease (COPD). This therefore excludes quite a high percentage of people that might otherwise have benefited from its use.

Zanamivir is a powder that is inhaled, twice a day, through a special inhaler. This is used for five days.

Zanamivir is recommended for the treatment of influenza in adults in the at risk groups, who can start treatment within 48 hours of the onset of symptoms.

Normally the advice is to treat yourself for the symptoms of 'flu. If zanamivir is used by everybody, it will mean a massive increase in people visiting their doctors within two days of symptoms starting. In an epidemic, this could overwhelm health services.

• Medinfo Influenza information
• GlaxoSmithKline Relenza product information [PDF]
• Flu treatment (flu.gov)