Medications to treat or prevent influenza (“the flu”)

Treatment with oseltamivir (Tamiflu®) or zanamivir (Relenza®) may prevent infection with influenza ("the flu"), or shorten the duration and severity of illness in people that already have influenza.

Last updated: 06 November 2006

Introduction

Influenza is caused by the influenza virus. The symptoms of influenza usually include the sudden onset of fever and chills, cough, muscle and joint pain, headache, tiredness and weakness. Some people also get a stuffy nose and sore throat. For more information about influenza, see the NSW Health influenza fact sheet.

The best way to prevent influenza is to have an annual influenza vaccination. Other things you can do to prevent influenza from spreading include: covering your nose and mouth with a tissue when coughing or sneezing, and washing your hands with soap and running water after coughing, or sneezing. If you are ill with influenza, you should stay at home until you feel better. If you need to go to the doctor, you should wear a mask while in the doctor's waiting room.

The most useful antiviral medications for treating and preventing infection with influenza are the group of drugs called the neuraminidase inhibitors - oseltamivir (trade name: Tamiflu®) and zanamivir (trade name: Relenza®). They can be used to treat and prevent both human influenza ("the flu") and avian influenza ("bird flu").

How do these medications work?

Neuraminidase inhibitors prevent the influenza virus from spreading inside your body. If started within 48 hours of the first symptoms of influenza, these medications can reduce the severity of symptoms, and can reduce the time taken to recover from illness.

What are these medications used for?

Treatment
Tamiflu can be used for treating people aged 1 year or older, who are infected with the human or avian influenza virus. Relenza can be used in those 5 years or older. These medications are only effective if they are started within 48 hours (2 days) of starting to feel unwell. The earlier they are started after the onset of symptoms, the more effective they are.

Prevention
These medications can be used to prevent getting influenza in those who have been exposed to people who have recently become ill with influenza. Tamiflu can be used to prevent influenza in people aged 13 years and older, and Relenza can be used to prevent influenza in adults and children aged 5 years and older if the appropriate influenza vaccine is not available.

What is the dosage?

Tamiflu comes as a capsule for adults, and as a suspension for children, which should be taken by mouth. The dosage in adults without severe kidney problems is:
• one capsule twice a day for 5 days when used to treat influenza, and
• one capsule daily for at least 7 days when used to prevent getting influenza.

Relenza is inhaled using an inhaler that comes with the pack. Follow the instructions in the pack on how to use the inhaler. The dose in adults and children over 5 years old is:
• two inhalations (two 5mg discs) twice a day for 5 days when used to treat influenza, and
• two inhalations (two 5mg discs) once daily for at least 10 days when used to prevent getting influenza.

Who should NOT take these medications?

You should not take Tamiflu or Relenza if you are allergic to these medications, or to any of the medication ingredients. Before starting treatment, tell your doctor about other medications you may be taking. You should also tell your doctor if you have any chronic or serious illnesses, in particular if you have kidney disease, asthma or lung disease, as special precautions may be needed.

What are common side-effects of taking these medications?

Overall, the neuraminidase inhibitors are very safe. The commonest side effects of these medications are nausea, vomiting and other gastrointestinal symptoms. These affect less than 1 in 10 people, most often the first time the medication is taken. Taking the medication with food may help to reduce or prevent these side effects. If you notice any other side effects or if you have any concerns about possible side effects, please talk to your doctor.

Can I take other medications at the same time?

Tamiflu and Relenza are generally safe to take with other medications, but you should still make sure that your doctor knows about any other medications you are taking. If you normally use certain asthma inhalers such as salbutamol (e.g., Ventolin), or terbutaline (e.g., Bricanyl), you should use these at least 5 minutes before taking Relenza.

What if I am pregnant or breast-feeding?

If you are pregnant or planning to become pregnant, tell your doctor before taking this medication. Both Tamiflu and Relenza are relatively new medications, and their safety during pregnancy or breast-feeding is not completely understood. They should therefore be avoided if possible during pregnancy or while breast-feeding, unless the risk from getting influenza is thought to outweigh the potential risk of these medications to the baby.