Treatment with oseltamivir (Tamiflu®) or zanamivir (Relenza®) may shorten the duration and severity of illness in people who already have influenza.

Influenza antivirals are also indicated for the prevention of influenza in adults and children (aged 1 year and older for Tamiflu; aged 5 years and older for Relenza) - see product information for further details. Vaccination is the preferred method of routine prophylaxis against infection with influenza virus.

Introduction

Influenza is caused by infection with two main types of virus: influenza A or influenza B. Influenza A is further classified into subtypes. Each year there are one or two types of influenza A and influenza B viruses circulating.

The most useful anti-influenza medications for treating infection with influenza are neuraminidase inhibitors - oseltamivir (trade name: Tamiflu®) and zanamivir (trade name: Relenza®). There has been no significant evidence of resistance to the neuraminidase inhibitors in recently circulating influenza A or B strains, but resistance may develop in the future.

Using anti-influenza medications for treatment

Empiric treatment with anti-influenza medications should be considered for anyone presenting with moderate or severe illness, and for those presenting with mild illness and who are from a vulnerable group at risk of severe illness (based on clinical judgment).

Anti-influenza treatment with zanamivir or oseltamivir should be initiated as soon as possible after the onset of symptoms. Evidence for benefits from treatment in studies of seasonal influenza is strongest when treatment is started within 48 hours of illness onset. However, some studies of treatment of seasonal influenza have indicated benefit, including reduction in mortality or duration of hospitalization, even for patients whose treatment was started more than 48 hours after illness onset.

Recommended duration of treatment is five days. The doses recommended are the same for treatment of all viral strains - whether Pandemic (H1N1) 2009 influenza or seasonal influenza. The recommended doses for adults or children 1 year of age or older are presented below. Safety data on the use of oseltamivir in younger children is limited. Retrospective data from the use of oseltamivir for seasonal influenza in children younger than one year have not demonstrated age-specific drug-attributable toxicities. If oseltamivir is considered for use in children younger than one year, a careful assessment of the potential risks and benefits is required and it is recommended that this occurs in consultation with a paediatrician.

Oseltamivir

G​​roup Treatment
Adults and children ≥ 13 yrs 75mg twice per day for 5 days
Children ≤15 kg 30mg twice daily for 5 days
Children >15-23kg 45mg twice daily for 5 days
Children >23-40kg 60mg twice daily for 5 days
Children >40 kg 75mg twice daily for 5 days

Zanamivir

​Group Treatment
Adults Two 5mg inhalations (10mg total) twice per day for 5 days
Children (5 yrs or older) Two 5mg inhalations (10mg total) twice per day for 5 days

Availability

Oseltamivir (Tamiflu®)

Tamiflu capsules are available in the following strengths: 30mg, 45mg and 75mg. Tamiflu comes in blister packs containing 10 capsules.

Tamiflu is also available as a powder for oral suspension in the following strengths: 6mg/mL and 12mg/mL.

  • Note well: If commercially manfuafctured Tamiflu powder for oral suspension is not available then Tamiflu capsules may be used to prepare oral suspension - see the Tamiflu product information for instructions for pharmacists.

Zanamivir (Relenza®)

Relenza is a fine powder packed in small "blisters" on a circular foil Disk, and is intended to be inhaled using a Diskhaler device.

Each blister contains 5mg of Relenza. Each Disk has four blisters. Each pack contains five Disks.

Recommendations for oseltamivir (Tamiflu®) use if patient is vomiting

Oseltamivir can cause nausea and vomiting in some people which can be reduced by taking it with food. The following advice is based on how oseltamivir is absorbed, distributed, metabolised, and eliminated in adults, and assumes the patient is taking oseltamivir with food. This should be considered as interim guidance until reliable evidence becomes available:

  1. If a patient vomits within 30 minutes of administration of oseltamivir a repeat dose should be given.
  2. If a patient vomits after 30 minutes of administration of oseltamivir a repeat dose should be administered if the capsule is visible in the vomitus.
  3. If the patient vomits after a repeat dose, the patient should contact a health professional for further advice. The use of anti-emetics may be considered, or the medication may be changed to zanamivir.

Pregnant women

Pregnancy should not be considered a contraindication to oseltamivir or zanamivir use. Evidence gathered from previous influenza pandemics, and studies of pregnant women who had seasonal influenza, has shown that pregnant women are at risk for serious influenza illness and adverse foetal outcomes. Recent reports from the northern hemisphere have indicated that pregnant women infected with Pandemic (H1N1) 2009 influenza are similarly at risk.

Pregnancy should not be considered as a contraindication to oseltamivir or zanamivir use. Evidence gathered from previous influenza pandemics, and studies of pregnant women who had seasonal influenza, has shown that pregnant women are at risk for severe illness from influenza and adverse fetal outcomes. Recent reports have indicated that pregnant women infected with Pandemic (H1N1) 2009 influenza are similarly at risk.

Oseltamivir and zanamivir are 'Pregnancy Category B1' medications, meaning limited data indicating safety in pregnancy. However, no adverse effects have been reported among women who received oseltamivir or zanamivir during pregnancy or among infants born to women who have received oseltamivir or zanamivir during pregnancy.

Data are limited as to whether oseltamivir or zanamivir should be the drug of choice in pregnancy. Oseltamivir is known to be more systemically active than zanamivir, which is inhaled and reaches low concentration in the blood. Therefore, if systemic activity is specifically required, oseltamivir should be used.

Respiratory complications that may be associated with zanamivir because of its inhaled route of administration need to be considered, especially in women at risk for respiratory problems.

Breastfeeding women

Breastfeeding should not be considered as a contraindication to oseltamivir or zanamivir use. Safety data is limited however early data suggest that clinical sequelae from maternal treatment with oseltamivir would not be expected in a breastfed infant. There are no data on zanamivir use during lactation but based on limited bioavailability the systemic exposure of a breastfed infant from maternal treatment is expected to be insignificant.

Adverse events and contraindications

Please refer to the product information for further details:

Page Updated: Thursday 12 May 2016