Antiviral recommendations

Antiviral Medication Use - Treatment

In PROTECT, antiviral treatment should be reserved for persons with an acute respiratory infection (see case definition) (even prior to confirmation of diagnosis of pandemic (H1N1) 2009 infection) who have the following:

Those with moderate or severe disease
Any person with confirmed pandemic (H1N1) 2009 infection who is deteriorating
Those identified as being in a vulnerable group. A clinical assessment should be made of their risk of deterioration, and laboratory confirmation should be made if it is available in time
Residents living in high-risk institutions such as aged care facilities or special schools in order to control outbreaks in these settings

Antiviral medication should be given to those defined above as soon as possible and within 48 hours of illness onset. Anti-influenza treatment may be commenced more than 48 hours after onset in rare circumstances where clinically indicated.

Anti-influenza medications have been shown to attenuate disease in cases of seasonal influenza if given early in the course of the illness (within 48 hours of developing symptoms).

Whilst information on the effectiveness of anti-influenza medications in the clinical setting for pandemic (H1N1) 2009 is limited, studies have shown that the pandemic (H1N1) 2009 virus is susceptible to Oseltamivir (Tamiflu) and Zanamivir (Relenza), but is resistant to amantadine.

Pregnant Women and Antiviral drug use

Pregnant women are known to be at higher risk for complications from infection with seasonal influenza viruses, and severe disease among pregnant women was reported during past pandemics. Cases of confirmed novel (H1N1) influenza virus infection in pregnant women resulting in severe disease have been reported. Oseltamivir and zanamivir are "Pregnancy Category B1" medications, indicating that these drugs have only been taken by a limited number of pregnant women, but without an increase in the frequency of malformation or other direct or indirect harmful effects on the human fetus having been observed. Studies in animals have not shown evidence of an increased risk of fetal damage. No specific clinical studies have been conducted to assess the safety of these medications for pregnant women.

As with any prescription of medication, the use of these medications in pregnant women should only be where the risk of the illness outweighs the risk to the woman or fetus.

Pregnancy should not be considered a contraindication to oseltamivir or zanamivir use. Because of its systemic activity, oseltamivir is preferred for treatment of pregnant women. The drug of choice for chemoprophylaxis is less clear. Zanamivir may be preferable because of its limited systemic absorption; however, 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.

The dosage of either oseltamivir or zanamivir to pregnant women is the same as the standard adult dose, depending on whether the drug is being prescribed for treatment or for prophylaxis.

Tamiflu® (oseltamivir)

Adults and adolescents

The recommended oral dose of Tamiflu capsules in adults and adolescents 13 years of age and older is 75 mg twice daily for five days. Adults and adolescents 13 years of age and older who are unable to swallow capsules may receive the appropriate dose of Tamiflu suspension.

Paediatric patients

The recommended oral dose of Tamiflu for paediatric patients 1 year and older who cannot swallow a 75 mg capsule is shown in Table 7 below.

Recommended oral dose of Tamiflu for paediatric patients 1 year and older who cannot swallow a 75 mg capsule
Body weight in kg	Recommended dose for 5 days
< 15kg	30 mg twice daily
> 15 - 23 kg	45 mg twice daily
> 23 - 40 kg	60 mg twice daily
> 40 kg	75 mg twice daily
Note: Tamiflu is not registered by the Therapeutic Goods Administration (TGA) for use in children under 12 months of age

For the oral suspension, an oral dosing dispenser with 30, 45 and 60 mg graduations is provided; the 75 mg dose can be measured using a combination of 30 and 45 mg. It is recommended that patients use this dispenser. Paediatric patients weighing > 40 kg who are able to swallow capsules may also receive treatment with a 75 mg capsule twice daily or one 30 mg capsule plus one 45 mg capsule twice daily as an alternative to the recommended dose of Tamiflu suspension.

Relenza® (zanamivir)

Treatment of influenzas

The recommended dose of Relenza is two oral inhalations (2 x 5 mg) twice daily for five days providing a total daily-inhaled dose of 20 mg. Treatment should begin as soon as possible after onset of symptoms for maximum benefit, and at the latest should commence within 48 hours of symptom onset. Administration is by oral inhalation.

Renal impairment

No alteration of dosage or frequency of administration is required (see Actions, Pharmacokinetics in renal impairment).

Hepatic impairment

There is currently no experience in this patient population. Zanamivir is not hepatically metabolised and no dose modification is required (see Actions, Pharmacokinetics).

Use in the elderly

Experience with zanamivir in the elderly (greater than or equal to 65 years) is limited. However, based on the pharmacokinetic properties of zanamivir no dose modification is required (see Actions, Pharmacokinetics).

Use in children (aged 5 years and older)

No dose modification is required. (See Actions, Pharmacokinetics.) When zanamivir is prescribed for children, it should be used only under adult supervision.
Please refer to the current prescribing information from the manufacturer for more information.

Antiviral Medication Use - Chemoprophylaxis

Under PROTECT, prophylaxis using anti-influenza medication is not indicated. The information below is provided for reference only.

Tamiflu® (oseltamivir)

Adults and adolescents

The recommended oral dose of Tamiflu for prevention of influenza following close contact with an infected individual is 75 mg once daily for ten days. Ideally therapy should begin within two days of exposure. The recommended dose for prevention during a community outbreak of influenza is 75 mg once daily. Safety and efficacy have been demonstrated for up to six weeks. The duration of protection lasts for as long as dosing is continued.

Paediatric patients

Children weighing > 40 kg, who are able to swallow capsules, may also receive prophylaxis with a 75 mg capsule once daily or one 30 mg capsule plus one 45 mg capsule once daily for ten days as an alternative to the recommended dose of Tamiflu suspension (see below).
The recommended prophylactic oral dose of Tamiflu suspension for children greater than or equal to 1 year of age is shown in Table 8. Please refer to table 8 in the prescribing information.
For the oral suspension a dosing syringe marked with 30, 45 and 60 mg dosing levels is provided.
Tamiflu is currently not registered by the Therapeutic Goods Administration (TGA) for use in children under 12 months of age

Relenza® (zanamivir)

Prophylaxis of influenzas

The recommended dose of Relenza is two inhalations (2 x 5 mg) once daily, providing a total daily-inhaled dose of 10 mg, for ten days. This may be increased up to 28 days if the period of exposure risk extends beyond ten days.
Relenza Rotadisks are for pulmonary administration by oral inhalation only, using the Diskhaler device provided. Patients scheduled to take inhaled drugs, e.g. fast acting bronchodilators, at the same time as Relenza, should be advised to administer that drug prior to administration of Relenza (see Precautions).

Renal impairments

No alteration of dosage or frequency of administration is required (see Actions, Pharmacokinetics in renal impairment).

Hepatic impairments

There is currently no experience in this patient population. Zanamivir is not hepatically metabolised and no dose modification is required (see Actions, Pharmacokinetics).

Use in the elderly

Use in children (aged 5 years and older)

No dose modification is required. (See Actions, Pharmacokinetics.) When zanamivir is prescribed for children, it should be used only under adult supervision.

Please refer to the current prescribing information from the manufacturer for more information.