Updated antiviral guidelines and rapid tests for diagnosing influenza Updated antiviral guidelines and rapid tests for diagnosing influenza

Guidelines for prescribing antivirals for people who have been in contact with suspected or confirmed cases of swine influenza (H1N1) have been updated by the Department of Health and Ageing following more confirmed cases in Australia. The Department now recommends the following.

Antiviral medication may be prescribed to close contacts of confirmed or influenza A positive suspected cases provided it is commenced within 7 days of last contact with the patient while the patient was still infectious.

Any prescription of antiviral medication should be on the recommendation of the local public health unit.

Current recommended protocols for prescribing antivirals for suspected cases

Antivirals should be prescribed within 48 hours of onset of symptoms in suspected cases, and continued until H1N1 influenza is excluded or an alternative diagnosis is made. Antiviral treatment may be commenced more than 48 hours after onset in rare circumstances where clinically indicated.

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 the table below.

Recommended oral dose of Tamiflu for paediatric patients 1 year and older who cannot swallow a 75 mg capsule

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 influenza. 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' in the product information).

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' in the product information).

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' in the product information).

Use in children (aged 5 years and older). No dose modification is required (See 'Actions, Pharmacokinetics' in the product information). 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.

Current recommended protocols for prescribing antivirals to those who may have been exposed

Close contacts of confirmed or influenza A positive suspected cases should be prescribed antivirals provided it is commenced within 7 days of last contact with the infected patient (while the patient was still infectious).

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 10 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 one year of age is shown in the table above.

For the oral suspension a dosing syringe marked with 30, 45 and 60 mg dosing levels is provided.

Relenza (zanamivir)

Prophylaxis of influenza. 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.

Renal impairment. No alteration of dosage or frequency of administration is required (see 'Actions, Pharmacokinetics in renal impairment' in the product information).

Hepatic impairment. There is currently no experience in this patient population. Zanamivir is not hepatically metabolised and no dose modification is required.

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.

Use in children (aged 5 years and older). No dose modification is required. 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.

The full Commonwealth Department of Health and Ageing H1N1 Influenza 09 (Human Swine influenza) – Summary Sheet for General Practitioners is available at www.health.gov.au.

These recommendations are in line with those issued by the US Centers for Disease Control (CDC), which can be accessed at www.cdc.gov/swineflu/recommendations.htm.

An article ‘Rapid tests for the diagnosis of influenza’ from the June edition of Australian Prescriber has been released early.

The article, written by Microbiology Registrar Hong Foo and Clinical Professor of Medicine, Dominic Dwyer, from the Centre for Infectious Diseases and Microbiology, Westmead Hospital, Sydney, outlines rapid influenza tests based on viral antigen detection with point-of-care tests and immunofluorescence, how they work and their limitations.

It is not expected that the Australian seasonal influenza vaccine will provide protection against this new strain of influenza virus. However, people over 65 and other vulnerable groups should still be encouraged to be vaccinated as this will provide protection against seasonal influenza.

Community pharmacists can access more detailed information through The Pharmacy Guild of Australia and Pharmaceutical Society of Australia websites.

Doctors and other prescribers can access further information through the AMA and RACGP websites.