HOW TO TREAT 31 use has not been associated with an increased risk of congenital malformations or adverse pregnancy outcomes . 43 , 44 Oseltamivir is preferred over inhaled zanamivir because of concerns regarding lower lung volumes in pregnancy causing reduced zanamivir distribution and potential bronchospasm . 16
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HOW TO TREAT 31 use has not been associated with an increased risk of congenital malformations or adverse pregnancy outcomes . 43 , 44 Oseltamivir is preferred over inhaled zanamivir because of concerns regarding lower lung volumes in pregnancy causing reduced zanamivir distribution and potential bronchospasm . 16
Baloxavir marboxil ( baloxavir ) was approved by the TGA in 2020 for those 12 years and older as prophylaxis or treatment of uncomplicated influenza within 48 hours of illness onset . Baloxavir inhibits viral transcription resulting in inhibition of influenza virus replication . It has activity against influenza A and B and is a single-dose formulation . 46 When taken within 48 hours of symptom onset , baloxavir decreased symptom duration , viral shedding , and antibiotic use in healthy individuals with uncomplicated influenza . 47 However , resistance occurred in 2-10 % of the trial participants who received baloxavir , showing viral escape and reduced drug susceptibility . 47 Baloxavir is not recommended in pregnant or breastfeeding women , outpatients with complicated or progressive illness , severely immunosuppressed patients , or hospitalised patients with influenza because of a lack of information in these groups . 7 , 16
Consider hospitalisation for the severely ill with complications of suspected or laboratory-confirmed influenza , especially when associated with respiratory distress , hypoxaemia , impaired cardiopulmonary function , altered mental status or significant dehydration . 16
Chemoprophylaxis
Use of antivirals outside of the higher-risk groups listed in box 1 is in general not recommended , except to prevent disease transmission in particular settings such as contacts in hospital or residents of an aged care facility or for patients with household contacts at higher risk of poor outcomes from influenza . 29 When indicated , chemoprophylaxis for influenza should be given regardless of immunisation status , especially when there is a major difference between the predominant influenza strains and the vaccine antigens , or when immunosuppression makes adequate vaccine response unlikely . 16
NAIs may reduce the risk of viral shedding and disease transmission . When NAIs are given within 24-48 hours of symptom onset , treatment of the index case alone has been demonstrated to offer about 40 % household protection against secondary cases . When given as post-exposure prophylaxis , NAIs have been demonstrated to be 70-90 % effective in preventing laboratory-confirmed seasonal influenza . 48
A single dose of baloxavir , given as post-exposure prophylaxis to close contacts within 48 hours of exposure to an index household member with influenza who has also received antiviral treatment , significantly reduced the development of influenza by 86 %
47 , 49 when compared with placebo . Note that influenza A viruses with reduced susceptibility to baloxavir can develop in those receiving single-dose baloxavir , and are associated with prolonged illness
47 , 49
.
Table 3 . Current antivirals available for management of influenza in adults
Antiviral agent
Oseltamivir
Zanamivir
Peramivir
Baloxavir
* All NNDSS data are preliminary and subject to change as updates are received . The number of influenza-associated deaths reported to the NNDSS does not represent the true mortality associated with this disease . The number of deaths is reliant on the follow-up of cases to determine the outcome of their infection . The follow-up of cases is not a requirement of notification and are only inclusive of laboratory-confirmed cases of influenza . Due to retrospective revision , the variation across jurisdictions in methodology , representativeness and timeliness of death data , year-on-year comparisons of deaths in notified cases of influenza may not be reliable . Department of Health and Aged Care
Figure 7 . Number of influenza-associated deaths notified to the National Notifiable Diseases Surveillance System ( NNDSS ) and case fatality rate by five-year age group , 1 January to 15 October 2023 .*
Mechanism of action Treatment dose Prophylaxis dose Comments
Reduces influenza virus replication by inhibiting the viral surface enzyme neuraminidase , preventing release of new virus from cells
Reduces influenza virus replication by inhibiting the viral surface enzyme neuraminidase , preventing release of new virus from cells
Reduces influenza virus replication by inhibiting the viral surface enzyme neuraminidase , preventing release of new virus from cells
Inhibits influenza virus endonuclease within the polymerase acidic protein subunit of viral polymerase to block virus replication in infected respiratory tract cells
Antiviral chemoprophylaxis is an important component of the multifactorial bundle of interventions to control institutional outbreaks . These include isolation , testing , implementation of infection prevention and control measures , vaccination and environmental cleaning and disinfection . 50 The early detection of influenza outbreaks in longterm care facilities and hospitals is particularly important because
Oseltamivir 75mg orally , 12-hourly for five days
10mg by inhalation using the device provided , 12-hourly for five days
One 600mg dose IV over 15-30 min
40 to less than 80kg : 40mg orally as a single dose
80kg or more : 80mg orally as a single dose
influenza virus transmission can occur rapidly , with high attack rates and high risk of complications and mortality . 23 Oseltamivir chemoprophylaxis is an effective adjunct in controlling outbreaks in residential aged care facilities . 23 , 50 Given the relative paucity of symptoms of influenza in the immunosuppressed or elderly , consider an initial administration of oseltamivir at treatment dosing twice daily for five days ,
75mg orally once daily ; usual duration 10 days *
10mg once daily ; usual duration 10 days *
N / A
Post-exposure prophylaxis : same dose as for treatment , single dose
* Longer courses may be warranted in the setting of institutional outbreaks . Source : Neuzil KM in Harrison ’ s Principles of Internal Medicine 2022 7 , Uyeki TM 2021 16 , Australian Medicines Handbook 2024 45
Active against influenza A and B viruses , but reduced effectiveness in influenza B Infrequent nausea , vomiting Rare serious skin reactions ( eg , Stevens – Johnson syndrome , erythema multiforme ) Abnormal behaviour , hallucinations and delirium have rarely been described ( mainly in children ) Resistance may emerge infrequently in the immunocompetent , more commonly in the severely immunosuppressed Reduce dose for creatinine clearance 60mL / min or less
Active against influenza A and B viruses , including some influenza A viruses resistant to other neuraminidase inhibitors Rare bronchospasm , oropharyngeal or facial oedema Contraindicated in patients with asthma or COPD Should not be used for treatment of severe influenza given limited data Rare serious skin reactions ( eg , Stevens – Johnson syndrome , erythema multiforme ) Abnormal behaviour , hallucinations and delirium have rarely been described ( mainly in children and oseltamivir use )
Reserved for patients who cannot tolerate oral or inhaled agents Insufficient data on efficacy for hospitalised patients Reduce dose if creatinine clearance less than 50mL / minute Do not use in pregnant patients ( given limited data ) Rare serious skin reactions ( eg , Stevens – Johnson syndrome , erythema multiforme ) Abnormal behaviour , hallucinations and delirium have rarely been described ( mainly in children and oseltamivir use )
Equivalent to five days of oseltamivir against influenza A ; greater benefit against influenza B than oseltamivir Do not use for treatment of severe influenza ( given limited data ), immunocompromised hosts ( given concern for emergence of resistance ), or pregnant patients ( given limited data ) Resistance may emerge during treatment
followed by once daily dosing until the outbreak is over . There are limited data to guide duration of chemoprophylaxis , it may be reasonable to continue for at least two weeks and for one week longer than after the last known case has been identified . Oseltamivir safety and efficacy has been demonstrated for up to six
23 , 45 , 50 weeks . Table 3 provides an overview of antiviral agents .
Australian Influenza Surveillance Report National Influenza Season Summary 2023 3
Behavioural strategies to prevent transmission
A comprehensive review of non-pharmaceutical interventions in the community setting concluded that evidence is limited for many interventions including hand hygiene , respiratory etiquette , face masks and environmental cleaning , though mechanistic studies support the potential effects of these interventions . 51