Antiviral medications for the prevention and treatment of seasonal influenza

Advisory Alert

November 7, 2016

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Antiviral medications are an important adjunct to influenza vaccination in the prevention and control of influenza, particularly among persons at high risk of influenza complicationsⁱ, for those with severe or complicated illness, and among residents and unimmunized staffⁱⁱ in institutional settings during influenza outbreaks. This Advisory Alert provides information on the recommended use of antiviral medications for the prevention and treatment of seasonal influenza.

Antiviral medications

In Canada, three products are licensed for use for chemoprophylaxis and treatment of influenza; however, only the neuraminidase inhibitors (NI) oseltamivir (Tamiflu®) and zanamivir (Relenza®) are recommended. NI’s work by blocking the exit of the influenza virus from respiratory cells, preventing further replication of the virus. Both are active against influenza A and B viruses.

Effectiveness

Clinical trials and observational data show that early treatment with antiviral medication can shorten the duration of symptoms; reduce the risk of influenza complications; reduce hospitalizations and duration of stay, and reduce the risk of death among patients hospitalized with influenza. Antivirals should be taken as soon as possible, ideally within 48 hours of symptom onset. However, they could still have some benefits in patients with severe, complicated, or progressive illness and in hospitalized patients when started after 48 hours of illness onset. Decisions about starting antiviral treatment should not wait for laboratory confirmation of influenza once influenza is circulating in the community. Although not routinely indicated, when used for chemoprophylaxis, antiviral medications are approximately 70 to 90% effective in preventing influenza.

Recommended recipients

Influenza antiviral medications are recommended for:

Treatment of moderate, progressive, severe, or complicated influenza, such as individuals who are hospitalized with influenza-like illness.
Treatment of those at high risk for complications of influenza, such as children less than 5 years of age, adults 65 years of age and over, and those with underlying medical conditionsⁱ.
Treatment and prevention in influenza outbreaks in institutional settings.

Indications, dosage and duration of therapy (for those without contraindications)

Oseltamivir (oral medication)

Authorized for use in persons 1 year of age and older; may be used in younger persons on a case-by-case basis.
Children ≥ 1 year of age: weight-based-dosing when ≤ 15 kg to 40 kg.
Older children and adults (> 40 kg):
- Treatment: 75 mg twice daily x 5 days
- Chemoprophylaxis: 75 mg once daily x 10 days (or in institutional outbreaks until the outbreak is declared over)
Dosing adjustments are required for patients with known renal impairments.

Zanamivir (dry powder for inhalation)

Authorized for use in persons 7 years of age and older.
Persons ≥ 7 years of age:
- Treatment: (two 5 mg inhalations) twice daily x 5 days
- Chemoprophylaxis: (two 5 mg inhalations) once daily x 10 days (or in institutional outbreaks until the outbreak is declared over)

Full treatment and chemoprophylaxis regimen information is available from the Association of Medical Microbiology and Infectious Disease Canada Guideline at: https://www.ammi.ca/Content/Guidelines/Flu%20%28published%20version%29%20FINAL.pdf.

There is very little resistance to oseltamivir or zanamivir among recently circulating strains of influenza. Prudent use of antiviral medication is advised to minimize development of resistance to these agents. Current antiviral resistance monitoring information is available through the Ontario Respiratory Pathogen Bulletin published weekly by Public Health Ontario available at: http://www.publichealthontario.ca/en/ServicesAndTools/SurveillanceServices/Pages/Ontario-Respiratory-Virus-Bulletin.aspx

Should you have any questions about antiviral medications for the treatment and prevention of influenza, please contact the control of infectious diseases program as per below.

Sincerely,
P. Sutcliffe, MD, MHSc, FRCPC
Medical Officer of Health

For all reporting, inquiries or comments, please contact the Sudbury & District Health Unit at 705.522.9200, ext. 301.

ⁱ List of conditions that increase the risk for influenza complications: chronic pulmonary disease, including asthma; cardiovascular disease (excluding hypertension); malignancy; chronic renal insufficiency; diabetes mellitus and other metabolic disease; anemia and hemoglobinopathies, such as sickle cell disease; immunosuppression due to disease or medication; neurologic and neurodevelopmental disorders; children younger than 5 years of age; individuals 65 years of age or older; people of any age who live in nursing homes or other chronic care facilities; pregnant women and up to 4 weeks post-partum; individuals 3 z-scores above the mean for age and gender; Indigenous peoples.
 ⁱⁱ Or for all staff working in institutions during an influenza outbreak when the circulating virus and vaccine are mismatched.

This item was last modified on November 7, 2016