Influenza Treatment (Antimicrobial)

Annual vaccination is essential for all those at risk of influenza. See Public Health Scotland and UKHSA recommendations for treatment and prophylaxis of Influenza. For otherwise healthy adults, antivirals are NOT recommended.

Seek advice for patients under the age of 13 and in current pregnancy (including up to 2 weeks post-partum).

Treat ‘at risk’ patients, only when influenza is circulating in the community and ideally within 48 hours of onset, or in a care home where influenza is likely. Directly acting antivirals (oseltamivir and zanamivir) have the greatest impact on influenza viral replication at the beginning of illness onset, or as post-exposure prophylaxis. As there is a greater body of evidence to support use of oseltamivir in severe influenza, treatment of severe influenza in a severely immunosuppressed patient with IV zanamivir is only recommended in circumstances where oseltamivir is unable to be administered or is unlikely to be effective. Historically, the supply of IV zanamivir has been unable to match the demand therefore use should be targeted towards patients with no enteral absorption.

In significantly unwell influenza patients, consider secondary bacterial infection and, if clinically indicated, add appropriate antibacterial cover (including staphylococcal cover) as per TAM guidance for community-acquired pneumonia.

At risk (of severe influenza and hospitalisation):

• Chronic neurological, hepatic, renal, respiratory or cardiovascular diseases
• Diabetes mellitus
• Immunocompromised (see below)
• Morbid obesity (BMI of 40 or greater)
• 65 years or over
• Current pregnancy and for 2 weeks post-partum
• Children under 6 months of age.

Examples of severe immunosuppression (this is not a comprehensive list) include:

• severe primary immunodeficiency
• current or recent (within 6 months) chemotherapy or radiotherapy for malignancy
• solid organ transplant recipients on immunosuppressive therapy
• bone marrow transplant recipients currently receiving immunosuppressive treatment, or within 12 months of receiving immunosuppression
• patients with current graft-versus-host disease
• patients currently receiving high dose systemic corticosteroids (equivalent to ≥40 mg prednisolone per day for >1 week in an adult, or ≥ 2mg/kg/day for ≥1 week in a child), and for at least 3 months after treatment has stopped
• people living with HIV with severe immunosuppression (CD4<200/μl or <15% of total lymphocytes in an adult or child over 5; CD4< 500/μl or <15% of total lymphocytes in a child aged 1 to 5; expert clinical opinion in a child aged under 1)
• patients currently or recently (within 6 months) on other types of highly immunosuppressive therapy or where the patient’s specialist regards them as severely immunosuppressed

Prescribing notes:

1. Swallowing difficulties or nasogastric administration in adults and children over 1 year: use capsules which are opened and mixed into an appropriate sugary liquid as oseltamivir has a very bitter taste. Avoid using the powder for suspension for children over 1 year of age and/or adults, as there may not be adequate quantities of the powder for suspension to meet demand for the under 1 year age group.
2. If oral, nasogastric or inhaled routes are unsuitable: intravenous zanamivir can be considered. See manufacturer's information for dosing in adults, children aged 6 years and over and in renal impairment.
3. In renal impairment: NHS Highland Renal specialists recommend using Renal Drug Database doses for oseltamivir in preference to doses quoted in UKHSA national guidance due to a wide safety margin for the drug and concerns of underdosing.  These doses have been added in the table below. For dosing in renal replacement therapies, please check the Renal Drug Database (password required).
4. In hepatic dysfunction or obesity: no dose adjustments are required.
5. Dosing in infants and children up to 12 years of age: see BNFc.
6. Vaccination whilst receiving influenza antiviral therapy: delay vaccination against influenza for 48 hours after antiviral treatment is finished to maximise efficacy.

For glossary of terms see Glossary.