Oseltamivir in the treatment influenza in the community

Use of Antivirals in the Treatment of adults and children in community/A&E (1,2)

• antiviral treatment with oral oseltamivir or inhaled zanamivir is recommended during active circulating influenza seasons for individuals at risk of severe disease presenting with acute non-severe influenza (1, 2)
• updated UK Health Security Agency (UKHSA) guidance aligns with WHO/ECDC international definitions, replacing the terms "complicated / uncomplicated" with "severe / non-severe" influenza (2)
• GPs may prescribe antivirals under General Medical Services (GMS) regulations once the Chief Medical Officer (CMO) confirms influenza is circulating in the community via the Central Alerting System (CAS), with treatment initiated as early as possible (within 48 hours of symptom onset) (1)

Indications and Illness Severity

Terminology and Clinical Presentation

• non-severe influenza: sudden onset of respiratory and systemic symptoms (fever, cough, sore throat, myalgia, headache, malaise) without signs of severe complications
• severe influenza: presence of clinical complications directly resulting from influenza virus infection (e.g., lower respiratory tract infection, pneumonia, sepsis, acute exacerbation of underlying disease, encephalopathy) requiring hospitalisation or critical care (2)

Risk Factors for Severe Influenza

• antiviral treatment should be offered to patients presenting with non-severe influenza who belong to clinical risk groups:
  • adults aged 65 years or older
  • chronic respiratory, cardiovascular (including congenital heart disease), renal, hepatic, or neurological conditions
  • diabetes mellitus
  • morbid obesity (BMI >= 40 kg/m2)
  • pregnancy (including up to 2 weeks post-partum)
  • children under 6 months of age
  • immunosuppression
• previously healthy individuals: routine antiviral treatment is not recommended unless the clinician judges the individual to be at high risk of rapid progression or severe complications

Severe Immunosuppression Criteria

• defined separately to guide antiviral choice, course duration, and resistance monitoring:
  • severe primary immunodeficiency
  • active or recent chemotherapy or radiotherapy for malignancy (within 6 months)
  • solid organ transplant recipients or bone marrow transplant recipients (within 12 months or on immunosuppression)
  • high-dose systemic corticosteroids (>=40 mg prednisolone daily for >1 week in an adult)
  • advanced HIV infection (CD4 < 200/microlitre)

Prescribing Pathways and Regimens

First-Line Treatment Options

• oseltamivir (oral neuraminidase inhibitor):
  • standard first-line agent for non-severe influenza in adults and children (including full-term neonates) (1)
  • standard adult dose: 75 mg twice daily orally for 5 days
  • initiation window: start within 48 hours of symptom onset for maximum clinical benefit
• zanamivir (inhaled neuraminidase inhibitor):
  • alternative first-line option for patients aged 5 years and over where oseltamivir is poorly tolerated
  • standard adult dose: 10 mg (2 inhalations) twice daily for 5 days
  • initiation window: start within 48 hours of symptom onset
  • note: avoid inhaled zanamivir in severe asthma or severe COPD due to risk of acute bronchospasm

Second-Line Agents and Resistance Management

• baloxavir marboxil (oral cap-dependent endonuclease inhibitor):
  • single-dose oral option for non-severe influenza in community settings (2)
• severe immunosuppression regimens:
  • oseltamivir 75 mg twice daily PO is first-line; extended 10-day courses may be indicated
• suspected or confirmed oseltamivir resistance:
  • inhaled zanamivir (10 mg twice daily for 5 days) is the preferred alternative; seek specialist virological advice if inhaled agents cannot be self-administered

Special Populations

• pregnancy and breastfeeding:
  • oral oseltamivir (75 mg twice daily for 5 days) remains the preferred first-line treatment at any stage of pregnancy due to robust safety profiles
• renal impairment:
  • adjust oseltamivir treatment dosage according to estimated glomerular filtration rate / creatinine clearance

Reference:

1. NHS England. Letter from the Chief Medical Officer and Chief Pharmaceutical Officer - Influenza season 2024/25: Use of antiviral medicines. Central Alerting System (CAS). Published 3 December 2024.
2. UK Health Security Agency (UKHSA). Guidance on use of antiviral agents for the treatment and prophylaxis of seasonal influenza. UKHSA Public Health Guidance. Updated October 2026.