Zanamivir

Zanamivir is an inhaled neuraminidase inhibitor licensed for the treatment and post-exposure prophylaxis of influenza A and B (1, 2)

• antiviral efficacy is highest when treatment is initiated early, reducing symptom duration by approximately 1 to 1.5 days in patients presenting with acute non-severe influenza during circulating seasons (2,3)
• during circulating seasons, prescribing in primary care is targeted at individuals in clinical at-risk groups or those with severe immunosuppression under NHS England General Medical Services (GMS) regulations (3,4)

Pharmacology and Mechanism of Action

Mechanism of Action

• selectively inhibits influenza A and B viral neuraminidase enzymes, preventing the release of viral progeny from infected respiratory epithelial cells and restricting viral replication (1,2)

Clinical Efficacy Summary

• symptom reduction: reduces the duration of major clinical symptoms by 1 to 1.5 days in previously healthy and high-risk populations when initiated within 48 hours of symptom onset (2)
• patient benefit: maximal therapeutic response occurs in individuals presenting early post-symptom onset with fever (≥37.8 degrees C) and those in clinical at-risk groups (2)
• diagnostic context: clinical diagnostic accuracy for influenza-like illness reaches 60% to 80% during peak community circulation, optimising positive predictive value for targeted antiviral prescribing (1)

Indications and Prescribing Regimens

Treatment Pathways

• indication: acute non-severe influenza in adults and children aged 5 years and over presenting within 48 hours of symptom onset (3,4)
• adult and paediatric dose (aged 5 years and over): 10 mg (2 inhalations) twice daily for 5 days via Diskhaler (3,4)
• clinical role: preferred first-line alternative where oral oseltamivir is unsuitable, poorly tolerated, or where oseltamivir-resistant influenza strains are suspected (4)

Post-Exposure Prophylaxis (PEP) Pathways

• indication: exposed at-risk individuals or severely immunosuppressed individuals following close contact with an index case, initiated within 36 hours of exposure (3,4)
• adult and paediatric dose (aged 5 years and over): 10 mg (2 inhalations) once daily for 10 days (3,4)

Precautions and Safety Considerations

Contraindications and Warnings

• severe airway disease: avoid inhaled zanamivir in patients with severe asthma or severe COPD due to the risk of acute bronchospasm and rapid decline in lung function (4)
• administration capacity: ensure patients and carers possess sufficient inhaler technique to effectively operate the breath-actuated Diskhaler device (3)

Summary of Product Characteristics

• consult the official Summary of Product Characteristics (SmPC) for full details on renal dosing adjustments, drug interactions and storage (4)

References:

1. Drug and Therapeutics Bulletin (DTB). Zanamivir for influenza. 1999;37(11):81-84.
2. Monto AS, Fleming DM, Henry D, et al. Efficacy and safety of the neuraminidase inhibitor zanamivir in the treatment of influenza A and B virus infections. J Infect Dis. 1999;180(2):254-261.
3. National Institute for Health and Care Excellence (NICE). Amantadine, oseltamivir and zanamivir for the treatment of influenza. NICE Technology Appraisal [TA168]. 2009.
4. 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.