What are the recommended zanamivir (Relenza) dosing regimens for treatment and post‑exposure prophylaxis in adults and children, and are dose adjustments needed for renal impairment or obstructive airway disease?

Zanamivir Dosing

For influenza treatment in adults and children ≥7 years, administer zanamivir 10 mg (two 5-mg inhalations) twice daily for 5 days; for prophylaxis in those ≥5 years, use 10 mg once daily for 10 days. 1

Treatment Dosing

Adults

• 10 mg (two 5-mg inhalations) twice daily for 5 days (approximately 12 hours apart) 1
• Licensed for treatment of uncomplicated acute influenza A or B 1

Children

• Age ≥7 years: 10 mg (two 5-mg inhalations) twice daily for 5 days 1
• Age <7 years: Not approved for treatment 1
• The twice-daily dosing should be approximately 12 hours apart 1

Prophylaxis (Post-Exposure) Dosing

Adults

• 10 mg (two 5-mg inhalations) once daily for 10 days 1, 2
• Licensed for chemoprophylaxis of influenza 1

Children

• Age ≥5 years: 10 mg (two 5-mg inhalations) once daily for 10 days 1
• Age <5 years: Not approved for prophylaxis 1

Renal Impairment: No Dose Adjustment Required

Zanamivir requires no dose adjustment regardless of renal function severity, making it the preferred antiviral for patients with renal impairment. 1, 2

• Mild-to-moderate renal impairment: No dose adjustment needed 1
• Severe renal impairment: No dose adjustment needed 1, 2
• Any degree of renal dysfunction: Standard dosing applies 2

The rationale is that while renal impairment decreases zanamivir clearance and increases systemic exposure, only 4-17% of inhaled zanamivir is absorbed systemically 1. Studies showed that healthy volunteers tolerated intravenous zanamivir at systemic levels substantially higher than those achieved with inhaled dosing at recommended doses 1. The local lung concentrations—not systemic levels—drive efficacy 3.

Elderly Patients (Age >65 Years)

• No dose reduction based on age alone 1
• Use standard adult dosing 1

Critical Contraindication: Obstructive Airway Disease

Zanamivir is contraindicated in patients with underlying airways disease (asthma or COPD) due to risk of life-threatening bronchospasm. 1, 2

• Do not use in patients with asthma 1, 2
• Do not use in patients with chronic obstructive pulmonary disease 1, 2
• Rare reports of bronchospasm and decline in respiratory function have occurred 4, 5
• While controlled trials showed no adverse pulmonary function effects, the risk outweighs benefits in this population 4, 5

Administration Details

Device and Technique

• Administered via oral inhalation using a proprietary "Diskhaler" device 1
• Available as dry powder formulation 1
• Not an aerosol—do not use with nebulizers, ventilators, or other aerosolization devices 1
• Patients must be instructed on correct device use 1

Pharmacokinetics

• 7-21% of inhaled dose reaches the lungs 1
• 70-87% deposits in the oropharynx 1
• Only 4-17% absorbed systemically 1
• Half-life: 2.5-5.1 hours 1
• Excreted unchanged in urine (absorbed portion) and feces (unabsorbed portion) 1

Special Populations

Hepatic Dysfunction

• Not studied in patients with liver disease 1
• No specific dosing recommendations available 1

Seizure Disorders

• Seizure events reported in postmarketing surveillance 1
• No epidemiologic evidence of increased seizure risk 1
• No specific dosing adjustments recommended 1

Clinical Efficacy

• Reduces median time to symptom alleviation by 1-2.5 days when started within 48 hours of symptom onset 4, 5
• Accelerates return to normal activities 4, 5
• Reduces complications requiring antibacterial use 4, 5
• Effective in otherwise healthy adults, high-risk patients, and children aged 5-12 years 4, 5

Key Clinical Pitfalls to Avoid

• Do not prescribe for patients with asthma or COPD—bronchospasm risk is unacceptable 1, 2
• Do not attempt to nebulize the powder—use only the provided Diskhaler device 1
• Do not reduce dose in renal impairment—standard dosing applies to all renal function levels 1, 2
• Do not use in children <7 years for treatment or <5 years for prophylaxis—not approved in these age groups 1