zanamivir
Brand: Relenza
Prototype: oseltamivir
Drug Class: neuraminidase inhibitor antiviral
Drug Family: antiviral
Subclass: inhaled neuraminidase inhibitor (influenza)
Organ Systems: infectious-diseaserespiratory
Mechanism of Action
Competitively inhibits influenza A and B neuraminidase, preventing cleavage of sialic acid from cell surface receptors; blocks viral release and spread from infected cells; inhaled formulation delivers drug directly to respiratory tract.
influenza neuraminidase (NA)
Indications
- treatment of influenza A and B (initiated within 48 hours of symptom onset)
- prophylaxis of influenza A and B in household contacts
Contraindications
- zanamivir hypersensitivity
- severe asthma or COPD (risk of bronchospasm)
Adverse Effects
Common
- cough (from inhalation)
- bronchospasm (particularly in reactive airway disease)
- sinusitis
Serious
- severe bronchospasm (with or without asthma/COPD — can be fatal)
- anaphylaxis
- neuropsychiatric events (particularly in pediatric patients)
Pharmacokinetics (ADME)
| Absorption | 4–17% systemic absorption (inhaled); rest deposited in oropharynx |
| Distribution | minimal systemic distribution from inhaled route |
| Metabolism | not metabolized (unchanged drug systemically available) |
| Excretion | renal (unchanged, absorbed fraction) |
| Half-life | 2.5–5.1 hours (systemic) |
| Onset | rapid (local respiratory tract) |
| Peak | 1–2 hours |
| Duration | 12 hours (twice-daily dosing for treatment) |
| Protein Binding | <10% |
| Vd | low (systemic) |
Drug Interactions
| Drug / Agent | Mechanism | Severity |
|---|---|---|
| live attenuated influenza vaccine | antiviral activity may reduce vaccine replication; do not administer 2 weeks before or 48 hours after zanamivir | moderate |
Nursing Considerations
- Teach inhaler technique: zanamivir is delivered via Diskhaler device; proper inhalation is essential for lung deposition.
- Assess for reactive airway disease before prescribing; contraindicated in severe asthma or COPD — have a bronchodilator available if zanamivir is used.
- Initiate within 48 hours of symptom onset for meaningful clinical benefit in influenza treatment.
- Counsel patients that zanamivir is not a substitute for annual influenza vaccination.
Clinical Pearls
- Zanamivir's inhaled route delivers very high concentrations directly to the respiratory epithelium, potentially advantageous for severe influenza pneumonia, while minimizing systemic exposure — though this also limits its role when systemic antiviral activity is needed.
- Resistance to zanamivir can develop but is less common than with oseltamivir; zanamivir retains activity against many oseltamivir-resistant H275Y strains.
Safety Profile
Pregnancy use-with-caution
Lactation use-with-caution
Renal Adjustment Not required
Hepatic Adjustment Not required
TDM Not required
Concordance Terms
Cross-referenced clinical concepts — click any term to see all content where it appears.