Neuraminidase inhibitor (antiviral) Pregnancy: Limited data (<300 pregnancy outcomes); as a precautionary measure it is preferable to avoid use during pregnancy unless the clinical condition of the woman is such that the potential benefit to the mother significantly outweighs the possible risk to the foetus. Breastfeeding: a risk to the breastfed child cannot be excluded — decide whether to discontinue breastfeeding or therapy.

Zanamivir

Brand names: Relenza

A neuraminidase inhibitor antiviral used for the treatment and prophylaxis of influenza A and B, administered most commonly by oral inhalation.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: 10 mg (two inhalations of 5 mg)

Route: Oral inhalation, using the Diskhaler device provided only

Frequency: Twice daily for 5 days (treatment of influenza)

Max: Total daily inhaled dose of 20 mg (treatment regimen)

Treatment of influenza (adults and children from age 5 years): two inhalations (2 x 5 mg) twice daily for five days, giving a total daily inhaled dose of 20 mg. Treatment should begin as soon as possible, within 48 hours after onset of symptoms for adults and within 36 hours for children. Post-exposure prophylaxis: two inhalations (2 x 5 mg) once daily for 10 days, begun as soon as possible and within 36 hours of exposure to an infected person. Seasonal prophylaxis during a community outbreak: two inhalations (2 x 5 mg) once daily for up to 28 days. Paediatric dosing in the SPC is the same fixed dose as adults from age 5 years — it is not weight-based. Inhaled drugs such as asthma medication should be administered before Relenza. Zanamivir inhalation powder must not be made into an extemporaneous solution for administration by nebulisation or mechanical ventilation, and must only be administered using the device provided. Elderly patients: no dose modification required. US labelling gives the same 10 mg dose but specifies treatment from age 7 years and community-outbreak prophylaxis in adults and adolescents.

Dose adjustments

Renal

Impaired renal or hepatic function: no dose modification is required (SPC §4.2)

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Hypersensitivity to the active substance or to any of the excipients
Milk protein allergy

Side effects

Rash (common)
Allergic-type reactions including oropharyngeal oedema; urticaria (uncommon)
Bronchospasm, dyspnoea, throat tightness or constriction (uncommon) — may be acute and/or serious; discontinue and seek medical evaluation
Vasovagal-like reactions shortly after inhalation, in patients with influenza symptoms such as fever and dehydration (uncommon)
Anaphylactic/anaphylactoid reactions, facial oedema (rare); severe skin reactions including erythema multiforme, Stevens-Johnson syndrome and toxic epidermal necrolysis (rare)
Convulsions and psychiatric events (depressed level of consciousness, abnormal behaviour, hallucinations, delirium) reported during administration in patients with influenza, mainly in children and adolescents

Interactions

Live attenuated influenza vaccine (intranasal): should not be administered within 2 weeks before or 48 hours after zanamivir unless medically indicated (US labelling; no §4.5 interactions section captured in the UK SPC extract)
Trivalent inactivated influenza vaccine can be administered at any time relative to zanamivir (US labelling)

Clinical monograph

How it works

It inhibits the influenza viral neuraminidase enzyme, preventing release of newly formed virions from infected cells and limiting spread within the respiratory tract.

Prescribing in practice

Inhaled zanamivir can precipitate bronchospasm and should be used with caution, and generally avoided, in people with asthma or chronic obstructive pulmonary disease who should have a short-acting bronchodilator available.
It is most effective when started as early as possible after symptom onset, in line with NICE criteria for antiviral use during influenza circulation.
The lactose-containing inhalation powder must not be reconstituted and given through a nebuliser or mechanical ventilator.

Monitoring

No routine laboratory monitoring is required; observe for respiratory deterioration after inhalation and for neuropsychiatric symptoms.

Counselling the patient

Use a short-acting reliever inhaler first if you have asthma and have it to hand.
Start treatment as soon as possible after symptoms begin for best effect.
Stop and seek advice if you develop wheeze or breathing difficulty after inhaling the dose.

Evidence & guidelines

Use is supported by NICE technology appraisal guidance on antivirals for influenza.

Reference: NICE NG34; UKHSA influenza guidance; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Drugs

Oseltamivir · Neuraminidase Inhibitor (Antiviral)

Pathways