What is Relenza?
Relenza (zanamivir) is an inhaled antiviral with Spanish product information for influenza A and B treatment and prevention. It uses the Diskhaler to deliver powder to the respiratory tract. Systemic absorption is low, approximately 10–20%, but this does not eliminate serious adverse effects.
Authorisation and treatment recommendations differ. WHO’s 2024 guideline strongly recommends against oseltamivir and zanamivir for non-severe influenza. It conditionally supports oseltamivir for severe influenza, with very low-certainty evidence. US CDC guidance dated March 2026 recommends prompt antiviral treatment for hospitalised, severe/progressive or higher-risk patients and allows selected early outpatient treatment. These are attributed recommendations, not a new Spanish prescribing policy. A clinician must apply the relevant official guidance, local epidemiology and individual circumstances.
How does Relenza work?
Influenza haemagglutinin helps the virus enter cells; neuraminidase helps newly formed virus particles leave infected cells. Zanamivir inhibits neuraminidase and limits spread to further respiratory cells. It does not treat every respiratory infection or replace vaccination.
Early assessment matters. The Spanish label specifies treatment within 48 hours after symptoms begin in adults and within 36 hours in children. Do not interpret these windows as a reason to avoid seeking care later.
Who is Relenza for?
Treatment: Adults and children aged 5 years and over with typical influenza symptoms when influenza is circulating, within the age-specific start windows.
Post-exposure prevention: Adults and children aged 5 years and over after contact with a clinically diagnosed household case; start within 36 hours. Seasonal prevention is reserved for exceptional circumstances and individual assessment.
The label does not establish efficacy for treating older adults aged 65 years and over. Evidence is insufficient in severe asthma, other chronic respiratory disease, unstable chronic illness and immunosuppression; institutional prevention evidence is also limited. These groups must not be presented as automatic candidates for Relenza.
Do not use Relenza if you are allergic to zanamivir, an excipient or milk proteins. Asthma and COPD are serious precautions in the Spanish label, not the same category as those contraindications. Severe asthma requires close supervision and facilities for bronchoconstriction. Patients unable to use the Diskhaler correctly need another clinical assessment; it is not indicated below 5 years.
Dosage
Use only the supplied Diskhaler, one blister per inhalation. Each blister contains 5 mg; the emitted amount is 4 mg per inhalation. These are different measurements, not a reason to change the prescribed two-inhalation dose.
| Indication | Dose | Frequency | Duration |
|---|---|---|---|
| Treatment (adults and children ≥5 years) | 10 mg (2 inhalations of 5 mg) | Twice daily | 5 days |
| Post-exposure prevention (adults and children ≥5 years) | 10 mg (2 inhalations of 5 mg) | Once daily | 10 days |
| Seasonal prevention (exceptional circumstances) | 10 mg (2 inhalations of 5 mg) | Once daily | Up to 28 days |
Take the two inhalations consecutively. Prescribed inhaled medicines, including maintenance bronchodilators, are used before Relenza. Patients with asthma or COPD selected for treatment must keep a rapid-acting bronchodilator available and follow their clinician’s instructions. Do not infer a routine rescue dose before every administration.
Never dissolve the powder for nebulisation or mechanical ventilation: obstruction of delivery equipment has caused a fatal outcome. Follow the leaflet’s device instructions.
Side effects
Labelled frequencies
Rash is common. Bronchospasm, breathlessness, throat tightness, urticaria and allergic-type reactions including throat swelling are uncommon. Anaphylaxis, facial swelling and severe skin reactions are rare. The label separately describes rare acute severe respiratory reports in patients with respiratory disease and very rare reports in those without such a history.
Serious risks
Stop Relenza and seek immediate medical help for wheezing, chest tightness, breathing difficulty, swelling or severe skin/mucosal reactions. Low absorption does not make these risks negligible.
Confusion, abnormal behaviour, hallucinations and other neuropsychiatric events have been reported, especially in children and adolescents. Influenza itself can cause such events. Monitor for behavioural changes and seek prompt assessment; their uncertain cause does not justify ignoring them.
Relenza and Tamiflu
| Feature | Relenza (zanamivir) | Tamiflu (oseltamivir) |
|---|---|---|
| Route | Inhaled through Diskhaler | Oral capsule or suspension |
| Treatment age in Spanish product information | 5 years and over | Includes full-term newborns |
| Respiratory considerations | Risk of bronchospasm; special precautions in asthma/COPD | Oral administration; individual clinical assessment |
| Important adverse effects | Bronchospasm and hypersensitivity | Nausea, vomiting and serious hypersensitivity |
This comparison does not rank treatments. Low systemic exposure alone is not a reason to prefer Relenza. CDC advice about later oseltamivir in severe or progressive influenza does not prove benefit from starting inhaled zanamivir late.
Online assessment for Relenza (Zanamivir)
Seek prompt assessment for flu symptoms, especially with breathing difficulty, deterioration or risk factors. Do not wait for an online consultation when urgent care is needed, and do not assume it is too late to seek help after 48 hours.
Prescrivia is a technology intermediary connecting patients with independent doctors and licensed pharmacies. We do not provide medical services, prescribe, employ doctors, sell or dispense medicines.
- Assessment: Provide your symptoms or travel plans, medical history and all current medicines.
- Independent review: A doctor decides whether a prescription is clinically appropriate; Prescrivia does not guarantee a prescription.
- Dispensing: Any lawful dispensing is the responsibility of a licensed pharmacy, subject to the applicable rules and product availability.
In Spain, distance selling of prescription medicines is prohibited. An online assessment or a product label does not establish that a medicine can legally be supplied or delivered through this platform. This information does not change eligibility or fulfilment rules.
Important safety information
Do not use Relenza with zanamivir, excipient or milk-protein allergy. Its lactose also makes it unsuitable with hereditary galactose intolerance, total lactase deficiency or glucose-galactose malabsorption.
Asthma/COPD requires the specific precautions above. Stop and seek immediate help for breathing difficulty after inhalation.
Pregnancy: The label prefers avoidance unless the potential maternal benefit substantially outweighs fetal risk. Breastfeeding requires a decision on stopping breastfeeding or avoiding/stopping treatment based on benefits and risks.
Vaccination: Relenza does not replace influenza vaccination. Its preventive protection lasts only while it is taken. Follow official vaccination recommendations and have unusual behaviour or worsening illness assessed promptly.
Sources
- AEMPS: Relenza, sections 2 and 4.1–4.8.
- AEMPS: Tamiflu, sections 4.1–4.2.
- WHO 2024: non-severe influenza, sections 7.1.4 and 7.1.7.
- WHO 2024: severe influenza, section 8.1.1.
- CDC: antiviral guidance, March 2026.
- BOE: Article 3.5.
This information does not replace advice from a qualified healthcare professional.
Frequently asked questions
- What is Relenza used for?
- The Spanish label covers treatment of influenza A and B and post-exposure prevention from age 5 years, under specified circumstances. Treatment starts within 48 hours of symptoms in adults and 36 hours in children; post-exposure prevention starts within 36 hours of contact. Authorisation does not mean routine treatment is recommended for every patient.
- Why does early assessment matter with Relenza?
- Zanamivir limits viral spread by inhibiting neuraminidase. Its labelled start window differs for adults, children and prevention. Seek prompt medical assessment even if that window has passed, especially for severe or worsening illness. Evidence for later oseltamivir treatment in selected patients must not be transferred to inhaled zanamivir.
- How is Relenza taken?
- Use only the supplied Diskhaler. Treatment consists of two inhalations of 5 mg (10 mg per dose), twice daily for 5 days. Each inhalation uses one blister. The powder must not be made into a solution for a nebuliser or mechanical ventilator.
- Can people with asthma or COPD use Relenza?
- The Spanish label requires careful assessment because bronchospasm can be severe. Severe asthma requires close medical supervision and facilities to manage bronchoconstriction. If prescribed, a rapid-acting bronchodilator must be available; maintenance inhaled bronchodilators are taken before Relenza. This is not an instruction for everyone to take a rescue dose before each inhalation.
- Is Relenza the same as Tamiflu?
- Both inhibit influenza neuraminidase, but Relenza is inhaled zanamivir and Tamiflu is oral oseltamivir. Age limits, administration, warnings and evidence differ. A doctor must assess whether any antiviral is appropriate rather than assume the products are interchangeable.
Related treatments
Compare related options in the same wider treatment route.
Intermediary notice: Prescrivia connects patients with independent doctors and licensed pharmacies. We do not provide medical advice, employ doctors, or sell medicines. All medical decisions are made by independent healthcare professionals, and prescription-only medicines require a valid prescription. Treatment is not guaranteed — whether a prescription is issued depends on an independent doctor's clinical assessment.
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