Zanamivir

Zanamivir is an antiviral drug with activity against influenza virus [see Microbiology ( 12.4 )] .

• RELENZA, an influenza virus neuraminidase inhibitor (NAI), is indicated for: Treatment of acute, uncomplicated influenza type A and B infections in patients aged 7 years and older who have been symptomatic for no more than 2 days. ( 1.1 ) Prophylaxis of influenza in patients aged 5 years and older.ICD-10: J11.1

• RELENZA is contraindicated in patients with history of allergic reaction to any ingredient of RELENZA, including milk proteins [see Warnings and Precautions ( 5.2 ), Description ( 11 )] . Do not use in patients with history of allergic reaction to any ingredient of RELENZA, including milk proteins.contraindicated

Indication Dose Treatment of Influenza ( 2.2 ) 10 mg twice daily for 5 days Prophylaxis: ( 2.3 ) Household Setting 10 mg once daily for 10 days Community Outbreaks 10 mg once daily for 28 days Note: The 10-mg dose is provided by 2 inhalations (one 5-mg blister per inhalation). ( 2.1 ) 2.1 Dosing Considerations • RELENZA is for administration to the respiratory tract by oral inhalation only , using the DISKHALER device provided [see Warnings and Precautions ( 5.6 )] . • The 10-mg dose is provided by 2 inhalations (one 5-mg blister per inhalation). • Patients should be instructed in the use of the delivery system. Instructions should include a demonstration whenever possible. If RELENZA is prescribed for children, it should be used only under adult supervision and instruction, and the supervising adult should first be instructed by a healthcare professional [see Patient Counseling Information ( 17 )] . • Patients scheduled to use an inhaled bronchodilator at the same time as RELENZA should use their bronchodilator before taking RELENZA [see Patient Counseling Information ( 17 )] . 2.2 Treatment of Influenza • The recommended dose of RELENZA for treatment of influenza in adults and pediatric patients aged 7 years and older is 10 mg twice daily (approximately 12 hours apart) for 5 days. • Two doses should be taken on the first day of treatment whenever possible provided there is at least 2 hours between doses. • On subsequent days, doses should be about 12 hours apart (e.g., morning and evening) at approximately the same time each day.

• Bronchospasm: Serious, sometimes fatal, cases have occurred. Not recommended in individuals with underlying airways disease. Discontinue RELENZA if bronchospasm or decline in respiratory function develops. ( 5.1 ) • Allergic Reactions: Discontinue RELENZA and initiate appropriate treatment if an allergic reaction occurs or is suspected. ( 5.2 ) • Neuropsychiatric Events: Patients with influenza, particularly pediatric patients, may be at an increased risk of seizures, confusion, or abnormal behavior early in their illness. Monitor for signs of abnormal behavior. ( 5.3 ) • High-Risk Underlying Medical Conditions: Safety and effectiveness have not been demonstrated in these patients. ( 5.4 ) 5.1 Bronchospasm RELENZA is not recommended for treatment or prophylaxis of influenza in individuals with underlying airways disease (such as asthma or chronic obstructive pulmonary disease). Serious cases of bronchospasm, including fatalities, have been reported during treatment with RELENZA in patients with and without underlying airways disease. Many of these cases were reported during postmarketing and causality was difficult to assess. RELENZA should be discontinued in any patient who develops bronchospasm or decline in respiratory function; immediate treatment and hospitalization may be required. Some patients without prior pulmonary disease may also have respiratory abnormalities from acute respiratory infection that could resemble adverse drug reactions or increase patient vulnerability to adverse drug reactions.

The following adverse reactions are discussed in greater detail in other sections of the labeling: • Bronchospasm [see Warnings and Precautions ( 5.1 )] . • Safety information in patients with underlying airways disease [see Warnings and Precautions ( 5.1 )]. • Allergic-like reactions [see Warnings and Precautions ( 5.2 )] . The most common adverse events reported in greater than 1.5% of subjects treated with RELENZA and more commonly than in subjects treated with placebo are: • Treatment Trials – sinusitis, dizziness. ( 6.1 ) • Prophylaxis Trials – fever and/or chills, arthralgia, and articular rheumatism. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact GlaxoSmithKline at 1-888-825-5249 or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch . 6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared with rates in the clinical trials of another drug and may not reflect the rates observed in practice. The placebo used in clinical trials consisted of inhaled lactose powder, which is also the vehicle for the active drug; therefore, some adverse events occurring at similar frequencies in different treatment groups could be related to lactose vehicle inhalation. Treatment of Influenza Clinical Trials in Adults and Adolescents: Adverse events that occurred with an incidence greater than or equal to 1.5% in treatment trials are listed in Table 1.

8.1 Pregnancy Risk Summary Available data from published studies suggest that use of RELENZA during pregnancy is not associated with an increased risk of birth defects or adverse maternal or fetal outcomes. However, these studies are limited by their small sample sizes, which preclude a definitive assessment of the risk (see Data). There are risks to the mother and fetus associated with influenza infection in pregnancy (see Clinical Considerations) . In animal reproduction studies, no adverse developmental effects were observed with intravenous or subcutaneous administration of zanamivir at exposures 300 and 150 times, respectively, the systemic exposure at the maximum recommended human inhalation dose (MRHID) of 10 mg twice daily (see Data) . The background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the U.S. general population, the background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2% to 4% and 15% to 20%, respectively.

Metabolism

Absorption and Bioavailability Pharmacokinetic studies of orally inhaled zanamivir indicate that approximately 4% to 17% of the inhaled dose is systemically absorbed. The peak serum concentrations ranged from 17 to 142 ng/mL within 1 to 2 hours following a 10‑mg dose.

Reports of overdosage from administration of RELENZA have been received during postmarketing experience. The reported clinical signs or symptoms were similar to those observed with therapeutic doses of RELENZA and the underlying disease. As zanamivir has a low molecular weight, low protein binding, and small volume of distribution, it is expected to be removed by hemodialysis.

• Jul 26, 1999NDANDA021036Glaxosmithkline

1. 1Abnormal Behaviour39816%
2. 2Overdose39516%
3. 3Drug Exposure During Pregnancy2449.7%
4. 4Hallucination1596.3%
5. 5Drug Exposure Via Breast Milk1234.9%
6. 6No Adverse Event1174.6%
7. 7Delirium1164.6%
8. 8Loss Of Consciousness1044.1%
9. 9Pyrexia1004.0%
10. 10Death702.8%
11. 11Dyspnoea692.7%
12. 12Aggression572.3%
13. 13Altered State Of Consciousness572.3%
14. 14Depressed Level Of Consciousness562.2%
15. 15Pneumonia542.1%

Recent PubMed references pinned to Zanamivir as a MeSH major topic. Citations link to pubmed.ncbi.nlm.nih.gov.

• Metabolism and excretion pathways of CD388, a novel drug-fragment crystallizable conjugate for prevention of seasonal or pandemic influenza.
  Drug metabolism and disposition: the biological fate of chemicals · 2026 · Snoeys J, Hough G, Flanagan S, et al.
  PMID 41916098DOI 10.1016/j.dmd.2026.100270
• Zanamivir-Amantadine Conjugate: A Dual-Action Agent with Broad-Spectrum Synergistic Antiviral Efficacy.
  Journal of medicinal chemistry · 2026 · Wang Y, Hua L, Duan H, et al.
  PMID 41744161DOI 10.1021/acs.jmedchem.5c03547
• A multivalent nanobody-drug conjugate to prevent and treat influenza virus infections.
  Proceedings of the National Academy of Sciences of the United States of America · 2025 · Harmand TJ, Pietrok L, Rich H, et al.
  PMID 41183201DOI 10.1073/pnas.2409565122
• Prophylactic Efficacy of CD388, a Novel Drug-Fc Conjugate, in a Human Influenza A/H3N2 Virus Challenge Model: A Randomized, Controlled Phase 2a Study.
  Clinical infectious diseases : an official publication of the Infectious Diseases Society of America · 2025 · Rojas RE, Equils O, Villacian J, et al.
  PMID 41060047DOI 10.1093/cid/ciaf465
• Zanamivir exposure in healthy rats and rats with acute lung injury.
  Annals of medicine · 2025 · Klouček A, Šmardová J, Sklenárová M, et al.
  PMID 40684449DOI 10.1080/07853890.2025.2534523
• One-shot flu drug may beat vaccines.
  Science (New York, N.Y.) · 2025 · Cohen J
  PMID 40608925DOI 10.1126/science.aea2477
• Absorption, distribution, metabolism, and excretion of an antiviral drug-Fc conjugate CD388 following subcutaneous administration of (14)C-CD388 in the rat.
  Drug metabolism and disposition: the biological fate of chemicals · 2025 · Laenen A, Flanagan S, Hough G, et al.
  PMID 40540979DOI 10.1016/j.dmd.2025.100103
• A monoclonal anti-hemagglutinin stem antibody modified with zanamivir protects against both influenza A and B viruses.
  Proceedings of the National Academy of Sciences of the United States of America · 2025 · Liu X, Balligand T, Le Gall C, et al.
  PMID 40193611DOI 10.1073/pnas.2424889122

The 10 most recently updated of 27 ClinicalTrials.gov registrations naming Zanamivir as an intervention. Registration is not evidence of efficacy or safety — reference crosswalk only.

• A Phase 2 Trial Comparing Antiviral Treatments in Early Symptomatic Influenza
  Recruiting · Phase 2 · Interventional · 3,000 enrolled · University of Oxford
  NCT05648448updated 2026-04-14
• A/Texas Flu Challenge
  Recruiting · Phase 1 · Interventional · 50 enrolled · Emory University
  NCT06753474updated 2026-03-03
• Zanamivir Treatment of Vascular Permeability in Dengue (ZAP-DENGUE)
  Recruiting · Phase 2 · Interventional · 74 enrolled · George Washington University
  NCT04597437updated 2025-07-28
• Role of Neuraminidase Activity on Endothelial Dysfunction in Type 2 Diabetes
  Completed · Phase 2 · Interventional · 14 enrolled · University of Missouri-Columbia
  NCT04867707updated 2025-04-25
• An Intravenous (IV) Zanamivir Pharmacokinetics (PK) Study in Hospitalized Neonates and Infants With Influenza Infection
  Recruiting · Phase 2 · Interventional · 12 enrolled · GlaxoSmithKline
  NCT04494412updated 2025-03-17
• Study to Assess Efficacy and Safety of Baloxavir Marboxil In Combination With Standard-of-Care Neuraminidase Inhibitor In Hospitalized Participants With Severe Influenza
  Completed · Phase 3 · Interventional · 363 enrolled · Hoffmann-La Roche
  NCT03684044updated 2021-01-06
• A Study of Intravenous Zanamivir Versus Oral Oseltamivir in Adults and Adolescents Hospitalized With Influenza
  Completed · Phase 3 · Interventional · 626 enrolled · GlaxoSmithKline
  NCT01231620updated 2018-10-15
• A Study of Intravenous Zanamivir in the Treatment of Hospitalized Patients With Influenza Infection
  Completed · Phase 3 · Interventional · 21 enrolled · GlaxoSmithKline
  NCT01527110updated 2018-02-22
• Safety and Efficacy of Investigational Anti-Influenza Immune Plasma in Treating Influenza
  Completed · Phase 2 · Interventional · 98 enrolled · National Institute of Allergy and Infectious Diseases (NIAID)
  NCT01052480updated 2017-09-05
• A Study to Evaluate the Effect of Intravenous Zanamivir on Cardiac Conduction in Healthy Volunteers
  Completed · Phase 1 · Interventional · 40 enrolled · GlaxoSmithKline
  NCT01353729updated 2017-07-21

Frequently asked questions

How does Zanamivir work?

Zanamivir is an antiviral drug with activity against influenza virus [see Microbiology ( 12.4 )] .

What is Zanamivir used for?

According to FDA labeling, Zanamivir carries indications including: RELENZA, an influenza virus neuraminidase inhibitor (NAI), is indicated for: Treatment of acute, uncomplicated influenza type A and B infections in patients aged 7 years and older who have been symptomatic for no more than 2 days. ( 1.1 ) Prophylaxis of influenza in patients aged 5 years and older.. This is a reference summary of labeled uses, not medical advice or a treatment recommendation.

What class of drug is Zanamivir?

Zanamivir is classified as Neuraminidase inhibitors, Neuraminidase Inhibitor, Neuraminidase Inhibitors, Cellular Activity Alteration.

What are the brand names for Zanamivir?

Zanamivir is marketed under brand names including Relenza.

What are the contraindications for Zanamivir?

Zanamivir labeling lists contraindications including: RELENZA is contraindicated in patients with history of allergic reaction to any ingredient of RELENZA, including milk proteins [see Warnings and Precautions ( 5.2 ), Description ( 11 )] . Do not use in patients with history of allergic reaction to any ingredient of RELENZA, including milk proteins.. Always consult the full prescribing information and a clinician.