RELENZA Drug Patent Profile

Which patents cover Relenza, and when can generic versions of Relenza launch?

Relenza is a drug marketed by Glaxosmithkline and is included in one NDA.

The generic ingredient in RELENZA is zanamivir. One supplier is listed for this compound. Additional details are available on the zanamivir profile page.

Summary for RELENZA

US Patents:	0
Applicants:	1
NDAs:	1
Finished Product Suppliers / Packagers:	1
Raw Ingredient (Bulk) Api Vendors:	73
Clinical Trials:	9
Patent Applications:	5,323
Drug Prices:	Drug price information for RELENZA
What excipients (inactive ingredients) are in RELENZA?	RELENZA excipients list
DailyMed Link:	RELENZA at DailyMed

See drug prices for RELENZA

Recent Clinical Trials for RELENZA

Identify potential brand extensions & 505(b)(2) entrants

Sponsor	Phase
University of Oxford	Phase 2
Hospital Authority	Phase 3
Food and Health Bureau, Hong Kong	Phase 3

See all RELENZA clinical trials

Pharmacology for RELENZA

Drug Class	Neuraminidase Inhibitor
Mechanism of Action	Neuraminidase Inhibitors

US Patents and Regulatory Information for RELENZA

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Exclusivity Expiration
Glaxosmithkline	RELENZA	zanamivir	POWDER;INHALATION	021036-001	Jul 26, 1999		RX	Yes	Yes

Expired US Patents for RELENZA

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	Patent No.	Patent Expiration
Glaxosmithkline	RELENZA	zanamivir	POWDER;INHALATION	021036-001	Jul 26, 1999
Glaxosmithkline	RELENZA	zanamivir	POWDER;INHALATION	021036-001	Jul 26, 1999
Glaxosmithkline	RELENZA	zanamivir	POWDER;INHALATION	021036-001	Jul 26, 1999
Glaxosmithkline	RELENZA	zanamivir	POWDER;INHALATION	021036-001	Jul 26, 1999
Glaxosmithkline	RELENZA	zanamivir	POWDER;INHALATION	021036-001	Jul 26, 1999
Glaxosmithkline	RELENZA	zanamivir	POWDER;INHALATION	021036-001	Jul 26, 1999
Glaxosmithkline	RELENZA	zanamivir	POWDER;INHALATION	021036-001	Jul 26, 1999

EU/EMA Drug Approvals for RELENZA

Company	Drugname	Inn	Product Number / Indication	Status	Generic	Biosimilar	Orphan	Marketing Authorisation	Marketing Refusal
GlaxoSmithKline Trading Services Limited	Dectova	Zanamivir	EMEA/H/C/004102Dectova is indicated for the treatment of complicated and potentially life-threatening influenza A or B virus infection in adult and paediatric patients (aged ≥6 months) when:The patient’s influenza virus is known or suspected to be resistant to anti-influenza medicinal products other than zanamivir, and/orOther anti-viral medicinal products for treatment of influenza, including inhaled zanamivir, are not suitable for the individual patient.Dectova should be used in accordance with official guidance.	Authorised	no	no	no	2019-04-26

International Patents for RELENZA

See the table below for patents covering RELENZA around the world.

Country	Patent Number	Title	Estimated Expiration
Australia	7533891
Slovakia	282950
Ireland	56060	MEDICAMENT-CONTAINING PACK
Norway	962545
Croatia	P941001	CRYSTALLINE N-ACETYL NEURAMINIC ACID DERIVATIVES AND PROCESSES FOR THEIR PREPARATION
Japan	H0620532
Germany	3682457

Supplementary Protection Certificates for RELENZA

Patent Number	Supplementary Protection Certificate	SPC Country	SPC Expiration	SPC Description
0526543	C990030	Netherlands		PRODUCT NAME: ZANAMIVIRUM, DESGEWENST IN DE VORM VAN EEN FARMACEUTISCH AAN- VAARDBAAR ZOUT EN/OF VAN EEN FARMACEUTISCH AANVAARDBARE ESTER; NAT. REGISTRATION NO/DATE: RVG 24094 19990707; FIRST REGISTRATION: 14997 19990209
0526543	99C0042	Belgium		PRODUCT NAME: ZANAMIVIR; NAT. REGISTRATION NO/DATE: 725 IS 380 F 11 19990906; FIRST REGISTRATION: SE 14997 19990209
0208846	99C0032	Belgium		PRODUCT NAME: ZANAMIVIR; NAT. REGISTRATION NO/DATE: NL 24 551 19990726; FIRST REGISTRATION: SE - 14 997 19990209
0526543	34/1999	Austria		PRODUCT NAME: ''ZANAMIVIR'' GEGEBENENFALLS IN FORM EINES PHARMAZEUTISCH ANNEHMBAREN SALZES ODER DERIVATS; NAT. REGISTRATION NO/DATE: 1-23120 19990702; FIRST REGISTRATION: SE 14997 19990209
0526543	SPC/GB99/030	United Kingdom		PRODUCT NAME: ZANAMIVIR, OPTIONALLY IN THE FORM OF A PHARMACEUTICALLY ACCEPTABLE SALT OR DERIVATIVE; REGISTERED: SE 14997 19990209; UK PL10949/0327 19990625
0526543	990030	Netherlands		PRODUCT NAME: ZANAMIVIRUM, DESGEWENST IN DE VORM VAN EEN FARMACEUTISCH AAN- VAARDBAAR ZOUT EN/OF VAN EEN FARMACEUTISCH AANVAARDBARE ESTER; NATL. REGISTRATION NO/DATE: RVG 24094 19990707; FIRST REGISTRATION: SE 14997 19990209

RELENZA: Market Dynamics and Financial Trajectory

Last updated: February 19, 2026

Relenza, an antiviral medication manufactured by GlaxoSmithKline (GSK), targets influenza A and B viruses by inhibiting viral neuraminidase. Its market presence and financial performance are shaped by factors including influenza season severity, competition, patent expirations, and regulatory landscape.

What is the current market size and projected growth for influenza antivirals?

The global influenza antiviral market is a significant segment within the broader infectious disease therapeutics sector. Market size is directly correlated with the incidence of seasonal influenza and the threat of pandemic influenza outbreaks.

• Current Market Size: In 2023, the global influenza antiviral market was valued at approximately $3.5 billion. This figure is derived from sales of prescription antiviral drugs, including neuraminidase inhibitors like Relenza and Tamiflu (oseltamivir), and baloxavir marboxil. [1]
• Projected Growth: The market is projected to grow at a compound annual growth rate (CAGR) of 4.2% from 2024 to 2030, reaching an estimated $4.7 billion by 2030. [1]
• Drivers of Growth: Key drivers include increasing awareness of influenza prevention, government initiatives for pandemic preparedness, and the development of new antiviral agents. The cyclical nature of influenza seasons also influences year-on-year sales.
• Restraints: Factors limiting growth include the development of antiviral resistance, the availability of generic alternatives following patent expirations, and the effectiveness of influenza vaccination programs.

What is Relenza's historical sales performance and market share?

Relenza, under the brand name Zanamivir, has been a consistent player in the influenza antiviral market since its approval. Its sales have been influenced by the timing and severity of influenza seasons.

• Peak Sales: Relenza achieved peak annual sales of approximately $600 million in the mid-2000s, driven by its efficacy against influenza A and B. [2]
• Declining Trend: In recent years, Relenza's sales have experienced a downward trend. In 2022, global sales for Relenza were reported to be around $85 million. [3] This decline is attributed to several factors, primarily the emergence of more convenient treatment options and generic competition.
• Market Share: Relenza's market share has decreased significantly from its peak. While it once held a substantial portion of the neuraminidase inhibitor market, it now represents a smaller fraction. Tamiflu (oseltamivir) has historically maintained a larger market share due to its oral administration and broader physician adoption.
• Geographic Distribution: Relenza sales are primarily concentrated in North America and Europe, where influenza surveillance and treatment protocols are well-established.

What are the key competitive products to Relenza?

The competitive landscape for Relenza is characterized by other antiviral medications targeting influenza, as well as preventative measures like vaccination.

• Neuraminidase Inhibitors (NIs):
  • Oseltamivir (Tamiflu): Developed by Roche, Tamiflu is an oral neuraminidase inhibitor and has been Relenza's primary competitor since its inception. Its ease of administration has contributed to its market dominance. Generic versions of oseltamivir are now widely available, increasing price competition.
  • Peramivir (Rapivab): Developed by BioCryst Pharmaceuticals, Peramivir is an intravenous neuraminidase inhibitor approved for hospitalized patients. Its use is more specialized and does not directly compete with Relenza for outpatient treatment.
• Cap-Dependent Endonuclease Inhibitors:
  • Baloxavir Marboxil (Xofluza): Developed by Shionogi and marketed by Genentech/Roche in the US, Xofluza represents a newer class of antivirals. It targets a different viral mechanism and offers a single-dose oral treatment. Xofluza has gained significant market traction due to its novel mechanism and single-dose regimen, posing a direct challenge to established NIs like Relenza. [4]
• Influenza Vaccines: While not a direct treatment competitor, influenza vaccines are the primary preventative measure. The effectiveness and uptake of annual flu vaccines directly impact the overall incidence of influenza, thereby influencing the demand for antiviral treatments.

What is the patent status and lifecycle of Relenza?

The patent protection surrounding Relenza has been a critical factor in its commercial viability.

• Original Patents: The original patents protecting zanamivir (Relenza) and its use were filed in the early to mid-1990s. Key patents began expiring in the United States around 2010 and in Europe shortly thereafter. [5]
• Patent Expirations: Following the expiration of primary patents, generic manufacturers have entered the market with their own versions of zanamivir. This has led to a significant reduction in pricing power for the branded product.
• Evergreening Efforts: GSK has historically pursued strategies to extend patent protection, such as seeking new method-of-use patents or formulation patents. However, these efforts have had limited success in significantly extending the market exclusivity for the core zanamivir molecule.
• Current Market Status: Relenza is now largely a genericized product. While GSK continues to market the branded version, the majority of zanamivir prescriptions are likely filled with generics, further impacting branded sales revenue.

What regulatory factors and policies influence Relenza's market access?

Regulatory approvals and evolving healthcare policies play a crucial role in the accessibility and adoption of influenza antivirals.

• FDA Approval: Relenza was first approved by the U.S. Food and Drug Administration (FDA) in 1999 for the treatment of uncomplicated influenza A and B in patients 7 years of age and older. [6] Subsequent approvals expanded its indications, including for prophylaxis.
• EMA Approval: The European Medicines Agency (EMA) granted marketing authorization for Relenza in 1999.
• Antiviral Stockpiling Programs: Governments worldwide maintain stockpiles of influenza antivirals for pandemic preparedness. Relenza has been a component of such stockpiles, though its inclusion and usage guidelines are subject to periodic review based on emerging scientific data and alternative treatment availability.
• Reimbursement Policies: Reimbursement policies by public and private payers influence physician prescribing habits and patient access. As generic zanamivir became available, payers often favored lower-cost alternatives, impacting Relenza's market share.
• Pandemic Influenza Preparedness: During pandemic influenza threats, regulatory agencies may fast-track approvals or provide emergency use authorizations for antiviral treatments. While Relenza has been considered, newer agents or broader-spectrum antivirals may receive priority depending on the specific pandemic strain.
• Antiviral Resistance Surveillance: Ongoing surveillance for antiviral resistance by public health organizations like the Centers for Disease Control and Prevention (CDC) influences treatment guidelines. If widespread resistance to neuraminidase inhibitors emerges, the utility and market for Relenza could be further diminished. [7]

What is the financial outlook for GlaxoSmithKline concerning Relenza?

GSK's financial performance related to Relenza is now a minor component of its overall revenue, reflecting the drug's mature stage and genericization.

• Revenue Contribution: Relenza's contribution to GSK's annual revenue has steadily declined. In 2022, it accounted for a negligible percentage of the company's total sales, which exceeded £29 billion. [8]
• Genericization Impact: The expiration of patents and the subsequent entry of generic zanamivir have eroded branded sales and reduced profit margins significantly. GSK's revenue from Relenza is now primarily derived from its remaining branded sales and potentially from agreements with generic manufacturers.
• R&D Focus Shift: GSK has largely shifted its research and development focus away from older antiviral agents like Relenza towards newer therapeutic areas, including oncology, immunology, and vaccines. Investment in new influenza treatments has been channeled into next-generation vaccines and potentially novel antiviral mechanisms.
• Portfolio Management: Relenza is managed as a legacy product within GSK's broader respiratory and antiviral portfolio. Its strategic importance has diminished as the company prioritizes products with higher growth potential and longer patent protection.

What are the key scientific and clinical considerations for Relenza?

Clinical efficacy, safety, and the emergence of resistance are paramount in understanding Relenza's long-term viability.

• Mechanism of Action: Relenza inhibits the neuraminidase enzyme on the surface of influenza viruses. This enzyme is crucial for the release of newly formed virus particles from infected cells and their spread to other cells. By blocking neuraminidase, Relenza prevents the spread of the virus within the respiratory tract.
• Efficacy: Relenza has demonstrated efficacy in reducing the duration of influenza symptoms by approximately one to two days when initiated within 48 hours of symptom onset. It is also effective in preventing influenza in individuals exposed to the virus.
• Administration: Relenza is administered via inhalation using a special device (Diskus). This method of delivery can be a barrier for some patients, particularly children and the elderly, or those with respiratory conditions like asthma. [9] This contrasts with oral medications like Tamiflu and Xofluza, which offer greater convenience.
• Safety Profile: Common side effects include headache, nausea, diarrhea, and sinusitis. Bronchospasm has been reported, particularly in individuals with underlying asthma or COPD, making it a contraindication in some patient populations. [9]
• Antiviral Resistance: Like other neuraminidase inhibitors, influenza viruses can develop resistance to zanamivir. Mutations in the neuraminidase gene can reduce the drug's binding affinity, rendering it less effective. The CDC and other global health organizations continuously monitor for resistance. [7] While resistance has been observed, it has not yet reached levels that render the drug completely ineffective against circulating strains, but it remains a concern.
• Clinical Trial Data: Numerous clinical trials have established Relenza's efficacy and safety profile. However, newer trials are increasingly focused on newer agents like Xofluza, or on novel vaccine technologies.

Key Takeaways

Relenza (zanamivir) faces significant market headwinds due to patent expirations, the emergence of more convenient oral antivirals like Xofluza, and the continued prevalence of generic oseltamivir. While it retains a place in influenza treatment and prophylaxis, its market share and financial contribution to GlaxoSmithKline have substantially diminished from their peak. The drug's inhaled administration is a key differentiator compared to its main competitors. Future demand will be influenced by influenza season severity, the development of antiviral resistance, and the ongoing evolution of treatment guidelines and public health preparedness strategies.

Frequently Asked Questions

1. Is Relenza still recommended for influenza treatment? Relenza is still recommended by some health authorities for the treatment of uncomplicated influenza A and B in individuals 7 years of age and older, provided treatment is initiated within 48 hours of symptom onset. However, its use is declining in favor of more convenient oral medications. [7]
2. What are the main advantages of Relenza over other influenza antivirals? Relenza's primary advantage is its mechanism of action and its efficacy when administered appropriately. However, compared to oral options, its inhaled delivery is generally considered a disadvantage in terms of convenience and patient adherence.
3. Can Relenza be used for pandemic influenza preparedness? Relenza has been considered and included in some national stockpiles for pandemic influenza preparedness. However, its utility in a pandemic scenario would depend on the specific influenza strain involved and its susceptibility to neuraminidase inhibitors. [7]
4. What is the primary reason for Relenza's declining sales? The primary reasons for Relenza's declining sales are the expiration of its patents, leading to generic competition, and the introduction of newer, more convenient oral antiviral medications like baloxavir marboxil (Xofluza).
5. Does GlaxoSmithKline continue to invest in the development of Relenza? GlaxoSmithKline has largely shifted its R&D focus away from older antiviral molecules like Relenza. Investments are now concentrated on newer therapeutic areas and next-generation influenza vaccines. [8]

Citations

[1] Grand View Research. (2023). Influenza Antiviral Drugs Market Size, Share & Trends Analysis Report. [2] GlaxoSmithKline plc. (Annual Reports, various years). [3] IQVIA. (Data accessed 2023). Global pharmaceutical sales data. [4] Shionogi & Co., Ltd. (2022). Shionogi Reports Full-Year Financial Results for Fiscal Year Ended March 31, 2022. [5] U.S. Patent and Trademark Office. (Patent database searches). [6] U.S. Food and Drug Administration. (1999). FDA Approves Relenza for Influenza. [7] Centers for Disease Control and Prevention. (2023). Antiviral Drugs for Influenza. [8] GlaxoSmithKline plc. (2023). Annual Report and Strategic Update 2022. [9] Prescribing Information for Relenza. (Current version). GlaxoSmithKline.