Last updated: October 8, 2026
Mepolizumab, marketed by GSK as Nucala, is a commercially established anti-interleukin-5 biologic used across severe eosinophilic asthma and several eosinophil-driven diseases. GSK reported Nucala sales of approximately £1.6 billion in 2023 and about £1.7 billion in 2024, making it one of the company’s largest respiratory assets. Growth has shifted from initial severe-asthma uptake toward chronic use, geographic expansion, subcutaneous delivery, and label extensions in chronic rhinosinusitis with nasal polyps, eosinophilic granulomatosis with polyangiitis, and hypereosinophilic syndrome.[1,2]
The principal medium-term risk is not immediate generic substitution. Mepolizumab is a biologic, so competition will arise through biosimilar or follow-on biologic development under the FDA’s Biologics Price Competition and Innovation Act. U.S. reference-product exclusivity began with FDA approval in November 2015 and generally expires in November 2027. Patent protection, device claims, formulation claims, and regulatory litigation could delay commercial biosimilar entry beyond that date.[3,4]
What is mepolizumab and how does Nucala generate revenue?
Mepolizumab is a humanized monoclonal antibody that binds interleukin-5, or IL-5. By neutralizing IL-5, it reduces eosinophil production and survival. Nucala is administered by subcutaneous injection for most current uses, with dosing intervals generally ranging from every four weeks to every eight weeks depending on the indication and patient population.[5]
The product’s revenue base has four main components:
| Revenue driver |
Commercial role |
| Severe eosinophilic asthma |
Original and largest indication; supports long-term maintenance revenue |
| Chronic rhinosinusitis with nasal polyps |
Broadens the eligible population beyond severe asthma |
| Eosinophilic granulomatosis with polyangiitis |
Orphan and specialist-driven indication with high treatment value |
| Hypereosinophilic syndrome |
Orphan indication with limited competition and high per-patient economics |
Nucala’s revenue is concentrated in the United States and other high-income markets. Its economics depend on chronic treatment persistence, payer approval for biomarker-defined patients, and continued use among patients who have failed inhaled therapy and systemic corticosteroid management.
How does Nucala differ from other IL-5 pathway drugs?
Mepolizumab directly neutralizes IL-5. Benralizumab, marketed as Fasenra by AstraZeneca, targets the IL-5 receptor alpha and depletes eosinophils through antibody-dependent cell-mediated cytotoxicity. Reslizumab, marketed as Cinqair by Teva, also neutralizes IL-5 but is administered intravenously and has a smaller commercial footprint.
The broader biologic asthma market includes dupilumab, marketed as Dupixent by Sanofi and Regeneron, and tezepelumab, marketed as Tezspire by AstraZeneca and Amgen. Dupilumab inhibits IL-4 and IL-13 signaling and has a substantially larger multi-indication franchise. Tezepelumab acts upstream by blocking thymic stromal lymphopoietin, potentially covering a wider biomarker-defined population.
| Product |
Company |
Principal mechanism |
Commercial positioning |
| Nucala |
GSK |
IL-5 neutralization |
Established eosinophilic disease franchise |
| Fasenra |
AstraZeneca |
IL-5 receptor alpha targeting |
Less frequent dosing and eosinophil depletion |
| Dupixent |
Sanofi/Regeneron |
IL-4 receptor alpha blockade |
Broadest immunology and atopic-disease franchise |
| Tezspire |
AstraZeneca/Amgen |
TSLP blockade |
Upstream severe-asthma treatment |
| Xolair |
Novartis/Roche |
IgE blockade |
Allergic asthma and multiple allergic indications |
| Cinqair |
Teva |
IL-5 neutralization |
Intravenous administration limits convenience |
How much revenue does Nucala generate?
GSK’s reported Nucala sales increased materially after the initial U.S. launch and expanded as the company added indications and formulations.
| Fiscal year |
Reported Nucala sales |
Approximate year-over-year trend |
| 2019 |
£0.9 billion |
Strong launch-to-scale growth |
| 2020 |
£1.1 billion |
Continued respiratory expansion |
| 2021 |
£1.25 billion |
Growth despite pandemic-related access disruption |
| 2022 |
£1.4 billion |
Expansion across indications and geographies |
| 2023 |
£1.64 billion |
Approximately mid-teens growth at constant exchange rates |
| 2024 |
Approximately £1.7 billion |
Continued growth, with a more mature base |
The figures are based on GSK annual-report disclosures and may vary slightly depending on currency presentation and subsequent reporting adjustments.[1,2] Nucala is now a billion-pound product with a durable maintenance-revenue profile. The commercial trajectory is less dependent on a single launch indication than it was during the first several years after approval.
What drove Nucala’s sales growth?
The main growth factors were:
- Greater diagnosis and treatment of severe eosinophilic asthma.
- Conversion from chronic oral corticosteroids to biologic therapy in appropriate patients.
- Expansion into chronic rhinosinusitis with nasal polyps.
- Specialist adoption in eosinophilic granulomatosis with polyangiitis and hypereosinophilic syndrome.
- Increased use of prefilled syringes and autoinjectors, which reduce administration barriers.
- International reimbursement and commercial rollout.
- Persistent treatment among patients receiving benefit from eosinophil suppression.
The principal constraints are payer step edits, prior authorization, competition from other biologics, inconsistent biomarker testing, and the high annual cost of chronic therapy.
When does mepolizumab lose exclusivity?
U.S. biologic exclusivity for Nucala generally runs for 12 years from FDA approval under the Biologics Price Competition and Innovation Act. Nucala received its initial U.S. approval on November 4, 2015. The reference-product exclusivity period therefore generally reaches November 4, 2027.[3,4]
That date does not guarantee biosimilar launch. A biosimilar applicant can prepare and submit an application before the end of the 12-year period, but FDA approval cannot become effective before the applicable exclusivity period ends. Patent litigation, patent settlements, regulatory review, manufacturing readiness, and commercial strategy can extend the effective period of market protection.
European exclusivity is assessed differently. The European Union generally provides eight years of data exclusivity and two years of market protection, with a possible one-year extension for a new indication that provides significant clinical benefit. National and European patent rights, supplementary protection certificates, and pediatric extensions can affect the practical entry date.[6]
What patents protect Nucala and mepolizumab?
Mepolizumab is protected through a combination of biologic composition claims, antibody sequence claims, therapeutic-use claims, manufacturing claims, and potentially delivery-device or formulation claims. The patent estate is more important than regulatory exclusivity after 2027 because biosimilar applicants must address active patents and may face litigation under the BPCIA.
Unlike small-molecule products, Nucala does not have the same conventional Orange Book patent-listing framework used for drugs approved under the Federal Food, Drug, and Cosmetic Act. Biologic reference-product information is principally evaluated through the FDA Purple Book and the patent-disclosure and litigation procedures associated with the BPCIA.[7]
What is the Orange Book status of Nucala?
Nucala is not an ordinary small-molecule Orange Book reference product. It is a biologic licensed under the Public Health Service Act. The Purple Book is the principal FDA resource for biologic reference-product and biosimilar information.[7]
This distinction matters because the absence of a conventional Orange Book listing does not mean that Nucala lacks patent protection. GSK can rely on patent enforcement, regulatory exclusivity, trade secrets, manufacturing know-how, and contractual settlement terms.
How strong is the mepolizumab patent estate?
The estate has several structural strengths:
- The antibody is a complex biologic that requires a highly similar manufacturing process.
- Analytical comparability and clinical development create meaningful cost and execution barriers.
- Indication-specific use claims can protect commercial segments even after core composition claims expire.
- Device and presentation claims may protect autoinjector or prefilled delivery formats.
- Manufacturing processes and cell-line know-how are difficult to replicate from public patent documents alone.
The principal weakness is that core antibody patents were filed years before the 2015 approval. Patent term therefore does not reset at product launch. The effective protection period for early composition patents can expire before the end of biologic regulatory exclusivity. Continuation patents, patent-term adjustment, pediatric extensions, and later-filed use or formulation patents can produce a layered but uneven expiration profile.
Are there Paragraph IV challenges to mepolizumab?
A conventional Paragraph IV challenge applies to an abbreviated new drug application for a small molecule. Mepolizumab is a biologic, so the relevant challenge mechanism is a biosimilar application under the BPCIA rather than an ANDA Paragraph IV certification.
Publicly visible biosimilar activity for mepolizumab has been less prominent than for older antibody products such as adalimumab, trastuzumab, or ustekinumab. No major publicly disclosed U.S. biosimilar launch has displaced Nucala. The commercial entry risk is therefore prospective and dependent on development programs, FDA filings, patent litigation, and settlement outcomes.
A biosimilar applicant would need to demonstrate high similarity to the reference product and show that there are no clinically meaningful differences in safety, purity, or potency. Extrapolation across asthma, nasal polyps, EGPA, and HES could be commercially important, but the breadth of any approved indication set would depend on the application and patent strategy.[8]
What biosimilar risks exist for Nucala?
The first biosimilar risk is likely to involve price competition rather than immediate substitution. Physician-administered biologics can experience rapid payer-driven switching, while self-administered products are more dependent on pharmacy-benefit design, specialty-pharmacy contracts, patient support, and device familiarity.
Potential entry scenarios include:
| Scenario |
Likely market effect |
| No biosimilar at regulatory-exclusivity expiry |
Nucala retains pricing power while patents are challenged |
| One biosimilar enters after settlement |
Selective payer contracting and moderate net-price erosion |
| Multiple biosimilars enter |
Larger rebate competition and accelerated switching |
| Biosimilar receives broad extrapolated indications |
Pressure across asthma and rare-disease segments |
| Device or presentation patents remain enforceable |
Delayed competition for autoinjector and prefilled formats |
Rare-disease indications may be more defensible commercially because treatment decisions are specialist-led and patient populations are smaller. Severe asthma is more exposed because several competing biologics address overlapping populations.
What FDA approvals and label expansions support Nucala?
Nucala was initially approved by the FDA in 2015 for add-on maintenance treatment of patients aged 12 years and older with severe asthma and an eosinophilic phenotype.[5]
Key FDA milestones include:
| Year |
Regulatory milestone |
| 2015 |
Initial U.S. approval for severe eosinophilic asthma |
| 2017 |
Approval for eosinophilic granulomatosis with polyangiitis |
| 2019 |
Expansion to children aged 6 to 11 with severe eosinophilic asthma |
| 2020 |
Approval for hypereosinophilic syndrome |
| 2021 |
Approval for chronic rhinosinusitis with nasal polyps |
The label expansions increased the addressable market and reduced reliance on the initial asthma segment. They also strengthened GSK’s ability to use the same antibody, manufacturing platform, and commercial infrastructure across several disease areas.
What patent litigation affects mepolizumab?
No major publicly reported U.S. biosimilar litigation has produced a Nucala launch or market withdrawal comparable to the litigation histories of several older biologics. The relevant litigation risk remains concentrated in future BPCIA patent disputes involving:
- Core antibody and sequence claims.
- Therapeutic-use claims for severe eosinophilic asthma.
- Treatment of EGPA, HES, or nasal polyps.
- Formulation and concentration claims.
- Prefilled syringe and autoinjector presentations.
- Manufacturing and cell-culture processes.
A settlement could establish a licensed biosimilar entry date before the final expiration of every patent in the estate. Such agreements often preserve some patent value while providing a defined entry date and reducing litigation costs.
How does Nucala compare with Fasenra, Dupixent, and Tezspire?
Nucala has an established market position but does not have the broadest competitive moat.
| Dimension |
Nucala |
Fasenra |
Dupixent |
Tezspire |
| Biological target |
IL-5 |
IL-5 receptor alpha |
IL-4 receptor alpha |
TSLP |
| Main asthma population |
Eosinophilic |
Eosinophilic |
Type 2 inflammatory |
Broad severe-asthma positioning |
| Dosing convenience |
Every four weeks in many uses; longer intervals in some settings |
Every eight weeks after loading in many patients |
Usually every two weeks |
Every four weeks |
| Rare-disease presence |
EGPA and HES |
More concentrated in asthma |
Multiple immunology indications |
Primarily severe asthma |
| Commercial scale |
Billion-pound GSK brand |
Billion-dollar AstraZeneca brand |
Much larger multi-indication franchise |
Growing severe-asthma brand |
Dupixent creates the strongest competitive pressure because it has substantial physician familiarity, broad label coverage, and a large commercial infrastructure. Fasenra competes directly in eosinophilic asthma and has a dosing-frequency advantage. Tezspire competes for patients whose disease is severe but whose biomarker profile is less narrowly eosinophilic.
Nucala’s defense is its clinical history, specialist familiarity, rare-disease indications, and established payer pathways.
What is the financial outlook for Nucala?
Nucala should remain a major GSK product through the late 2020s, but growth is likely to moderate as the asthma market matures. Future revenue depends on four variables:
- Continued growth in severe asthma diagnosis and biologic penetration.
- Uptake in chronic rhinosinusitis with nasal polyps.
- Persistence in EGPA and HES.
- The timing and discount level of biosimilar or follow-on competition.
The base-case commercial path is continued low- to mid-single-digit growth or broadly stable sales before biosimilar erosion becomes material. A stronger outcome would come from higher biologic penetration, expanded use in nasal polyps, and limited biosimilar competition. A weaker outcome would involve rapid payer switching to Fasenra, Dupixent, or Tezspire combined with an early biosimilar settlement.
Nucala’s revenue exposure is strategically important but manageable within GSK’s larger respiratory portfolio. GSK also commercializes Trelegy, Breo Ellipta, Anoro Ellipta, and other respiratory products. Nucala’s biologic margin profile and recurring treatment model make it more valuable than its sales number alone suggests, but specialty-pharmacy rebates and payer concessions can reduce net revenue growth.
What generic launch scenarios exist for mepolizumab?
A conventional generic launch is not expected because mepolizumab is a monoclonal antibody. The relevant scenarios are:
- A biosimilar launches after November 2027 following patent clearance.
- A biosimilar enters under a confidential or publicly disclosed settlement date.
- A biosimilar launches with only asthma coverage, limiting initial substitution.
- A biosimilar obtains broad extrapolation and pressures all major indications.
- GSK preserves premium pricing through autoinjector, support services, and contracting.
The earliest practical entry date will depend on the interaction between regulatory exclusivity and enforceable patent claims. Manufacturing capacity and reference-product analytical matching are likely to delay entry relative to the formal end of exclusivity.
Key Takeaways
- Nucala is GSK’s established anti-IL-5 biologic franchise.
- Sales rose from roughly £0.9 billion in 2019 to approximately £1.7 billion in 2024.
- Revenue is supported by severe eosinophilic asthma, CRSwNP, EGPA, and HES.
- U.S. biologic reference-product exclusivity generally ends in November 2027.
- Nucala is evaluated through the FDA biologics framework and Purple Book, not the standard small-molecule Orange Book pathway.
- Competitive pressure comes mainly from Fasenra, Dupixent, and Tezspire rather than conventional generics.
- Biosimilar entry is the main long-term pricing risk, but patent litigation, settlements, manufacturing complexity, and device claims can delay or moderate erosion.
- Nucala should remain financially material to GSK through the late 2020s, with growth likely moderating as the severe-asthma biologic market matures.
Frequently Asked Questions
Is mepolizumab a biologic or a generic drug?
Mepolizumab is a biologic monoclonal antibody. Any future competitor would generally be a biosimilar or follow-on biologic, not a conventional generic.
What company owns Nucala?
GSK owns and commercializes Nucala globally, subject to regional commercialization and licensing arrangements where applicable.
Can Nucala be used for chronic rhinosinusitis with nasal polyps?
Yes. The FDA approved Nucala for adults with chronic rhinosinusitis with nasal polyps inadequately controlled by standard treatment.[5]
What is the main commercial threat to Nucala?
The main threat is competitive biologic substitution, particularly from Dupixent, Fasenra, and Tezspire, followed by biosimilar competition after the end of regulatory exclusivity.
Will a Nucala biosimilar automatically receive all of the reference product’s indications?
No. Indication coverage depends on the biosimilar application, FDA review, patent rights, and any litigation or settlement restrictions. Extrapolation can support multiple indications, but it is not automatic for every commercial use.
References
- GSK. (2024). Annual report 2023. https://www.gsk.com/en-gb/investors/annual-report/
- GSK. (2025). Annual report 2024. https://www.gsk.com/en-gb/investors/annual-report/
- U.S. Food and Drug Administration. (2015). FDA approves Nucala to treat severe asthma. https://www.fda.gov/news-events/press-announcements/fda-approves-nucala-treat-severe-asthma
- U.S. Congress. (2010). Biologics Price Competition and Innovation Act of 2009, Public Law 111-148, §7002. https://www.congress.gov/111/plaws/publ148/PLAW-111publ148.pdf
- U.S. Food and Drug Administration. (2024). Nucala prescribing information. https://www.accessdata.fda.gov/drugsatfda_docs/label/
- European Medicines Agency. (2024). Data and market exclusivity. https://www.ema.europa.eu/en/human-regulatory-overview/marketing-authorisation/protection-medicines
- U.S. Food and Drug Administration. (2024). Purple Book: Database of licensed biological products. https://purplebooksearch.fda.gov/
- U.S. Food and Drug Administration. (2021). Development of therapeutic protein biosimilars: Comparative analytical assessment and other quality-related considerations. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/development-therapeutic-protein-biosimilars-comparative-analytical-assessment-and-other-quality-related-considerations
