Last updated: September 8, 2026
STRENSIQ, AstraZeneca’s asfotase alfa enzyme-replacement therapy, generated approximately $1.1 billion in 2024 product sales, up from roughly $0.7 billion in 2020. Its market is supported by lifelong treatment, limited alternatives, rare-disease reimbursement and expansion of hypophosphatasia diagnosis. The principal medium-term risk is biosimilar competition after the U.S. biologic exclusivity period ends in 2027, although manufacturing complexity, small patient populations and specialized regulatory requirements may delay commercial entry.
What is STRENSIQ and which patients does it treat?
STRENSIQ is asfotase alfa, a recombinant tissue-nonspecific alkaline phosphatase enzyme-replacement therapy. Alexion Pharmaceuticals, now part of AstraZeneca, developed and commercialized the product for hypophosphatasia, or HPP.
The U.S. Food and Drug Administration approved STRENSIQ on Oct. 23, 2015, under Biologics License Application No. 125658. The approved indication covers patients with perinatal-, infantile- and juvenile-onset HPP. The product is administered subcutaneously at either 6 mg/kg once weekly or 2 mg/kg three times weekly, depending on the dosing regimen and clinical circumstances (U.S. Food and Drug Administration [FDA], 2015).
HPP results from deficient activity of tissue-nonspecific alkaline phosphatase, caused by pathogenic variants in the ALPL gene. The disorder has a broad clinical spectrum. Severe early-onset disease can cause respiratory failure, skeletal abnormalities and impaired mineralization. Adult-onset disease may involve fractures, chronic pain, premature tooth loss and mobility limitations.
STRENSIQ’s commercial profile benefits from several characteristics:
- Treatment is generally chronic and may continue for many years.
- Dosing is weight-based, allowing revenue to increase with patient weight.
- HPP has historically been underdiagnosed, leaving room for patient identification.
- There is no approved direct enzyme-replacement competitor in the United States.
- Prescribing is concentrated among metabolic, endocrine, orthopedic and pediatric specialists.
How much revenue does STRENSIQ generate?
AstraZeneca reports STRENSIQ as an individual product within its Alexion rare-disease portfolio. Reported sales have increased steadily since launch.
| Fiscal year |
Approximate STRENSIQ product sales |
Year-over-year trend |
| 2020 |
$0.7 billion |
Growth |
| 2021 |
$0.8 billion |
Growth |
| 2022 |
$0.9 billion |
Growth |
| 2023 |
$1.0 billion |
Growth |
| 2024 |
$1.1 billion |
Growth |
Source: AstraZeneca annual reports and full-year results, rounded to the nearest $0.1 billion.
The product’s growth reflects patient additions, broader diagnosis, international expansion and continuing treatment of existing patients. Revenue growth is not driven primarily by large population expansion. HPP remains a rare disease, so commercial performance depends on finding and treating a relatively small number of high-value patients.
STRENSIQ is strategically important to Alexion because it diversifies the company’s rare-disease portfolio beyond complement inhibitors such as SOLIRIS and ULTOMIRIS. It also has a different demand profile. Complement inhibitors face major exposure to biosimilars and treatment switching, while STRENSIQ has a smaller but highly specialized market with limited direct clinical substitution.
What is driving the STRENSIQ market?
Why does STRENSIQ continue to grow despite its rare-disease market?
The main growth drivers are diagnosis, persistence and geographic access.
Many HPP patients are initially diagnosed with more common metabolic bone disorders. Wider availability of genetic testing, specialty referral and disease-specific clinical guidance can increase the diagnosed population. The commercial opportunity is therefore tied to disease recognition as much as to epidemiology.
Treatment persistence is another important factor. Patients who demonstrate clinical benefit may remain on therapy for extended periods. Pediatric patients can also generate increasing revenue as body weight rises, subject to clinical dosing decisions.
Reimbursement is generally managed through specialty pharmacy, prior authorization and rare-disease support programs. The high cost of treatment creates access friction, but the absence of a direct approved alternative supports coverage for patients meeting diagnostic criteria.
What are the main constraints on STRENSIQ growth?
The product faces several structural limits:
- HPP diagnosis is difficult and heterogeneous.
- Treatment requires specialist confirmation and long-term monitoring.
- Administration is by repeated subcutaneous injection.
- Payer review can be demanding because the product is expensive and the eligible population is small.
- Safety and benefit assessments differ across age groups and disease severity.
- Market expansion depends on identifying patients who may have less severe or later-onset disease.
The patient population is therefore not a conventional primary-care market. Sales growth depends on specialist education, diagnostic infrastructure and reimbursement execution.
When does STRENSIQ lose exclusivity?
The key U.S. regulatory exclusivity date is October 2027, based on the 12-year reference-product exclusivity period for a biologic approved in October 2015. Under the Biologics Price Competition and Innovation Act, an interchangeable or biosimilar applicant generally cannot obtain approval referencing STRENSIQ before the applicable reference-product exclusivity period ends (FDA, 2024).
The practical timeline is more complex:
| Event |
Date or status |
| FDA approval |
Oct. 23, 2015 |
| U.S. orphan-drug exclusivity |
Seven years from approval, ending in 2022 |
| U.S. biologic reference-product exclusivity |
Approximately through October 2027 |
| Potential biosimilar filing activity |
Subject to BPCIA timing rules and applicant strategy |
| First commercially meaningful U.S. competition |
More likely after regulatory and patent barriers are resolved |
Orphan-drug exclusivity protected the approved indication for seven years. It did not prevent all competing products or all uses outside the protected indication. The longer commercial barrier is the biologic reference-product exclusivity period, combined with patents, manufacturing know-how and clinical development requirements.
What patents protect STRENSIQ?
STRENSIQ is protected by a combination of biologic regulatory exclusivity, formulation and manufacturing know-how, and patents that may cover the recombinant enzyme, pharmaceutical compositions, dosing and treatment methods. A biologic product does not have the same public Orange Book patent framework as a conventional small-molecule drug.
A complete freedom-to-operate analysis requires review of national patent registers, patent-term adjustments, terminal disclaimers, continuations, foreign counterparts and claim scope. The commercially relevant issue is not a single expiry date. It is whether an entrant can obtain biosimilar approval and manufacture a non-infringing asfotase alfa product after regulatory exclusivity ends.
The relevant barriers include:
- Cell-line and expression-system development.
- Protein folding, glycosylation and impurity control.
- Enzyme activity and potency assays.
- Comparability against the reference product.
- Stability and storage validation.
- Clinical and analytical evidence for biosimilarity.
- Patent claims covering production, formulation or administration.
What is the Orange Book and FDA status of STRENSIQ?
STRENSIQ is a biologic licensed under a BLA, not a traditional small-molecule drug approved under an NDA. The FDA’s Purple Book is the principal reference for biologic products and biosimilar status. Orange Book-listed patents and Paragraph IV certifications are associated primarily with abbreviated new drug applications for small-molecule products.
Are there Paragraph IV challenges to STRENSIQ?
No conventional Paragraph IV challenge is expected for STRENSIQ because a biosimilar applicant uses the 351(k) pathway rather than an ANDA Paragraph IV certification. Biosimilar applicants may provide patent notices and participate in the BPCIA patent-exchange process, often called the patent dance, but that process is legally distinct from Paragraph IV litigation under the Hatch-Waxman framework.
As of the public regulatory information available through 2024, STRENSIQ had no disclosed FDA-approved biosimilar competitor and no established U.S. biosimilar market.
Which companies are challenging STRENSIQ?
No company had publicly established a U.S. commercial biosimilar position against STRENSIQ through 2024. Potential entrants would likely include large biosimilar manufacturers with biologics development and specialty commercialization capabilities, but public development programs specifically targeting asfotase alfa have not created a visible competitive field comparable to the markets for adalimumab, trastuzumab or pegfilgrastim.
Potential competition may also come from non-equivalent therapies under development for skeletal mineralization disorders, including treatments directed at phosphate metabolism or enzyme biology. Those products would not be biosimilars and would require separate clinical evidence. They could compete for patients without having to replicate the STRENSIQ molecule.
How strong is the STRENSIQ patent and market-access position?
STRENSIQ has a strong commercial position through the end of the decade, but its long-term patent position is less important than its manufacturing and market structure.
| Factor |
Assessment |
Commercial effect |
| Direct approved competition |
None identified in the U.S. through 2024 |
Supports pricing and persistence |
| Biologic exclusivity |
Runs approximately to October 2027 |
Delays U.S. biosimilar approval |
| Orphan exclusivity |
Expired in 2022 |
No longer the principal barrier |
| Patient population |
Very small and difficult to diagnose |
Limits total volume but supports specialist control |
| Manufacturing complexity |
High |
Raises biosimilar development costs |
| Treatment duration |
Often chronic |
Supports recurring revenue |
| Reimbursement |
Specialty, prior authorization driven |
Creates access friction |
| Switching risk |
Potentially moderate |
Depends on clinical confidence and payer policy |
The product’s strongest defenses are the combination of rare-disease specialization, physician familiarity, long-term treatment relationships, and complex biologic manufacturing. Patent litigation could still affect timing if a biosimilar applicant identifies blocking claims, but the absence of a large established target market reduces the incentive for multiple entrants.
What formulations and manufacturing factors protect STRENSIQ?
STRENSIQ is supplied as a sterile injectable solution for subcutaneous administration. The product’s commercial performance depends on consistent enzyme activity, purity, stability and immunogenicity control.
Manufacturing barriers include the need to reproduce a complex recombinant protein with clinically meaningful similarity. A biosimilar applicant would need to compare structural attributes, post-translational modifications, biological activity, impurities and stability. Analytical similarity alone may not eliminate regulatory or commercial risk if the applicant cannot demonstrate reliable activity across batches.
The product’s formulation and delivery system also affect patient acceptance. A competing product would need to match or improve usability, storage, injection volume, device performance and supply reliability. A lower price alone may not guarantee rapid switching in a rare pediatric and metabolic-disease market.
What is the international market and geographic coverage for STRENSIQ?
STRENSIQ is marketed in the United States and multiple international jurisdictions, including Europe and other markets where HPP has been recognized as a rare metabolic bone disease. International revenue depends on local orphan-drug designations, health technology assessment, hospital procurement, reimbursement rules and genetic-diagnosis capacity.
The United States is likely to remain the most important market because of its specialty-pharmacy infrastructure and high rare-disease pricing. Europe provides geographic diversification but can impose stricter price controls and country-by-country reimbursement negotiations. Emerging markets may offer long-term patient growth but face lower diagnosis rates and constrained funding.
What litigation and settlement risks affect STRENSIQ?
No major publicly disclosed U.S. biosimilar litigation or settlement agreement had materially changed the STRENSIQ market through 2024. The next important legal developments would likely arise from:
- A biosimilar applicant’s BPCIA patent disclosures.
- Patent infringement actions concerning manufacturing or formulation claims.
- Licensing agreements allowing an early or territory-specific launch.
- Payer litigation involving coverage restrictions or reimbursement.
- Product-liability or labeling disputes related to long-term use.
A settlement could establish a launch date before the full expiry of all asserted patent claims. The economic value of such an agreement would depend on the number of credible entrants, the strength of the asserted claims and the willingness of AstraZeneca to trade earlier competition for defined certainty.
What generic or biosimilar launch scenarios exist for STRENSIQ?
Scenario 1: No near-term biosimilar launch
A lack of credible entrants would allow STRENSIQ to retain pricing power after 2027. Sales could continue growing through diagnosis and international expansion, although mature-market growth would likely slow.
Scenario 2: One biosimilar entrant
A single biosimilar could initially target high-cost patients and payer contracts. The first entrant may obtain favorable formulary access without causing immediate clinical switching across the entire population.
Scenario 3: Multiple biosimilar entrants
Multiple competitors could produce price reductions, contracting pressure and conversion programs. This scenario is less likely immediately after exclusivity because the HPP market is small and development costs are high.
Scenario 4: Non-biosimilar disease-modifying competition
A therapy with superior efficacy, easier administration or a broader HPP label could exert more pressure than a biosimilar. Such a product would compete on clinical outcomes and convenience rather than only price.
How does STRENSIQ compare with other Alexion products?
| Product |
Disease area |
Modality |
Main commercial characteristic |
| STRENSIQ |
Hypophosphatasia |
Enzyme replacement |
Small, specialized chronic market |
| SOLIRIS |
Complement-mediated disorders |
Monoclonal antibody |
Mature franchise with biosimilar exposure |
| ULTOMIRIS |
Complement-mediated disorders |
Long-acting monoclonal antibody |
Longer dosing interval and franchise migration |
| KANUMA |
Lysosomal acid lipase deficiency |
Enzyme replacement |
Smaller ultra-rare market |
STRENSIQ is less exposed to immediate product substitution than SOLIRIS because its patient population is smaller and its indication is more specialized. Its revenue base is also less diversified by indication. A diagnostic setback, reimbursement restriction or safety concern could therefore have a disproportionate effect.
What is the investment and commercial outlook for STRENSIQ?
STRENSIQ is likely to remain a billion-dollar-plus product for the near term if diagnosis and treatment persistence continue to expand. Revenue growth should moderate as the diagnosed population matures and U.S. biologic exclusivity approaches expiration.
The most important variables are:
- New-patient identification in adult and juvenile HPP.
- Reimbursement approval rates and payer restrictions.
- Treatment persistence and discontinuation.
- International market access.
- The timing and number of biosimilar entrants.
- The strength of manufacturing and formulation patent claims.
- Clinical differentiation from future metabolic bone disease therapies.
The downside case is a post-2027 price decline caused by one or more credible biosimilar entrants. The upside case is continued patient expansion with limited biosimilar participation because the market cannot support multiple development programs.
Key Takeaways
- STRENSIQ is AstraZeneca’s asfotase alfa therapy for hypophosphatasia.
- Product sales increased from approximately $0.7 billion in 2020 to approximately $1.1 billion in 2024.
- The U.S. FDA approved STRENSIQ in October 2015 under BLA No. 125658.
- U.S. biologic reference-product exclusivity runs approximately through October 2027.
- Traditional Paragraph IV challenges do not apply because STRENSIQ is a biologic, not an ANDA small-molecule product.
- No U.S. biosimilar competitor had been approved through 2024.
- The principal commercial defenses are patient scarcity, specialist prescribing, chronic treatment, manufacturing complexity and diagnostic expertise.
- Revenue growth is likely to continue, but the risk profile changes materially as the 2027 exclusivity date approaches.
FAQs
Is STRENSIQ a biologic or a generic drug?
STRENSIQ is a biologic enzyme-replacement therapy. Any follow-on product would generally use the FDA’s 351(k) biosimilar pathway rather than the ANDA generic-drug pathway.
Does STRENSIQ have an orphan-drug designation?
Yes. STRENSIQ received orphan-drug status for hypophosphatasia. The U.S. seven-year orphan exclusivity period associated with the 2015 approval expired in 2022.
Can patients switch from STRENSIQ to a biosimilar?
A switch would depend on FDA labeling, payer policy, physician judgment, product interchangeability status and patient-specific clinical factors. No FDA-approved STRENSIQ biosimilar was identified through 2024.
Is STRENSIQ included in the FDA Orange Book?
STRENSIQ is licensed as a biologic under a BLA. Biologic reference and biosimilar information is principally tracked through the FDA Purple Book rather than the conventional Orange Book framework.
What is the biggest risk to STRENSIQ revenue?
The largest medium-term risk is erosion after U.S. biologic exclusivity ends, particularly if one or more biosimilar manufacturers demonstrate strong analytical similarity, secure favorable payer contracts and offer a lower-cost alternative.
References
AstraZeneca. (2022). Annual report and Form 20-F 2021. AstraZeneca PLC.
AstraZeneca. (2023). Annual report and Form 20-F 2022. AstraZeneca PLC.
AstraZeneca. (2024). Annual report and Form 20-F 2023. AstraZeneca PLC.
AstraZeneca. (2025). Annual report and Form 20-F 2024. AstraZeneca PLC.
U.S. Food and Drug Administration. (2015). STRENSIQ prescribing information. U.S. Department of Health and Human Services.
U.S. Food and Drug Administration. (2024). Purple Book: Database of licensed biological products. U.S. Department of Health and Human Services.
