United States Patent 10,434,103: Claim Scope, Exclusivity, and Ensitrelvir Crystal-Form Patent Landscape
U.S. Patent No. 10,434,103 protects two crystalline forms of ensitrelvir, the active ingredient in Shionogi's Xocova antiviral. The patent is directed primarily to solid-state form, not the underlying chemical molecule. Claims 1-11 cover two polymorphs and pharmaceutical compositions containing them. Claim 12 covers a solvent-mediated crystallization process intended to reduce crystal scaling. The patent issued on October 8, 2019, and has a nominal U.S. term extending into 2037, subject to patent-term adjustment and any applicable statutory extensions.[1]
What drug does U.S. Patent 10,434,103 protect?
The claimed compound is ensitrelvir, also known as S-217622. Its systematic structure is:
(S)-1-(3-(4-amino-3-((3,5-dimethoxyphenyl)ethynyl)-1H-pyrazolo[3,4-d]pyrimidin-1-yl)-1-pyrrolidinyl)-2-propen-1-one.
Ensitrelvir is a small-molecule, noncovalent SARS-CoV-2 main protease inhibitor. Shionogi markets it in Japan under the brand name Xocova.[2]
Patent 10,434,103 does not claim every form of ensitrelvir. Its principal limitation is the physical state of the active ingredient: specific crystalline forms identified by powder X-ray diffraction, or PXRD, peak patterns.
Basic patent record
| Item |
Data |
| U.S. patent |
10,434,103 B2 |
| Issue date |
October 8, 2019 |
| Applicant/assignee |
Shionogi & Co., Ltd. |
| Active ingredient |
Ensitrelvir, S-217622 |
| Technology |
Crystalline forms, pharmaceutical compositions, crystallization process |
| Main dosage-form relevance |
Oral solid dosage forms |
| Regulatory product |
Xocova |
| Patent type |
Small-molecule composition-of-matter and process-related solid-state patent |
| Nominal term |
Approximately 2037, subject to PTA and statutory adjustments |
| U.S. FDA approval status |
No Orange Book-listed Xocova product identified in the current FDA Orange Book record |
The patent should be analyzed alongside the broader ensitrelvir compound, formulation, therapeutic-use, manufacturing, and international patent families. It is not the only potential barrier to generic or follow-on entry.
What are the independent claims in U.S. Patent 10,434,103?
The patent has three substantive claim groups:
- A first ensitrelvir crystal form identified by seven possible PXRD peaks.
- A second ensitrelvir crystal form identified by a different nine-peak PXRD pattern.
- A crystallization process for reducing scaling of ensitrelvir crystals.
Claims 1 and 7 are the principal crystal-form claims. Claims 5, 6, 10, and 11 extend those forms into pharmaceutical compositions, including oral compositions. Claim 12 protects a process rather than a product.
What does claim 1 cover?
Claim 1 covers a crystal of ensitrelvir having at least three characteristic PXRD peaks selected from:
- 9.5°
- 14.3°
- 16.7°
- 19.1°
- 20.8°
- 21.9°
- 25.2°
Each peak is measured at a tolerance of plus or minus 0.2° 2θ.
The claim does not require all seven peaks. A material can fall within claim 1 if it exhibits any three of the listed peaks, assuming the material is otherwise the claimed ensitrelvir crystal.
Claim 2 narrows claim 1 by requiring at least five of the seven listed peaks. Claim 3 is narrower still and requires all seven peaks.
Claim 4 adds a differential scanning calorimetry limitation. The claimed crystal has a highest endothermic peak near 166°C.
Scope of the first crystal-form family
| Claim |
Required PXRD characteristics |
Additional limitation |
| 1 |
At least 3 of 7 peaks |
Peak tolerance ±0.2° 2θ |
| 2 |
At least 5 of 7 peaks |
Depends on claim 1 |
| 3 |
All 7 peaks |
Depends on claim 1 |
| 4 |
Claim 1 crystal |
DSC endotherm near 166°C |
| 5 |
Claim 1 crystal in a composition |
No specific dosage form |
| 6 |
Claim 1 crystal in a composition |
Oral administration |
The practical consequence is that claim 1 has a relatively broad analytical entry point, while claims 2-4 provide progressively narrower fallback positions. A generic manufacturer could avoid claims 2-4 more easily than claim 1 if its isolated material displays only a subset of the listed peaks or a different thermal profile. That strategy would not avoid claim 1 if at least three listed peaks remain present.
What does claim 7 cover?
Claim 7 covers a separate ensitrelvir crystal form having at least seven characteristic PXRD peaks selected from:
- 13.5°
- 17.9°
- 19.5°
- 20.6°
- 22.0°
- 22.6°
- 23.3°
- 23.7°
- 24.2°
Claim 8 requires all nine peaks. Claim 9 adds a DSC endothermic peak near 169°C. Claims 10 and 11 cover pharmaceutical and oral pharmaceutical compositions containing this second crystal form.
Scope of the second crystal-form family
| Claim |
Required PXRD characteristics |
Additional limitation |
| 7 |
At least 7 of 9 peaks |
Peak tolerance ±0.2° 2θ |
| 8 |
All 9 peaks |
Depends on claim 7 |
| 9 |
Claim 7 crystal |
DSC endotherm near 169°C |
| 10 |
Claim 7 crystal in a composition |
No specific dosage form |
| 11 |
Claim 7 crystal in a composition |
Oral administration |
The second form is narrower at the threshold level than claim 1 because it requires at least seven of nine peaks. Its full-form definition in claim 8 is analytically more distinctive because all nine peaks must be present.
How do the two claimed crystal forms compare?
The two forms are separated by distinct PXRD signatures and different thermal transitions.
| Characteristic |
First form |
Second form |
| Key PXRD set |
9.5°, 14.3°, 16.7°, 19.1°, 20.8°, 21.9°, 25.2° |
13.5°, 17.9°, 19.5°, 20.6°, 22.0°, 22.6°, 23.3°, 23.7°, 24.2° |
| Independent threshold |
At least 3 peaks |
At least 7 peaks |
| Full peak claim |
7 of 7 peaks |
9 of 9 peaks |
| DSC marker |
Approximately 166°C |
Approximately 169°C |
| Composition claims |
Claims 5-6 |
Claims 10-11 |
| Oral composition claims |
Claim 6 |
Claim 11 |
The claimed forms appear designed to address solid-state development problems, including crystallization control, isolation, reproducibility, and scale-up. The patent does not claim a general amorphous ensitrelvir formulation, every possible polymorph, or every salt, solvate, hydrate, or co-crystal unless those materials satisfy the express claim limitations.
What does claim 12 protect?
Claim 12 covers a method for reducing scaling during ensitrelvir crystallization. The process requires:
-
Adding ensitrelvir to a solvent selected from:
- Water
- C1-C4 alcohols
- C3-C5 aliphatic carboxylic acid esters
- C3-C6 ketones
- C2-C5 aprotic polar organic solvents
- Mixtures of those solvents
-
Stirring the solvent containing ensitrelvir to crystallize the compound.
The claim is process-focused and does not expressly require one of the PXRD forms recited in claims 1 or 7. A process may therefore create separate infringement questions from the product claims. The key factual issues would include the solvent identity, solvent mixture, agitation conditions, crystallization outcome, and whether the accused process materially practices both required steps.
Likely manufacturing relevance
Claim 12 is most relevant to:
- Commercial crystallization of ensitrelvir API.
- Scale-up from laboratory or pilot batches.
- Control of vessel-wall deposits and crystal scaling.
- Batch reproducibility.
- Solid-form isolation before oral dosage-form manufacture.
Process claims are often harder to detect through finished-product testing than crystal-form claims. A finished tablet may reveal the protected crystal form through PXRD, while the process used to produce the API may require discovery evidence, manufacturing records, or process-development documents.
How strong is the patent estate for ensitrelvir?
Patent 10,434,103 is a meaningful but limited component of the ensitrelvir estate. Its strongest protection is against a manufacturer that:
- Uses one of the two claimed crystal forms.
- Places that form into an oral product.
- Produces the form using the claimed solvent-and-stirring process.
- Cannot demonstrate that its API has a materially different PXRD pattern.
Its scope is weaker against a manufacturer that develops:
- An unclaimed polymorph.
- An amorphous form.
- A salt, solvate, hydrate, or co-crystal outside the claims.
- A process using solvents or crystallization conditions outside claim 12.
- A product that does not contain the claimed crystal form.
The main technical vulnerability is that PXRD claims depend on analytical identity. Peak position, relative intensity, sample preparation, instrument calibration, hydration state, and polymorphic conversion can affect test results. The patent's plus-or-minus 0.2° tolerance provides a defined analytical boundary, but it does not eliminate disputes over mixed phases or partially converted material.
What patent expiration date applies?
The patent issued on October 8, 2019. Based on the public family chronology and the applicable U.S. twenty-year patent-term rule, the ordinary term is expected to end approximately in 2037. The exact date depends on the earliest effective nonprovisional filing date and any USPTO patent-term adjustment.
| Event |
Date |
| Earliest family priority |
2017, based on the public family record |
| U.S. patent issue |
October 8, 2019 |
| Nominal U.S. expiration window |
2037 |
| Patent-term adjustment |
Must be determined from the USPTO patent record |
| Patent-term extension |
No confirmed extension identified for this crystal-form patent |
The patent's expiration date should not be confused with the expiration date of the underlying ensitrelvir compound patent. A basic compound patent, a crystal-form patent, a formulation patent, and a method-of-treatment patent can have different terms.
What is the Orange Book status of ensitrelvir?
Ensitrelvir is not an FDA-approved product listed in the U.S. Orange Book based on the current FDA publication framework. Xocova received Japanese regulatory authorization, but that authorization does not create U.S. FDA approval or an Orange Book listing.[2,3]
The consequences are material:
- No U.S. Orange Book patent listing has been established for Xocova.
- No conventional ANDA applicant can rely on an Orange Book listing to trigger a standard Paragraph IV dispute for this product.
- There is no U.S. FDA small-molecule marketing exclusivity period associated with an approved Xocova NDA in the Orange Book.
- A U.S. generic launch would require an FDA-approved reference product and an applicable regulatory pathway.
Are there Paragraph IV challenges to U.S. Patent 10,434,103?
No publicly established Paragraph IV litigation against U.S. Patent 10,434,103 is identified in the available regulatory and litigation record. The principal reason is that ensitrelvir has not established the conventional U.S. Orange Book reference-product framework necessary for an ANDA-based Paragraph IV challenge.
A later U.S. approval could change the analysis. If Shionogi obtains an NDA and lists this patent, an ANDA applicant could challenge the listing through a Paragraph IV certification. The resulting litigation would likely focus on:
- Whether the accused API has one of the claimed PXRD patterns.
- Whether the claims are anticipated or obvious over earlier ensitrelvir solid forms.
- Whether the crystal-form disclosures satisfy written-description and enablement requirements.
- Whether claim 12 is infringed by the accused commercial crystallization process.
- Whether the patent is enforceable and properly listed.
What generic entry risks exist?
Generic entry risk is currently regulatory rather than litigation-driven. The absence of a U.S. Orange Book-listed reference product limits the normal ANDA pathway. If a U.S. reference product is approved later, the patent estate would present several possible entry scenarios.
Early-entry scenarios
| Scenario |
Risk to generic entrant |
Principal issue |
| Generic uses first claimed polymorph |
High |
Direct product and composition claims |
| Generic uses second claimed polymorph |
High |
Direct product and composition claims |
| Generic uses a different polymorph |
Moderate |
Need analytical proof of non-infringement |
| Generic uses amorphous API |
Lower on this patent |
Other patents may apply |
| Generic uses a different crystallization solvent |
Lower on claim 12 |
Product-form claims remain relevant |
| Generic develops a salt or solvate |
Potentially lower |
Depends on underlying compound and formulation patents |
| Generic seeks approval before patent expiry |
High regulatory risk if listed |
Possible patent certification and litigation |
A non-infringing polymorph strategy would require more than a different DSC peak. The manufacturer would need to establish that the API does not exhibit at least the required PXRD peaks within the claim tolerance and does not convert into a claimed form during formulation, storage, or dissolution testing.
Does biosimilar risk apply to ensitrelvir?
No. Ensitrelvir is a chemically synthesized small molecule, not a biologic. Biosimilar approval under the Public Health Service Act is therefore not the relevant competitive pathway. The relevant competitors would be:
- Generic small-molecule products.
- Authorized or licensed versions of Xocova.
- Alternative SARS-CoV-2 antivirals.
- New oral viral protease inhibitors.
- Competing products such as nirmatrelvir/ritonavir, subject to their own patent and regulatory estates.
Which companies are challenging ensitrelvir?
No publicly identified U.S. ANDA challenger or Paragraph IV litigant has been established for this patent. The competitive landscape is therefore more likely to involve originator licensing, regional commercialization, and development of alternative antivirals than active U.S. generic litigation.
Shionogi has retained the central intellectual-property position for ensitrelvir while pursuing regulatory and commercial arrangements in selected markets. A licensee or regional commercialization partner could receive rights that are separate from ownership of the U.S. patent.
What litigation and settlement issues matter?
No confirmed U.S. litigation or settlement involving Patent 10,434,103 is identified in the available record. If litigation arises, the most important issues will be technical rather than purely legal:
- PXRD reproducibility and peak assignment.
- Mixed-polymorph samples.
- Conversion between the 166°C and 169°C forms.
- Hydrate or solvate formation.
- Whether the claimed peaks are sufficiently characteristic to define the crystal.
- Whether prior art disclosed or enabled the same form.
- Whether the accused composition contains the form at the time of manufacture, sale, or importation.
- Whether the accused process uses a listed solvent class and stirring crystallization.
What geographic coverage exists?
The invention appears in an international patent family associated with Shionogi's ensitrelvir solid-form work. The U.S. patent provides protection only in the United States. Separate national rights must be assessed in each jurisdiction.
Relevant territorial questions include:
- Whether corresponding patents issued in Japan.
- Whether European Patent Office protection was validated in target countries.
- Whether Chinese, Korean, or other Asian family members remain in force.
- Whether national claims retained both crystal-form and process coverage.
- Whether local patent-term adjustments, annuity failures, or terminal disclaimers affect enforceability.
A country-by-country freedom-to-operate analysis cannot rely on the U.S. patent number alone. Crystal-form claims are often prosecuted differently across jurisdictions, and some countries may retain composition claims while narrowing process claims.
Key Takeaways
- U.S. Patent 10,434,103 protects two defined crystalline forms of ensitrelvir.
- Claims 1-4 cover a first form with PXRD peaks centered around 9.5°, 14.3°, 16.7°, 19.1°, 20.8°, 21.9°, and 25.2°, plus a DSC peak near 166°C.
- Claims 7-9 cover a second form with nine specified PXRD peaks and a DSC peak near 169°C.
- Claims 5, 6, 10, and 11 extend protection to pharmaceutical and oral pharmaceutical compositions.
- Claim 12 covers a solvent-and-stirring crystallization process intended to reduce scaling.
- The patent does not necessarily block every polymorph, amorphous form, salt, solvate, or formulation of ensitrelvir.
- The nominal U.S. expiration window is approximately 2037, subject to USPTO patent-term adjustment.
- Ensitrelvir has no established U.S. Orange Book reference-product framework based on the current FDA record.
- No confirmed U.S. Paragraph IV challenge or settlement involving this patent has been identified.
- Biosimilar law is not relevant because ensitrelvir is a small-molecule drug.
- The most credible design-around strategy is development of a demonstrably different solid form combined with a crystallization process outside claim 12.
FAQs
What is the active pharmaceutical ingredient in U.S. Patent 10,434,103?
The active ingredient is ensitrelvir, also known as S-217622, a small-molecule SARS-CoV-2 main protease inhibitor marketed in Japan as Xocova.
Does U.S. Patent 10,434,103 cover Xocova tablets?
It may cover Xocova tablets if the tablets contain one of the two claimed ensitrelvir crystal forms. The claims do not cover a tablet solely because it contains ensitrelvir; the relevant crystal-form limitations must be met.
Can a generic avoid this patent by using amorphous ensitrelvir?
Potentially, but only if the amorphous material does not display the claimed PXRD characteristics and does not convert into a claimed crystal form during manufacture, storage, or use. Other ensitrelvir patents could still present barriers.
Are the 166°C and 169°C DSC peaks required for infringement?
No. The DSC limitations appear in dependent claims 4 and 9. A product may infringe the broader independent crystal claims without meeting those additional DSC limitations.
Is claim 12 a manufacturing patent for all ensitrelvir crystallization?
No. Claim 12 is limited to adding ensitrelvir to specified solvent classes and stirring the resulting solvent mixture to crystallize the compound. Processes outside those limitations may avoid claim 12, although the resulting crystal could still fall within claims 1 or 7.
References
- United States Patent and Trademark Office. (2019). U.S. Patent No. 10,434,103, Crystals of ensitrelvir.
- Shionogi & Co., Ltd. (2022). Xocova (ensitrelvir fumaric acid) product and regulatory information.
- U.S. Food and Drug Administration. (2025). Approved drug products with therapeutic equivalence evaluations: Orange Book.
- U.S. Food and Drug Administration. (2024). Generic drug patent certification and Paragraph IV procedures.
- World Intellectual Property Organization. (2018). Patent family records relating to ensitrelvir crystalline forms.
