U.S. Patent 8,618,109: Claim Scope, Brexpiprazole Coverage, Expiration, and Patent Landscape
U.S. Patent 8,618,109 is a treatment-method patent covering the use of a broad class of heterocyclic compounds for schizophrenia. Its dependent claims expressly include brexpiprazole, the active ingredient in Rexulti. The patent does not claim every use of brexpiprazole, nor does the provided claim set independently establish composition-of-matter protection, formulation protection, or protection for indications other than schizophrenia.
The commercial significance of U.S. 8,618,109 depends on four issues: whether the patent remains enforceable, whether it is listed in the FDA Orange Book for the relevant product, whether a generic applicant has made a Paragraph IV certification, and whether the proposed generic label would induce infringement of the schizophrenia method claims.
What drug does U.S. Patent 8,618,109 protect?
The patent covers methods of treating schizophrenia with specified heterocyclic compounds or their pharmaceutically acceptable salts. Claim 2 expressly identifies the compound chemically known as brexpiprazole.
Brexpiprazole has the following chemical identity:
| Item |
Description |
| Generic name |
Brexpiprazole |
| Brand |
Rexulti |
| Primary sponsor |
Otsuka Pharmaceutical Co., Ltd. |
| U.S. marketing partner |
Lundbeck |
| Chemical class |
Quinolinone derivative |
| Key structural motif |
Benzo[b]thiophene-substituted piperazine linked through an alkoxy chain |
| FDA initial approval |
July 10, 2015 |
| Initial indications |
Schizophrenia and adjunctive treatment of major depressive disorder |
| Patent at issue |
U.S. 8,618,109 |
The compound in claim 2, item 4, is:
“7-[4-(4-benzo[b]thiophen-4-yl-piperazin-1-yl)butoxy]-3,4-dihydro-1H-quinolin-2-one.”
That structure corresponds to brexpiprazole. Claim 2 therefore creates direct species-level coverage for administering brexpiprazole, or a salt of brexpiprazole, to treat schizophrenia.
What does independent claim 1 cover?
Claim 1 is a Markush-style method claim. It covers administering a compound represented by a broad structural formula, or a salt thereof, to a human or animal for treating schizophrenia.
The claim has four principal limitations:
- The treatment must be for schizophrenia.
- The compound must fall within the defined heterocyclic formula.
- The compound must contain the specified ring Q and linker architecture.
- Administration must occur to a human or animal.
The claim is broader than the individual compounds listed in claims 2 and 3. It reaches multiple ring systems, substitutions, linker lengths, and oxidation states, subject to the structural limitations in the formula.
Structural elements
The claim permits:
- A ring Q containing nitrogen and carbon atoms in alternative arrangements.
- Single or double bonds at the specified positions of the heterocyclic skeleton.
- Substitution with alkyl, alkenyl, alkynyl, aryl, cycloalkyl, halogen, hydroxy, alkoxy, amino, nitro, carbonyl, carboxy, and related groups.
- An R2 substituent consisting of hydrogen or lower alkyl.
- A linker A consisting of an oxygen-containing alkylene or alkenylene group, or a lower alkylene group.
- Special restrictions when A is a lower alkylene group.
The claim therefore covers a genus of compounds rather than only brexpiprazole. The breadth is constrained by the exact chemical definitions, ring topology, and linker conditions. A compound with a similar pharmacological profile but a different ring system or linker may fall outside the literal language.
How do claims 2 and 3 narrow the patent?
Claims 2 and 3 identify twelve specific compounds. These claims are narrower than claim 1 because they recite defined molecular species rather than the broader genus.
Claim 2 compounds
| Claim 2 item |
Core structure |
| 1 |
7-[4-(benzo[b]thiophene-piperazinyl)butoxy]-1H-quinolin-2-one |
| 2 |
7-[3-(benzo[b]thiophene-piperazinyl)propoxy]-1H-quinolin-2-one |
| 3 |
7-[3-(benzo[b]thiophene-piperazinyl)propoxy]-3,4-dihydro-1H-quinolin-2-one |
| 4 |
7-[4-(benzo[b]thiophene-piperazinyl)butoxy]-3,4-dihydro-1H-quinolin-2-one |
| 5 |
N-methyl analogue of item 4 |
| 6 |
6-substituted 3,4-dihydroquinolin-2-one analogue |
Item 4 is brexpiprazole.
Claim 3 compounds
Claim 3 covers six isoquinolinone analogues, including:
- 7-[3-(4-benzo[b]thiophen-4-yl-piperazin-1-yl)propoxy]-3,4-dihydro-2H-isoquinolin-1-one;
- methyl-substituted isoquinolinone analogues;
- butoxy-linked isoquinolinone analogues; and
- unsaturated isoquinolinone analogues.
These compounds are structurally related to brexpiprazole but are not necessarily the same active ingredient. They expand the patent’s species coverage beyond the quinolinone structure in claim 2.
Does U.S. 8,618,109 cover brexpiprazole as a composition of matter?
No, not based on the provided claims.
The claims are directed to a method of treatment. They require administering a covered compound to treat schizophrenia. They do not recite:
- Brexpiprazole as a standalone chemical composition;
- A pharmaceutical composition containing brexpiprazole;
- A dosage form;
- A tablet, capsule, suspension, or injectable formulation;
- A specific crystalline or polymorphic form;
- A manufacturing process; or
- A method of treating major depressive disorder.
A separate compound patent may protect brexpiprazole itself. A separate formulation or solid-state patent may protect a particular product configuration. Those rights must be analyzed independently from U.S. 8,618,109.
What is the infringement theory for a generic brexpiprazole product?
The most important infringement theory is induced infringement based on the generic product’s labeling.
A generic manufacturer generally does not administer the drug to patients. Instead, it seeks FDA approval to market the product. If the proposed label instructs use for schizophrenia, the manufacturer may face an argument that it encourages or induces the administration covered by claims 1 and 2.
The relevant infringement questions are:
| Issue |
Relevance |
| Active ingredient |
The product must contain brexpiprazole or another claimed compound |
| Indication |
The label must direct treatment of schizophrenia |
| Patient administration |
The claimed act occurs when the drug is administered |
| Knowledge and intent |
Induced infringement requires more than merely selling a product |
| Label carve-out |
Removing a patented indication may reduce risk, but cannot eliminate liability if other label content encourages the use |
| Claim construction |
The accused compound must fall within the structural claim language |
A generic label limited to major depressive disorder could present a different risk profile from a label that includes schizophrenia. The patent’s method claims make indication management central to any abbreviated new drug application strategy.
What is the patent expiration date?
The precise enforceable expiration date cannot be determined from the claim text alone. Patent term depends on the earliest effective nonprovisional or PCT filing date, patent term adjustment, patent term extension, and any terminal disclaimer.
U.S. Patent 8,618,109 was granted on December 31, 2013. Public patent records associate the family with Japanese priority filings in 2006 and a later international or U.S. filing. On a conventional 20-year term calculated from an international filing in 2007, the base term would fall in 2027, before any patent term adjustment.
| Event |
Date or timing |
| Earliest family priority |
2006 family priority is reported |
| U.S. patent grant |
December 31, 2013 |
| Base statutory term |
20 years from the relevant nonprovisional or PCT filing |
| Indicative base expiry window |
2027, subject to the actual filing chain |
| Possible adjustment |
PTA, terminal disclaimer, or other term modification may change the date |
The patent’s enforceable expiration date should be taken from the USPTO Patent Center term data and any applicable FDA Orange Book listing. The grant date is not the expiration date.
What is the Orange Book status of brexpiprazole patents?
Rexulti is an FDA-approved small-molecule product. Its relevant patents may be listed in the Orange Book if they meet FDA listing requirements and relate to the approved drug substance, drug product, or method of use.
The Orange Book can include:
- Drug-substance patents;
- Drug-product or formulation patents; and
- Method-of-use patents.
A method claim directed to schizophrenia can be Orange Book-relevant if it covers an approved use of brexpiprazole. The claim text alone does not establish whether U.S. 8,618,109 is currently listed, delisted, expired, or subject to a use-code limitation. FDA listing status is product-specific and may change through updates to the Orange Book. [2]
The distinction is commercially important. An Orange Book-listed patent can trigger the Hatch-Waxman certification and litigation framework. A patent that is not listed may still support an infringement action, but it generally does not create the same statutory stay mechanism.
When does Rexulti lose exclusivity?
Rexulti’s exclusivity has several components:
| Exclusivity layer |
General effect |
| New chemical entity exclusivity |
Blocked abbreviated applications for five years from approval, subject to statutory exceptions |
| Pediatric exclusivity |
Can add six months to qualifying exclusivity or patent terms |
| Composition patent |
Can block products containing brexpiprazole until expiration |
| Method-of-use patent |
Can create indication-specific entry risk |
| Formulation patent |
Can protect a particular dosage form or release technology |
| Regulatory data protection |
Protects FDA submission data for the statutory period |
FDA approved Rexulti in July 2015. The five-year NCE period therefore ran into July 2020, subject to any applicable pediatric extension. Patent protection, rather than NCE exclusivity, has been the more important long-term barrier for generic entry. [3]
Brexpiprazole is a small molecule, so biosimilar provisions do not apply. A competing product would be filed as a generic through the ANDA pathway, not as a biosimilar under the Public Health Service Act.
Which companies could challenge the patent through Paragraph IV?
Potential challengers would be generic manufacturers filing ANDAs for brexpiprazole tablets. A Paragraph IV certification asserts that an Orange Book-listed patent is invalid, unenforceable, or will not be infringed by the proposed product.
A Paragraph IV challenge can lead to:
- Notice to the patent owner and NDA holder;
- A patent infringement action within the statutory period;
- A potential 30-month stay of FDA approval;
- Claim-construction and validity litigation;
- Settlement, license, or launch-at-risk outcomes.
The principal invalidity theories would likely include:
- Lack of enablement across the full genus in claim 1;
- Written-description deficiencies for the broad Markush scope;
- Anticipation by prior heterocyclic antipsychotic compounds;
- Obviousness based on known piperazine, quinolinone, and benzo[b]thiophene chemistry;
- Indefiniteness in structural definitions; and
- Noninfringement based on a different molecular structure or a carved-out indication.
The strongest defense depends on which claim is asserted. Claim 2’s express recitation of brexpiprazole is narrower and may be easier to analyze for anticipation or obviousness than the broad genus in claim 1. A narrower species claim can also be harder to design around if the generic product necessarily contains the claimed molecule.
What formulation patents may affect generic entry?
U.S. 8,618,109 does not recite a formulation. Other Rexulti patent families may address:
- Tablet composition;
- Excipient selection;
- Stability;
- Particle size;
- Crystalline form;
- Salt form;
- Manufacturing conditions; or
- Dosage regimens.
A generic applicant may avoid some formulation patents by using a different excipient system or manufacturing process. It cannot avoid a composition-of-matter patent merely by changing excipients if the active ingredient remains the same.
The principal freedom-to-operate layers are therefore:
| Layer |
Design-around potential |
| Compound patent |
Usually low if the approved active ingredient is required |
| Method-of-use patent |
Potentially higher through indication carve-out |
| Formulation patent |
Often moderate, depending on claim limitations |
| Polymorph or solid-state patent |
Depends on whether the generic uses the same form |
| Process patent |
Often higher if an alternative manufacturing route is available |
How strong is the patent estate represented by U.S. 8,618,109?
The patent is commercially meaningful because claim 2 identifies brexpiprazole directly and ties it to the schizophrenia indication. Its principal strengths are:
- Direct coverage of the marketed active ingredient;
- Species-specific dependent claim language;
- Use in an FDA-approved indication;
- Potential relevance to generic labeling;
- Additional genus coverage in claim 1; and
- Related analogue coverage in claim 3.
Its principal limitations are:
- It is not, on the provided claims, a composition-of-matter patent;
- It does not expressly cover major depressive disorder;
- It does not claim a formulation;
- It may be vulnerable to a label carve-out depending on FDA labeling;
- The broad genus may face written-description or enablement scrutiny; and
- Enforceability depends on the actual patent term, listing status, prosecution history, and litigation record.
The species claim covering brexpiprazole is likely more commercially important than the broad genus claim. A generic manufacturer could challenge the genus while still facing a direct species claim directed to brexpiprazole.
What litigation and settlement issues affect generic entry?
A complete litigation assessment requires the current Orange Book, FDA Paragraph IV notices, federal court dockets, and settlement filings. The patent document itself does not establish whether a particular generic company has challenged U.S. 8,618,109.
Potential outcomes include:
| Outcome |
Commercial effect |
| Patent upheld and no license |
Entry delayed until expiration |
| Patent invalidated |
Earlier approval or launch possible |
| Noninfringement ruling |
Product may proceed if no other blocking patents remain |
| Settlement with licensed entry |
Entry occurs on an agreed date |
| Authorized generic agreement |
Earlier competition under an originator-controlled supply arrangement |
| Label carve-out |
Generic may launch only for noninfringing indications |
| At-risk launch |
Generic launches before final resolution and assumes damages risk |
The key distinction is between patent litigation over the method claim and regulatory approval of the ANDA. FDA approval does not itself resolve infringement. A generic may receive approval but remain subject to patent restrictions, settlement terms, or launch-related litigation.
How does U.S. 8,618,109 compare with the likely core compound patent?
| Attribute |
U.S. 8,618,109 |
Core compound patent |
| Claim type |
Method of treating schizophrenia |
Chemical composition |
| Brexpiprazole coverage |
Expressly included in claim 2 |
Typically direct compound coverage |
| Indication limitation |
Yes |
Usually no |
| Formulation coverage |
None in supplied claims |
Usually none unless separately claimed |
| Design-around potential |
Possible through indication or compound changes |
Low for the same active ingredient |
| Generic relevance |
Label-dependent |
Product-dependent |
| Orange Book potential |
Method-of-use listing |
Drug-substance listing |
| Main legal issue |
Induced infringement and use-code scope |
Validity, infringement, and patent term |
The compound patent generally provides the strongest barrier to a generic product containing brexpiprazole. U.S. 8,618,109 adds indication-specific protection and may remain relevant after other patents expire if the schizophrenia use is included in the generic label.
Key Takeaways
- U.S. 8,618,109 is a method-of-treatment patent, not a standalone composition patent based on the supplied claims.
- Claim 2 expressly covers brexpiprazole administered to treat schizophrenia.
- Claim 1 provides broader genus coverage over related heterocyclic compounds.
- Claim 3 covers additional isoquinolinone analogues.
- The patent does not expressly cover major depressive disorder, formulations, dosage forms, polymorphs, or manufacturing processes.
- Generic risk depends heavily on the proposed label and any indication carve-out.
- Brexpiprazole is a small molecule, so biosimilar law does not apply.
- The indicative statutory term falls in the 2027 period, but the exact expiration date requires the recorded patent-term calculation.
- Orange Book listing, Paragraph IV activity, litigation, and settlement status cannot be inferred from the claim language alone.
- The strongest commercial protection for Rexulti is likely the combination of composition, method-of-use, formulation, and regulatory exclusivity rights.
FAQs About U.S. Patent 8,618,109 and Brexpiprazole
Does U.S. Patent 8,618,109 cover Rexulti?
Yes. Claim 2 expressly recites the chemical structure of brexpiprazole, the active ingredient in Rexulti, when administered to treat schizophrenia.
Can a generic launch brexpiprazole for depression without infringing this patent?
Possibly, because the supplied claims are limited to treating schizophrenia. The generic label, actual promotional conduct, product instructions, and other patents would determine the overall risk.
Is U.S. 8,618,109 a composition-of-matter patent?
No. The supplied claims are method claims. A separate patent may claim brexpiprazole itself.
Does this patent protect injectable brexpiprazole?
Not from the supplied claims alone. The claims do not specify a dosage form, route of administration, formulation, or injectable product.
Does the patent block biosimilars?
No. Brexpiprazole is a chemically synthesized small molecule. Competing products would generally proceed through the ANDA generic-drug pathway rather than the biosimilar pathway.
References
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U.S. Patent No. 8,618,109, “Heterocyclic compound,” U.S. Patent and Trademark Office, issued December 31, 2013.
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U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
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U.S. Food and Drug Administration. (2015). Rexulti prescribing information. Otsuka Pharmaceutical Co., Ltd.
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U.S. Food and Drug Administration. (2024). ANDA submissions: Refuse-to-receive standards and Paragraph IV certifications. FDA.
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U.S. Code, 35 U.S.C. §§ 154, 271, and 282.
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U.S. Code, 21 U.S.C. §§ 355(j) and 355(q).
