1. Outline of the Japanese Patent Linkage System
Japan does not have a patent linkage system related to pharmaceutical products that incorporates civil litigation procedures between disputing parties as adopted in some other jurisdictions. Rather, Japan has introduced its own system (hereinafter, "the Japanese patent linkage system"), which is administered by the Ministry of Health, Labour and Welfare (MHLW).
 
There are no statutory provisions concerning patent linkage in Japan. Instead, the system has been operated based on an administrative notification issued in 2009 (hereinafter, "the Notification"). The Notification stipulates that the MHLW does not grant marketing authorization for a generic drug when there is a product or use patent covering a brand-name drug, as follows.
 

(1) When a patent exists for the active ingredient of a brand-name drug and, as a result, the manufacture of said active ingredient itself is precluded, approval of a generic drug shall not be granted.
 
(2) Where a patent exists for some of the indications, dosage, or administration (hereinafter collectively referred to as the "indications, etc.") of a brand-name drug, but the manufacture of a drug claiming other indications, etc. is possible, approval of a generic drug shall be permitted. In such a case, approval is not granted for the patented indications, etc.

 
In the Notification of 2009, it was not explicitly stated whether or not biological products were also covered by this approach. However, in an updated administrative notification dated October 8, 2025, it is clearly indicated that the system also applies to biological products.
 
2. Issues concerning Japanese Patent Linkage System
Under the current system, the MHLW makes a determination as to whether or not a patent would be infringed by the manufacture and sale of a generic drug or a biosimilar product. However, since the MHLW was not established as an authority that specializes in determining the scope or effect of patent rights, various concerns have been raised, including a lack of transparency regarding the criteria applied, and inconsistencies between determinations of equivalence under the Patent Act and determinations made from a regulatory perspective.
 
In the following, several recent court decisions of note are introduced and summarized.
 
3. Relevant Court Decisions
3-1. Eribulin Mesylate (Halaven) Case
(Intellectual Property High Court, May 10, 2023; Case No. 2022 (Ne) 10093 – Appeal Case for Declaratory Judgment of Non-existence of Right to Seek Injunction and Damages for Patent Infringement; Nipro Corporation v. Eisai Co., Ltd.)
 
This was an appeal case in which the plaintiff of the first instance, who filed a marketing authorization application for the generic drug "eribulin mesylate," brought an action against the defendant of the first instance, seeking a declaratory judgment that the defendant had no right to seek an injunction or damages for patent infringement, in light of the fact that their generic drug was not approved by the MHLW.
 
The Intellectual Property High Court decided that the fact that the generic drug was not approved by the MHLW was an issue concerning the appellant (the plaintiff in the first instance) and the MHLW, and was not an issue between the parties to the case. Accordingly, the Court dismissed the appellant’s claims on the ground that there was "no legal interest (standing) to file the action."
 
This case represents an instance of a judicial remedy to a dispute between parties being denied in relation to the patent linkage system operated by the MHLW. For generic and biosimilar product manufacturers, if marketing authorization is not granted, their only means of contesting such a decision would then seem to be to file an administrative appeal or take other remedial measures against the MHLW.
 
3-2. Aflibercept (Eylea) Case
(Tokyo District Court, October 28, 2024; Case No. 2024 (Yo) No. 30029 – Petition for Provisional Injunction Based on Violation of the Unfair Competition Prevention Act; Samsung Bioepis Co., Ltd. v. Bayer HealthCare LLC)
 
In this case, the plaintiff, who had filed a marketing authorization application for a biosimilar product, sought a provisional injunction against the defendant, the patentee, on the grounds that the defendant’s act of notifying the MHLW that the manufacture and sale of the biosimilar product would constitute patent infringement was a violation of the Unfair Competition Prevention Act.
 
The timeline of events was as follows.
 
(1) The defendant had been manufacturing and selling the product "Eylea" since November 2012, for indications such as "age-related macular degeneration with subfoveal choroidal neovascularization".
 
(2) Meanwhile, in May 2023, the plaintiff filed a marketing authorization application for a biosimilar product for indications such as "age-related macular degeneration with subfoveal choroidal neovascularization" and other uses that would overlap with those of the brand-name product.
 
(3) In July 2023, the defendant was granted and registered a patent relating to an aflibercept formulation. The patent is directed to a pharmaceutical composition comprising aflibercept, administered to a population of wet age-related macular degeneration (wAMD) patients selected according to specific inclusion and exclusion criteria. The claim of the granted patent reads as follows.
 

• 1. A pharmaceutical composition for use in the treatment of a patient with wet age-related macular degeneration (wAMD) having an active choroidal neovascular (CNV) lesion size of less than 50% of the total lesion size as determined by fluorescein fundus angiography, the composition comprising aflibercept as an anti-VEGF agent,
• wherein the wAMD patient satisfies the following key inclusion criteria (omitted), and
• wherein the wAMD patient satisfies the following key exclusion criteria (omitted).

 
(4) In connection with the marketing authorization application for the biosimilar product, the plaintiff held consultations with the MHLW on and after September 2023. During this process, the MHLW instructed the plaintiff to delete "wAMD" from the indications after being informed by the defendant (the brand-name drug manufacturer) that approval of the biosimilar product would constitute infringement of its patent. Thereafter, the plaintiff deleted "wAMD" from the indications and obtained marketing authorization for the biosimilar product.
 
(5) The plaintiff filed suit on the grounds that the defendant’s act of notifying the MHLW that approval of the biosimilar product would infringe its patent constituted unfair competition.
 
In this case, the defendant’s patent was granted after the plaintiff filed the marketing authorization application for the biosimilar product, as a result of which approval of the biosimilar product was then blocked despite the absence of any clear ruling as to whether or not it would actually have conflicted with the patent. The patent claim in question includes detailed inclusion and exclusion criteria for patient selection, and it is debatable whether the manufacture and sale of the biosimilar product would have directly constituted an act of patent infringement.
 
The District Court presented the following findings and held that the defendant’s act did not constitute unfair competition:
 
(a) Manufacture and sale of the biosimilar product by the plaintiff cannot be regarded as actions performed solely for administration to the specific patient group described in the patent and, therefore, do not constitute patent infringement. Moreover, if one assumes that the manufacture and sale of the biosimilar product did infringe the patent, given that the defendant’s own brand-name product had been manufactured and sold prior to the priority date of the patent and had been administered to patients belonging to the same group specified in the patent, the patent should be deemed invalid due to prior public use. Therefore, the defendant’s notification to the MHLW constitutes a false statement of fact.
 
(b) However, in view of the purpose and intent of the patent linkage system, the defendant’s notification to the MHLW was, to some extent, unavoidable and cannot be regarded as entirely lacking reasonable justification. Therefore, the defendant's act does not correspond to an act of unfair competition.
 
This case, therefore, represents an instance in which, considering the purpose of the patent linkage system, the court determined that the act of a brand-name drug manufacturer of notifying the MHLW that the manufacture and sale of a biosimilar product would constitute patent infringement, did not itself directly constitute an act of unfair competition.
 
3-3. Dasatinib (Sprycel) Case
(Tokyo District Court, May 15, 2025; Case No. 2023 (Wa) 70527 – Action for Declaratory Judgment of Non-existence of Infringement; Case No. 2024 (Wa) 70016 – Counterclaim for Damages; Sawai Pharmaceutical Co., Ltd. v. Bristol-Myers Squibb Holdings Ireland Unlimited Company)
 
In this case, the plaintiff, a generic drug manufacturer, filed an action seeking a declaratory judgment that the patent right of the defendant, the brand-name drug manufacturer, did not extend to the generic drug. The defendant owned a patent directed to dasatinib or a salt thereof, while the plaintiff had obtained marketing authorization for, and had commenced manufacture and sale of, its generic drug.
 
The defendant’s patent had been registered for a patent term extension and was within the extended period. According to the Patent Act and relevant court precedents, the effect of an extended patent right is limited to acts involving the patented invention with respect to the product and use approved for the original brand-name drug, and those that are substantially identical thereto (e.g., Decision of the Intellectual Property High Court, January 20, 2017, Case No. 2016 (Ne) 10046, Action for Injunction against Patent Infringement).
 

Article 68-2 of the Patent Act
Where the duration of a patent right as provided in Article 67(1) has been extended under the provisions of Article 67(4) (including cases deemed extended under the main paragraph of Article 67-2(5) as applied mutatis mutandis pursuant to Article 67-5(4), the effect of the patent right shall not extend to any act other than the working of the patented invention with respect to the product that was the subject of the disposition prescribed by Cabinet Order under Article 67(4) that was the ground for the registration of the extension (or, where a specific use for which the product is used is designated in the disposition, the product used for such use).

 
In the present case, while the brand-name drug (Sprycel) contained dasatinib hydrate as its active ingredient, the generic drug contained dasatinib anhydrate, and further contained different additives. The main issue at dispute was whether the scope of the extended patent right covered the generic drug by virtue of being "substantially identical" thereto.
 
The District Court held that, in view of the fact that the generic drug used the anhydrate form and that its stability and other properties had been improved by changing the additives, the brand-name and generic drugs were not substantially identical. Accordingly, the Court found that the effect of the extended patent right did not extend to the generic drug.
 
This case represents an instance in which while a brand-name drug and a generic drug were determined to be "biologically equivalent" from a regulatory standpoint, they were not deemed substantially identical under the Patent Act. This suggests the possibility that, even where bioequivalence is recognized for regulatory purposes, application of the patent linkage system might be avoided by designing a formulation with a specific technical effect that differentiates a generic drug from the brand-name drug or known techniques.
 
4. Comments
One of the challenges faced by the Japanese patent linkage system appears to lie in the fact that the MHLW, which is a regulatory authority for pharmaceuticals, also functions as the primary decision-making body responsible for determining possible patent infringement. There are many cases in which the patent claims and the actual labelling of a pharmaceutical product do not entirely correspond with one another.  Further, there are no clear guidelines for determining the scope of "substantial identity" between a brand-name drug and a generic drug or a biosimilar product when assessing the effect of an extended patent right. In such circumstances, detailed consideration from the perspective of patenting criteria is required in order to properly assess the effect of the patent right. In light of recent disputes and issues that have come to the fore, the MHLW has been engaging in discussions aimed at improving the operation of the current system. The progress of these discussions will be of continued interest.

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This article was provided by the International Information Group
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