Japan: IP High Court Launches Amicus Call on the Scope of PTE

On March 3, 2026, the Osaka District Court dismissed a patent infringement lawsuit seeking an injunction against a generic drug, addressing an unprecedented question regarding the scope of extended patent rights under Japan’s Patent Term Extension (PTE) system. The dispute, widely known as the Amitiza® (lubiprostone) case, was initiated by Viatris Pharmaceuticals (the exclusive licensee in Japan and Plaintiff) alongside Sucampo Pharma (the patentee and the Intervener assisting the Plaintiff) on October 10, 2025, against Sawai Pharmaceutical, a leading Japanese generic manufacturer. The case has now been appealed to the Intellectual Property High Court (IP High Court), which has issued a call for public comments (amicus briefs) on the scope of PTEs, among other important issues.

Background and Japan's Distinctive PTE System

The dispute involves patents directed to medical uses of prostaglandins (lubiprostone). Under the landmark Supreme Court decision in the Bevacizumab case (2015), Japan established a "disposition-by-disposition" framework for granting PTEs. If a patentee or its licensee obtains multiple regulatory approvals for the same active ingredient at different times, the patentee can obtain independent, separate PTEs based on each separate regulatory approval (i.e. disposition), provided the subsequently approved product in terms of its components, dose strength, dosage and administration, and indication is not entirely encompassed by the earlier one.

In the Amitiza® case, the regulatory history unfolded as follows:

The First (Prior) Approval (2012): Granted for Amitiza® Capsules 24µg for chronic constipation. The approved dosage and administration was: "The approval stipulated a recommended dosage for adults of 24 µg of lubiprostone, administered orally twice daily, after breakfast and dinner. The dose may be appropriately reduced depending on the symptoms.." Based on the approval, the patentee obtained PTEs which extended two patents until July 2024 and April 2025 respectively.

The Subsequent Approval (2018): Granted for a newly developed low-dose formulation, Amitiza® Capsules 12µg, for the exact same indication and identical total recommended dosage instruction as above (patients take two 12µg capsules at a time to achieve the standard 24µg dose, which can be reduced depending on the symptoms). The patentee obtained 5-year PTEs based on the subsequent approval, extending the patents until December 2028 and April 2027 respectively.

The Defendant Sawai subsequently sought regulatory approval for a generic version of the 24µg capsule on February 24, 2023, and was waiting for the approval when the litigation began. Because the original PTEs tied to the 24µg approval had already expired, Sawai argued it was free to launch. However, Viatris and Sucampo asserted that Sawai’s 24µg generic infringed the patents extended by the subsequent 12µg approval, which were still active.

The Osaka District Court’s Ruling on the Scope of Extended Patent Rights

The core legal battlefield was Article 68-2 of the Japan Patent Act, which restricts the effects of an extended patent to the specific "product" (defined by its components, dose, usage, etc.) specified in the regulatory approval that served as the reason for that specific extension.

Viatris relied on the IP High Court’s Oxaliplatin decision (2017), which held that an extended patent would be infringed by products that are "substantially identical" to the approved product, arguing that a mere difference in strength (12µg vs. 24µg) constitutes a minor formal variance since their technical features and therapeutic effects are the same. However, the Osaka District Court rejected this argument, ruling that a constraint applies to the “substantially identical” boundary in circumstances where there are overlapping PTEs. The court reasoned that, because Sawai's generic 24µg product is identical in dose and structure to the original 24µg product whose extension had already expired, extending the life of the 12µg-based PTE to cover the 24µg space would disrupt the equitable balance between the patentee and third parties. The court emphasized that allowing a subsequent low-dose PTE to encompass a prior regular-dose product after the prior PTE's expiration would grant the patentee an unjustified double-recovery and effectively revive a monopoly over a product that had legally entered the public domain.

Thus, the court held that Sawai’s 24µg generic was not substantially identical to the 12µg approved product and dismissed the injunction claims.

IP High Court Steps In: The Amicus Call

The Plaintiffs appealed the decision to the IP High Court (Case No. 2026 (Ne) 10041). Recognizing the profound systemic impact on innovative pharmaceutical lifecycle management and generic entry strategies, the IP High Court’s First Division launched a public amicus call on June 29, 2026. The court has invited public comments on the scope of protection conferred by PTEs, including:

• the proper approach to determine the scope of protection conferred by an extended patent, as well as the relationship between the scope of protection and the requirements for obtaining the PTE, and
• specifically, whether the scope of a 12µg-based PTE extends to a generic product of a 24µg strength in the same dosage form that has the same indication and dosage instructions as the originator’s 12µg product but contains different excipients.

In addition, although this article does not cover other legal issues in this case, the court has also invited comments on other impactful issues, as follows:

• the factors to be considered when determining infringement of a medical use patent, and
• the appropriate scope of an injunction against infringement of the medical use patent when the accused infringing product can also be used for non-patented purposes.

The deadline for the submission of amicus briefs is September 30, 2026.

Perspective

After the Supreme Court's landmark Bevacizumab decision (2015) established that patent term extensions may be granted on a disposition-by-disposition basis, innovative pharmaceutical companies gained greater opportunities to obtain multiple PTEs based on separate marketing approvals. However, the scope of protection conferred by those extended patents has remained uncertain. The IP High Court's Oxaliplatin decision (2017) sought to clarify this issue but left important questions unresolved. Regardless of whether the IP High Court affirms or reverses the Osaka District Court's decision, its forthcoming judgment is expected to provide much-needed guidance and enhance legal certainty for both innovators and generic manufacturers. The decision will therefore be closely watched by patent practitioners and pharmaceutical companies worldwide.