On March 3, 2026, the Osaka District Court issued a noteworthy decision concerning the scope of patent rights where the same patent has received multiple term extensions based on separate marketing approvals for different dosage strengths of the same drug.
The case concerned Amitiza (lubiprostone). Two patents covering the drug had each received extensions based on, first, the approval of the 24μg product in 2012, and later, the approval of the 12μg product in 2018.
After the earlier extensions based on the 24μg approval had expired, Viatris sought injunctive relief against Sawai Pharmaceutical’s 24μg generic product, relying on the still-effective extensions based on the later 12μg approval.
The key issue is whether the later 12μg-based extensions could extend to Sawai’s 24μg product.
Under Japanese Patent Law, the effect of an extended patent is not necessarily confined to the exact product covered by the relevant marketing approval. Existing case law recognizes that the extended right may also reach products that are considered “substantially identical” to the approved product.
Here, Sawai’s 24μg product differed from the later-approved 12μg product in the amount of the active ingredient, but was otherwise the same in terms of the active ingredient, indication, dosage and administration. Viewed solely from the perspective that the difference is only the quantity of the same active ingredient, there was room for the 24μg product to be regarded as “substantially identical” to the 12μg product.
However, the 24μg product had already been the subject of the earlier extension registrations, and those extended terms had expired. Taking those earlier extensions into account, the Osaka District Court held that the later 12μg-based extensions did not extend to Sawai’s 24μg product.
The court therefore dismissed Viatris’s claims, even though Sawai’s product fell within the technical scope of the patented inventions.
Why does this decision matter?
The decision is significant because it indicates that, when determining the scope of “substantial identity,” the analysis may need to take account not only of the differences between the later-approved product and the allegedly infringing product, but also of any earlier approval and extension registration relating to the same patent.
In practical terms, the decision suggests that a later extension cannot be used to effectively prolong exclusivity for a product after the extension specifically associated with that product has already expired.
This has potentially important implications for both originator companies managing multiple patent term extensions across different strengths or other variations of the same drug, and generic companies assessing market entry timing in Japan.
The ruling is a first-instance decision and is not yet final. The case is currently on appeal before the Intellectual Property High Court of Japan (Reiwa 8 (Ne) No. 10041).