Life Sciences Intellectual Property Basics
Unlike the United States—a country known for its litigious culture – Japan sees relatively few patent lawsuits. However, the situation is somewhat different in the life sciences sector. In May of this year, a high-profile patent dispute of brand vs. Gx, over Toray’s antipruritic drug Remitch, resulted in a ruling by the Intellectual Property High Court ordering over 20 billion yen in damages – a case that made major headlines. More recently, on October 21, 2025, news broke that Asahi Kasei Pharma had received a 4-billion-yen settlement from Sawai Pharmaceutical in a patent infringement case involving the osteoporosis drug Teribone. These developments vividly illustrate the Samrai Era-like intensity of litigation in this field. For those working in the pharmaceutical industry, it’s no exaggeration to say that litigation could strike at any time.
In this volume, I’d like to walk you through what to expect in a patent infringement lawsuit.
Vol. 6: Sued for Patent Infringement?
– Here’s How the Litigation would Unfold –
What Is Patent Infringement?
Strictly speaking, “patent infringement” refers to the infringement of a patent right, which is defined under Japanese Patent Law as follows:
“An unauthorized third party who works a patented invention in the course of trade”
(Article 68, Article 2(3) of the Patent Act)
In this context, “an unauthorized third party” means someone who has no relationship with the patent holder and does not possess any license or permission to use the patented invention.
The phrase “works …… in the course of trade” refers to commercially manufacturing or selling a patented invention.
A “patented invention” is the subject matter described in the “Claims” section of the patent gazette. For example, it may be stated as “An antipruritic agent comprising nalfurafine hydrochloride” as shown in the drawing below. For more information about patent gazettes, please refer to Volume 3 of this column.
What Is a Patent Infringement Lawsuit?
A patent infringement lawsuit is a legal action brought against a party who has infringed – or is likely to infringe – a patent. The plaintiff typically seeks remedies such as:
• Injunction: to stop the infringing acts
• Damages: to compensate for losses caused by the infringement
Infringing acts generally refer to the manufacture and sale of products that violate the scope of a valid patent. To initiate such a lawsuit in Japan, the plaintiff must file a complaint with either the Tokyo District Court or the Osaka District Court, both of which have exclusive jurisdiction over patent litigation.
Litigation Process
Let’s walk through the patent litigation process with reference to the diagram below. A lawsuit begins when the plaintiff (the patent holder) files a complaint with the court. The court then sends the complaint to the defendant named in the filing. In a patent infringement case, the plaintiff asserts that the defendant is infringing their patent and demands that the infringing acts be stopped. The plaintiff may also seek compensation for damage caused by the infringement. In response, the defendant may argue that they are not infringing the patent, or that the plaintiff’s patent is invalid in the first place.
The court hears arguments from both sides and examines whether the defendant has indeed infringed the plaintiff’s patent rights. If the defendant challenges the validity of the patent, the court also reviews whether the patent is valid or invalid.
Once the court reaches a conclusion, it issues a judgment:
• If the defendant is found to have infringed a valid patent, the court will issue a judgment in favor of the plaintiff (i.e., the claim is upheld).
• If the defendant is found not to have infringed the patent, or if the patent is deemed invalid, the court will dismiss the plaintiff’s claim.
If You Disagree with the Judgment
If you are dissatisfied with the district court’s decision, you may file an appeal with the High Court. In patent litigation, appeals are handled by the Intellectual Property High Court (IPHC). If you are still dissatisfied with the IPHC’s ruling, you may file a final appeal or a petition for acceptance of appeal with the Supreme Court of Japan. However, the Supreme Court does not accept all cases, and in patent litigation, most appeals are dismissed without review.
When Does Litigation End?
Litigation ends when there are no further avenues for appeal and the case can no longer be contested. This is referred to as the case being “finalized” or “confirmed.” Once finalized, the judgment becomes legally binding, and the parties must comply with the court’s decision.
For example, the Remitch case mentioned earlier is still pending before the Supreme Court and has not yet been finalized. In contrast, the Teribone case has been settled with the court-issued settlement record finalizing the matter. As a result, Sawai Pharmaceutical is now legally obligated to pay the settlement amount to Asahi Kasei Pharma.
What Should You Do If You’re Sued for Patent Infringement?
If you receive a complaint from the court, the first step is to carefully review the contents and retain legal counsel. Because patent litigation is highly specialized, it is essential to hire an attorney with extensive experience in pharmaceutical patent disputes. In addition, it is highly recommended to seek support from a patent attorney (benrishi) who is well-versed in pharmaceutical technologies.
Together with your legal team, you should examine the complaint in detail to determine:
• Whether your product infringes the plaintiff’s patent rights
• Whether the plaintiff’s patent may be invalid
In parallel with the litigation, you may also consider filing a patent invalidation trial with the Japan Patent Office to squash the plaintiff’s patent, which is a strategy that can be highly effective.
“Wait! Squash a patent?” Some of you may be surprised to hear that. But in fact, invalidation trials to squash a patent are the most frequently employed counteraction in response to patent infringement lawsuits.
With that in mind, let’s explore how to strategically challenge patents that may be blocking your business in the life science field. In the next volume, I’ll be talking about invalidation trials—your tactical guide to dismantling problematic patents. Stay tuned!
Author Profile
Yasuko Tanaka
President & Patent Attorney, S-Cube International Patent Office / CEO, S-Cube Corporation
Outside Director, Strategic Capital Inc.; Part-time Lecturer, Tokyo University of Agriculture and Technology Graduate School; Expert Commissioner in Intellectual Property Litigation
Previously served in the intellectual property departments of Teijin, Pfizer, and 3M Japan, with extensive experience in domestic and international IP practice, IP strategy development, contract negotiation, IP education, and project management. Founded S-Cube Corporation in April 2013 to strengthen global competitiveness of Japanese companies through IP strategy, and subsequently established S-Cube International Patent Office in August 2013 to provide seamless services including patent prosecution. Holds a B.Sc. in Biochemistry from Chiba University (1990).
