Japanese Government Considers Potential Improvements to Patent Linkage System for Generics

In Japan, there is no equivalent of the Orange or Purple Book in the United States, which lists patents said to cover an innovator's pharmaceutical brand product. Instead, the manufacturer or the marketing authorization holder of the brand product ("the brand company") submits to the MHLW a list of its patents it believes are relevant to any generic counterpart. The MHLW then reviews the substance and use patents on the list that expire after the planned approval date for any potential infringement by the generic product. It also seeks the views of both the generic applicant and the brand company. The MHLW does not approve the generic product if it believes there is potential infringement, as that could adversely affect the stability of supply of the product in the market. 

The MHLW lacks sufficient legal experience, and sometimes the necessary information regarding the generic product, to accurately assess whether a generic product will, if approved, infringe a third-party patent. Further, there is no equivalent of a U.S. ANDA litigation that can help resolve the question of whether there is patent infringement, and Japanese courts do not allow generic companies to obtain a declaratory judgment of noninfringement at the preapproval stage, on the ground that generic companies have no legal interest to seek such relief before the MHLW's approval. Consequently, in an effort to improve the Japanese patent linkage system, the MHLW published a report titled "Research Towards Establishment of a System to Reflect Opinions of Experts in Pharmaceutical Patents in the Japanese Patent Linkage System" on June 30, 2025. The report proposes using a panel of experts to help assess the risk of patent infringement by a generic product. The MHLW will appoint three or five experts as needed on a case-by-case basis. 

Other features of the proposed system include the following:

Experts

The experts will be academic experts, or lawyers or patent attorneys with extensive experience in pharmaceutical patents. They—and their family members, and lawyers and patent attorneys working in the same firm—must have no conflicts of interest and pledge to maintain confidentiality of information they receive.

Selection of Panel Experts

The MHLW will select one academic expert, one lawyer, and one patent attorney from a list of vetted experts for a panel of three experts. It will not disclose their identity, thus neither side will be able to object to their appointment. 

Submission of Arguments and Evidence

The MHLW will notify both sides of its decision to appoint experts. Both sides shall then identify supporting documents that they agree to share with the experts, such as a brief, relevant legal precedents, and expert reports.

Written Opinion

After reviewing the relevant documents and information, the appointed experts will submit a joint written opinion on the risk of patent infringement to the MHLW, who may ask questions to the appointed experts. The MHLW will make the final decision on whether to approve the generic product. 

The above procedure will also apply to biosimilar applications. The MHLW is currently assembling its list of experts and will start the system likely within this year. 

Additional Points 

• The MHLW will continue its practice of reviewing only substance and use patents.
• The MHLW will disclose the written opinion of the experts to both sides after masking confidential information. 
• It appears unlikely the expert panel will assess the validity of the patents. 
• The MHLW will not provide copies of the submissions of one side to the other, which could constrain the ability of either side to rebut fully. 
• The use of experts will not alter the one-year length of time for the MHLW's examination of generic applications. 

The MHLW has yet to decide the duration of the trial period for this new expert panel system. It remains to be seen whether it will accomplish the stated goal of reducing the frequency of post-approval patent disputes and whether it will be adopted on a permanent basis. 

In the meantime, brand companies with a product nearing the end of its reexamination period should continue to carefully prepare and submit a complete list of their relevant substance and use patents. The list is submitted as part of a Drug Patent Information Report, and for already-registered patents, it must be submitted before the end of the reexamination period for them to be considered by the MHLW. With the new expert panel system, the written submissions should be tailored toward academic experts and practicing lawyers and patent attorneys.