Daiichi Sankyo loses six Chinese patent-linkage cases over mirogabalin

CNIPA reportedly finds generic versions of two dosage strengths fall outside three Daiichi Sankyo formulation patents.

Daiichi Sankyo has lost six Chinese patent-linkage cases concerning generic versions of mirogabalin after China’s National Intellectual Property Administration (CNIPA) reportedly determined that two generic dosage strengths fell outside the protection scope of three formulation patents.

The decisions, reported by specialist publication ip fray on September 16, 2026, add to a series of Chinese patent-linkage proceedings concerning Daiichi Sankyo’s mirogabalin product and highlight the role of CNIPA’s administrative adjudication mechanism in disputes between innovative drug companies and generic manufacturers.

Mirogabalin is marketed by Daiichi Sankyo under the brand name Tarlige. The drug was developed as an α2δ ligand for the treatment of peripheral neuropathic pain. Daiichi Sankyo received marketing approval for Tarlige in Japan in January 2019 in 2.5 mg, 5 mg, 10 mg, and 15 mg tablet strengths.

Six adverse decisions

According to ip fray, the six newly reported CNIPA decisions concern two generic dosage strengths and three formulation patents covering Daiichi Sankyo’s mirogabalin product.

CNIPA found that the generic products at issue did not fall within the protection scope of the patents, resulting in six decisions against Daiichi Sankyo. The proceedings are significant because the disputed patents form part of the additional protection surrounding the drug beyond Daiichi Sankyo’s underlying compound patent.

According to analysis published by Wanhuida Intellectual Property, Daiichi Sankyo has registered four patents relating to mirogabalin on China’s Marketed Drug Patent Information Registration Platform: one compound patent, which expires in September 2028, and three formulation patents expiring successively in April 2034, March 2036, and December 2040.

The generic applicant Chengdu Easton Biopharmaceuticals previously made a Category 3 declaration concerning the compound patent, undertaking not to market its generic before that patent expires. It made Category 4.2 declarations concerning the three formulation patents, asserting that its generic products did not fall within their protection scopes.

Earlier mirogabalin proceedings

The latest decisions follow earlier CNIPA proceedings concerning Chengdu Easton’s proposed generic mirogabalin product.

In December 2025, CNIPA published three administrative decisions concerning Chengdu Easton’s generic mirogabalin besylate tablets. Wanhuida reported that the decisions found that three dosage forms of the generic did not infringe Daiichi Sankyo’s formulation patent ZL201480001374.3, titled “Solid composition of amino carboxylate salt.”

The December 2025 decisions examined issues including claim construction, the doctrine of equivalents, and the consequences of amendments made to Daiichi Sankyo’s patent claims during prosecution.

Wanhuida reported that the granted claim incorporated technical features relating to excipients, particle sizes and the preparation method, thereby narrowing the scope of protection. CNIPA’s reasoning indicated that where a technical feature had been added to a claim during prosecution, the patentee could face an evidential burden if it subsequently sought to argue that technical solutions falling outside the amended wording nevertheless remained within the patent’s scope.

The earlier decisions therefore provide useful context for the latest proceedings, particularly concerning the importance of claim drafting and amendment history when formulation patents are asserted against generic products.

China’s patent-linkage mechanism

China introduced its pharmaceutical patent-linkage framework following the 2020 amendments to the Patent Law, with Article 76 providing for the early resolution of patent disputes relating to generic drug applications.

CNIPA’s rules provide both judicial and administrative routes for resolving disputes concerning whether the technical solution of a proposed generic drug falls within the protection scope of a listed patent. Under the system, generic applicants make one of four categories of patent declaration in relation to each relevant patent listed for the reference drug.

A Category 3 declaration indicates that the applicant will not market the generic before the relevant patent expires. A Category 4 declaration concerns a patent that the applicant considers should be invalidated or a generic product that the applicant considers does not fall within the patent’s protection scope. Category 4 declarations are further divided into Categories 4.1 and 4.2.

For a Category 4 dispute, the patent owner or interested party can bring proceedings before a people’s court or request administrative adjudication by CNIPA concerning whether the proposed generic falls within the relevant patent’s protection scope. Where the relevant conditions are met, the regulatory process can be subject to a nine-month waiting period while the patent dispute is addressed.

CNIPA’s administrative patent-linkage procedure is therefore distinct from conventional post-launch patent litigation. Its purpose is to address certain patent disputes during the regulatory process, before the generic product reaches the market.

Formulation patents in focus

The mirogabalin disputes also illustrate the importance of formulation patents in China’s pharmaceutical patent landscape. While the compound patent covering Daiichi Sankyo’s mirogabalin product has a reported expiry date of September 2028, the three formulation patents registered for the product extend considerably further.

That does not mean that the formulation patents will necessarily prevent generic entry until those dates. Their practical significance depends on the scope and validity of the individual patents and, in a patent-linkage proceeding, whether the technical solution of the proposed generic falls within that scope. The earlier CNIPA rulings demonstrate how closely the agency can examine the relationship between the technical features of a generic product and the wording and prosecution history of the asserted patent claims.

For pharmaceutical patent owners, the proceedings underline the importance of drafting formulation claims with potential generic products in mind and of considering the consequences of amendments made during prosecution. For generic manufacturers, meanwhile, the Category 4.2 route provides a mechanism for challenging the assertion that a proposed product falls within the scope of a listed patent.

Significance for China’s patent-linkage system

The six newly reported decisions add to the growing body of administrative patent-linkage practice in China. CNIPA’s role is particularly significant because China’s framework expressly provides an administrative alternative to court proceedings for disputes concerning whether a proposed generic falls within a listed patent’s protection scope.

The mirogabalin proceedings consequently provide a useful case study in how formulation patents are being tested against proposed generic products under China’s early patent-dispute resolution framework.

For originators and generic manufacturers alike, the cases highlight the importance of the precise technical scope of pharmaceutical patents — and, in particular, the interaction between claim language, prosecution amendments, and the formulation of the proposed generic product.

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