Assessing the inventive step of a crystalline form patent in China
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Assessing the inventive step of a crystalline form patent in China

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Xiaohui Wu and Jianhui Li of Wanhuida Intellectual Property discuss the crystalline form patent application when determining the inventive step

Given that China’s Guidelines for Patent Examination makes no mention in terms of the examination on crystalline form patent application, practitioners primarily rely on judicial decisions and the China National Intellectual Property Administration’s (CNIPA) invalidity decisions to fathom the examination criteria adopted by the judiciary and the agency.

Our analysis of a slew of recent decisions leads to the finding that the criteria for assessing the inventive step of crystalline form invention tends to be consistent. The criteria adopted in assessing the inventiveness of a compound sharing a structure similar to a known compound should also be applicable to crystalline form invention, that is, only those inventions achieving unexpected technical effects involve an inventive step.

Once again, with no explicit parameters articulated in the Guidelines for Patent Examination as to a crystalline form’s achieving of unexpected technical effect, this article aims to unravel the parameters to be considered in establishing the unexpected technical effect of crystalline form invention through analysis of two recent invalidity decisions.

The invention patent No. ZL200780022338.5 relates to the beta crystalline form of vortioxetine hydrobromide. The embodiments of its description prepare and characterise a variety of salts of vortioxetine and different crystalline forms of hydrobromide. The validity of the patent was challenged in an invalidity proceeding before the CNIPA, which rendered on April 29 2021, an invalidation decision #48337 upholding its validity.

The decision finds that the difference between Claim 1 of the patent at issue and Evidence 1 of the closest prior art is that Evidence 1 merely discloses the free base of vortioxetine, rather than the salt forms and crystalline forms of the patent.

The contention of the case focuses on whether the beta form of vortioxetine hydrobromide brings any unexpected technical effect over the prior art. In assessing the unexpected technical effect, the decision not only compares the data of the melting point, hygroscopicity and water solubility of the crystalline forms of the patent at issue with that of the free base of the prior art, but also extend comparisons to the crystalline forms of other salts disclosed by the patent at issue.

It should be noted that the beta form claimed by the patent at issue is not the most superior among the crystalline forms disclosed by the patent at issue insofar as the melting point, hygroscopicity and water solubility. However, the decision opines that apart from maintaining a high melting point (thermal stability), the alpha and beta forms of vortioxetine hydrobromide retain substantially lower hygroscopicity and higher water solubility in comparison to other salts. Such overall performances cannot be expected by the person skilled in the art based on the salt crystals enumerated by the patent at issue.

“The criteria for assessing the inventive step of crystalline form invention tends to be consistent”

Invalidation decision #49520, rendered by the CNIPA on April 30 2021, finds that the invention patent No. ZL 200480036184.1, which relates to the crystalline form of lenvatinib methanesulfonate, invalid.

The decision adopts an analogous approach utilised by decision #48337 in ascertaining the unexpected technical effect. It first compares the crystalline form of lenvatinib methanesulfonate (Form C) in Claim 1 of the patent at issue with the free base of the prior art and then moves on to Form C and the crystalline forms of other acid addition salts disclosed by the patent at issue.

Nevertheless, after a comparative analysis of the solid stability, hygroscopicity, solubility and bioavailability of Form C, the free base and other salts, decision #49520 concludes that the said technical features of Form C are superior to those of the free base, but inferior to some other salts, thus the achieved effect is within the expected range.

In the above cases, the effects achieved by other technical solutions disclosed in the description of the patent at issue are used as a benchmark in ascertaining whether the technical effect of the claimed crystalline form can be expected.

Practitioners should be wary of the fact that such an approach is not applicable unless there is evidence showing that the effects achieved by the benchmark technical solutions are equivalent to those to be expected by the person skilled in the art based on the prior art, or else they risk jumping to an erroneous conclusion.

For example, if the exploitation of an invention leads to a single crystalline form, there will be no point of reference in conducting comparison and proving the unexpected technical effect. However, if the exploitation of an invention simultaneously leads to two crystalline forms with varying properties, by employing the methodology utilised in the aforesaid cases, it seems rational to establish one crystalline form in producing unexpected technical effect.

In case the properties of the two crystalline forms are barely distinguishable, it would be difficult to establish unexpected technical effects, even if both effects are superior. In such a context, the inventive step assessment of a crystalline form over the prior arts, which hinges on the contents disclosed by the invention, may vary if the patentee opts to disclose different contents.

In a nutshell, the technical solutions simultaneously disclosed at the filing date should have no bearing on the objective assessment on the inventive step of an invention over the prior art. Whether it is justifiable to use the technical solutions achieved by the patent application as a frame of reference in attesting to the level of expectation of the person skilled in the art remains questionable.


Xiaohui Wu

Senior patent counsel

Wanhuida Intellectual Property


Xiaohui Wu is a senior patent counsel at Wanhuida Intellectual Property. Her areas of technical expertise are biology, pharmaceuticals, chemicals, and chemical engineering.

Xiaohui’s experience as the R&D project director at a local pharmaceutical company has equipped her with a better understanding and anticipation of the needs of the firm’s biopharma clients in respect of patent prosecution, enforcement and dispute resolution field.

Xiaohui was one of the lead counsels that helped a pharmaceutical multinational corporation enforce its invention patents against the infringers offering to sell products exploiting the client’s patents in two cases, which are selected as one of the National Ten Exemplary Patent Administrative Enforcement Cases in 2019 and 2018 by the China National Intellectual Property Administration.


Jianhui Li


Wanhuida Intellectual Property


Jianhui Li is a paralegal at Wanhuida Intellectual Property. Her areas of technical expertise are biology, pharmaceuticals, chemicals and biomedical engineering.

Jianhui assists the firm’s senior patent practitioners in patent infringement, patent validity analysis, free-to-operate and other patent legal affairs for a few multinational biological and pharmaceutical corporations both at home and abroad.

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