Since crystalline form patents typically do not claim entirely new compounds, it is often challenging to overcome ‘inventive step’ rejections during the prosecution of such patent applications. Even after obtaining patent approval, they may face an invalidation attack (see “Exploring the Challenges Faced in Exercising Crystalline Form Patents Through Pharmaceutical Patent Linkage Litigation”, a report by Saint Island International Patent & Law Offices on two Taiwanese court rulings involving crystalline form patents). Therefore, besides inventive step, the definiteness of claims and the enabling requirement are crucial issues that need to be carefully addressed in drafting such patent specifications.
The Supreme Administrative Court’s ruling
On January 25 2024, Taiwan’s Supreme Administrative Court ruled on Patent No. I406661, finding the claims indefinite and the specification insufficiently enabling.
Claim 11 defines “[a] substantially pure crystalline form B of compound X, characterised by an X-ray powder diffraction (XRPD) pattern with at least one maximum value selected from 7.2°, […], 19.2°, […], 27.0° (2θ degrees); wherein ‘substantially pure’ means that more than 50% of crystalline compound X exists in the specified crystalline form.” The full name of compound X is lengthy, and is omitted here for easier reading.
Claim 12 is identical to Claim 11 except that it requires “at least four” maximum values instead of “at least one”.
The patent specification discloses that the crystalline forms of compound X include types A, A’, A”, and B. For each crystalline form, the specification provides illustrative descriptions similar to the following for crystalline form A: “Crystalline form A shows at least one, preferably at least two, and most preferably all maximum values selected from approximately […] and 19.2° (2θ) in the XRPD pattern.”
From this example of crystalline form A, it is clear that the maximum values of 2θ degrees used to characterise several crystalline forms (such as form A) are the same as those used to characterise crystalline form B.
Therefore, the court held that since forms B, A, and A” are merely designations (i.e., codes), the crystal structure defined by the same 2θ-degree maximum values should logically be the same. In claims 11 and 12, crystalline form B is characterised by “at least one” and “at least four” 2θ-degree maximum values, respectively, while the specification also characterises other crystalline forms (such as forms A and A”) using the same one or four maximum values of 2θ degrees. As a result, crystalline form B cannot be distinguished from these other crystalline forms, making it difficult, if not impossible, for a person skilled in the art to determine which claims 11 and 12 refer to; namely, “substantially pure crystalline form B” or “substantially pure crystalline forms A, A”, etc.? Consequently, claims 11 and 12 were deemed unclear in meaning.
Additionally, the patent specification discloses that in certain solvents, both crystalline forms A and B in a mixed crystalline state can be produced. A person skilled in the art would understand that crystalline form B can mix with other crystalline forms.
Given the court’s finding that crystalline form B cannot be distinguished from other crystalline forms, when interpreting “substantially pure crystalline form B” recited in claims 11 and 12, it cannot rule out the possibility of producing mixed crystalline forms besides impurities. However, the specification does not disclose any technical means for determining that crystalline form B constitutes more than 50% in a mixed crystalline state. Therefore, the court opined that the descriptions in the specification that correspond to the recitations of claims 11 and 12 do not clearly and sufficiently disclose the invention such that a person skilled in the art could not understand and implement it.
Implications of the ruling for claims involving crystalline form patents
This ruling provides important insights.
When defining claims for crystalline form patents, it is crucial to ensure that the crystalline structure of the specific crystalline form being claimed should be distinguished from other crystalline forms disclosed in the specification.
Consideration must be given to whether ‘more’ XRPD or other measurement values are needed to define the crystalline structure clearly and ensure the claims are definite in meaning. In this case, had the applicant used sufficient XRPD or other measurement values to define “substantially pure crystalline form B”, the term would likely have been interpreted as “crystalline form B compared to other impurities”, potentially avoiding the enabling issue.
