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T1303/18

A recent EPO Decision centred around the issue of priority and provides a useful reminder of the care needed when deciding to change the definition of the invention in a subsequent application claiming priority.

As we know, when claiming priority from an earlier application, one of the tests for a valid priority claim is that it relates to the “same invention”; this being essentially the same as the test for added matter and requiring a “direct and unambiguous” disclosure of the features of the claims of the subsequent application in the priority application. While it is very tempting to “improve” the definition of the invention, or specific features thereof, in the subsequent application, for example once there has been further development or more is known about the relevant prior art, great care is needed to ensure that any priority claim is valid.

In the case of a recent Decision (T1303/18), the only real issue to be decided was whether the priority claim was valid based on the “same invention” test. There was use of the subject matter of the claims between the priority and filing dates, and thus loss of the priority date would be fatal.

The patent relates to polymorphic forms of Rotigotine (Neurpo), a dopamine agonist approved for treatment of Parkinson’s disease and restless leg syndrome.

The priority document defines the new polymorphic form of Rotigotine by reference to a number of ways of characterising the form. The first involved 14 X-ray diffraction peaks, suggesting that 1, 2, 3, 4 or more of these can be used for confirmation. The second related to Raman spectrum results, listing 16 specific peaks. A third characterisation related to melting points and differential scanning calorimetry (DCS).
However, the claims as granted define the polymorphic form differently, and as having at least one of (a) 4 X-ray diffraction peaks, (b) 18 Raman spectrum peaks, (c) a specific DSC peak, or (d) a specific melting point. In addition, the error margins quoted in the priority document were different from those in the claims as granted.

These differences, including the different number and relevance of the peaks on both the X-ray diffraction and Raman spectra, as well as the differences in error margins, and the options of the use of the melting point or DSC data, not considered characteristic in the priority document, meant that the polymorph defined in the claim was not clearly and unambiguously disclosed in the priority application, according to the Opposition Division.

The Patentee tried to argue that as both the priority application and subsequent application contained the same Figures of the results from the X-ray diffraction and Raman spectrometry, and the form was consistently described as Form II, it was clear that both the priority application and claim as granted related to the same form of the compound. The Appeal Board did not find this persuasive – a name is not characterising.

The Patentee also tried to argue that as at the priority date only two forms of the compound has been identified, Form I being known and Form II being new, if the polymorph being identified was not Form I it must be Form II, and thus the priority document did relate to the same invention as the claims as granted. The Board noted that while this was understandable while only two forms had been identified, if a third form was to be found, then this argument could no longer be considered logical, and priority would retroactively become invalid. As this argument runs against the principle of legal certainly, it could not be accepted.

Finally, the Proprietor tried to argue that the burden of proof lay with the Opponent for demonstrating that the polymorph described in the priority document was different from the polymorph described in the claims. As they had not done this the Patentee argued, the burden of proof had not been discharged and the priority claim should be considered valid. The Board disagreed. The burden of proof lay with the Proprietor, who had created the definitions in the priority document and the claims, and thus introduced the differences.

Thus, the Board concluded that the priority claim must fail, as a as a result of the prior use, the claims lacked novelty and the patent was revoked.

This case acts as a useful reminder that changing definitions of the invention or important features thereof, between the priority application and subsequent filing, can be dangerous, and care is needed. While fiddling with a definition can be tempting, as a result of additional knowledge of the invention or prior art, this should be resisted where possible. While sometimes changes may be needed, it is preferable to do these by addition or explanation rather than deletion or fundamental changes. Indeed, if changes that are not purely addition are needed, it may be sensible to include the original definition as an alternative to provide a fall back, possibly in the form of a divisional application, should priority be challenged.


Our articles are for general information only. They should not be considered specific legal advice, which is available upon request. All information in our articles is considered to be accurate at the date of publishing.

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