It is often argued that salt and polymorph screening during pharmaceutical drug development is now so routine that any resultant salts and polymorphs must be obvious from a patent perspective. This certainly seems to have been the stance of the EPO Examining Division in recent times where the bar for an inventive salt and/or polymorph has been set very high. Indeed the Board of Appeal has not really lowered this bar but has indicated that it is possible to get over it and seems to have adopted a more conciliatory tone in connection with this type of application.
In the first case (T0771/13), an application to “crystalline clopidogrel besylate” was first rejected for lack of novelty and then, following a substantial procedural violation and successful appeal (T2033/08), for added matter after amendments were submitted to “unsolvated…”, “non-solvated…” and “solvent-free crystalline clopidogrel besylate”. During this second appeal, the Board agreed with the Examining Division’s opinion on novelty and added matter. The application seemed to be doomed but for the Appeal Board leaving the door open for the Appellant Applicant to amend by querying the clarity of the X-Ray Diffraction (XRD) data in some of the dependant claims. The claims, duly amended to include XRD and melting point data, were subsequently considered to be novel by virtue of the higher melting point and inventive because of improved storage stability and non-hygroscopicity over the prior known amorphous form.
In T0643/12, the Appellant Applicant appealed the refusal of an application to lenvatinib mesylate polymorphic forms A and C. The Examining Division has refused the application for lack of inventive step over a prior known crystalline form of the drug. In its decision, the Appeal Board acknowledged that there is a general trend for salt formation to improve dissolution and bioavailability and suggested that improvements in solubility and bioavailability alone are not enough to justify inventive step. In this case the polymorphic forms also had favourable stability and hygroscopic properties and it was the combination and optimisation of all four of these properties that won the Board over.In one sense these decisions should not change patent prosecution practice in this field. Data demonstrating improvements in and optimization of physiochemical properties is essential for a successful outcome but it is always reassuring to see the Appeal Boards reaffirming this approach. Pharmaceutical salts and polymorphs can be novel and inventive and can only act to enhance the patent portfolio around a particular pharmaceutical compound.
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