Patent strategy and solid forms such as salts and polymorphs
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Solid form patents are powerful tools to protect the Intellectual Property (IP) of pharmaceutical products.  Solid form patents provide composition of matter protection since the crystal structure is directly related to the chemical structure of the Active Pharmaceutical Ingredient (API).  Such patents are considered among the strongest lines of defense. 

A well drafted crystalline form patent should, not only, specify the physical properties of the form, such as color, shape, melting point, density, hygroscopicity, aqueous solubility and dissolution rate, but also, the analytical characteristics, such as the crystal structure determined by single crystal X-ray diffraction (XRD) or powder XRD (PXRD), thermal data by DSC and TGA, spectral data obtained by Raman, infra red spectroscopy and (solid state) NMR.  In addition, the patent should discuss the utility of the form in terms of therapeutic activity and process utility, the making of the form in terms of reproducibility, and the formulation containing the form. 

Patentability of an initial solid form of a New Chemical Entity is typically not an issue if the above points are taking into consideration.  Problems may, however, arise when new solid forms are discovered during the development phases of the API.  In such cases, it is important to be able to demonstrate anticipation (novelty), obviousness and enablement. 

Inventions that fail the novelty criteria are considered anticipated.  This arises when each and every element of the claimed invention is found in the prior art, either expressly or inherently.  Here is where the problems start.  Although one may think that for the first solid form of the API no prior art exists, a substance patent describing the invented API as a “white crystalline powder” already anticipated a specific polymorphic form.  Therefore, as part of the drug discovery and development plan, a patent strategy needs to be defined to avoid a scenario where earlier patent applications claiming the substance and/or the original solid form will anticipate any later patent application claiming newly discovered solid forms. 

The obviousness criteria, although related to the novelty criteria, is somewhat easier to overcome.  This criterion may be satisfied by doing good research and collecting unexpected results.   Making a salt to improve the solubility of an API is considered obvious.  However, if many different counter-ions are used and all salts are investigated generating a wide spread of solubility, then it can be argued that it would be unexpected that a certain counter-ion leads to a salt with a high solubility.  Such a result would make the invention non-obvious.  Comparative data from animal pharmacokinetic studies may contribute significantly in demonstrating the non-obviousness of the invention.

Finally, the invention must be enabled.  The application should clearly describe how a person skilled in the art can make and use the claimed novel form(s).  Often this is not an issue when the research principle is followed and the claimed form(s) are well characterized.

The view that patent offices take on solid form patents has significantly changed over the last 10 years.  In the past, it was relative easy to obtain an IP position with (novel) solid forms.  Today, a comprehensive strategy with well planned research to collect the data is necessary to ensure a strong patent application.  Despite the difficulties, many solid form patents applications are filed and granted.