ILPTO update: Salt Patents may still be obtained – despite another restrictive ILPTO decision

In a recent decision relating to the tosylate salt of lumateperone, the ILPTO again expressed a highly restrictive view in connection with salt patents. However, salt patents may still be obtained if proper evidence is submitted to establish that the patent is not merely a reflection of routine salt screening.

The ILPTO rejected the Patent Application claiming the tosylate salt of lumateperone but following an appeal to the District Court the matter was remanded for reconsideration of inventive step. In the decision following the remand, the ILPTO acknowledged that salt screening is inherently unpredictable and that it is not possible to predict in advance which specific salt form would possess a combination of properties rendering it amenable for use in a commercial solid dosage form. The ILPTO however held that in most cases the research team would have a reasonable degree of certainty that by conducting a series of routine experiments it will produce some salt forms which will work and that such ‘Try and See’ approach using routine procedures does not give rise to inventive step.

The decision accordingly provided an opportunity for the ILPTO to reiterate its restrictive position on patentability of salt patents and the take-home message is that traditional arguments that salt formation is inherently unexpected or requires significant efforts and numerous experiments is insufficient to establish inventive step. Obtaining salt patents nowadays requires a different approach to establish a combination of one or more factors such as that it was not obvious to improve the physical properties of the compound by salt formation in general or by the specific salt form that was obtained; that crystallization was not straightforward and required procedures or parameters which went beyond routine screening; that identifying the salt eventually selected for the solid dosage form required a series of complex selections among several candidates; that the improved properties of the salt are not of the type routinely identified in salt screening (e.g. improved chemical stability); or that the advantageous properties would not have been expected with the particular counterion that was selected. Showing that the research leading to the claimed salt was fraught with difficulties is also of critical importance for establishing inventive step.

Salt patents are accordingly still available but obtaining protection for a salt will require an in-depth analysis of the development history as well as generating creative arguments supporting inventive step which may supplement real time development rationale. If such information is already reported in the specification, dependent claims capturing physical properties of the salt such as stability, morphology, particle size and stickiness or in vitro dissolution profile and in vivo PK parameters may also be helpful. The key objective must be to expand the scope of the arguments beyond the traditional ‘lack of predictability’ of the salt screen.

This update article is provided for general information only and is not in lieu of legal advice. Please contact us directly for any required advice on specific matters.