On 17 October 2023, Mr Justice Mellor of the UK High Court handed down the long-awaited judgment (some 14 months after trial) in the patent infringement action commenced by Astellas against Teva and Sandoz, in relation to their proposed generic mirabegron tablets, which is used to treat overactive bladder.
The action between the parties concerned EP 2,345,410 (EP'410), a modified release formulation patent with a priority date of 2008. The defendants alleged that the patent was invalid for insufficiency and obviousness, arguing that the claims of EP'410 were excessively broad and exceeded any relevant technical contribution to the art.
The problem allegedly solved by EP'410 was reducing the 'food effect' associated with conventional formulations of mirabegron (that is, pharmacokinetic differences between patients in fed vs fasted states). The claims of EP'410 recite a modified release formulation of mirabegron comprising specified additives, and having a prescribed drug dissolution rate.
In summary, the case turned on the correct construction of claim 1 of the patent. Mellor J found that, on his construction of EP'410, the patent as amended was valid but not infringed. Conversely, if his construction was incorrect (and under the construction proposed by the patentee itself), then EP'410 was invalid. This is a win for the defendants as, two months earlier, their challenge to another Astellas patent covering mirabegron (the method of treatment patent, EP 1,559,427) was unanimously dismissed by the UK Court of Appeal.
The issue on construction related to whether or not the term "a pharmaceutical composition for modified release" in claim 1 required a reduction in food effect. The patentee argued that claim 1 only required that the formulation had the recited composition and satisfied the claimed dissolution test. Conversely, the defendants argued, and the Court accepted, that the outcome is an element of the claim. On the patentee's argument that such a construction may require costly and time-consuming in vivo studies to prove infringement, Mellor J had little sympathy observing it was for them to draft the patent in a way to avoid such requirements.
On the ground of insufficiency, the defendants argued that it was not plausible that the invention worked with substantially all formulations falling within the scope of claim 1, on the basis of the sole experimental example in the patent that presents pharmacokinetic data in humans. After a highly detailed analysis of the description of the patent and the expert evidence, Mellor J did not agree.
In relation to inventive step, all three pieces of prior art relied upon aspects of an oral controlled absorption system developed in the early 2000s by a company now owned by the patentee. Mellor J had to grapple with heated dispute between the parties as to the meaning and impact of the various prior art documents. The finding of obviousness depended on which construction of claim 1 was accepted – on the patentee's own construction, which did not require the amelioration of food effects as an integer, EP'410 would be obvious in light of the prior art, whereas on the defendant's construction, it would not be.
Finally, on infringement, Sandoz had disputed that its proposed product fell within the scope of the claims and Mellor J agreed that, on his construction of the claims, infringement had not been established as there was no evidence of the reduction of food effects of the Sandoz formulation as compared to a conventional formulation of the drug. The infringement of Teva's revised product could not be determined at trial.
Thus Astellas is left with another valid patent in its mirabegron arsenal, but one that may be more difficult to assert against generics.
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