Benefits and pitfalls of functional patent claims (and why the UK is out of step with the EPO on claim construction): Astellas v Teva [2023] EWHC 2571 (Pat)

In the recent UK decision Astellas v Teva [2023] EWHC 2571 (Pat) Mr Justice Mellor in the High Court considered sufficiency, inventive step and infringement of Astellas' formulation patent for mirabegron.  The construction of a functional limitation in the claim was central to the case, highlighting the benefits and pitfalls of functional claim language. The decision also deviates from EPO practice on sufficiency and the inventive step of selection inventions. Particularly, in construing the claim for sufficiency and inventive step, the judge imported the purported technical effect of the invention as a limitation into the claim. The claim was then found inventive based solely on the technical effect as the distinguishing feature. The patentee also found themselves in an inventive step and infringement squeeze. Particularly, it was not proved that the alleged infringement had the purported technical effect of the invention relied on for inventive step, despite all of the other features of the invention being present. To this Kat, the court's approach was thus oddly circular and based on a failure to distinguish between the claimed features of an invention and its technical effect.  

Case background

Astellas alleged that sale of Teva's and Sandoz's generic mirabegron products would infringe Astella's formulation patent EP (UK) 2345410. The patent related to a slow release formulation of mirabegron. Teva and Sandoz counterclaimed that the patent was invalid for insufficiency and lack of inventive step. 

The absorption of an oral drug may be affected by how much food a patient has in their stomach. The problem purportedly solved by the claimed invention was to reduce this "food effect" on the absorption of mirabegron. The defendants argued that it was not possible from the data provided in the application as filed to make a reasonable prediction (i.e. it was not "plausible") that the claimed formulations did in fact reduce the food effect on mirabegron. The defendants also argued that the claim was obvious given that the claimed formulation would have been produced in routine formulation development. Finally, it was submitted that the claim was not in any case infringed, as the generic products did not have all of the claimed features. 

Construing the claim to include the purported technical effect

UK case law currently diverges from the EPO on the criteria for considering "plausibility" under the heading of either sufficiency or inventive step (IPKat). At the EPO, the standard of evidence for a technical feature is considered in sufficiency if the technical feature is claimed, e.g. as in a second medical use claim relating to the technical effect of treating disease. The standard of evidence for a technical effect is considered under inventive step if the technical effect is not a claimed feature (IPKat), e.g. in a product claim defined by structural features. Under recent Boards of Appeal EPO case law, the technical effect does not always even have to be mentioned in the application as filed in order to be relied on for inventive step (IPKat). By contrast, the UK courts currently consider the standard of evidence for both claimed and unclaimed technical effects of the invention relied on for inventive step under the umbrella test of plausibility (IPKat). 

Tackling the humpty-dumpty
question of plausibility
In the present case, the claim did not explicitly specify the technical effect relied on for inventive step under a normal construction of the claim language. The claim merely specified that the claimed pharmaceutical composition was "for modified release" of mirabegron. However, Mr Justice Mellor construed this feature as expressly asserting the technical effect of "reducing the effect of food", in view of definitions provided in the description. This approach to construction is out of step with recent Boards of Appeal case law on claim construction, see for example T 1924/20 (IPKat). 

Regardless of the construction point, the judge considered the relevant legal test to be that of "plausibility" under the heading of sufficiency. The judge was very clear that, in contrast to the EPO, and in line with UK case law, plausibility is a legal test under sufficiency in which it was necessary to establish the evidence for which an invention works (i.e. solves the problem it purports to solve) (para. 233). The judge concluded that it did not matter for the sufficiency point whether or not the functional limitation of "reduced food effect" was construed as an express limitation of the claim. The judge thus considered under sufficiency whether it was "plausible" that substantially all compounds following under the claim would have the technical effect of reducing the effects of food.

The UK ab initio plausibility test 

On "plausibility", the judge considered the Supreme Court decision in Warner Lambert as requiring there to be "some reasons for supposing" that a claimed invention has its purported technical effect (para. 226). Importantly these reasons for believing also have to be "disclosed in the specification" (para. 231). The UK approach to the standard of evidence for a technical effect can be characterised as an "ab initio plausibility" standard, whereby it must be plausible in view of the application as filed that an invention has the purported technical effect. This case law puts the UK out of step with the EPO Enlarged Board of Appeal decision G 2/21 (IPKat) and its interpretation by the Boards of Appeal (IPKat).

The question of plausibility in the present case required consideration of a large quantity of data, helpfully summarised by the judge in a table in paragraph 276. In view of the application as filed and extensive expert testimony, the judge was convinced that there were sufficient reasons for supposing that the claimed formulations would lead to the desired technical effect of a reduced food effect. In view of these data, Mr Justice Mellor consequently rejected the insufficiency attack (para. 278). 

"Food effect"

Inventive step for a selection invention

The judge next went on to consider the question of inventive step. The judge's construction of the claim to include the technical effect of "reduced food effect" was critical to whether the claims could be considered non-obvious. 

The judge found that if the claim was not construed to include the feature that the formulation had a "reduced food effect", it would have been obvious for a skilled team to produce formulations having all the other features of the claim. Particularly, the skilled person would likely make such formulations as part of routine formulation development (para. 413). It would be a matter of chance whether any of these formulations had a "reduced food effect" (para. 430). The judge considered that a claim lacking the "reduced food effect" limitation would be obvious in view of this possibility (para. 422). 

However, the judge did construe the claim as including the "reduced food effect" limitation. As established for plausibility, the judge was also convinced that the range of selected parameters specified in the claim would lead to a "reduced food effect". The judge was further convinced that the skilled team would not know to select or test these parameters in order to produce a formulation with a reduced food effect (para 413). The judge concluded that the claim construed to include the technical effect of a "reduced food effect" was inventive. 

To this Kat, the judge has here failed to consider the appropriate criteria for the inventive step of a selection invention, such as the one defined by the claim in question. The invention was characterised by the judge themselves as the selection of the range of parameters ("dissolution rate") for a formulation (para. 419). The selection of these parameters, as established by the judge under sufficiency, was to provide the unexpected technical effect of a reduced food effect (para. 277). Under normal inventive step analysis for a selection invention of this type, the selection of the parameter range should therefore be considered inventive regardless of whether the unexpected technical effect per se was construed as a feature of the claim. Particularly, it is established case law of the EPO Board of Appeal that the selection of range is inventive if it has an unexpected technical effect, regardless of whether it would have been obvious for the skilled person to randomly produce something falling within the range (EPO Guidelines for Examination, G-VII, 12). In the present case, the judge found it necessary for the claim to also explicitly specify the technical effect of the selected range as a limitation. This seems to be rather a circular approach to inventive step, and implies that the claim lacked essential features of the invention.

Inventive step / infringement squeeze

The judge thus found the patent sufficiently disclosed and inventive in view of the prior art. However, unfortunately for Astellas, Mr Justice Mellor went on to find the patent not infringed by the generics. The key question for infringement was whether Astellas had established that Sandoz's formulation had the feature of "reduced food effect". Construction was therefore also critical to the question of infringement. 

The judge had already concluded for sufficiency and inventive step that the claim should be construed as including the limitation that the formulation had a "reduced food effect". For infringement, the judge noted that it needed to be proved that the alleged infringement had a reduced food effect (para 447).  Particularly, the judge noted that "plausibility is a different standard to that required to prove infringement and I have held that, to prove infringement, at least some reduction in food effect must be demonstrated" (para 447). Whilst the alleged infringing formulation had all of the other features of the claim, the judge was not convinced that a "reduced food effect" had thereby been proved (para. 447). The claim was therefore found not infringed. 

Again, the judge's conclusion appears to imply that essential features of the invention were missing from the claim. The curious importation of the unexpected technical effect into the claim also had the effect of creating an obviousness/infringement squeeze for Astellas. For the judge, if the claim was alternatively construed as not including the feature of "reduced food effect", it would be infringed but also obvious, given the conclusion that the skilled team would have produced such formulations by chance. As such, if the claim was infringed it would then become invalid for obviousness (para. 450). 

Final thoughts

To this Kat, UK patent law appears confused on the fundamental question of whether it is necessary for the inventive effect of an invention to be construed as a feature of the claim itself. The UK tendency is to consider the technical effect of an invention as a claimed feature of the invention. This tendency leads to the consideration of the evidence standard for both an invention and its purported technical effect under the same heading of "plausibility" in a sufficiency analysis. By contrast, the EPO considers the evidence standard for an unclaimed technical effect under inventive step (IPKat). 

The judge in the present case, by incorporating the technical effect of the invention as a feature of the claim, also found themselves in an oddly circular position on inventive step and infringement. The claim became inventive solely for the reason that it possessed the technical effect as a claimed feature. However, given that it had not been proved that the technical features of the claim would necessarily produce the technical effect, an alleged infringement having all of these features was not considered infringing. This analysis begs the question of whether the alleged infringing embodiment would be novelty destroying. To this Kat, a critical issue here was also a failure to recognise the invention as a selection invention based on an unexpected technical effect. Under EPO case law relating to selection inventions, it is not necessary for the technical effect of a selected range to be specified in the claim. 

Leaving aside the peculiarities of UK patent law, however, the present decision is interesting for another reason. The decision also highlights the potential benefits and pitfalls of functional claim language. In contrast to the US, broad functional claim language is generally acceptable in Europe. A functional claim can provide broader coverage than a claim defined only by structural features and may also be harder for potential infringers to design around. However, as demonstrated in the present case, a potentially huge pitfall of functional claim language is that, to prove infringement of such a claim, it is necessary to prove that the alleged infringement also has the claimed function. It is therefore wise to restrict functional claim language to clear and easy to measure functional properties. If the decision in Astellas v Teva is any guide, it would also be wise to be extremely careful with descriptions of purported technical effects of the invention in the specification, in case these are construed into the claim by an English judge. 

Further reading


Claim construction 

Image credit: DALLE-3

Benefits and pitfalls of functional patent claims (and why the UK is out of step with the EPO on claim construction): Astellas v Teva [2023] EWHC 2571 (Pat) Benefits and pitfalls of functional patent claims (and why the UK is out of step with the EPO on claim construction): Astellas v Teva [2023] EWHC 2571 (Pat) Reviewed by Rose Hughes on Monday, November 06, 2023 Rating: 5


  1. Astellas was caught here between a rock and a hard place. The above author rightly observes that if the claim was devoid of the "reducing the food effect" functional feature the judge found it would have been obvious to make formulations with the claimed dissolution rate range, so the patent would have been invalid. However, even adopting the Judge's construction of the claim (based on the use of terms and phrases in the claim that were clearly defined in the patent specification), Astellas could have significantly strengthened its position on infringement simply by showing that its own product (to which the generic products were bioequivalent) had the disclosed functional feature - i.e. that the Betmiga formulation actually possessed the technical effect promised in the patent and reduced the food effect seen with a conventional formulation. Why Astellas did not do that is not known from the judgment but one possible inference is that this patent was granted on the basis of a claimed advantage for which the patentee had/has no supporting data. Perhaps that is the real story here, i.e. should patentees be permitted to obtain patents on the basis of claimed technical effects that have no basis in real world data? Perhaps in such circumstances those patents should be unenforceable? This is effectively what the English Court has done by requiring the patentee to made good on the promised technical effect in its infringement analysis (which it cannot do because it does not have the data). That seems fair and certainly a better solution than treating every claim that contains a technical limitation as being a selection invention which absolves the patentee from any deficiencies its evidence base might have.

    There may yet be a good argument that the UK courts are out of step with the EPO on functional claim language but there have to be better hills to die on than this particular patent in order to make the argument stick.

  2. I agree this case deviates from EPO case law, but can be understood as being consistent with what Birss did in Fibrogen, in terms of reading the technical effect into the claim as a limiting feature, and essentially then taking the position that the skilled person would be able to identify what 'works' by routine means. The claim (see below) does refer to a composition for 'modified release' and so it seems OK to import the technical effect as a limiting feature, and in para 240 there is an explicit reference to Fibrogen and the idea of a step 2 functional feature.

    It's only now that we are really seeing how revolutionary Fibrogen was as decided by Birss, and of course if that decision falls at the Supreme Court (i.e. the Supreme Court believes Birss was wrong on construction and plausibility), then the present case could also be reversed in appeal.

    Claim considered by the present court - [sorry the mark up has been lost in pasting this here]:

    A: A pharmaceutical composition for modified release, comprising: (1) 10 mg to 200 mg of (R)-2-(2-aminothiazol-4-yl)-4'-[2-[(2-hydroxy-2-phenylethyl)amino]ethyl]acetic acid anilide, or a pharmaceutically acceptable salt thereof,
    B: (2) at least one additive which ensures penetration of water into the pharmaceutical composition and which has a solubility such that the volume of water required for dissolving 1 g of the additive is 10 mL or less, and
    C: (3) a hydrogel-forming polymer having an average molecular weight of 100,000 to 5,000,000 or a viscosity of [deleted: 12 mPa-s or more in a 5% aqueous solution at 25°C], 400 mPa・s or more in a 2% aqueous solution at 25˚C and 7,500 mPa・s or less in a 1% aqueous solution at 25°C;
    D: wherein the additive which ensures penetration of water into the pharmaceutical composition is one compound, or two or more compounds selected from the group consisting of polyethylene glycol, polyvinylpyrrolidone, D-mannitol, lactose, sucrose, sodium chloride, and polyoxyethylene polyoxypropylene glycol and wherein the amount of the additive which ensures penetration of water into the pharmaceutical composition is 20% by weight to 60% by weight to the total weight of the pharmaceutical composition;
    E: wherein the hydrogel-forming polymer is one compound, or two or more compounds selected from the group consisting of polyethylene oxide, hydroxypropyl methylcellulose, and hydroxypropyl cellulose and wherein the amount of the hydrogel-forming polymer is 10% by weight to 40% by weight with respect to the total weight of the pharmaceutical composition; and
    F: wherein the drug dissolution rate from the pharmaceutical composition is 75% or less after 1.5 hours and at least 75% after 7 hours from the beginning of the dissolution test and wherein the dissolution test is carried out in accordance with the paddle method described in the United States Pharmacopoeia under the conditions that 900 mL of USP buffer, pH 6.8, is used and the paddle rotation speed is 50 to 200 rpm.

    From para 240 of the present decision:
    Step 2: The answer to the second step, determine what it means to say that the invention works, is again clear. “Working”, in this case, means the formulation reduces a food effect. In terms of the problem to be solved, it is to provide a composition that is capable of reducing the food effect that is seen in conventional tablets (see e.g. the first sentence in the Patent). In other words, it is the achievement of the effect in [0023]. On the Defendants’ construction, this requirement of reducing the effects by food is expressly incorporated in integer A. On Astellas’ construction, it is not an express feature of the claim (and therefore not relevant to infringement) but for the reasons Birss LJ explained in Fibrogen at [57] (by reference to Idenix) it is nonetheless a ‘step 2 functional feature’ for the purposes of inventive step and reasonable prediction/plausibility (because one needs to know what the compounds are supposed to be useful for).


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