IP Information & News

UK Supreme Court introduces ‘doctrine of equivalents’ into law on claim interpretation

One of the key issues in patent infringement is the extent of protection conferred by the claims. That is to say, it’s important in patent infringement proceedings to determine what a claim covers. This enables the court to, in turn, determine whether the alleged infringing article falls within the scope of a claim and thus determine whether there is infringement.

The interpretation of the wording of claims enables the Court to determine the extent of protection of the claim. Infringement proceedings therefore usually involve the Court to separate a claim into features which are each individually interpreted to formulate a meaning. This determines whether the allegedly infringing article has those features.

A simple example

To illustrate this, albeit crudely, consider a claim as below:

A mug comprising a glass handle.

Consider an allegedly infringing article, a mug, with a handle made exclusively from aluminium. This does not contain any compounds which could be considered glass.

The question is does the infringing article fall within the scope of the claim? The infringing article is a mug — there is no arguing with that — but it has an aluminium handle. Therefore, the allegedly infringing article does not ‘literally’ infringe the claim.


Eli Lilly alleged infringement of claim one and claim 12 of European Patent 1,313,508 by Actavis’ proposed pemetrexed medicine. Claim one is as follows:

“Use of pemetrexed disodium in the manufacture of a medicament for use in combination therapy for inhibiting tumour growth in mammals wherein said medicament is to be administered in combination with vitamin B12 or a pharmaceutical derivative thereof”.

The English Court of Appeal held that the proposed Actavis pemetrexed product did not infringe claim one according to the previously held rules on claim interpretation, as the product proposed by Actavis did not use pemetrexed disodium. Rather, the active ingredient in those products was (a) pemetrexed diacid, (b) pemetrexed ditromethamine or (c) pemetrexed dipotassium.

The Court of Appeal applied the current (at the time) law on claim interpretation and found that the active ingredient employed by Actavis did not fall within the scope of the term “pemetrexed disodium”.

Eli Lilly appealed to the Supreme Court on this matter and their Lords provided a lengthy judgement.

In considering the question of infringement, the Lords went back to first principles in determining whether the variations of pemetrexed used by Actavis fell within the scope of claim one. To this end, the Lords introduced the following questions as guidelines:

  1. Notwithstanding that it is not within the literal meaning of the relevant claim(s) of the patent, does the variant achieve substantially the same result in substantially the same way as the invention, i.e. the inventive concept revealed by the patent?
  2. Would it be obvious to the person skilled in the art, reading the patent at the priority date, but knowing that the variant achieves substantially the same result as the invention, that it does so in substantially the same way as the invention?
  3. Would such a reader of the patent have concluded that the patentee nonetheless intended that strict compliance with the literal meaning of the relevant claim(s) of the patent was an essential requirement of the invention?

In clarifying, Lord Neuberger said:

In order to establish infringement in a case where there is no literal infringement, a patentee would have to establish that the answer to the first two questions was 'yes' and that the answer to the third question was 'no'.”

In answering these questions, the Lords found direct infringement by Actavis’ proposed product and in doing so, introduced a doctrine of equivalents into the law surrounding claim interpretation in the UK. In short, the Lords considered (a), (b) and (c) to be immaterial variants as they achieved the same result as the invention (as defined by claim one) in substantially the same way as the invention and, because of that, the skilled person would have found it obvious to investigate variants (a), (b) and (c) as a routine exercise.

Our example

Going back to our overtly simple example, would an aluminium handle be considered an immaterial variant to a glass handle?

It should be added here that this example is hypothetical and limited only to the illustration of the legal principle — the vastly different thermal conductivities of aluminium and glass mean that, in reality, they are not immaterial variants.

The first question asks us to consider what the variant achieves. The aluminium handle enables the cup to be held by a user — which is the same functionality as the glass handle of the claim — so the answer to the first question is surely yes.

The second question asks us to consider whether such a variant would be obvious to the skilled person upon reading the patent at the priority date. This would require a review of the patent but, in the absence of any disclaimer ruling out an aluminium handle, the answer to this question would also likely be yes.

The third question asks whether the patentee intended strict compliance with the literal meaning of the relevant claims. A patentee would always intend claims to be as broad as possible and would not likely intend to exclude an aluminium handle. That is to say, the answer to this question would be no.

Therefore, it is likely that infringement would be found as the aluminium handle is an immaterial variation of a glass handle.

This example is very simple and it cannot be said that infringement proceedings before the court are routinely that straightforward. It’s likely that to answer any of the three questions, a certain amount of review of the description would be required — and possibly a review of the prosecution history.

The relevance of the prosecution history was also considered by the Supreme Court.

Prosecution history

During proceedings, Actavis relied upon the prosecution history of Eli Lilly’s European patent. The Supreme Court held that the prosecution history did not justify the conclusion that Actavis infringed the patent.

However, the Supreme Court did hold that reference to the prosecution history would only be appropriate where (i) the point at issue is truly unclear if one confines oneself to the specification and claims of the patent, and the contents of the file unambiguously resolve the point, or (ii) it would be contrary to the public interest for the contents of the file to be ignored.

That is to say, there are circumstances in which the prosecution history should be considered.


There has been talk recently over whether the courts in the UK are pro-patent or anti-patent and, at least from this author’s humble perspective, this decision does nothing to settle that debate.

The introduction of a doctrine of equivalents is a pro-patentee doctrine as it enables patentee’s to go beyond what is determined to be the ambit of their claims provided the questions set out above are answered accordingly. However, the consideration of the prosecution history could be considered to be an anti-patent doctrine, as it means that an infringer can essentially use the prosecution history to undermine the patentee’s arguments about what its claim covers.

The introduction of a doctrine of equivalents brings us closer to our neighbours in Germany and other European jurisdictions and provides wiggle room to patentees when they seek to enforce a patent against infringers who are simply offering articles of immaterial variance to that covered by a patent.

However, the admission by the Supreme Court that there are circumstances in which the prosecution history can be used in resolving ambiguities in claims should be at least a reminder to patent attorneys that caution is advisable when drafting any correspondence which is to be placed on the public file. Nailing ones flag to the mast on the meaning of the words in a claim could come back to bite at some point.

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