Is Potassium Equivalent to Sodium? – The UK Supreme Court Thinks So

04 August 2017


Following a lengthy battle in the English courts between Eli Lilly (Lilly) and Actavis, the UK Supreme Court has recently decided (see full judgment here) that Actavis’s proposed forms of the anti-cancer drug pemetrexed in combination with vitamin B12 directly infringe Lilly’s patent for the use of pemetrexed disodium salt in combination with vitamin B12 for cancer therapy, in the UK, France, Italy and Spain.

The interest in this case lies in the fact that none of Actavis’s products would use the specific salt pemetrexed disodium. They would all use other salts or pemetrexed itself (the so-called “free acid”).

The only way in which the Actavis products could directly infringe the Lilly patent would be if they are all equivalent to pemetrexed disodium in a patent sense. The Supreme Court’s reasoning as to why they are equivalent thus opens up significant new possibilities to patent owners seeking to catch competitors in the UK, and raises significant new issues and dangers to businesses seeking to avoid their competitors’ patents. 


The judgment (at paragraph 10) reviews in detail the correct approach under UK law (and the other countries considered) as to the interpretation of patent claims, and in particular the requirement to take account of “equivalents”, as instructed by the Protocol to Article 69 EPC as amended in 2000 (see here). As it was put in paragraph 34 of the judgment: How far does one have to be outside the wording of a patent claim, to prevent the patentee from enjoying protection against products or processes which are not within the ambit of the actual claim language?

The judgment also addressed the extent to which it is permissible to make use of the examination history of a patent, when determining its scope.


The use of pemetrexed free acid as an anti-cancer drug was precluded owing to damaging side-effects. Lilly found that these side-effects could be largely avoided if pemetrexed disodium was administered together with vitamin B12. Lilly’s patent claimed the use of pemetrexed disodium in the manufacture of a medicament for use in combination with vitamin B12 for the treatment of cancer.

Actavis wished to use the same idea, but contended that, because its proposed products did not include pemetrexed disodium, as required by Lilly’s claims, there was no infringement.

Lilly sued, arguing that there would be either direct or indirect infringement if Actavis launched any of its products on the market in the UK, France, Italy or Spain because they are medicaments to be used as a treatment for cancer consisting of pemetrexed free acid, or a pemetrexed salt, with vitamin B12, which represents the essence of the teaching and claim of the patent.

At first instance (see full judgment here) the UK High Court found that none of the Actavis products would directly or indirectly infringe Lilly’s patent. Lilly appealed. The Court of Appeal (see full judgment here) allowed Lilly’s appeal to the extent that there would be indirect infringement, but agreed with the first instance decision on direct infringement.

The Supreme Court Judgment

Having acknowledged that, on a literal interpretation of Lilly’s claims, the Actavis products would not infringe the patent, the court considered how far a variant should be able to be caught outside the literal wording of the claims, according to the proper effect to Article 69 EPC and its Protocol.

From a review of the key cases, the court decided (Judgment, paragraph 66) that the way to establish the true scope of protection should use the following sequence of questions:

  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 order to establish infringement, a patentee would have to establish that the answer to the first two questions was “yes” and to the third “no”.

As a major departure from the previous law and the decision of the Court of Appeal, the Supreme Court considered that, for the second question, the person skilled in that art should be treated as knowing that the Actavis products do work (Judgment, paragraph 62). Further, in addressing the third question, the Supreme Court decided that the Court of Appeal “adopted an approach which places too much weight on the words of the claims and not enough weight on Article 2 of the Protocol” (Judgment, paragraph 71).

On this basis, it was held that the Actavis products directly infringed Lilly’s claims.

As to the examination history of the patent, in which Lilly had limited their claims to pemetrexed disodium to comply with the strict amendment practice of the European Patent Office, the Supreme Court considered that “the circumstances in which a court can rely on the prosecution history to determine the extent of protection or scope of a patent must be limited”, but did not rule out the possibility that the file history could be relevant (Judgment, paragraph 87).

In this particular case, the Supreme Court saw nothing in the file history which would justify departing from the conclusion it had previously reached, noting that “even if the Examiner was right or at least justified in taking the stance that he did, I do not consider that the consideration can have any bearing on the question whether any pemetrexed salts other than pemetrexed disodium should be within the scope of the patent pursuant to the doctrine of equivalents” (Judgment, paragraph 89).

It appears from this that at least formal issues from the examination, such as issues relating to a patent office’s amendment practice, are very unlikely to be given any weight by a UK court for determining the scope of protection.

Our Experts
David Brown
David Brown
Location: Bristol (UK)
Magnus Johnston
Magnus Johnston
Location: Glasgow (UK)

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