There are a number of issues of direct patent infringement that frequently arise in the area of pharmaceuticals, biologics and medical devices. The answers to these are not, however, always straightforward. In particular, they may involve issues of how the claims of a patent protecting a product or process should be interpreted. Here, we continue our series of short articles on direct infringement by considering how the UK courts construe ranges in patent claims, a subject that may have been affected by the recent Supreme Court decision in Actavis v Eli Lilly.

What the UK courts say about numerical ranges

Numerical ranges or limits are frequently encountered in patents in the pharmaceuticals and life sciences area, particularly in the context of processes for making drugs and the specifications of medical devices. As a result, there have been several cases dealing with this issue in the UK, which had appeared to clarify the courts' approach to the interpretation of such limits. However, with the introduction of a doctrine of equivalents in the UK, there is now fresh doubt about how to read such limits.

The leading authority in which a numerical range / limitation in a claim is addressed is the decision of the Court of Appeal in Smith & Nephew Plc v Convatec Technologies Inc1. This case concerns a patent to a process for the silverisation of gel-forming fibres in wound dressings. The process includes the step of subjecting the gel-forming fibres to a binding agent, for which the patent claims that the binding agent must be present in a concentration of "between 1 per cent and 25 per cent".

The court in Convatec held that the skilled person would understand the claim language, in the context of the patent specification and his common general knowledge, to be expressing the range to the nearest whole number. Therefore, all concentrations greater than or equal to 0.5 per cent, and less than 25.5 per cent, were encompassed by the claim.

In Convatec, the court also discusses the meaning of numbers in a scientific context, more broadly. In particular, the standard-practice for scientists deliberately to express numerical values to a particular degree of accuracy:

"…the degree of precision with which any particular number is written conveys to the reader how the author intended the number to be understood. This may be important for a number of reasons. It may, for example, allow the author to convey the level of accuracy with which a calculation needs to be performed or it may indicate the experimental uncertainty in a measurement which needs to be taken. …Thus, as Professor Burrell, Smith & Nephew's expert, explained, the number 25% is expressed to two significant figures and, as such, would be understood from a scientific perspective to encompass all numbers in the range from 24.50% to 25.49%. It is also, I would add, expressed as a whole number and to zero decimal places."

There is earlier first instance authority in PLG Research Ltd v Ardon International Ltd2 which takes a more liberal approach to numerical ranges. In this case, a minimum junction thickness in the strands of the defendant's net measured at between 60% and 72% of that of the strands themselves was considered to fall within a claim to a net made of cross-strands to have a thickness of "not less than 75 per cent" of the thickness of the mid-point of a strand. However, this is regarded by the Court of Appeal in Convatec as representing the “high-water-mark” of a more liberal approach. Kitchin LJ explains in Convatec that the numerical limits of the claim in PLG Research must be seen in the light of the particular circumstances of that case, in which the manner of making the net inevitably produced variations in the thickness and junctions of the strands. This meant that the skilled person would have realised it was not necessary for the 75% limitation to apply in all cases. The judge was not saying that the numerical range should be understood as simply a guide or a general indication of the boundaries of the claim and Kitchin LJ considers that it would be rare for a claim with a numerical range to be given such an expansive interpretation. Instead, where the patentee has defined an integer of his claim in terms of a range with specified numerical limits at each end, his purpose must be taken to have been to claim thus far and no further.

In Napp Pharmaceuticals Holdings Limited v Dr Reddy's Laboratories (UK) Limited3, Arnold J applies the whole numbers approach of Kitchin LJ in Smith & Nephew v Convatec. In this case, a claim to use 10% buprenorphine would be understood to be expressed in terms of whole numbers, and applying conventional rounding extends to ≥9.5 to <10.5 %-wt buprenorphine. Furthermore, the case deals with the effect of the word ʽaboutʼ in a claim. Here, another integer of the claim ʽabout 10 %-wt oleyloleateʼ was held to permit a slightly broader protection of 9% to 11%.

The impact of Eli Lilly on interpretation of numerical limits

While the cases on the interpretation of numerical claim limits are currently still good law, the approach taken is that of the House of Lords authority Kirin-Amgen Inc v Hoechst Marion Roussel Ltd4 on claim construction, which pre-dates Eli Lilly. The key principle in Kirin-Amgen is that the question to be asked when interpreting a claim is always what a skilled person would have understood the patentee to be using the words of the claim to mean5. This is now only the means to the ordinary interpretation of the claims in the first step of the Actavis v Eli Lilly two step approach. There is now a question whether the second step in that case, which now allows immaterial variants to be included in the scope of a patent claim in certain circumstances, is accounted for in the numerical range cases.

The only guidance from the courts on how Eli Lilly may apply to numerical claim limitations since the decision is at a preliminary stage, in Generics (UK) Ltd & Synthon BV v Yeda Research & Development Company Ltd and Teva Pharmaceutical Industries Ltd6. This decision concerns permission sought by the defendants to amend pleadings to include a counterclaim for infringement of a patent which covers a filtration process carried out at a temperature between 0 and 17.5ºC. The temperature used by the claimants is confidential. However, despite adducing evidence that the claimants' process is carried out at a temperature that is not within the range claimed in the patent, Arnold J granted permission to amend. He stated in his judgment that if the law on claim construction had remained as stated in Kirin-Amgen, he would not have allowed the amendment. However, because of the change in law in Eli Lilly, he could not be certain, without more information about the claimants' process, that this process did not now fall within the scope of protection of the patent.

More recently, at the UCL IBIL panel discussion on the doctrine of equivalents, Lord Neuberger, who gave the leading judgment in Eli Lilly, suggested that in cases where the patentee has defined their claim by 'book-ending' a range with numerical limits, there may be an argument that the patentee does not intend to go beyond the range specified, providing the context of the specification does not indicate otherwise. However, this was extra-judicial comment and has no authoritative value for the time being therefore, the issue of how to interpret numerical ranges in claims remains unclear.