Where does a range end?

John P. Hull and Anna L. Hatt | July 2015

Smith & Nephew plc v ConvaTec Technologies Inc.

This decision looks at ranges of ingredients and how far those ranges extend.

The decision relates to an appeal from the earlier judgment by Birss J ([2013] EWHC 3955 (Pat). The case relates to European Patent (UK) No. 1343510 of ConvaTec, which is directed to wound dressings. The lead judgment was given by Kitchin LJ with the other judges agreeing.

In earlier proceedings, Smith & Nephew had sought to revoke the patent. However, the patent had been maintained in amended form at first instance and upheld by the Court of Appeal ([2012] EWCA Civ 1638. Smith & Nephew had previously developed a range of silverised gel-forming wound dressings using a process (“the original process”) which arguably fell within the claims as amended.

Smith & Nephew therefore developed a new process (“the modified process”) which it considered did not infringe the patent. At the first instance, Smith & Nephew sought a declaration of non-infringement for the modified process. ConvaTec counterclaimed for infringement and also alleged infringement by “the original process” which provided data that Smith & Nephew used to support an application for marketing approval.

The case at first instance had turned on the interpretation of the range of binding agent used, defined in the claims as being “between 1 and 25%”. Birss J construed this range as covering from 0.95 to 25.5% based on a “significant figure” approach. As a result, the modified process, which used a binding agent of not more than 0.77%, did not infringe. However, four examples from “the original process”, which were used for the marketing approval, were found to infringe.

Both sides appealed. The Smith & Nephew position was that the range should be construed as being exactly 1 to 25%, with the Judge’s previous decision being asserted as a fall-back position. ConvaTec’s position was that the range should be construed as being from 0.5 to 25.5% based on a “whole numbers” approach, namely that the values would be seen in terms of whole numbers and applying basic rounding conventions the claim would cover any value which would be rounded to the whole number in the range.

Kitchin LJ provided a detailed discussion of the law in relation to construction when considering ranges, including consideration of both UK and EPO case law. He concluded that the judge was correct to reject the Smith & Nephew argument that the claim range was exactly 1 to 25%:

Taken as a whole, the matters to which I have referred leave me in no doubt that the skilled reader would not believe that is how the patentee intended the claimed limits to be understood. To the contrary, in the light of the common general knowledge and the teaching of the specification, the skilled reader would believe that the patentee intended the limits to be understood in a less precise way. Just how precisely is the question I must now consider.

Kitchin LJ found that the whole numbers approach was the correct approach to use and that there was no logical basis for using the significant figure approach chosen at first instance. The judge then considered where he thought Birss J had erred:

In my judgment he fell into error in the following three important respects. First, he considered that the skilled person would reject the whole numbers approach because he would see that many of the ranges in paragraph [0028] of the specification are defined by limits that are not whole numbers. The judge was plainly correct that some of the ranges in paragraph [0028] are defined by limits expressed in whole numbers and that others are not, and Professor Kennedy did not at any stage suggest otherwise. Some of those limits are expressed to an accuracy of zero decimal places (that is to say, in whole numbers), others are expressed to an accuracy of one decimal place, and yet others are expressed to an accuracy of two decimal places. But all this shows is that the author knew full well how to express numbers with different degrees of precision, and that when it came to the claim, he chose limits expressed to an accuracy of zero decimal places.

Second, the judge considered that the anomalies which arise from the application of the significant figures approach were of little significance... Those anomalies are significant because they highlight that the application of the significant figures approach to the claim produces a result that bears no relationship to the distribution of random error in practice. The skilled reader would have no reason to suppose the patentee intended the numerical limits of the claim to be understood in such a way.

Third, the judge appears to have attached some importance to the relative error margins at the top and bottom of the range. As he explained, the whole numbers approach means that at the bottom of the range the error margin is as high as 50% whereas at the top of the range it is only 2%. I accept that this is so, but the skilled reader would appreciate that this is the inevitable consequence of the adoption by the patentee of such a wide range of permissible concentrations. Accordingly, it is not a matter which carries much weight in favour of the significant figures approach.

As a result, Kitchin LJ considered that the correct construction was that the range covered from 0.5 to 25.5%. As such, he allowed the ConvaTec appeal, whilst rejecting the Smith & Nephew appeal.