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Court of Appeal clarifies the scope of numerical ranges in patent claims

The way numerical ranges used to limit the scope of a patent claim should be interpreted has been clarified by the Court of Appeal in London.

The Court said that whole numbers can be read as meaning more precise figures to one or two decimal points and that they can "imply a range of values extending beyond the integer", However, it said the decision must be made by reference to how a 'skilled person' would have interpreted the "particular degree of exactitude" of the patented range.

The judgment is important for all businesses where numerical ranges are used to define the scope of patents and whether they have been infringed by rivals' science, particularly in the life sciences industry where the proportion of solutions, compounds or other materials are common components of the patented claims. 

The Court of Appeal has reconsidered the numerical range in a patent claim made by ConvaTec in a dispute between the patent holder and rival Smith & Nephew. ConvaTec's patent is concerned with a process for the silverisation of gel-forming fibres used in wound dressings.  In its patent claim, the company said that a binding agent was necessary to ensure its "light stabilised silverised antimicrobial materials" would join with the polymers in the dressing. The patent claim stated that the agent made up “between 1% and 25% of the total volume of treatment” applied to the dressing, the judgment said.

In previous legal proceedings, the High Court examined the rival silverisation processes developed by Smith & Nephew to see whether they infringed ConvaTec's patent rights. The range 'between 1% and 25% of the total volume of treatment' was held, in those proceedings, to mean a range between 0.95% and 25.5% and that the first silverisation process Smith & Nephew had developed had therefore infringed those rights. 

The concentration of binding agent used by Smith & Nephew in a second "modified" process, used in four experiments during development but which were relevant to Smith & Nephew's application for marketing authorisation, made up no more than 0.77% of the treatment applied to its rival wound dressing product.  Consequently, the High Court judge determined that this was outside the numerical range covered by ConvaTec's patent.

On appeal, Smith & Nephew argued that ConvaTec must have intended the range specified in its patent claim to mean 'between 1% and 25% of the total volume of treatment' exactly but the Court of Appeal ruled that those numbers would be interpreted as defining a broader range, one that ultimately encompasses the proportion of binding agent Smith & Nephew had used.

The Court of Appeal overturned the decision of the High Court that the numerical range was to be interpreted using 'significant figures' – digits in a precise number that carry meaning. Instead, they are to be interpreted by reference to the degree of precision used by the patentee when drafting the claims, it ruled. 

"The meaning and scope of a numerical range in a patent claim must [also] be ascertained in light of the common general knowledge and in the context of the specification as a whole." Lord Justice Kitchin said. ConvaTec had used whole numbers in the claims, but there was evidence of a wider numerical range referenced in the patent description. This was indicative that the numerical principle to be applied in this case was whole numbers, meaning that the range of "between 1% and 25%" encompassed concentrations of between 0.5% and 25.5%, the judge said.

"This clarification of how numerical ranges should be interpreted reflects the numerical conventions used in science and corrects the slight deviation of the first instance decision towards strict interpretation based on significant figures," life sciences and patent lawyer Kirsteen McEwen of Pinsent Masons, the law firm behind Out-Law.com, said. "This decision now mirrors the approach taken by the European Patent Office and should offer some comfort to parties in respect of such claims, particularly at a time where the tests to be applied by the Unitary Patent Court are still unknown." 

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