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Number crunching from the Court of Appeal

06/07/2015
BackgroundThis is potentially the last episode in the long running dispute between ConvaTec and Smith & Nephew over a ConvaTec patent for wound dressings. The latest judgment centres on claim Background

This is potentially the last episode in the long running dispute between ConvaTec and Smith & Nephew over a ConvaTec patent for wound dressings. The latest judgment centres on claim construction of a numerical range and whether using the mathematical convention of rounding to the nearest number is the correct approach.

First instance decision

At issue was the concentration of a chemical agent involved in making light-stabilised silverised antimicrobial materials for the silverisation of gel-forming fibres in wound dressings. Claim 1 of ConvaTec's patent provides that the chemical binding agent be present in a concentration of "between 1% and 25%".

Smith & Nephew made its own version of wound dressings, using the chemical binding agent at a concentration of 0.77%. ConvaTec argued that Smith & Nephew's wound dressings infringed its patent because, in a scientific context, numerical values are stated using the standard rounding convention so that "between 1% and 25 %" in fact encompasses concentrations greater than or equal to 0.5% and less than 25.5%.

Smith & Nephew argued the claim should "mean what it says" and that the lower boundary of 1% was absolute. Failing this, the lower boundary of 1% ought to be read as being quoted to one significant figure, so that 0.95% was the lower boundary.

In his first instance decision, Judge Birss sided with Smith & Nephew and stated that rounding to the nearest whole number was incorrect and the range must be interpreted on the basis of significant figures instead. Thus, the Judge found that, in this case, the concentration range was greater than or equal to 0.95% and less than 25.5%. Although this finding was favourable to Smith & Nephew, it did not get them off the hook entirely as the Court also held that the process used by Smith & Nephew in some experiments during the development of their wound dressings did infringe ConvaTec's patent.

Both ConvaTec and Smith & Nephew appealed this decision.

Court of Appeal Decision

On Wednesday 24 June 2015 the Court of Appeal allowed ConvaTec's appeal and dismissed Smith & Nephew's cross-appeal. The Court of Appeal confirmed that interpretation of claims containing a numerical range is no different to any other claim but also provided the following series of points of particular relevance to such claims:

  1. the scope of any such claim must be exactly the same whether one is considering infringement or validity;

  2. there can be no justification for using rounding or any other kind of approximation to change the disclosure of the prior art or to modify the alleged infringement;

  3. the meaning and scope of a numerical range in a patent claim must be ascertained in light of the common general knowledge and in the context of the specification as a whole;

  4. it may be that the skilled person would understand that the patentee has chosen to express the numerals in the claim to a particular but limited degree of precision and so intends the claim to include all values which fall within the claimed range when stated with the same degree of precision;

  5. the skilled person's understanding depends upon all the circumstances including the number of decimal places or significant figures to which the numerals in the claim appear to be expressed.


 

The Court of Appeal has held that the 'skilled person' in this context would understand that the patentee had chosen to express the numerical limits of the range to only a limited degree of accuracy, meaning the phrase "between 1% and 25%" was expressed to the nearest whole number. This means the skilled person would have understood that ConvaTec intended the claim to encompass concentrations of binding agent greater than or equal to 0.5% and less than 25.5%. The effect of construing the claim in this way is that Smith & Nephew's wound dressings, using the chemical binding agent at a concentration of 0.77%, fall within the scope of the claim and infringe ConvaTec's patent.

Comment

Courts in future cases need not necessarily arrive at the same conclusion as the Court of Appeal in this case – the key factor being what the skilled person would understand particular numerical values to mean. Care is needed when drafting patents which include numerical values to ensure that such values do not have the effect of making a claim inadvertently fall within the scope of prior art or, conversely, obtaining narrower protection than originally intended.

This article was co-authored by Olivia Rogers.

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