Smith & Nephew Plc v Convatec Technologies Inc & Anor

Numerical limits in patent claims must be construed in the context of the particular specification and the common general knowledge. Where a claimed value is a target against which measured or calculated values are compared, a significant-figures approach may be appropriate. A claim expressed as “between 1% and 25%” therefore covered concentrations from 0.95% up to, but not including, 25.5%.

In a proper patent case the court may grant final springboard relief restraining otherwise lawful activity. The remedy requires identification of an unwarranted advantage obtained through infringement, a proportionate duration and form of order, and care not to overcompensate the patentee. On the facts, the advantage had expired and no injunction was justified.

The claimant sought relief concerning European Patent (UK) No 1,343,510, relating to silverised gel-forming fibres used in wound dressings. The defendant sought a declaration that its revised Durafiber Ag manufacturing process did not infringe, while the claimant counterclaimed for infringement.

The issues were the construction of the claimed concentration range, whether the revised commercial process and four development experiments infringed, and whether the defendant should be restrained from selling its product by a springboard injunction based on earlier infringement and regulatory approval obtained using data generated by that infringement.

1. Construction. The phrase “between 1% and 25% of the total volume of treatment” required the volume of fluid carried over from an earlier treatment step to be included where substantial carryover occurred. The lower limit was construed by reference to significant figures. Thus 1% was expressed to one significant figure and the effective lower boundary was 0.95%; 25% was expressed to two significant figures and the upper boundary was less than 25.5%.
2. The construction of a numerical limit remains a matter of construing the particular patent specification in its technical context. Earlier decisions applying rounding conventions did not establish an inflexible rule. The relevant context included the common general knowledge of numerical precision and measurement.
3. The commercial process used a salt concentration of 0.77% and did not infringe. The four development experiments were within the claim on the only reliable figures available. The defendant’s later empirical carryover calculations were too uncertain to establish that the true concentrations were below 0.95%. Although the legal burden of proving infringement remained with the claimant, the defendant bore an evidential onus to establish that its alternative calculations were reliable or conservative.
4. Springboard relief. The court had jurisdiction, in a proper case, to restrain otherwise lawful sales in order to deprive an infringer of an unwarranted advantage obtained through earlier infringement. The relevant considerations included the nature and causal connection of the advantage, proportionality of the form and duration of relief, avoidance of overcompensation, and the availability of damages or an account of profits.
5. The defendant had remained off the relevant European market pending judgment. The likely regulatory approval period following development of the non-infringing process had expired or was equally likely to have expired by the date of judgment. Any springboard advantage had therefore expired. The commercial process did not infringe, the development experiments did infringe, but no sales injunction was granted.

This was a first-instance decision. The judgment records earlier litigation between the parties concerning related patents, including [2011] EWHC 2039 (Pat), upheld at [2012] EWCA Civ 520, and an earlier decision concerning the same patent at [2012] EWHC 1602 (Pat), upheld at [2012] EWCA Civ 1638. Those decisions formed part of the procedural background and were not decisions under appeal in this action.