Mayne Pharma (USA) Inc & Anor v Teva UK Ltd & Anor

For a patent claim defined by a numerical measurement, the court must identify the technical significance of the measurement before deciding how precisely it must be performed. Sufficiency is not defeated merely because more than one measurement method exists, provided the skilled person has a default method derived from common general knowledge. Obviousness is assessed by identifying the inventive concept, the skilled person and common general knowledge, the steps bridging the gap, and whether those steps would have been obvious. Hindsight must be guarded against, but a claim is invalid where the prior publication would direct the skilled person to the claimed solution.

The claimants alleged infringement of European Patent (UK) 0 835 657, concerning a stable injectable paclitaxel composition. Teva admitted relevant dealings with the product but denied infringement and alleged that the patent was invalid for insufficiency and obviousness, relying on common general knowledge and the publication referred to at trial as Richheimer.

The principal issues were the construction of the claim’s reference to pH in a non-aqueous paclitaxel formulation, whether the disclosure was sufficient, and whether acidification of the formulation was obvious.

1. Construction and sufficiency. The claim covered the existing cremophor/ethanol/paclitaxel formulation improved by acidification of approximately two to four pH points. The numerical limits had no independent technical significance because the specification supplied no technical support for them. The inventive concept was the acidification of the formulation.
2. The skilled addressee was a pharmaceutical formulator using ordinary laboratory equipment and common general knowledge. Where a claim requires a measurement, the skilled person will use the common general knowledge method unless the specification directs another method. The existence of more than one possible method does not itself establish insufficiency if there is a default method. Teva had not shown that the alleged measurement difficulties arose in practice. The patent was sufficient.
3. Obviousness. Applying the four-stage approach in Windsurfing v Tabur Marine [1985] RPC 59, the court rejected the common-general-knowledge challenge. The proposed routes involved open-ended investigations, and the court lacked confidence that the patent lacked invention on that basis.
4. Richheimer materially directed the skilled person towards acidifying paclitaxel solutions to improve stability. Although hindsight had to be guarded against, the court considered the route from the position of a skilled person investigating degradation in 1992 and held the patent obvious. The patent was infringed but invalid.