Mayne Pharma Ltd & Anor v Debiopharm SA & Anor

In purposively construing a patent claim, the court must determine what the skilled person would understand the chosen words to mean in the specification’s context. A claim requiring adjustment by adding an alkali solution was not infringed by adding an acidic ammonium oxalate solution, even though the resulting pH fell within the claimed range.

A process patent was obvious where the skilled person would investigate the trade-off between reaction rate and impurity formation across the relevant pH range. A formulation patent was insufficient where terms such as “stable” and “effective stabilising amount” did not provide a reliable test, and was in any event obvious as an application of Le Chatelier’s principle.

The claimants sought revocation of patents relating to oxaliplatin and declarations of non-infringement. By trial, the dispute concerned the validity of EP(UK) 1308454, a process patent, and EP(UK) 0943331, concerning stable oxaliplatin solutions.

The alleged process used ammonium oxalate to prepare oxaliplatin. The alleged formulation used no added oxalate. The court had to construe the relevant claims, determine infringement, and decide challenges based on anticipation, obviousness and insufficiency.

1. Construction and infringement of ’454. The claims required a distinct step involving the addition of an alkali solution. An oxalate salt could be chemically equivalent to oxalic acid neutralised with alkali, but that did not remove the express requirement for the addition of alkali. The specification was directed to correcting processes in which insufficiently dissociated oxalate was produced. The use of mildly acidic ammonium oxalate, without further alkali addition, therefore did not infringe. A declaration of non-infringement was appropriate.
2. Validity of ’454. The skilled person knew that increasing pH improved oxalate dissociation and reaction rate, but also increased impurity formation. The competing reactions had different pH dependencies, so the skilled person would investigate the intermediate range rather than reject it a priori. The claimed ranges were obvious in light of common general knowledge and Gill & Rosenberg. If the claims had instead covered adding an oxalate salt alone, Kidani would have disclosed an enabling synthesis of oxaliplatin and would have anticipated claims 1 and 2.
3. Construction and insufficiency of ’331. “Stable” meant pharmaceutically stable over prolonged storage, namely two years or more. “An effective stabilising amount” required a test by which the skilled person could determine whether the claimed amount had been used. Claims 1 and 18 failed that requirement because the specification supplied no reliable test and, on its reasoning, no added oxalate might be needed. The more specifically defined claims were not insufficient on that ground.
4. Obviousness of ’331. Adding oxalic acid or an oxalate to stabilise oxaliplatin was an application of the known Le Chatelier principle, analogous to stabilising cisplatin with chloride. The patent was therefore obvious in light of common general knowledge. It was invalid and had to be revoked. The claimants’ entitlement to a declaration of non-infringement was conceded.