In Ranbaxy v AstraZeneca [2011] EWHC 1831 (Pat), Ranbaxy was granted a declaration for non-infringement with respect to AstraZeneca’s patent relating to magnesium esomeprazole. Kitchin J held that the skilled person would have understood the relevant claim to be directed to the use of magnesium esomeprazole to manufacture a medicament containing that active ingredient.

Background

AstraZeneca owned a patent covering its drug, Nexium, which inhibits gastric acid secretion and is used to treat gastric acidrelated diseases. The active ingredient was magnesium esomeprazole, the magnesium salt of the S enantiomer of omeprazole. The patent claimed the use of magnesium esomeprazole with a high optical purity, expressed in terms of enantiomeric excess (e.e.), i.e., the fraction of the compound present as the major enantiomer, less the fraction of the compound present as the minor enantiomer. The characteristic of this compound was that the optical purity was 99.8 per cent e.e. Ranbaxy, an importer of generic pharmaceuticals, planned to import a pharmaceutical product, the starting material of which was ≥99.8 per cent e.e. magnesium esomeprazole that would be mixed with omeprazole racemate, so that the final product did not contain 99.8 per cent e.e. magnesium esomeprazole. Ranbaxy sought a declaration of noninfringement so that it could start importing its product. AstraZeneca counterclaimed, alleging infringement.

Decision

Kitchin J started by establishing the construction of Claim 1 of AstraZeneca’s patent:

The use of a magnesium salt of (-)-5-methoxy-2[[(4-methoxy- 3,5-dimethyl-2-pyridinyl)methyl]sulfinyl]-1H-benzimidazole ((- )-omeprazole) with an optical purity of ≥ 99.8% enantiomeric excess (e.e.) for the manufacture of a medicament for the inhibition of gastric acid secretion.

AstraZeneca contended that Ranbaxy’s product was directly obtained by its claimed process and that the claim did not require that the medicament contained magnesium esomeprazole at all. Ranbaxy’s purposive construction was that the claimed process was for the manufacture of a medicament containing magnesium esomeprazole with an optical purity of 99.8 per cent e.e., and that its product was therefore outside that claim as it was not formulated using, and did not contain, magnesium esomeprazole with that optical purity.

Kitchin J adopted the purposive construction approach in Kirin Amgen v Hoechst Marion Roussel [2005] RPC 9, reinforced in Virgin Atlantic Airways v Premium Aircraft Interiors [2010] RPC 8, which says that a patent is not addressed to inter rusticos and so the interpretation should be based on what the skilled person would have understood the patentee to be using the language of the claim to mean, in light of his common general knowledge and the purpose of the invention. He also noted that Monsanto & Company v Merck & Co Inc [2000] RPC 77 required Swiss claims, or “second medical use” claims, to be subject to the same measure of purposive construction.

The judge said that the specification neither suggested nor provided for the use of any analogue or derivative of magnesium esomeprazole or, indeed, any other active ingredient for the treatment of gastrointestinal disorders or any other condition. Neither did it suggest a new way of making a medicament. In his opinion, the patent merely taught the production of optically pure magnesium esomeprazole and its use in particular therapies. He thus supported Ranbaxy’s construction, stating that the skilled person would understand the claim to be directed to the use of magnesium esomeprazole to manufacture a medicament containing that active ingredient. This interpretation was reinforced by the fact that the claims in the specification were grouped in various sets: those drafted as Swiss claims and directed to the use of 99.8 per cent e.e. magnesium esomeprazole for the manufacture of medicaments, and those drafted as conventional product claims directed to optically pure magnesium esomeprazole. Kitchin J rejected AstraZeneca’s contention that the skilled person would interpret the word medicament so broadly that it need not contain any magnesium esomeprazole at all, saying that this would be erroneous in light of the specification and the common general knowledge. Accordingly, Ranbaxy was granted a declaration of non-infringement and AstraZeneca’s counterclaim for infringement was rejected.