IVAX Pharmaceuticals (UK) Ltd v Chugai Seiyaku Kabushiki Kaisha

A patent claim is obvious where routine formulation work would lead the skilled person to use a claimed substance for its conventional purpose, even if the patent discloses an unexpected additional benefit. Claims must, however, be assessed by their actual scope. A claim covering a technical advance together with an obvious conventional use is invalid.

For added matter, the amended subject matter must be clearly and unambiguously disclosed, expressly or implicitly, in the application as filed. A narrowing amendment may still add matter where it teaches a qualitative distinction or technical contribution not previously disclosed.

Ivax sought revocation of Chugai’s patent for producing stable nicorandil pharmaceutical preparations. Chugai counterclaimed for infringement and applied unconditionally to amend the patent.

The granted claims were challenged for obviousness over U.S. Patent 4,200,640 and Japanese Patent Application 57 145 659. The proposed amendment limited the claimed formulation to palmitic or stearic acid at a concentration of at least 3 per cent. The issues were whether the granted claims were obvious, whether the amendment added matter, and whether the amended claim was obvious.

1. Granted claims. The court applied the structured approach in Windsurfing International Inc. v Tabur Marine (Great Britain) Ltd [1985] RPC 59: identify the inventive concept, the skilled person’s common general knowledge, the differences from the prior art, and whether those differences required invention.

2. The inventive concept was producing a stable nicorandil preparation by mixing nicorandil with a saturated higher aliphatic acid or higher alcohol. The 640 patent disclosed nicorandil formulations using conventional excipients, including magnesium stearate. Routine pre-formulation work would have led the skilled person to test stearic acid as an alternative lubricant. There was no technical reason to reject it, and its use in a conventional amount would fall within the claims.

   The claims therefore covered an obvious use of stearic acid for lubrication. Any unexpected stabilising benefit did not save the claims. Claims 1, 3 and 6 were invalid for obviousness.

3. The alternative case based on replacing magnesium stearate after a stability problem added nothing. The evidence did not establish that instability would be attributed to magnesium stearate or that changing lubricant was a recognised solution.

4. The 659 application taught coating nicorandil crystals with stearic acid using a solvent. It taught that mixing a lubricant such as magnesium stearate did not solve the stability problem and that coating was necessary. The skilled person would therefore have no reason to suppose that simple mixing with stearic acid would work. The 659 application taught away from the invention claimed in the patent.

5. Added matter. Under Patents Act 1977, s.76(3)(a), the amended subject matter had to be clearly and unambiguously disclosed in the application as filed. The original disclosure taught that at least 0.5 per cent of broad classes of acids or alcohols could provide stability. It did not disclose that palmitic and stearic acid formed a distinct subclass having the same stabilising characteristics at 3 per cent. The amendment therefore introduced a qualitative change and was not allowable.

6. The court nevertheless considered obviousness of the amended claim. Three per cent stearic acid was not shown to be a conventional lubricant concentration in a new formulation, and there were technical reasons to use no more lubricant than necessary. The amended claim would not have been obvious over either citation.

7. Conclusion: the granted claims were invalid but would have been infringed. The amendments were refused. The proposed amended claim would not have been invalid for obviousness and would have been infringed.