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Merrell Dow Pharmaceuticals Inc v HN Norton & Co Ltd
Factual and Procedural Background
“Company A,” a pharmaceutical manufacturer with a United Kingdom subsidiary, discovered and patented an anti-histamine drug (“terfenadine”) in 1972. Subsequent research revealed that, once ingested, terfenadine is almost completely metabolised in the liver to create a previously unidentified compound (the “acid metabolite”). Company A obtained a second, later patent in 1980 covering the acid metabolite (claim 24).
After the original terfenadine patent expired in December 1992, other pharmaceutical companies (“Company B” and others) began marketing terfenadine. Company A sued for infringement, alleging that supplying terfenadine necessarily resulted in consumers’ livers producing the patented metabolite, thereby infringing section 60(2) of the Patents Act 1977. The defendants applied to strike out the claims. Judge [Aldous] held the metabolite patent invalid for lack of novelty; the Court of Appeal affirmed. Company A appealed to the House of Lords, which is the decision summarised here.
Legal Issues Presented
- Whether the manufacture of the acid metabolite within the human body, triggered by ingestion of terfenadine, was “new” for the purposes of section 2 of the Patents Act 1977 and Article 54 EPC.
- Whether prior clinical use of terfenadine and public disclosure in the original terfenadine patent specification anticipated (i.e., destroyed the novelty of) the later metabolite patent.
- Whether “uninformative” or “secret” prior use constitutes part of the state of the art under post-1977 U.K. patent law.
Arguments of the Parties
Appellant’s Arguments (Company A)
- The 1977 Act aligns U.K. law with the EPC, requiring that information—not mere prior activity—must be made available to the public to constitute prior art. Because no one knew the metabolite existed before 1980, neither clinical use nor the 1972 specification disclosed it.
- Section 60(2) is infringed when terfenadine is commercially supplied, as consumers inevitably produce the metabolite; thus Company A’s monopoly should endure until 2000.
- Any apparent hardship to competitors was contemplated by Parliament and addressed, where appropriate, through the limited personal rights preserved in section 64 of the 1977 Act.
Respondents’ Arguments (Company B and Others)
- The invention lacks novelty because:
- Clinical volunteers ingested terfenadine in 1977-78, inevitably creating the metabolite (anticipation by prior use).
- The original terfenadine patent publicly taught how to make and use terfenadine; following that teaching inevitably produces the metabolite (anticipation by disclosure).
- Under section 60(1)(a), infringement is absolute; therefore, the test for novelty must be co-extensive—if making the metabolite now would infringe, its prior making destroys novelty.
- The 1977 Act did not abolish the long-standing principle that a patentee cannot stop others from doing what was done before; it merely refined the concept of what is “made available.”
Table of Precedents Cited
| Precedent | Rule or Principle Cited For | Application by the Court |
|---|---|---|
| Bristol-Myers Co. (Johnson’s) Application [1975] RPC 127 | Prior secret or uninformative use under pre-1977 law could destroy novelty. | Illustrated the contrast between old law and the EPC approach; court held uninformative use alone is no longer sufficient. |
| PLG Research Ltd. v. Ardon International Ltd. [1993] FSR 197 | Prior sale of a product does not always provide an enabling disclosure under the 1977 Act. | Supported the view that mere availability of a product is insufficient unless it enables the skilled person to work the invention. |
| Decision G02/88 MOBIL/Friction Reducing Additive [1990] EPOR 73 | State of the art concerns what is “made available,” not what is merely inherent; hidden use is not novelty-destroying. | Quoted extensively to distinguish between uninformative use and enabling disclosure. |
| Decision T12/81 BAYER/Diastereomers [1979-85] EPOR Vol B 308 | A substance may be anticipated when a process inevitably produces it, even if not described by chemical name. | Used to support anticipation via inevitable product of known process. |
| Decision T303/86 CPC/Flavour Concentrates [1989] 2 EPOR 95 | Cooking recipes that inevitably yield a product can anticipate a patent for that product or process. | Analogous reasoning: terfenadine ingestion inevitably yields the metabolite. |
| Decision G01/92 Availability to the Public [1993] EPOR 241 | Chemical composition becomes prior art if the skilled person can discover and reproduce it without undue burden. | Distinguished; court noted composition knowledge is not always required to destroy novelty. |
Court's Reasoning and Analysis
Judge Hoffmann (with the concurrence of Judges Browne-Wilkinson, Mustill, and Lloyd) began by clarifying that a product claim confers an absolute monopoly over every method and form of manufacture. Novelty must therefore be assessed co-extensively: if any method of making the product is in the prior art, the claim fails.
The court rejected “anticipation by use” insofar as it relied solely on the uninformative ingestion of terfenadine in clinical trials; such secret or non-enabling use, post-1977, does not place information in the public domain.
However, the court accepted “anticipation by disclosure.” The 1972 terfenadine patent specification was a public document teaching ingestion of terfenadine for its anti-histamine effect. For a skilled reader, following that teaching inevitably produces the acid metabolite in the liver. Thus, even though the metabolite’s chemical structure was unknown at the time, the invention was made available under the description “the anti-histamine reaction produced in the body by terfenadine.” That description was sufficient to enable the public to work the claimed invention in the only form now asserted—production inside the human body.
The court emphasised that patent law does not require disclosure of chemical composition in every case; what matters is whether the public had enough information to perform the act that the patentee now seeks to monopolise. Accordingly, the metabolite patent lacked novelty under section 2 and Article 54 EPC.
Holding and Implications
APPEAL DISMISSED. The House of Lords affirmed the Court of Appeal’s order striking out the infringement actions and declared claim 24 (the acid-metabolite product claim) invalid for lack of novelty.
Implications: Competitors may lawfully market terfenadine because producing the metabolite within the body was already anticipated by the original terfenadine disclosure. The decision re-affirms that, under the 1977 Act and EPC, enabling disclosure—not mere prior activity—determines novelty, and that a product unavoidably produced by following prior public instructions cannot be re-patented merely by identifying its chemical structure. No new precedent was set, but the ruling clarifies the boundary between informative disclosure and secret or inherent use.
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