In the case of Merrell Dow v. Norton the English Court of Appeal was confronted with a situation wherein the patent in suit was directed to a metabolite produced in the body by conversion of a previously administered compound. Prior to the applicant's invention the existence of the metabolite was unknown. However, the compound from which it was metabolized had previously been patented for the same purpose. The invention in question had derived from the applicant's realization that it was not the compound of the first patent that was the active ingredient for the purpose in question, but rather a metabolite that was produced in the body. After the expiration of the patent for the first compound, the patentee sought to enforce its patent on the metabolite against competitors selling the compound described in the expired patent on the ground that there was contributory infringement of the second patent when the body metabolized that compound so as to produce the compound that was the subject of the patent in suit.

Since the harmonization of the British patent law with the European Patent Convention, the test of whether a publication destroys novelty is whether that publication had "made available to the public" the invention in question. The court held that since the prior patent had taught the administration of the parent compound to patients and since, once such administration had occurred, conversion into the compound that was the subject of the patent in suit inevitably occurred, this was sufficient to result in the invention having been made available to the public. The court noted that the subsequent discovery of more information about the way a process worked could not have the effect of removing that process from the public domain. The court felt confirmed in its view by looking at the provisions of the English statute on prior use rights that permitted one who had previously used an invention secretly to continue doing so after a patent had been granted for that which had been done previously. The court analogized the situation to one in which a previously unsuspected metabolite of aspirin was discovered, and observed it would be absurd that, under such situations, a patent could be granted for the metabolite that could prevent anyone (not just previous manufacturers of aspirin) from entering the aspirin market. It therefore rejected the suggestion that the existence of prior user rights provided the public with adequate protection against effective extension of the monopoly term for the original patent by the filing of patent applications on metabolites. Possibly the decision would have been different had the claim in the suit been directed to a pharmaceutical composition containing the metabolite.

There are difficulties in reconciling this decision with decisions of the European Patent Office which, in interpreting the same definition of novelty, have, for example, held a claim to use of a particular compound as a friction-reducing additive in an oil-based composition to be patentable over use of the same compound in an identical composition for rust inhibition. In one such decision the European Patent Office Enlarged Board of Appeal rejected the concept that an invention could be held to be unpatentable on the ground that it had been "inherent" in what is carried out in the prior art. The reasoning of the English Court of Appeal in the present case seems very close to reviving such "inherency" arguments.

Clearly, there is ample scope for further development of the law in this area.

June 1994 Index