The controversial doctrine of the “promise” of the patent has received a great deal of attention recently with some unfavourable decisions for Canadian patent holders.  The promise doctrine essentially states that in order to constitute a useful (and therefore patentable) invention, an invention must not only be useful for some purpose, but it must also deliver any utility promised in the patent specification. 

The promise doctrine has its origins in English law, but has only become an important aspect of Canadian case law in the last few years.  In recent Canadian decisions applying the promise doctrine, patents for what appear to be quite useful inventions have been declared invalid because the promised utility could not be established as of the applicant’s filing date.

These court decisions have become so controversial that Eli Lilly has filed a Notice of Intent to submit a claim pursuant to Chapter 11 of the North American Free Trade Agreement (NAFTA), alleging that the application of the promise doctrine violates Canada’s obligations under NAFTA.  Eli Lilly seeks $100 million in damages.  The claim is based on a decision of the Federal Court (upheld on appeal) invalidating Eli Lilly’s patent for the drug Strattera, used to treat attention-deficit disorder.  The Supreme Court of Canada refused to hear Eli Lilly’s appeal.

The way that a court construes the promise of a patent can greatly influence the determination of the patent’s validity. For example, if the promise of a patent for a new compound is that it is useful as an inhibitor of enzyme X (known to be implicated in disease Y), the factual basis required in the application to demonstrate or soundly predict such utility could be limited to enzyme assay data.  However, if the promise of the same patent is that the new compound is useful to treat disease Y, further data in the application such as in vivo testing may be demanded by the courts to establish a factual basis supporting the promised utility (and therefore, validity) of the patent.

One case that illustrates both how unpredictable the promise doctrine is and how far the courts can go beyond the claim language to construe the promise of the patent is Pfizer Canada Inc. v. Apotex Inc., 2011 FCA 236.  That case dealt with the use of the drug latanoprost for the treatment of glaucoma.  The patent specification included test results in both animals and healthy humans showing that the drug worked with minimal irritating side effects.  However, no long-term studies had been performed as of the filing date.  The Federal Court of Appeal concluded that the patent was invalid because the promised utility could not be soundly predicted as of the filing date.  In reaching this conclusion, the Court determined that glaucoma is a chronic disease, and that one skilled in the art would have known that the disorder was a chronic condition requiring prolonged treatment.  Therefore, even though the patent claims made no mention of the chronic nature of the condition or ongoing use of the drug, the Court concluded that the promise of the patent was to treat glaucoma and intraocular hypertension on a chronic basis without causing substantial side effects.  Because only single dose studies had been conducted, it could not be soundly predicted that the compound would lack irritating side effects after repeated and prolonged use, and the patent was held to be invalid.  This decision conflicts with an earlier court decision holding that the same patent was valid (Pfizer v. Pharmascience, 2011 FCA 102 aff’g 2009 FC 1294), illustrating how subjective and unpredictable the promise doctrine can be.

Although the promise doctrine has been most extensively applied in the context of pharmaceutical inventions, the doctrine was recently applied to a mechanical invention in Eurocopter v. Bell Helicopter Textron Canada Ltd., 2012 FC 113 (currently under appeal).  The case involved a design for helicopter landing gear which, according to the patent specification, reduced several drawbacks of conventional landing gear.  The patentee had tested landing gear in which a cross piece of the gear was offset forwards, but had not tested a corresponding design in which the cross piece was offset backwards.  The Federal Court concluded that the utility of the latter design had not been demonstrated or soundly predicted as of the filing date, and claims covering this embodiment were therefore held invalid.  It will be interesting to see whether the Federal Court of Appeal takes the same view of the matter.

Given the uncertainty in this area, patent applicants should be wary of making any statements in their applications that could potentially be construed as a promise of some enhanced utility.  However, as the cases demonstrate, courts may nonetheless construe some promise of a greater utility from the specification or from the context in which an invention operates.