Publication Date of Second Patent is Not the Date for Assessing Double Patenting

Mylan Pharmaceuticals ULC v Eli Lilly Canada Inc (NOC) 2016 FCA 119, Rennie JA, Trudel, Dawson JJA aff’g 2015 FC 17 de Montigny J
            2,226,784 / tadalafil / CIALIS

The main question addressed in this appeal was the date for assessing obviousness type double-patenting. Double patenting is a judicially created doctrine which prevents an inventor from obtaining a second patent for an invention which is an obvious variant of an invention disclosed in its own prior unpublished prior application, even though that prior application is not part of the state of the art defined in s 28.3. So, in Com'r of Patents v. Farbwerke Hoechst [1964] SCR 49, the SCC held that Hoechst’s application for a patent for a medicine consisting of sulphonyl urea diluted by a carrier should be rejected as not inventively distinct over Hoechst’s prior application for a patent for sulphonyl urea, given that there was no inventive step in mixing sulphonyl urea with a carrier.

If the state of the art does not change, then the date at which double patenting is assessed does not matter; in Hoechst it had always been common general knowledge that a medicine could be mixed with a carrier. But when the common general knowledge changes, the date is important. That is what happened in this case.

The question was whether Lilly’s ‘784 patent was invalid for obviousness-type double patenting over Lilly’s 2,181,377 patent. The ‘377 patent claimed tadalafil, which is a PDE V inhibitor. It had a priority date of 21 Jan 1994. The ‘784 patent claimed tadalafil for the treatment of erectile dysfunction (ED). It had a priority date of 14 July 1995. The publication date of the ‘784 patent was 6 Feb 1997. Between the first date and the last there were two new pieces of information available to the public. On 22 Dec 1994, Pfizer’s ‘902 US patent application was published, disclosing that sildenafil, another PDE V inhibitor, was useful for treating ED [6]. In June 1996 the Boolell study was published, which provided good evidence that a PDE V inhibitor could be administered orally for safe, effective treatment of ED [7]. The timeline was conveniently summarized by Rennie JA in this chart:


If the relevant date for assessing double patenting was the publication date of the‘784 patent, then it was uncontroversial that it would be obvious, because the ‘377 patent disclosed that tadalafil is a PDE V inhibitor and the Boolell paper disclosed that any PDE V inhibitor would be effective to treat ED [46].

The FCA rejected that date. Mylan had argued that Whirlpool 2000 SCC 67 mandated the use of the publication date of the later patent [15], presumably on the basis that Whirlpool [55] had held that the claims had to be construed as of the date of publication [55, 56]. Rennie JA held that Whirlpool was not controlling authority on this point, essentially on the basis that the question of the correct date was not at issue [48]. The refusal to decide the issue by exegesis of Whirlpool strikes me as sound both in law and as a matter of policy. In R v Henry, 2005 SCC 76 [57] the SCC pointed out that its dicta is to be treated as binding only when obviously “intended for guidance,” and “[t]he notion that each phrase in a judgment of this Court should be treated as if enacted in a statute is not supported by the cases and is inconsistent with the basic fundamental principle that the common law develops by experience.” It is better to rely on the considered reasoning of the FCA on the merits of the issue, rather than an attempt to discern what the SCC might have intended on an issue which it never addressed.

Turning to the merits, Rennie JA held that it would be inappropriate to use any date later than the claim date of the second patent because that would permit consideration of information arising after the patent’s claim date, contrary to s 28.3 [50]. For example, pretend the the ‘377 patent didn’t exist and suppose the Boolell paper was published in August of 1996, so that no one knew that PDE V inhibitors could be used to treat ED until then. If double patenting was assessed as of February 1997, the ‘784 patent would be held invalid for obviousness, even though on the claim date of the ‘784 patent it was not obvious to anyone that tadalafil could be used to treat ED – not even to someone with full knowledge that tadalafil was a PDE V inhibitor, as disclosed by the ‘377 patent. That cannot be right, as Lilly would have made two distinct contributions to knowledge, namely that tadalafil was a PDE V inhibitor, and that tadalafil could be used to treat ED.

The next question is whether the claim date of the ‘377 patent should be used, or the claim date of the ‘784 patent. Rennie JA held it was not necessary to decide [52], because de Montigny J had held [147] that notwithstanding the disclosure of Pfizer’s ‘377 patent, on the claim date of the ‘784 patent it was still not thought that oral administration of a PDE V inhibitor would be effective in treating ED. That is, the ‘377 patent did not change the common general knowledge and therefore the use of tadalafil to treat ED would not have been obvious over the ‘377 patent and the common general knowledge even at the priority date of the ‘784 patent. This was a finding of fact which was entitled to deference [53]. It might be said that the FCA should have decided the point anyway to provide clarity, particularly since it was fully argued, but on the whole I think the point is difficult enough that the FCA was right to leave it to a case in which it is determinative. I haven’t had any fresh thoughts of my own on which of those dates is preferable since I wrote my post on the decision of de Montigny J (here) and the more fully considered comments on Gleason J’s decision (here).