On April 20, 2016 the Court of Appeal dismissed Mylan’s appeal of a prohibition Order in respect of Mylan’s proposed tadalafil product. As reported here, Justice deMontigny had previously allowed Lilly’s prohibition application in respect of Canadian Patent. No. 2,226,784, generally directed to the use of tadalafil for the treatment of erectile dysfunction.
Mylan’s double patenting allegation relied on Canadian Patent No. 2,181,377 directed to tadalfil and its use in various disorders where smooth muscle relaxation was desired, including hypertension. While the specification of the 377 Patent indicated that tadalafil was a phosphodiesterase-5 inhibitor, this property is not mentioned in any claim. Nor did the 377 Patent specifically mention erectile dysfunction. On appeal, Mylan argued that analysis should be the same as that for obviouness, namely whether the claims of the 784 Patnet were obvioous in light of the entirety of the 377 Patent, including its specification.
Obviousness vs. Double Patenting
Before specifically addressing Mylan’s double patenting argument, the Court of Appeal distinguished between obviousness and double patenting. Obviousness is concerned whether there is an invention at all whereas double patenting is animated by preventing evergreening, the practice of extending the monopoly on an earlier patent by obtaining a new patent that does not offer a new invention to the public. The issue in double patenting is whether the second patent contains a new or inventive element of process beyond that claimed in the first. TheCourt distinguished the two concepts as follows:
 Invalidity on the basis of obviousness-type double-patenting is not the same as invalidity on the basis of obviousness. Obviousness is directed at the question of whether an “invention” (in the legal sense) exists at all. Obviousness-type double-patenting has a different policy justification; the prevention of evergreening an existing patent through what would otherwise be a valid patent but is, in effect, an extension of the patent that has already been granted: Merck & Co., Inc. v. Pharmascience inc., 2010 FC 510, at para. 124, 368 F.T.R. 1.
Citing Justice Hughes in Merck v. Pharmascience, the Court of Appeal held that the proper inquiry is to compare the claims of the second patent against the claims of the first patent. The Court therefore held that the Applications Judge had erred in relying on the specification when construing the claims of the earlier 377 Patent, the latter of which made no reference to PDE-5 inhibition. The Court of Appeal held that where there is no ambiguity in the claims, there can be no recourse to the specification. While holding that the application judge erred below, this error was of no consequence as he came to the correct conclusion with respect to obviousness type double patenting.
Relevant Date for Obviousness-Type Double Patenting
Turing to the relevant date for assessing double patenting, the Court acknowledged that the law was unsettled and the question a difficult one. The Court considered three possible dates: (1) the publication date of the later patent; (2) the priority date of the later patent; and (3) the priority date of the earlier patent. as shown in the following diagram:
The court quickly eliminated the publication date of the later patent, holding that it would be inappropriate to use any date after the claim date of the second patent. As between the remaining two options, the Court held that it did not have to resolve the issue because Mylan’s appeal could not succeed using either of these dates:
 This leaves the first date, on which the appellant Mylan uncontroversially fails, and the middle date, on which there is an evidentiary dispute. It is not necessary to determine the question of which of these dates is the appropriate one. This is because, on the facts of this case, even if the correct date is the more appellant-friendly middle date, I find that the judge did not err in finding that there was no double-patenting. As I will explain, there was no change in the common general knowledge between the first date and the middle date
A copy of the Court of Appeal’s Reasons for Judgment may be found here.