2,371,684 – tadalafil dosage form – CIALIS
The ‘684 patent was for tadalafil in a dosage form of less than 20mg, with separate claims to various specific dosage forms (eg “5. The dosage form of claim 3 comprising about 5 mg of the compound in unit dosage form”). A question arose as to whether a maximum daily dosage of 20mg should be considered to be an essential element of the claims . de Montigny J rejected this argument, relying in part on the file history. The application originally filed with the Patent Office contained claims reciting the method of treating sexual dysfunction comprising administering about 1 to 20 mg tadalafil, up to a maximum total dose of 20 mg per day. These claims were rejected for claiming a method of medical treatment. In response, Lilly redrafted these claims as “use” claims and removed any reference to a maximum total dose per day . Citing his own prior decision in Distrimedic 2013 FC 1043, [209-10], held that it was proper to use this file history in interpreting the claims:
 While the file history of a patent application is generally considered as extrinsic evidence and not admissible, I have already held that a change in the wording of a claim as a result of an objection from the Patent Office is an objective fact that can be considered and from which an inference may de drawn
This is notwithstanding the SCC’s insistence in Free World 2000 SCC 66 that in light of the objective nature of claim construction “To allow . . . extrinsic evidence [such as statements or admissions made in the course of patent prosecution] for the purpose of defining the monopoly would undermine the public notice function of the claims, and increase uncertainty as well as fuelling the already overheated engines of patent litigation” . As I argued in my post on Distrimedic, de Montigny J is right to allow this use of the file history and the SCC is wrong. This Tadalafil Dosage Form decision provides another illustration of why it is wrong to allow a patentee to try to reclaim in litigation a limitation that it gave up in prosecution. As discussed here, the alternative approach to dealing with this kind of shifting position is to invoke s 53(1), potentially resulting in the invalidation of the entire patent. Patentees might prefer to embrace file wrapper estoppel.