The Federal Court has found that prosecution history evidence is inadmissible to rebut representations made by a patent licensee (as opposed to the patentee) on claims construction. The Court also considered the issues of “essential elements”, infringement, and obviousness in the context of a formulation patent.


The Court’s decision concerns Canadian Patent No. 2,507,002 (002 Patent), which is listed on the patent register against Allergan Inc.’s (Allergan) silodosin capsules (marketed as RAPAFLO®) under an exclusive license in Canada granted by Kissei Pharmaceutical Co., Ltd. (Kissei). Allergan brought an action against Sandoz Canada Inc. (Sandoz) under subsection 6(1) of the Patented Medicines (Notice of Compliance) Regulations (Regulations) seeking a declaration that Sandoz’s generic alternative to RAPAFLO® would infringe claims 1–3 and 6 of the 002 Patent. Sandoz denied infringement and counterclaimed for a declaration that the 002 Patent was invalid for obviousness. Kissei, the patentee, denied invalidity but took no position on infringement.

The claims of the 002 Patent related to capsules comprising the active ingredient silodosin (used for the treatment of dysuria) and specific excipients, manufactured so as to achieve a defined rapid dissolution profile.

Claims valid but not infringed

The Court found against Allergan on the issues of claims construction and infringement, but rejected Sandoz’s invalidity counterclaim.

The crux of the claims construction issue was whether claim elements relating to wet granulation—a manufacturing process that Sandoz did not use—were essential. The Court concluded that Allergan had failed to meet its burden of proving that these claim elements were non-essential. This finding was supported by a purposive construction of the claims and the 002 Patent specification as a whole, which taught “away from the use of a dry manufacturing process and towards the wet granulation process”. The Court accepted that “the Skilled Person would not have understood that a dry process could be substituted for the wet granulation process without materially affecting the working of the invention”. As discussed in greater detail below, the Court refused to consider the prosecution history of the patent in reaching its conclusion.

Following from its finding on claims construction, the Court concluded that Sandoz’s product would not infringe claims 1–3 or 6 of the 002 Patent: it was agreed that the product did not contain granules and was not manufactured with the wet granulation process.

On the issue of obviousness, the Court reiterated that “it may be inventive to recognize that a problem to be solved exists in the first place”. Here, the Court found that the 002 Patent’s invention overcame previously unknown problems relating to the “‘potent adhesive and electrostatic properties’ and the very low solubility of silodosin,” as well as unknown capsule filling problems. Applying the “obvious to try” test, the Court concluded that the differences between the state of the art and the inventive concept of the 002 Patent constituted steps that were not obvious.

Licensee not bound by patentee’s representations to the Patent Office

This decision adds to a growing list of judgments interpreting section 53.1 of the Patent Act (see e.g., here and here). Section 53.1 was introduced in 2018 and creates a limited exception to the long-standing rule that extrinsic evidence is inadmissible when construing the claims of a patent, providing that the prosecution history “may be admitted into evidence to rebut any representation made by the patentee in the action or proceeding as to the construction of a claim”.

Sandoz sought to tender the prosecution history of the 002 Patent in support of its position on claim construction (i.e., that claim elements relating to wet granulation were essential).

The Court held that the prosecution history evidence was inadmissible because it was being tendered to rebut the representations of a licensee (Allergan)—not the patentee (Kissei), as required by subsection 53.1(1). In particular, the Court reasoned that:

  • The plain wording of subsection 53.1(1) limits the scope of that provision to rebutting representations made by a patentee. Here, the patentee had made no such representations: Kissei had denied invalidity and adopted Allergan’s submissions, but did not itself appear at the trial.
  • Representations by Allergan could not trigger subsection 53.1(1) because a licensee is not a “patentee” as defined in section 2. Rather, a licensee is a “person claiming under” the patentee within the meaning of subsection 55(1).
  • The legislative history suggests that Parliament was aware of this distinction and intended to limit the scope of subsection 53.1(1) to representations made by patentees: in fact, Parliament rejected an amendment seeking to address the “loophole” in section 53.1 by including “persons claiming under the patentee” in the provision.

The case is Allergan Inc. v. Sandoz Canada Inc., 2020 FC 1189.