Earlier this week, in Actelion Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Inc., No. 22-1889, 2023 U.S. App. LEXIS 29433 (Fed. Cir. Nov. 6, 2023), the Federal Circuit confronted the common situation where patent claims specify that a certain measurement be met but fail to specify the level of precision or range of error associated with the measurement, but infringement turns on this very issue.  Thus, the determination of the appropriate precision required by the claim was left to the court in claim construction, a decision on which billions of dollars can turn.  In Actelion, the Federal Circuit reversed a district court’s construction of the claim term “a pH of 13 or higher” in a claim directed toward a formulation of epoprostenol, a drug for treatment of cardiovascular diseases, made from a solution with such a pH.  The court reasoned that the district court failed to address the extrinsic evidence, such as textbooks, explaining how a person of ordinary skill in the art would understand the significant digits of a pH value, such as the one set forth in the claims and the intrinsic evidence, which consists of the claim language; specification; and prosecution history, was equivocal on this. 

In claim construction, courts first look to, and primarily rely on, the intrinsic evidence, which is usually dispositive.  If a claim term remains ambiguous after this analysis, the court relies on extrinsic evidence (i.e., other relevant evidence).

On the basis of intrinsic evidence alone, the district court had accepted Actelion’s proposed construction that “a pH of 13” in the context of the claims is “a value of acidity that is given as an order of magnitude that is subject to rounding.”  This encompassed pH 12.5 used by Mylan’s accused product, which rounds to 13.  Mylan argued that the proper construction could cover any pH values less than 13, but if measurement errors were to be included, textbooks cited by Actelion supported a narrower range of 12.995-13.004.

Turning to the claim language, the Federal Circuit rejected Mylan’s argument that there was a rule that statement of a range foreclosed rounding. The court also found that lack of approximation language, such as “about”, even when it may be found elsewhere in the claims, did not dictate a precise value.  This is the case because the absence of approximation language might suggest no approximation, but that the nature of measuring a pH value might nonetheless reasonably require a margin of error.

            The court also considered the specification ambiguous as to the desired level of precision.  Mylan argued that the statement that “[t]he pH of the bulk solution is preferably adjusted to about 12.5-13.5, most preferably 13” meant that “13” in “a pH of 13 or higher” cannot be an approximation or range of values, especially a range that encompasses 12.5 because the inventor knew how to use approximation language but chose not to, distinguished a pH of 12.5 from one of 13, and distinguished between a range and an exact value.  However, Actelion countered that “13” should allow rounding or else a preferred embodiment of the invention, meaning a pH of about 12.5 to 13.5, would be excluded from the claim scope. Additionally, the court noted that the specification uses both “13” and “13.0” and various degrees of precision for pH values throughout.  The Federal Circuit then distinguished AstraZeneca AB v. Mylan Pharmaceuticals Inc., 19 F.4th 1325 (Fed. Cir. 2021), which held that a polyvinylpyrrolidone (“PVP”) concentration of “0.001” meant precisely meaning of precisely 0.001% with variations more minor than 0.001% within one significant figure (i.e., 0.0005% to 0.0014%) because the specification made clear that a 0.001% PVP formulation is more stable than, and different from a 0.0005% PVP formulation. In contrast, in Actelion, nothing in the specification indicated that pH differences between 12 and 13 mattered in the context of the invention. 

The prosecution history also did not provide clarity.  While it showed that the examiner drew a distinction between the stability of a composition with a pH of 13 and one of 12, the court found that this does not illuminate the narrower issue of whether a pH of 13 could encompass values that round to 13, in particular 12.5.

Accordingly, the court found that the proper claim construction cannot be reached without the aid of extrinsic evidence, and that the district court should have considered, at minimum, the textbook excerpts offered and addressed by the parties. Indeed, the parties disagreed on the implications of these textbooks for the understanding of a person of ordinary skill in the art of the pH term.  Actelion argued that they supported the proposition that “[t]o describe a specific pH value, and not an order of magnitude, there would need to be a significant figure to the right of the decimal point or clear context to the contrary.”  Mylan argued that they supported a pH range of 12.995-13.004 if the court were inclined to include measurement errors. The court did not decide the proper interpretation of these references and their implications for the understanding of pH 13 by a person of ordinary skill in the art as well the issues as how many significant figures “a pH of 13” has or what it would mean for the pH or hydrogen ion concentration to have zero significant figures, as Actelion’s interpretation of pH 13 would suggest, but left them for the district court on remand.