Actelion Pharmaceuticals v. Mylan Pharmaceuticals — Federal Circuit Affirms That pH Claims Require Standard-Temperature Measurement

Background

Actelion Pharmaceuticals owns U.S. Patent Nos. 8,318,802 and 8,598,227, which cover pharmaceutical compositions of epoprostenol — the active ingredient in Actelion’s hypertension drug Veletri®. Epoprostenol is unstable in water because hydrogen ions catalyze its degradation. The patents describe a method of creating a highly basic bulk solution (pH 13 or higher) before freeze-drying the composition into a powder, which yields a more stable drug that can be reconstituted with standard intravenous fluids at room temperature — a significant improvement over the prior Flolan® product that required special diluent and refrigeration.

Mylan filed an abbreviated new drug application (ANDA) to market a generic epoprostenol product. Actelion sued for patent infringement, and the case turned on a deceptively simple question: what does “a pH of 13 or higher” mean? Specifically, at what temperature should the pH measurement be taken? Because pH changes with temperature — a cold solution can register a higher pH than the same solution at room temperature — the answer determined whether Mylan’s generic product fell within the patent claims.

This case previously visited the Federal Circuit in 2023, when the court vacated an earlier infringement judgment and remanded for the district court to consider extrinsic evidence on how skilled artisans understand pH measurements. On remand, after a bench trial, the district court found no infringement — either literal or under the doctrine of equivalents.

The Court’s Holding

The Federal Circuit affirmed, holding that “a pH of 13 or higher” in the patent claims refers to a pH measurement taken at standard temperature (25±2°C), not at whatever temperature the bulk solution happens to be during manufacturing.

Judge Taranto, writing for the panel, found support for this construction in both intrinsic and extrinsic evidence. The specification defines an “alkaline environment” as one with “pH>7” — a definition that is accurate only at standard temperature. The specification’s many experimental results compare pH values in a straightforward manner without accounting for temperature variations, which the court found implies all measurements were taken under the same standard conditions. Both parties’ experts agreed that the vast majority of pH measurements in the specification — including every reference to a pH 13 bulk solution in the experimental results — referred to standard-temperature values.

Extrinsic evidence reinforced this reading. The United States Pharmacopeia (USP), which both experts agreed is influential in the pharmaceutical industry, prescribes that “unless otherwise specified,” pH measurements are made at 25±2°C. General chemistry textbooks similarly treat standard temperature as the default for pH values.

The court also rejected Actelion’s doctrine of equivalents arguments on two independent grounds. First, prosecution history estoppel applied: during prosecution, Actelion narrowed the pH limitation from “greater than 12” to “13 or higher” in response to an obviousness rejection, surrendering the territory between pH 12 and 13. Actelion’s attempt to invoke the tangentiality exception failed because the very reason for the amendment — that unexpected stability results were shown only at pH 13 and above — was directly related to the difference between the claim scope and the alleged equivalent. Second, the disclosure-dedication rule independently barred equivalents, because the specification disclosed pH ranges of 12–13 and 12.5–13 as alternatives to the claimed pH 13, dedicating those unclaimed ranges to the public.

Key Takeaways

• Industry standards inform claim construction. Where a patent uses a scientific term (like pH) without specifying measurement conditions, courts will look to established industry standards — here the USP — to determine how skilled artisans would understand the term. Patent drafters who intend a non-standard measurement protocol must say so explicitly.
• Prosecution history estoppel’s tangentiality exception is narrow. When an applicant narrows a claim’s numerical range to overcome an obviousness rejection, arguing that the narrowing is “tangential” to a functionally equivalent product outside that range will not succeed — the amendment itself confirms that the boundary matters.
• The disclosure-dedication rule applies to overlapping ranges. Disclosing a preferred range of “12.5–13.5, most preferably 13” while claiming only “13 or higher” dedicates the sub-13 portion to the public, even though the disclosed ranges overlap with each other.

Why It Matters

This precedential decision has immediate practical significance for pharmaceutical patent drafting and ANDA litigation. It establishes that pH values in patent claims are presumed to be measured at standard temperature unless otherwise specified, aligning patent claim construction with established pharmaceutical industry practice under the USP. Pharmaceutical companies drafting patents around formulation processes should clearly state measurement conditions for any physical or chemical parameter — especially where the parameter varies with temperature, pressure, or other environmental conditions.

The decision also reinforces that patent applicants cannot have it both ways: if the specification discloses a broad range and prosecution narrows the claims to a subset, both estoppel and disclosure-dedication will prevent recapturing the surrendered territory through the doctrine of equivalents. For generic drug manufacturers, this ruling provides meaningful protection against attempts by brand-name companies to stretch narrow patent claims to cover products that fall outside the literal claim scope.