Federal Circuit Affirms ‘pH 13 or Higher’ Means ‘pH 12.98 or Higher’ in Actelion v. Mylan: Generic Epoprostenol Cleared of Infringement

The U.S. Court of Appeals for the Federal Circuit on May 13, 2026 issued a precedential decision in Actelion Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Inc., No. 24-1641, affirming a district court ruling that Mylan’s generic epoprostenol formulation neither literally infringes nor infringes under the doctrine of equivalents Actelion’s injectable epoprostenol composition patents. Authored by Judge Taranto, the opinion clarifies how extrinsic evidence informs the construction of numerical claim terms when intrinsic evidence is silent on a precise value, and reaffirms the reach of prosecution history estoppel and the disclosure-dedication rule in cabining doctrine-of-equivalents arguments.

At issue were independent claims of U.S. Patent No. 8,318,802 and U.S. Patent No. 8,598,227, both related to Actelion’s Veletri (epoprostenol sodium) for pulmonary arterial hypertension. The disputed limitation requires the final pharmaceutical composition to be “formed from a bulk solution having a pH of 13 or higher.” Actelion secured the patents on the theory that the high-pH bulk solution confers the stability that has made Veletri commercially viable, and sued Mylan after Mylan submitted an Abbreviated New Drug Application (ANDA) for a generic version.

Second Trip to the Federal Circuit

The case reached the Federal Circuit for a second time. In 2023, the court had vacated the district court’s first claim construction, holding that “proper construction cannot be reached without reference to extrinsic evidence.” On remand, the district court considered extrinsic evidence and construed “pH of 13 or higher” to mean “pH of 12.98 or higher,” reflecting how the relevant artisans handled significant figures in pH measurements. That 12.98 threshold became the analytical pivot for infringement.

Mylan’s bulk solution pH falls well below 12.98 as a matter of established fact. Actelion sought to bridge the gap by arguing that the relevant pH should be measured at the refrigerated storage temperature of Mylan’s finished product rather than at room temperature during bulk manufacture. The district court rejected that approach, and the Federal Circuit found no reversible error: the phrase “formed from a bulk solution having a pH of 13 or higher” refers to the pH of the bulk solution at manufacture, measured under standard conditions. Judge Taranto noted that both the intrinsic context, namely the description of the process by which the composition is “formed from a bulk solution,” and the extrinsic record on how those of ordinary skill measure pH supported the district court’s reading.

Doctrine of Equivalents Foreclosed on Two Independent Grounds

The opinion’s treatment of equivalents is its more consequential contribution. The Federal Circuit held that prosecution history estoppel bars Actelion’s equivalents theory because Actelion had narrowed the claims during prosecution in a way that surrendered the territory it now sought to reclaim. Citing the familiar Festo framework, the court explained that having narrowed the claims to secure issuance, Actelion could not later use equivalents to recapture the very subject matter that the amendment relinquished, and Actelion offered no rebuttal that the amendment was made for a reason unrelated to patentability.

The court then held, as an independent ground, that the disclosure-dedication rule also forecloses the equivalents argument. Under that doctrine, subject matter disclosed in the specification but not claimed is deemed dedicated to the public and cannot be recaptured through the doctrine of equivalents. The specifications here disclosed lower-pH embodiments that were not made part of the claim scope. As the court put it, what was disclosed and yet left out of the claims cannot be reasserted as an equivalent.

Numerical Claim Terms and Generic Drug Litigation

The decision has two layers of practical significance. First, it confirms that for numerical claim limitations, the measurement practices of the relevant artisan, including temperature conditions, significant figures and tolerances, can serve as extrinsic evidence that draws the operative boundary of the claim. Coming on the heels of Enviro Tech v. Safe Foods, which addressed indefiniteness of the term “about” earlier in May 2026, this opinion is part of an ongoing Federal Circuit effort to bring discipline to the construction of numerical claim language.

Second, for ANDA litigation and the pharmaceutical field more broadly, the decision underscores that prosecution-era amendments and the contents of the specification can each independently truncate the reach of the doctrine of equivalents long after the patent has issued. Branded manufacturers must now even more carefully consider how each narrowing amendment and each unclaimed disclosure in the specification will be used to limit later infringement theories. Generic manufacturers gain a clearer template for resisting equivalents arguments by combining extrinsic-evidence challenges with estoppel and dedication defenses.

U.S. ANDA litigation activity remained at high levels through 2025, and the Federal Circuit has continued to take up numerical-claim cases. Veletri itself was FDA-approved in 2008 as an injectable product for pulmonary arterial hypertension, and expanding generic availability has implications for patient access. With Mylan’s generic epoprostenol now cleared on both literal infringement and equivalents, attention turns to whether Actelion will seek certiorari review at the U.S. Supreme Court.

Sources: Actelion Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Inc., No. 24-1641 (Fed. Cir. May 13, 2026) (precedential). Related coverage: IPWatchdog “CAFC Says Generic Hypertension Drug Does Not Infringe Actelion’s Patents” (May 13, 2026); Patently-O “Twice Ambiguous: Actelion v. Mylan and the Contextual Reading of pH 13” (May 2026); Knobbe Martens “Federal Circuit Says Extrinsic Evidence Should Have Been Considered in Claim Construction.”