The US Court of Appeals for the Federal Circuit affirmed a noninfringement finding, concluding that a claim limitation reciting a pH range having only a lower limit referred to pH measured at standard temperature in the art. The Court also found that prosecution history estoppel and the disclosure-dedication rule foreclosed reliance on the doctrine of equivalents to capture a pH below the express lower limit. Actelion Pharms. Ltd. v. Mylan Pharms. Inc., Case No. 24-1641 (Fed. Cir. May 13, 2026) (Reyna, Taranto, Stoll, JJ.)

Actelion owns patents covering lyophilized epoprostenol formulations used to treat cardiovascular disease. Epoprostenol is unstable in water because acidic conditions catalyze its degradation. The patents sought to improve stability by manufacturing highly basic bulk solutions, thereby producing freeze-dried formulations that remained stable after reconstitution in typical intravenous fluid. The asserted claims recite bulk solutions having a pH “of 13 or higher” or “greater than 13.”

Mylan sought approval to market a generic version of Actelion’s Veletri® product and was sued under 35 U.S.C. § 271(e)(2). The district court construed “a pH of 13 or higher” to mean “a pH of 12.98 or higher.”

It was undisputed that Mylan’s bulk solution measured below a pH of 12.98 at standard temperature (25±2°C). Actelion nevertheless contended that infringement existed because the solution exceeded pH 13 at lower temperatures during refrigerated manufacturing.

The district court disagreed, finding that the claim term “a pH of 13 or higher” referred to a pH measured at a temperature standard in the field, and that therefore Mylan did not literally infringe. The district court further ruled that Actelion was barred from asserting and had not proved infringement under the doctrine of equivalents. Actelion appealed.

The Federal Circuit agreed with the district court that a person of ordinary skill would interpret the claimed pH values as measurements taken at standard temperature, absent an express indication otherwise. Although the claims did not specify measurement conditions, the specification consistently treated pH values as standard-temperature measurements. The Court emphasized that the specification compared results across pH levels without suggesting temperature-dependent variation and described an “alkaline environment” as “pH > 7,” a statement accurate only at standard temperature.

The Federal Circuit found that extrinsic evidence reinforced that understanding. The United States Pharmacopeia and expert testimony established that, in pharmaceutical formulations, pH is ordinarily measured at 25±2°C unless otherwise specified. The Court found no clear error in the district court’s factual findings on industry practice.

Because Mylan’s product failed to meet the pH limitation under that standard, the Federal Circuit affirmed the finding of no literal infringement.

The Federal Circuit also rejected Actelion’s doctrine of equivalents theory. During prosecution, Actelion amended the claims from “greater than 12” to “a pH of 13 or higher” after the examiner recognized unexpected results at pH 13 but not at pH 12. The Court found that this narrowing amendment gave rise to prosecution history estoppel, barring Actelion from recapturing lower pH values through equivalence.

Separately, the Federal Circuit applied the disclosure-dedication rule. The patents [...]

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