IP Law Daily, PATENT—Fed. Cir.: Actelion’s epoprostenol formulation patents not infringed by Mylan’s generic product, (May 14, 2026)

By Ravindra Kumar Singh, B.L.

The claimed pH limitation referred to standard-temperature measurement, which the accused product did not meet.

Mylan Pharmaceuticals Inc.’s proposed generic version of an epoprostenol drug did not infringe asserted claims of two patents covering stable pharmaceutical formulations because the claimed “pH of 13 or higher” referred to a standard-temperature measurement that the accused product did not satisfy, the U.S. Court of Appeals for the Federal Circuit has determined. The appellate court affirmed a judgment of the Northern District of West Virginia finding no literal infringement and no infringement under the doctrine of equivalents (Actelion Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Inc., No. 24-1641 (Fed. Cir. May 13, 2026)).

Infringement allegations. Patent owner Actelion Pharmaceuticals Ltd, a developer of treatments for cardiovascular diseases, markets Veletri®, an epoprostenol-based drug used to treat pulmonary arterial hypertension. Mylan Pharmaceuticals Inc., a generic drug manufacturer, filed an Abbreviated New Drug Application (ANDA) seeking approval to market a generic epoprostenol product before the expiration of Actelion’s patents. Actelion brought suit under the Hatch-Waxman Act, alleging that Mylan’s proposed product infringed its patents either literally or under the doctrine of equivalents.

The asserted patents included U.S. Patent Nos. 8,318,802 (the ’802 patent) and 8,598,227 (the ’227 patent), both titled “Epoprostenol Formulation and Method of Making Thereof.” The patents describe lyophilized pharmaceutical compositions of epoprostenol designed to improve stability upon reconstitution into aqueous solutions. The invention addressed the known instability of epoprostenol in water by using highly basic bulk solutions. The claims required that the compositions be formed from a bulk solution having “a pH of 13 or higher”.

Following Mylan’s ANDA filing in February 2020, Actelion brought suit in June 2020 under the Hatch-Waxman Act, alleging infringement of the ’802 and ’227 patents. The district court initially construed the phrase “a pH of 13 or higher” to include values as low as 12.5 based on ordinary rounding principles, after which the parties stipulated to a judgment of infringement and entry of a permanent injunction. On appeal, the Federal Circuit vacated that judgment and remanded, holding that the claim construction required consideration of extrinsic evidence.

On remand, the district court construed “a pH of 13 or higher” to mean a pH of approximately 12.98 or higher and proceeded to a bench trial focused on whether Mylan’s bulk solution satisfied that limitation. The court determined that the claimed pH referred to a measurement taken at standard temperature (25±2°C) and rejected Actelion’s position that pH should be assessed at refrigerated manufacturing conditions. Applying that construction, the court found no literal infringement because Mylan’s bulk solution, when measured at standard temperature, fell below the claimed threshold.

The district court also rejected Actelion’s doctrine-of-equivalents theory, holding that prosecution history estoppel barred Actelion from recapturing pH values below 13 after narrowing its claims during prosecution, and that the disclosure-dedication rule independently precluded reliance on unclaimed pH ranges disclosed in the specification. The court further found that Actelion failed to prove equivalence on the merits. Actelion appealed.

Claim construction. On appeal, Actelion argued that the district court erred by interpreting the pH limitation as requiring measurement at standard temperature, contending instead that pH should be assessed at the solution’s actual operating temperature during manufacture. The Federal Circuit rejected that argument.

The appellate court held that the claim language itself did not specify measurement conditions, requiring resort to intrinsic and extrinsic evidence. The specification repeatedly referred to pH values without specifying temperature, but described neutral pH as 7, an understanding accurate only at standard temperature. The court also found that the patent’s experimental data and comparative stability analyses were most consistent with measurements taken under uniform, standard conditions. The Federal Circuit further relied on extrinsic evidence, including the United States Pharmacopeia (USP), which provides that pH measurements are taken at 25±2°C unless otherwise specified. The court concluded that a person of ordinary skill in the art would understand the claimed pH values to refer to standard-temperature measurements. Because Mylan’s product did not meet that requirement, the finding of no literal infringement was affirmed.

Doctrine of equivalents. The Federal Circuit also upheld the district court’s determination that Actelion was barred from asserting infringement under the doctrine of equivalents. First, the court held that prosecution history estoppel applied. Citing Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002), the court noted that Actelion had narrowed its claims during prosecution from “greater than 12” to “13 or higher” to overcome an obviousness rejection. The examiner had indicated that only pH values at or above 13 demonstrated unexpected results sufficient for patentability. The court concluded that this narrowing amendment surrendered the territory between the original and amended claim scope, and that Actelion failed to show that the alleged equivalent was only tangential to that amendment.

Second, the court held that the disclosure-dedication rule independently barred Actelion’s equivalents theory. Citing Johnson & Johnston Associates Inc. v. R.E. Service Co., 285 F.3d 1046 (Fed. Cir. 2002), the court explained that the patents disclosed alternative pH ranges, including values below 13, but did not claim them. Those disclosed but unclaimed ranges were therefore dedicated to the public and could not be recaptured through the doctrine of equivalents. Given these independent bars, the Federal Circuit affirmed the rejection of Actelion’s equivalents theory without needing to rely on the district court’s alternative merits analysis.

Thus, the Federal Circuit affirmed the district court’s judgment, holding that Mylan’s ANDA product did not infringe the asserted patents either literally or under the doctrine of equivalents.

The Case is No. 24-1641.

Judge: Taranto, R.

Attorneys: Lisa Glasser (Irell & Manella LLP) for Actelion Pharmaceuticals, Ltd. Deepro Mukerjee (Katten Muchin Rosenman LLP) for Mylan Pharmaceuticals Inc.

Companies: Actelion Pharmaceuticals, Ltd.; Mylan Pharmaceuticals Inc.

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