Last week, the U.S. Court of Appeals for the Federal Circuit issued a precedential decision in Actelion Pharmaceuticals Ltd v. Mylan Pharmaceuticals Inc., No. 2024-1641 (May 13, 2026), relying on extrinsic evidence concerning pH measurements in affirming that Mylan’s epoprostenol composition does not infringe Actelion’s product-by-process claims covering epoprostenol compositions for treating hypertension. This is the second recent Federal Circuit decision addressing pH measurements after its decision affirming indefiniteness in Enviro Tech Chemical Services.
Actelion’s U.S. Patent Nos. 8,318,802 and 8,598,227 claim epoprostenol compositions “formed from a bulk solution having a pH of 13 or higher.” Though the ’802 and ’227 patents make “ubiquitous references to pH,” there is no discussion of the temperature conditions under which pH should be measured in either patent. The temperature conditions used in pH measurements can significantly impact results which, critically, can lead to different conclusions as to whether third-party epoprostenol compositions infringe Actelion’s claims.
At the district court, Mylan argued that it does not infringe because, when measured at the standard ambient temperature of 25±2°C, the pH of its bulk solution is undisputedly lower than 13. Actelion argued that Mylan’s bulk solution was refrigerated when manufactured thus pH should be measured at that “operating temperature,” not at 25±2°C, resulting in a pH above 13. The district court agreed with Mylan, explaining that a skilled artisan would understand that pH should be measured at the ambient temperature of 25±2°C. Actelion appealed.
The Federal Circuit affirmed non-infringement, and extrinsic evidence was key. The Court considered publications from United States Pharmacopeia and chemistry textbooks, as well as the intrinsic record, and determined that skilled artisans would take pH measurements at 25±2°C. The Court also applied the disclosure-dedication doctrine to Actelion’s claims because the patents’ specifications disclose pH ranges lower than 13 but do not claim them. Finally, the Court held that Actelion could not rely on the doctrine of equivalents to capture “infringing” compositions with a pH lower than 13 because it narrowed the pH limitation from “greater than 12” to “13 or higher” in prosecution.
This decision illustrates two important points. First, extrinsic evidence can be used to determine applicable measurement protocols absent guidance in the specification for claims using quantitative properties like pH. Second, the doctrine of equivalents is unlikely to capture unclaimed numerical values if the patent owner has narrowed numerical ranges during prosecution or disclosed broader ranges that are not found in the claims.
