Twice Ambiguous: Actelion v. Mylan and the Contextual Reading of pH 13

"Ask a lay person what pH 13 means and you will get a straightforward answer: very basic, near the top of the 14-point scale. Ask a PhD patent attorney in a Hatch-Waxman dispute the same question and the answer becomes: it depends."

"The Federal Circuit's decision in Actelion Pharmaceuticals Ltd v. Mylan Pharmaceuticals Inc., No. 2024-1641 (Fed. Cir. May 13, 2026), affirmed a finding of non-infringement that required refence to extrinsic evidence to understand the meaning of the claim term "pH of 13 or higher." The problem is that the solution's pH varied depending upon whether taken at standard ambient temperature or instead at the temperature of the bulk solution during manufacture."

"The same claim construction dispute was before the court in 2023. In that case, the court vacated the district court's first claim construction and remanded with instructions that extrinsic evidence had to be consulted before a proper construction could be reached. Actelion Pharm. Ltd. v. Mylan Pharm. Inc., 85 F.4th 1167 (Fed. Cir. 2023)."

"The decision also rejected Actelion's doctrine of equivalents theory on two independent grounds, prosecution history estoppel and the disclosure-dedication rule. That makes Actelion the second DOE rejection from the Federal Circuit this week, following Bissell, Inc. v. International Trade Commission, Nos. 2024-1509 & 2024-1709 (Fed. Cir. May 11, 2026)."

A claim term requiring “pH of 13 or higher” created a latent ambiguity that could not be resolved solely from the intrinsic record. The pH value varied depending on whether it was measured at standard ambient temperature or at the temperature of the bulk solution during manufacture. The Federal Circuit affirmed a non-infringement finding that depended on consulting extrinsic evidence to understand the claim meaning. A prior appeal vacated an earlier claim construction and required extrinsic evidence before a proper construction could be reached. That earlier dispute involved how many significant figures the number “13” carried. The decision also rejected a doctrine of equivalents theory based on prosecution history estoppel and the disclosure-dedication rule.

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