Failure to define the parameters governing numerical values for claim limitations, such as pH, can result in undesired outcomes in litigation. In some cases, claim terms relating to measured parameters have been found to be indefinite and therefore invalid. But even when the scope of the claim terms is capable of being interpreted, undefined parameters can lead to limited interpretations, allowing accused infringers to avoid the claim scope. In a recent patent case, claim terms relating to pH values were found to be limited to pH values measured at standard temperatures (25 °C) because the patent did not define the pH measurements to include pH values measured at other temperatures. Further, the patent owner was estopped from arguing infringement under the doctrine of equivalents.
The patent owner asserted two patents claiming freeze-dried compositions of epoprostenol formed from a bulk solution having a pH of 13 or higher with the aim of reducing uncontrolled breakdown of epoprostenol. The freeze-dried composition can be dissolved in commercially available injectable liquids to give a more stable epoprostenol for use in treating high blood pressure in the lungs. The patent owner sued a competitor, arguing that the competitor’s product performs the same function of reducing the breakdown of epoprostenol by providing a higher pH, as in the patent.
Initially, the trial court ruled in favor of the patent owner, finding a pH of 13 or higher to include pH as low as 12.5. The competitor appealed. The appeals court vacated and remanded the initial decision. On remand, the trial court found no infringement after construing the pH of 13 or higher to mean pH of 12.98 or higher. Importantly, the pH of the competitor’s bulk solution at 25 ± 2 °C was not within the claim’s range as interpreted by the district court. The competitor argued that the pH of the patented bulk solution is well above 13 during manufacture because the cooling process used by the patent owner in manufacturing would increase the pH of the solution. The problem as stated by the trial court is that the patent owner did not define the conditions for the measurement of the pH of the bulk solutions in its patents, and in the absence of a definition, the industry standard is to assume that all pH measurements were done at standard temperature, i.e., 25 ± 2 °C . In addition, though the patent owner had disclosed pH ranges well below 13 in its patent, the patent owner surrendered the lower pH ranges during patent prosecution and did not claim them in the issued patent.
For patent owners, this ruling reinforces how decisions made during patent preparation and prosecution can affect infringement lawsuits, especially when terms and conditions of inventions are not clearly spelled out and claimed.
The case is Actelion Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Ltd., Case No. 24-1641 (US, May 13, 2026). If you have questions about how this decision may affect your business, please contact the authors or any member of the McCarter & English Intellectual Property practice to help manage risks in this area.