A recent ruling by the United States Court of Appeals for the Federal Circuit affirmed a lower court's decision in a patent infringement case involving Actelion Pharmaceuticals Ltd and Mylan Pharmaceuticals Inc. The case, docket number 24-1641, centers around the pharmaceutical composition of epoprostenol, a drug used to treat pulmonary arterial hypertension. The court's decision is significant as it clarifies the interpretation of patent claims related to pharmaceutical formulations and could impact future patent infringement cases in the pharmaceutical industry.

Actelion Pharmaceuticals Ltd, the plaintiff, holds patents for two formulations of epoprostenol, specifically U.S. Patent Nos. 8,318,802 and 8,598,227. These patents describe methods for creating stable formulations of epoprostenol, which is known to be unstable in aqueous solutions. Mylan Pharmaceuticals Inc., the defendant, sought to produce a generic version of this drug and submitted an abbreviated new drug application (ANDA) to the Food and Drug Administration (FDA). Actelion sued Mylan for patent infringement, claiming that Mylan's generic drug would infringe on its patents.

The dispute arose when Mylan's ANDA indicated that its bulk solution for the drug had a pH level below the threshold specified in Actelion's patents. The patents claimed that the bulk solution should have a pH of 13 or higher for optimal stability. The case was initially heard in the Northern District of West Virginia, where the district court ruled in favor of Mylan, stating that there was no literal infringement of Actelion's patents.

Actelion appealed the district court's decision, arguing that the court had misinterpreted the claim regarding the pH measurement. The central issue was whether the phrase "a pH of 13 or higher" should be interpreted to mean a pH measured at standard temperature conditions or at the actual temperature of the solution. The district court had ruled that the pH must be measured at standard temperature, which was a key factor in determining that Mylan's product did not infringe the patents.

The Federal Circuit, in its ruling on May 13, 2026, upheld the district court's interpretation of the pH measurement. The court stated, "The claim language, standing alone, does not resolve the question of the proper interpretation of 'a pH of 13 or higher.'" The judges agreed that the intrinsic evidence from the patent specification supported the district court's conclusion that pH measurements are generally understood to be taken at standard temperature, specifically 25±2°C. As a result, the court found that Mylan's bulk solution did not meet the pH requirement outlined in Actelion's patents.

Furthermore, the court addressed Actelion's argument regarding infringement by equivalents, which would allow for some flexibility in the interpretation of the claims. The district court had ruled that Actelion was barred from asserting this argument due to prosecution history estoppel and the disclosure-dedication rule. The Federal Circuit agreed, stating that Actelion had narrowed its claims during the patent application process and could not later claim that Mylan's product was an equivalent.

This ruling has significant implications for the pharmaceutical industry, particularly for companies involved in the development of generic drugs. It reinforces the importance of precise language in patent claims and the need for patent holders to clearly define the parameters of their inventions. The decision also highlights the challenges that generic manufacturers may face when attempting to navigate existing patents and the potential consequences of patent infringement litigation.

Moving forward, the ruling sets a precedent for how courts may interpret patent claims related to pharmaceutical formulations, particularly those involving pH levels and stability. It emphasizes the necessity for patent applicants to carefully consider the language used in their claims and the potential implications of any amendments made during the application process.

As for the future of this case, it is unclear if Actelion plans to appeal the ruling to the Supreme Court. No related cases are currently pending that would directly impact this decision. However, the outcome of this case may influence how future patent disputes are handled within the pharmaceutical sector, particularly regarding the interpretation of technical specifications in patent claims.