Background
Actelion Pharmaceuticals Ltd. holds patents directed to formulations of epoprostenol — a drug used to treat severe pulmonary arterial hypertension (PAH) — that require a specific pH level for stability. The patents, which cover Actelion’s branded product Veletri®, specified that the drug formulation must have “a pH of 13 or higher.” When Mylan Pharmaceuticals filed an abbreviated new drug application (ANDA) seeking to market a generic version of Veletri, Actelion sued for patent infringement under the Hatch-Waxman Act.
The central dispute was over the meaning of “a pH of 13.” Actelion argued the term should be interpreted to include pH values that round to 13 — specifically, values as low as 12.5. Mylan argued the term meant exactly 13.000 or higher, or at most values from 12.995 to 13.004. The district court construed “a pH of 13” as encompassing values from 12.5 to 13.4, relying solely on intrinsic evidence (the patent specification and prosecution history). The district court declined to consider the parties’ textbook evidence because it was extrinsic to the patent. Based on that construction, the court found Mylan’s generic formulation infringed. Mylan appealed.
The Court’s Holding
The Federal Circuit vacated the infringement finding and remanded. The court held that the district court erred by categorically excluding the parties’ extrinsic evidence — specifically, chemistry textbooks explaining how a person of ordinary skill in the art would interpret significant figures in scientific measurements like pH values. The court reaffirmed the established claim construction methodology: courts should first look to intrinsic evidence (claim language, specification, prosecution history), but may consult extrinsic evidence such as technical dictionaries, textbooks, and expert testimony to help understand how a person of skill in the art would interpret the claim language at the time of the invention.
The court found that “pH of 13” is a scientific measurement that a skilled chemist would interpret in light of significant figure conventions — and that the parties had introduced competing textbook evidence about how such conventions apply. The district court was required to consider that extrinsic evidence before settling on a construction; it could not simply ignore extrinsic evidence that bore directly on how the relevant technical community would understand the disputed claim term. The case was remanded for the district court to conduct claim construction properly, taking the extrinsic evidence into account.
Key Takeaways
- Courts may not categorically exclude relevant extrinsic evidence in claim construction — when a party submits textbooks, dictionaries, or expert testimony that bears on how a skilled artisan would interpret a claim term, the court must consider it.
- Scientific claim terms involving measurements (pH, temperature, concentration, wavelength) may require consideration of technical conventions — such as significant figure rules — that are reflected in extrinsic scientific literature rather than in the patent itself.
- In ANDA pharmaceutical litigation, small differences in claim construction of numerical ranges can determine whether a generic product infringes, making rigorous extrinsic evidence on scientific meaning critically important.
- Patent prosecutors should clearly define numerical claim limitations in the specification if they intend a specific rounding or significant figure convention, rather than leaving it to be resolved by external scientific standards.
Why It Matters
Actelion v. Mylan clarifies that courts must engage with relevant extrinsic evidence in claim construction, particularly for scientific and technical terms where the ordinary meaning to a skilled artisan is shaped by field-specific conventions. This has practical implications across pharmaceutical, chemical, and materials patents that use numerical parameters — pH, temperature, viscosity, particle size, and other quantitative specifications may have meanings in the relevant scientific community that differ from a lay reading of the numbers. Pharmaceutical companies defending ANDA litigation should ensure that their claim construction briefing includes robust extrinsic evidence explaining how technical terms are understood by chemists and formulators in their field, not just intrinsic patent history.