The US Court of Appeals for the Federal Circuit has affirmed a district court’s claim construction and grant of a preliminary injunction in a pharmaceutical patent case.
The ruling came in Otsuka America Pharmaceutical, Inc. v. Hetero Labs Limited, Case No. 25-2016, decided by the Federal Circuit on July 1, 2026.
Otsuka sued Hetero Labs, alleging that Hetero Labs’ generic drug product would infringe Otsuka’s patent rights in the branded treatment Nuedexta.
Otsuka moved for a preliminary injunction to prevent Hetero Labs from entering the market, and the district court granted the motion after concluding Otsuka was likely to succeed on its infringement claim.
The central dispute concerned how to calculate the patent’s claimed weight ratio involving dextromethorphan and quinidine, two compounds combined in the drug formulation.
The representative claim requires administering dextromethorphan in combination with quinidine, with the proviso that the “weight to weight ratio of dextromethorphan to quinidine is 1:0.5 or less.”
Hetero Labs argued that when the compounds are administered as salts, the ratio must be calculated using only the weight of the active moieties rather than the full compound weights.
The Federal Circuit rejected that argument, finding the intrinsic evidence supported construing “dextromethorphan” and “quinidine” to include both the free base compounds and their pharmaceutically acceptable salts.
The Court found that Hetero Labs’ proposed construction would produce the “highly improbable” result of excluding Otsuka’s Orange Book-listed Nuedexta product from the scope of the claims.
The Court also rejected Hetero Labs’ indefiniteness argument, concluding that claims were not rendered indefinite simply because they encompassed formulations using either free bases or pharmaceutically acceptable salts.
Judge Dyk dissented in part, arguing that calculating the claimed ratio using the full weight of pharmaceutically acceptable salts distorted therapeutic relationships by incorporating the weight of carrier ions that have no therapeutic significance.
Judge Dyk also disagreed with the majority’s reliance on Otsuka’s commercial embodiment, distinguishing the case from the Court’s 2007 decision in Osram GmbH v. ITC on the basis that Otsuka had narrowed its claims during prosecution to overcome an obviousness rejection.
In Judge Dyk’s view, it was not unusual for a commercial product ultimately to fall outside the scope of the asserted claims, making the majority’s approach to claim construction questionable in this context.
The case reaffirms that a patentee’s perceived preference to draft a claim to read on a commercial embodiment, especially an Orange Book-listed brand drug, may weigh in favour of construing a claim to cover such an embodiment.
Legal analysts note the ruling also clarifies that the construction of a ratio term will not be rendered indefinite where arguably different measurement methods are used to account for different circumstances.