This is a very weird case interpreting “consisting of”. The Federal Circuit recently affirmed a ruling of non-infringement in Azurity Pharmaceuticals v. Alkem Laboratories. Azurity had sued Alkem for allegedly infringing patent claims related to a drinkable antibiotic.
The patent at issue—Azurity’s U.S. Patent No. 10,959,948—was a continuation of an earlier application that had been rejected due to prior art referencing the ingredient propylene glycol. To overcome that rejection, Azurity amended its claims to disclaim propylene glycol, arguing that its absence distinguished the invention from the prior art. Instead, Azurity used the more generic term “flavoring agent.”
At trial, both parties stipulated that “flavoring agents” in the asserted claims could include substances with or without propylene glycol. Azurity argued that this meant a product containing a flavoring agent with propylene glycol would still infringe, regardless of the claim’s “consisting of” language.
The district court disagreed. It held that Alkem’s product—though it did contain propylene glycol—did not infringe the asserted claims because Azurity had clearly and unmistakably disclaimed that ingredient during prosecution.
As a reminder, in patent claim language:
- “Comprising” means the invention includes the listed elements, but may also include others.
- “Consisting of” is much narrower—it limits the invention strictly to the elements explicitly listed, excluding anything else.
The court concluded that Azurity’s use of “consisting of,” along with its prosecution history, was clear enough to exclude propylene glycol—and, by extension, Alkem’s product—from the scope of the claims.