Azurity Pharmaceuticals, Inc. v. Alkem Laboratories Ltd., decided April 8, 2025

This Federal Circuit opinion details a patent infringement lawsuit between Azurity Pharmaceuticals and Alkem Laboratories concerning U.S. Patent No. 10,959,948, which covers a liquid vancomycin formulation. The appeal follows a district court ruling that Alkem's Abbreviated New Drug Application (ANDA) for a generic version did not infringe Azurity's patent. The central issue revolved around whether Azurity disclaimed the inclusion of propylene glycol during the patent's prosecution. The court affirmed the lower court's decision, finding that Azurity did clearly disclaim propylene glycol, and because Alkem's proposed generic product contains it, no infringement occurred.

Case Name and Citation: AZURITY PHARMACEUTICALS, INC. v. ALKEM LABORATORIES LTD., Appeal No. 2023-1977, United States Court of Appeals for the Federal Circuit, Decided: April 8, 2025.

Court: United States Court of Appeals for the Federal Circuit (Appeal from the United States District Court for the District of Delaware).

Issue: Did the District Court correctly find that Alkem Laboratories Ltd.’s Abbreviated New Drug Application (ANDA) for a vancomycin liquid formulation did not infringe claims 5, 7, 8, and 9 of Azurity Pharmaceuticals, Inc.’s U.S. Patent No. 10,959,948 due to Azurity’s disclaimer of propylene glycol during the patent prosecution history, and did a stipulation between the parties during discovery negate this disclaimer?

Holding: The Federal Circuit affirmed the District Court's finding of non-infringement, holding that Azurity clearly and unmistakably disclaimed any presence of propylene glycol in the claimed invention during the prosecution of the ’948 patent, and that a stipulation entered by the parties did not preclude Alkem from relying on this disclaimer.

Main Themes and Important Ideas/Facts:

The Patent and the Infringement Allegation:

• Azurity’s ’948 patent claims non-sterile drinkable liquid formulations containing the antibiotic vancomycin for oral administration, used to treat Clostridium difficile infection. The claims, particularly representative claim 5, specify a formulation "consisting of" a buffering agent, water, a sweetener, a preservative, vancomycin hydrochloride, and a flavoring agent.

• Azurity sued Alkem for infringement under the Hatch-Waxman Act following Alkem’s submission of an ANDA for a generic version of Azurity’s product.

• Alkem’s ANDA product undisputedly contains propylene glycol, both as a separately listed co-solvent and as an ingredient in the flavoring agent.

Prosecution History Disclaimer:

• The core of the Federal Circuit's decision rests on the doctrine of prosecution history disclaimer. This doctrine allows courts to narrow the scope of patent claims based on clear and unmistakable disavowals made by the patentee during the examination process.

• The ’948 patent originated from a continuation application (’400) of an earlier application (’059) that was repeatedly rejected over a prior art reference (Palepu).

• Palepu disclosed an intravenously administered liquid vancomycin formulation containing "a polar solvent including propylene glycol."

• During the prosecution of the ’059 application, Azurity attempted to distinguish its invention from Palepu. Initially, Azurity proposed negative limitations excluding propylene glycol, but the examiner found these insufficient because Palepu also disclosed polyethylene glycol.

• The examiner suggested using "consisting of language." Subsequently, Azurity amended claims to include "consisting of" preambles and argued that "[t]he absence of propylene glycol and polyethylene glycol in the claimed invention [of then claim 20], in part, distinguish it from [Palepu]."

• Azurity’s Chief Scientific Officer, Dr. Dinh, also stated that the formulations "do not have propylene glycol or polyethylene glycol, both of which were noted as important components in Palepu’s compositions."

• The examiner ultimately allowed the claims of the ’059 application, explicitly stating that "[t]he instant claims exclude the presence of propylene glycol or polyethylene glycol in view of the consisting of language, and thus overcome the teachings of Palepu which requires the propylene glycol or polyethylene glycol to be present with the vancomycin hydrochloride."

• Because the ’400 application (leading to the ’948 patent) was a continuation of the ’059 application and adopted the same "consisting of" preambles, the disclaimer made in the ’059 prosecution history applied equally to the ’948 patent. The court cited Elkay Mfg. Co. v. Ebco Mfg. Co., stating, "When multiple patents derive from the same initial application, the prosecution history regarding a claim limitation in any patent that has issued applies with equal force to subsequently issued patents that contain the same claim limitation."

• The Federal Circuit found Azurity’s disclaimer of propylene glycol to be "clear, unambiguous, and complete."

The "Consisting Of" Transition:

• The court emphasized the significance of the "consisting of" transition phrase in the claims, noting that it is a closed term "meaning that the claimed invention contains only what is expressly set forth in the claim."

• Azurity’s adoption of this language was directly linked to overcoming the prior art by excluding propylene glycol.

Relevance of Statements in a Related Patent Application (’421):

• Azurity argued that a statement made in a later-filed related patent application (’421) disclaiming the disclaimer of propylene glycol in the ’059 application should be considered.

• The Federal Circuit rejected this argument, finding that this "unilateral and belated statement" made after the allowance of the ’400 application carried no weight in interpreting the claims of the ’948 patent. The court emphasized the importance of public notice.

The Stipulation Regarding Flavoring Agents:

• During discovery, the parties stipulated that "[s]uitable flavoring agents for use in the Asserted Claims include flavoring agents with or without propylene glycol."

• Azurity argued that this stipulation meant Alkem conceded that a flavoring agent containing propylene glycol could still be "suitable" for the claimed invention, thus negating the disclaimer, at least with respect to the "flavoring agent" claim term.

• The Federal Circuit disagreed with Azurity's interpretation. The court reasoned that:

• Alkem explicitly stated it did not dispute infringement except for the presence of propylene glycol in its ANDA product, making Azurity's interpretation illogical as it would have Alkem concede the central issue.

• Unlike other stipulations concerning claim limitations, this one did not state that Alkem's product meets the "flavoring agent" limitation if it contains propylene glycol.

• The stipulation originated from Azurity's infringement theory that any propylene glycol in Alkem’s product, even if separate, could be considered part of the "flavoring agent." The stipulation simply acknowledged that flavoring agents themselves do not necessarily need to contain propylene glycol.

• The court concluded that the stipulation "says nothing about whether Alkem’s ANDA contains a flavoring agent with propylene glycol" in the context of the disclaimer.

Finding of Non-Infringement:

• Because the Federal Circuit upheld the District Court’s finding of a clear disclaimer of propylene glycol and rejected Azurity’s argument regarding the stipulation, the presence of propylene glycol in Alkem’s ANDA product meant that it did not meet the "consisting of" limitations of the asserted claims in the ’948 patent.

• The court stated, "The infringement inquiry here is very simple: propylene glycol was disclaimed; the ANDA contains propylene glycol; therefore there is no infringement."

Quotes:

• "Because the district court correctly found that Azurity disclaimed any presence of propylene glycol in the prosecution history of the ’948 patent, Alkem’s ANDA product contains propylene glycol, and a stipulation entered by the parties during discovery does not preclude Alkem’s disclaimer argument, we affirm."

• "'Consisting of’ is a term of patent convention meaning that the claimed invention contains only what is expressly set forth in the claim."

• "The instant claims exclude the presence of propylene glycol or polyethylene glycol in view of the consisting of language, and thus overcome the teachings of Palepu which requires the propylene glycol or polyethylene glycol to be present with the vancomycin hydrochloride." (Examiner's statement for allowance)

• "When multiple patents derive from the same initial application, the prosecution history regarding a claim limitation in any patent that has issued applies with equal force to subsequently issued patents that contain the same claim limitation." (Elkay Mfg. Co. v. Ebco Mfg. Co.)

• "Suitable flavoring agents for use in the Asserted Claims include flavoring agents with or without propylene glycol." (Stipulation)

• "The infringement inquiry here is very simple: propylene glycol was disclaimed; the ANDA contains propylene glycol; therefore there is no infringement."

  
  

Conclusion: The Federal Circuit's decision reinforces the importance of the prosecution history in interpreting patent claims and the binding nature of clear and unmistakable disclaimers made during patent examination. It also clarifies that stipulations made during discovery must be interpreted in their proper context and do not automatically override established legal doctrines like prosecution history disclaimer. The case ultimately hinged on Azurity's deliberate choice to use "consisting of" language to distinguish its invention from prior art disclosing propylene glycol, thereby excluding it from the scope of its patent claims.