In Patent Prosecution, You Have the Right to Remain Silent. Anything You Say Can and Will Be Used Against You in the Court of Law

While a Miranda warning isn't given prior to starting substantive examination, perhaps it should be. In Azurity Pharmaceuticals, Inc. v. Alkem Laboratories, Ltd., a precedential decision issued on April 8, 2025, the Federal Circuit provides us with a great lesson on prosecution disclaimer and implications regarding the entanglement of future related applications due to the disclaimer.[1]

Azurity Pharmaceuticals, Inc. ("Azurity") is the patentee of U.S. Patent No. 10,959,948 ("the '948 patent"), having certain claims directed to liquid formulations of vancomycin, a glycopeptide antibiotic. Alkem Laboratories Ltd. ("Alkem") submitted an Abbreviated New Drug Application (with a Paragraph IV notice) for a vancomycin formulation containing propylene glycol. This decision stems from a suit brought by Azurity against Alkem for infringement of certain claims of the '948 patent. While certain issues arise based on a discovery stipulation, the Federal Circuit spends much of the decision on the merits of prosecution disclaimer, which we focus on below.

"A patentee may, through a clear and unmistakable disavowal in the prosecution history, surrender certain claim scope to which he would otherwise have an exclusive right by virtue of the claim language."[2]Such prosecution disclaimer applies to "[s]tatements that clearly and unmistakably disavow claim scope to one skilled in the art are binding, 'even if [the patentee] said more than needed to overcome a prior art rejection.'"[3]

Here, the specific prosecution statements in question were made in the parent application ("the parent '059 application," which issued as U.S. Patent. No. 10,959,946).

During prosecution of the parent '059 application, Azurity amended formulation claims to contain a "consisting of" transitions phrase following the preamble and argued that "[t]he absence of propylene glycol and polyethylene glycol in the claimed invention, in part, distinguishes it from the cited reference," Palepu.[4]Palepu discloses a liquid formulation containing vancomycin and propylene glycol as a polar solvent carrier. In the Notice of Allowance in the parent '059 application, the Examiner confirmed that 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."

In construing the scope of the claims at issue in the '948 patent, the court emphasizes that the claims of US 16/941,400, which issued as the '948 patent, "included the same 'consisting of' transition phrases added during the prosecution of the parent '059 application."[5]Moreover, in the reasons for allowance, the Examiner emphasizes the "consisting of" language as part of the reasons the claims are allowable over Palepu. In view of the prosecution histories, the court concludes that this "leaves no room to doubt that Azurity adopted the 'consisting of' transition specifically to narrow the claims and overcome Palepu and its disclosure of propylene glycol."[6]The court notes that "[t]his is true even though the patent at issue, U.S. Patent No. 10,959,948, was allowed without rejection and the originally filed claims included the "consisting of" transition phrase."[7]

The court made this decision over several arguments presented by Azurity to remove or limit the scope of the disclaimer. For example, Azurity argued that the transition phrase "consisting of" was meant to only exclude propylene glycol as a carrier as taught in Palepu, rather than as a component in the entire composition. Moreover, Azurity argued that Alkem stipulated that flavoring agents (as recited in the claims) could include propylene glycol, and thus the claimed formulations are not devoid of any propylene glycol. But, as summarized above, the statements Azurity repeatedly made during prosecution are not so nuanced. Consequently, while acknowledging that Palepu may only teach propylene glycol as a carrier, the court held that "what matters most is the broad language that Azurity used to distinguish Palepu. Just as the echo matches the shout, Azurity's repeated, sweeping statements-endorsed by the examiner-return an equally sweeping disclaimer."[8], [9]

Following Alkem's ANDA submission, Azurity included this statement in another related application: "For the record, Applicant did not disclaim propylene glycol when submitting the arguments in [the '059 application, which resulted in the claims at issue,] and reserves the right to claim propylene glycol in the instant and future cases in this patent family."[10]The court concludes that this statement carries no weight on the above prosecution disclaimer analysis. In reaching this conclusion, the court noted that such statements were "unilateral and belated," and that "[h]olding patentees to their definitive statements made during prosecution protects the public and promotes the notice function of intrinsic evidence."[11]Such conclusion was found to be consistent with precedent, as previous decisions from the Federal Circuit "have focused on how such statements have been relevant to later issued patents."[12]It remains an open question whether the result of prosecution disclaimer here would have been different had the "for the record" statement been put on the record during prosecution of the patent at issue.

The Federal Circuit concludes that prosecution disclaimer applies to the '498 patent at issue, and thus the claims at issue specifically carve out a vancomycin formulation having propylene glycol. As Alkem's ANDA is for a vancomycin formulation containing propylene glycol, the court swiftly upheld a finding of non-infringement.

Practice tips

During prosecution, it is critical to consider risk of prosecution disclaimer by making sweeping statements regarding claim scope and reference characterization. This is especially true because prosecution disclaimer impacts an instant application as well as future related applications containing the same or similar claim features. While it sometimes may be necessary to make arguments on the record to overcome cited prior art or other rejections, it would always be prudent to take a step back and examine whether such arguments are unnecessarily broad. Whenever possible, statements should be carefully crafted with qualification and specificity. Care should also be taken in reviewing the Examiner's characterization of the claims, including in the reasons for allowance, so that clarifications can be made on the record in a timely manner.

[1] Azurity Pharms., Inc. v. Alkem Labs. Ltd., 2025 U.S.P.Q.2d 590 (Fed. Cir. 2025).

[2]Page *5.

[3]Page *5, citing to Data Engine Techs., 10 F.4th at 1383.

[4]Palepu, US 2016/0101147.

[5]Page *7.

[6]Page *7.

[7]Page *2.

[8]Page *7.

[9]While prosecution history estoppel is not at issue in the instant decision, this discussion provides an opportunity to touch on another avenue that can result in limitations to the ultimate scope afforded to a claim. As discussed above, prosecution disclaimer is the result of a clear and unmistakable surrender of claim scope, which then limits the literal scope of claimed subject matter during claim interpretation. In contrast, prosecution history estoppel is triggered by claim amendments and/or arguments related to the patentability of claims. The resulting focus of prosecution history estoppel is the Doctrine of Equivalents and whether such amendments and/or arguments limit the use of equivalents when assessing what is captured by the scope of a claim.

[10]Page *4.

[11]Page *5.

[12]Page *6.