IP Law Daily, PATENT—Fed. Cir.: Alkem’s vancomycin oral solution did not infringe Azurity’s liquid antibiotic formulation patent, (Apr 8, 2025)

By Saurabh Kashyap, B.A., LL.B., LL.M.

Federal Circuit affirmed noninfringement after finding that Azurity had disclaimed propylene glycol during prosecution, and Alkem’s generic formulation included that excipient.

The U.S. Court of Appeals for the Federal Circuit affirmed a federal district court ruling that Alkem Laboratories Ltd. did not infringe Azurity Pharmaceuticals, Inc.’s asserted patent directed to stable, non-sterile, liquid formulations of the antibiotic vancomycin. The appellate court concluded that Azurity had clearly disclaimed propylene glycol during the prosecution of the patent family, and Alkem's generic product—containing propylene glycol as an excipient and within a flavoring agent—fell outside the scope of the asserted "consisting of" claims. The Federal Circuit also rejected Azurity's reliance on a litigation stipulation and found no merit in its attempt to retract the disclaimer through subsequent prosecution statements. Alkem was awarded costs (Azurity Pharmaceuticals, Inc. v. Alkem Laboratories Ltd., No. 23-1977 (Fed. Cir. Apr. 8, 2025)).

Background. The plaintiff/appellant, Azurity Pharmaceuticals, Inc., is a U.S.-based specialty pharmaceutical company focused on developing and commercializing liquid oral medications tailored for pediatric, geriatric, and dysphagic populations. The defendant/appellee, Alkem Laboratories Ltd., is an Indian generic pharmaceutical manufacturer and frequent Abbreviated New Drug Applications (ANDAs) filer. The case involved Azurity's U.S. Patent No. 10,959,948 (the '948 patent), which claims a non-sterile, stable liquid formulation of vancomycin hydrochloride suitable for oral administration.

In 2021, Azurity sued Alkem in the District of Delaware under 35 U.S.C. §271(e)(2) after Alkem submitted an ANDA seeking approval to market a generic version of Azurity's vancomycin oral solution. Azurity asserted infringement of dependent claims 5, 7, 8, and 9 of the '948 patent, which recites formulations using a specific combination of inactive ingredients, ending with the closed transitional phrase "consisting of." At trial, the key dispute turned on whether Alkem's inclusion of propylene glycol, a common pharmaceutical solvent, caused its product to fall outside the scope of Azurity's patent claims. The district court found that Azurity had disclaimed such compositions during prosecution and granted a judgment of noninfringement. Azurity appealed.

Disclaimer during prosecution. The Federal Circuit examined whether Azurity had disclaimed formulations containing propylene glycol during the prosecution of the '948 patent or its parent. During the examination of the parent application, the examiner rejected claims based on prior art intravenous vancomycin formulations that included polar solvents such as propylene glycol. In response, Azurity amended the claims to recite "consisting of" and explicitly removed any reference to propylene glycol. Additionally, Azurity submitted a declaration from its Chief Scientific Officer confirming that the claimed invention excluded propylene glycol.

The examiner relied on these representations to allow the claims, stating in the Notice of Allowance that the prior art was distinguishable because it included propylene glycol, which the amended claims excluded. The court found these statements clear and unmistakable disclaimers of claim scope. The appellate court emphasized that a patentee’s prosecution statements narrowing claim scope to overcome prior art are binding and enforceable even if they later prove to be overbroad or unnecessary. Citing Tech. Props. Ltd. LLC v. Huawei Techs. Co., 849 F.3d 1349, 1359 (Fed. Cir. 2017), the court reiterated that “a disclaimer must be clear and unmistakable, but once made, it cannot be retracted.” The appellate court concluded that the disclaimer was not ambiguous, as both the claim amendments and accompanying statements collectively conveyed an intent to exclude propylene glycol entirely from the claimed invention.

ANDA formulation and claim language. Azurity argued that the propylene glycol in Alkem's ANDA product should not count against the claim scope because it was present only as part of a flavoring agent and was not listed separately in the claims. However, the court rejected this argument, finding that Alkem's ANDA formulation listed propylene glycol both independently as an excipient and as a component of its grape flavoring agent.

The claims at issue used the closed transitional phrase “consisting of,” which excludes all unlisted ingredients unless they are insubstantial and do not affect the basic and novel properties of the invention. Because Azurity had disclaimed propylene glycol and the compound was explicitly present in Alkem’s formulation, the “consisting of” language precluded a finding of infringement. The appellate court cited Ferring B.V. v. Watson Lab’ys, Inc.-Fla., 764 F.3d 1401 (Fed. Cir. 2014), and Par Pharm., Inc. v. Eagle Pharms., Inc., 44 F.4th 1379 (Fed. Cir. 2022), reaffirming that when a generic product is defined in an ANDA with specific components, courts must adhere to that definition and cannot rewrite it based on functional arguments.

Effect of discovery stipulation. Azurity also relied on a joint stipulation entered during discovery, in which both parties agreed that “suitable flavoring agents for use in the asserted claims include flavoring agents with or without propylene glycol.” Azurity argued that this stipulation should be read to prevent Alkem from asserting that the presence of propylene glycol, as part of a flavoring agent, was outside the claims.

The Federal Circuit disagreed. The appellate court found that the stipulation merely acknowledged that, in general, suitable flavoring agents in the field may contain propylene glycol. It did not waive the clear prosecution disclaimer or suggest that flavoring agents containing propylene glycol fell within the specific scope of Azurity's claimed invention. The court noted that stipulations must be interpreted in the context of the entire record and cannot contradict or expand the meaning of claim terms as defined by the intrinsic evidence. Citing Ring & Pinion Serv. Inc. v. ARB Corp., 743 F.3d 831, 836 (Fed. Cir. 2014), the court held that litigation conduct does not override claim scope defined during prosecution.

Attempt to undo disclaimer in related prosecution. In a later application (the ’421 application), Azurity tried to disavow the earlier disclaimer, stating that it had never intended to exclude propylene glycol. The court rejected this effort, noting that the ’421 application was not in the same lineage as the ’948 patent and that the disclaimer had already been relied upon during the ’948 prosecution.

The Federal Circuit emphasized that once a disclaimer is made and relied upon, it cannot be undone unilaterally or retroactively. The court emphasized the principle that subsequent prosecution cannot rewrite the history of a patent that has already been issued based on the patentee's representations.

Conclusion. Thus, the Federal Circuit affirmed the district court’s judgment that Alkem’s proposed generic vancomycin oral solution did not infringe Azurity’s ’948 patent. The court found that Azurity had made a binding disclaimer of propylene glycol during prosecution, and Alkem’s product contained that excipient. The court also rejected Azurity’s attempt to reinterpret a discovery stipulation and found its later efforts to withdraw the disclaimer ineffective. Alkem was awarded costs.

The Case is No. 23-1977.

Judge: Chen, R.

Attorneys: Tung On Kong (Wilson, Sonsini, Goodrich & Rosati, PC) for Azurity Pharmaceuticals, Inc. Alan Henry Pollack (Windels Marx Lane & Mittendorf, LLP) for Alkem Laboratories Ltd.

Companies: Azurity Pharmaceuticals, Inc.; Alkem Laboratories Ltd.

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