Azurity Disclaimed Propylene Glycol to Win Its Patent. It Could Not Stop Alkem.

Liquid formulation chemistry is often a balancing act between solubility, chemical degradation, and organoleptic palatability. In the Hatch-Waxman arena, that chemical balancing act frequently collides with the strict doctrine of prosecution history disclaimer.

That collision was on full display in Azurity Pharmaceuticals, Inc. v. Alkem Laboratories Ltd. (Fed. Cir. No. 2023-1977, decided April 8, 2025), where the U.S. Court of Appeals for the Federal Circuit affirmed that brand pharmaceutical patentee Azurity could not enforce its oral vancomycin patent against Indian generic manufacturer Alkem Laboratories. The ruling offers a textbook demonstration of how aggressive concessions made during patent prosecution permanently circumscribe enforcement options against generic formulators.

The Chemistry of Liquid Vancomycin

However, formulating vancomycin as a stable aqueous solution is notoriously difficult. In the presence of water, vancomycin undergoes hydrolytic degradation, deamidation of its asparagine residues, and epimerization, forming crystalline degradation products (CDP-1) that destroy therapeutic potency. Because of this chemical instability, hospitals historically had to reconstitute intravenous vancomycin powder into oral syrups extemporaneously, resulting in short refrigerator shelf lives and foul-tasting solutions that discouraged pediatric and geriatric patient compliance.

Azurity Pharmaceuticals (formerly CutisPharma) commercialized Firvanq, a convenient compounding kit containing pre-measured vancomycin hydrochloride dry powder and an aqueous diluent containing sweetening and flavoring agents, producing a 25 mg/mL or 50 mg/mL oral liquid solution stable for up to 14 days under refrigeration.

The Prosecution Wall: Distinguishing the Palepu Prior Art

The legal downfall of the '948 patent began years before litigation, during the prosecution of its parent application (No. 15/126,059).

To escape Palepu and persuade the examiner to grant allowance, Azurity took two decisive, narrow-tailored drafting steps:

1. It amended its claim transition language from open ('comprising') to strictly closed ('consisting of'). The resulting independent claims recited a liquid formulation 'consisting of' a buffering agent, water, a sweetener, a preservative, vancomycin hydrochloride, and a flavoring agent.

Persuaded by this categorical disavowal, the examiner allowed the claims, stating in the Reasons for Allowance: '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.'

Alkem's Generic ANDA and the 'Mix-and-Match' Theory

When developing its generic formulation, Alkem's scientists included propylene glycol in the product for two distinct roles: directly as an intentional co-solvent, and as an excipient component inside its commercial grape flavoring mixture ('Grape Flavor 501417C', which consists of propylene glycol, flavoring substances, and ascorbic acid).

Azurity filed suit in the U.S. District Court for the District of Delaware, alleging that Alkem's ANDA infringed claims 5, 7, 8, and 9 of the '948 patent.

Azurity also leaned heavily on a pretrial discovery stipulation, in which the parties had agreed that: 'Suitable flavoring agents for use in the Asserted Claims include flavoring agents with or without propylene glycol.' Azurity claimed this stipulation operated as a formal concession by Alkem that any flavoring agent containing propylene glycol satisfied the claim limitations.

The Federal Circuit Ruling: Sweeping Statements Yield Sweeping Disclaimers

On appeal, the Federal Circuit unanimously affirmed in a precedential decision authored by District Judge Stephen R. Murphy III (sitting by designation with Chief Judge Moore and Circuit Judge Chen).

The Federal Circuit dismantled Azurity's arguments across every front:

2. Unilateral Statements in Distant Applications Carry No Weight: Azurity pointed to statements made in a parallel patent application ('the '421 application') in an effort to walk back its earlier remarks. The court dismissed this argument, noting that the '421 application was merely a 'grand-nephew' application prosecuted after the examiner had already allowed the direct ancestor claims. Under foundational public notice principles, patent applicants cannot undo public disclaimers made to secure allowance by filing self-serving remarks in distant collateral applications.

3. The Echo Matches the Shout: Most critically, the Federal Circuit reinforced the breadth of prosecution surrender under established precedent (such as Technology Properties Ltd. LLC v. Huawei Technologies Co.). Addressing Azurity's plea that its disclaimer should be limited only to carrier solvents rather than flavoring agents, the court held:

Because Azurity's disclaimer was complete and unequivocal, and because Alkem's generic ANDA formulation undisputedly contains propylene glycol, Alkem was entitled to a judgment of non-infringement as a matter of law.

Strategic Implications for Generic Formulation and Patent Drafting

- Excipient Disclaimer as a Design Pathway: Generic formulation teams closely scrutinizing brand prosecution histories can discover powerful, ironclad design-around avenues. When an innovator explicitly disclaims a functional excipient (such as an alcohol, polyol, or preservative) to overcome obviousness or anticipation rejections, that disclaimed chemical becomes an impenetrable shield against patent infringement.

- The Danger of the 'Consisting Of' Trap: While adopting 'consisting of' transitions is a standard examiner-pleasing tactic to push recalcitrant chemical claims through the USPTO, it severely weakens the patentee's commercial enforcement perimeter. Innovators who sacrifice intermediate transitional language ('consisting essentially of') leave themselves vulnerable to competitor formulations incorporating even minor unlisted excipients.