Par Pharmaceutical & Endo v. Baxter: Vasopressin Patent Case Dismissed Without Prejudice
Par Pharmaceutical, Endo USA, and affiliated entities filed suit against Baxter International in the District of Delaware asserting three patents covering VASOSTRICT vasopressin injection formulations. The case closed without prejudice after 687 days — leaving Baxter’s exposure unresolved and the patent assertions technically live.
Endo-Par vasopressin patent assertion ends without merits ruling
Filed on 29 March 2023, this infringement action in the U.S. District Court for the District of Delaware brought together Par Pharmaceutical, Inc., Endo USA, Inc., Endo Operations Limited, Par Sterile Products, LLC, and Endo Par Innovation Company, LLC as co-plaintiffs against a single defendant, Baxter International, Inc. The asserted patents — US11135265B2, US9993520B2, and US11207372B2 — cover vasopressin injection formulations, directly tied to the branded VASOSTRICT product offered in 40 units/100 mL and 20 units/100 mL concentrations, as well as vasopressin in 0.9% Sodium Chloride Injection.
The case closed on 13 February 2025 via a Stipulation of Dismissal, with the basis of termination recorded as dismissed without prejudice. A dismissal without prejudice means no final judgment on the merits was entered; the plaintiffs remain legally free to refile the same claims, subject to applicable statutes of limitations and any strategic considerations. For Baxter, this outcome provides short-term relief without the finality of a full adjudication — and critically, does not extinguish the underlying patent assertions.
At 687 days, the case ran for nearly two years before resolution, suggesting substantive litigation activity — likely including claim construction preparation, discovery, or parallel proceedings — before the parties agreed to step back. The public record does not disclose whether a settlement was reached, whether Baxter launched or withdrew its accused product, or whether the Endo group’s ongoing bankruptcy restructuring influenced the decision to dismiss. The absence of a with-prejudice dismissal is commercially significant and warrants monitoring by market participants in the vasopressin space.
Filing to Dismissed without Prejudice in 687 days
687 days — above the median for pharmaceutical ANDA-style patent disputes in Delaware
Dismissed without prejudice: what this outcome means for both sides
Stipulated dismissal without prejudice explained
A dismissal without prejudice, entered by stipulation of the parties, terminates the current action without adjudicating the merits. Unlike a with-prejudice dismissal, it does not bar the plaintiffs from reasserting the same patent claims in a new action. The court enters no judgment on infringement, validity, or enforceability — the legal slate is reset rather than resolved. This mechanism is commonly used when parties reach a commercial resolution they prefer to keep confidential, or when a plaintiff wishes to preserve optionality.
No merits ruling enteredEndo-Par entities retain full right to refile
Because the dismissal is without prejudice, Par Pharmaceutical and its co-plaintiffs have not surrendered their infringement claims. They may refile against Baxter — or any other party — based on the same three patents, provided relevant statutes of limitations have not elapsed. The public record does not confirm whether a confidential settlement accompanied this dismissal. The Endo group’s restructuring context may have influenced timing, but the patent assets themselves remain enforceable tools in the portfolio going forward.
Claims legally preservedBaxter escapes judgment — but faces lingering exposure
Baxter International obtains no declaratory judgment of non-infringement or invalidity from this outcome. While the immediate litigation burden is lifted, the three vasopressin patents — US11135265B2, US9993520B2, and US11207372B2 — remain valid and enforceable. If Baxter continues to manufacture or sell vasopressin in 0.9% Sodium Chloride Injection, it remains potentially exposed to a refiled action. Competitors and generic entrants in the vasopressin space should note that these patents have not been adjudicated or invalidated.
No invalidity or non-infringement findingVasopressin market uncertainty persists post-dismissal
VASOSTRICT is a critical care vasopressor used in septic shock and other low-blood-pressure emergencies, making this a commercially significant patent family. The unresolved dismissal suggests ongoing market tension around generic and branded vasopressin formulations. Companies developing competing vasopressin injection products — particularly those targeting the 40 units/100 mL and 20 units/100 mL concentration formats — should treat these three patents as active IP risk until they are adjudicated, expired, or formally licensed. A freedom-to-operate analysis is advisable before commercial launch.
Active IP risk for competitorsFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Par Pharmaceutical, Inc. | Company | Pharmaceutical patent holders — asserting three vasopressin injection formulation patents including US11135265B2Search in Eureka ↗ |
| Co-Plaintiff | ENDO USA, INC. | Company | Search in Eureka ↗ |
| Co-Plaintiff | ENDO OPERATIONS LIMITED | Individual | Search in Eureka ↗ |
| Co-Plaintiff | Par Sterile Products, LLC | Company | Search in Eureka ↗ |
| Co-Plaintiff | Endo Par Innovation Company, LLC | Company | Search in Eureka ↗ |
| Defendant | Baxter International, Inc. | Company | Baxter International, Inc. — global medical products company and manufacturer of injectable pharmaceutical productsSearch in Eureka ↗ |
| Plaintiff counsel | Aaron S. Lukas | Attorney | Counsel for Par Pharmaceutical, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Kaan Ekiner | Attorney | Counsel for Par Pharmaceutical, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Keri L. Schaubert | Attorney | Counsel for Par Pharmaceutical, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Kerry B. McTigue | Attorney | Counsel for Par Pharmaceutical, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Madison H. McNulty | Attorney | Counsel for Par Pharmaceutical, Inc.Search in Eureka ↗ |
| Plaintiff counsel | William B. Coblentz | Attorney | Counsel for Par Pharmaceutical, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Cozen O’connor PC | Law Firm | Representing Par Pharmaceutical, Inc.Search in Eureka ↗ |
| Defendant counsel | Alejandro Hernandez | Attorney | Counsel for Baxter International, Inc.Search in Eureka ↗ |
| Defendant counsel | Greg L. Goldblatt | Attorney | Counsel for Baxter International, Inc.Search in Eureka ↗ |
| Defendant counsel | Jonathan A. Choa | Attorney | Counsel for Baxter International, Inc.Search in Eureka ↗ |
| Defendant counsel | Katie A. Boda | Attorney | Counsel for Baxter International, Inc.Search in Eureka ↗ |
| Defendant counsel | Kevin E. Warner | Attorney | Counsel for Baxter International, Inc.Search in Eureka ↗ |
| Defendant counsel | Paul J. Molino | Attorney | Counsel for Baxter International, Inc.Search in Eureka ↗ |
| Defendant counsel | Philip A. Rovner | Attorney | Counsel for Baxter International, Inc.Search in Eureka ↗ |
| Defendant counsel | Wojciech Jankiewicz | Attorney | Counsel for Baxter International, Inc.Search in Eureka ↗ |
| Defendant law firm | Potter, Anderson & Corroon LLP | Law Firm | Representing Baxter International, Inc.Search in Eureka ↗ |
| Presiding judge | Judge N/A | Judge | Delaware District CourtSearch in Eureka ↗ |
Official order — verbatim text
The recorded verdict — Stipulation of Dismissal — reflects a jointly agreed procedural termination rather than a judicial merits determination. No finding of infringement, validity, or damages was made. The without-prejudice basis means neither party obtained a binding legal conclusion they can assert in future proceedings. For practitioners advising clients on freedom-to-operate or litigation risk, this outcome should be read as a suspension rather than a resolution: the three asserted vasopressin patents retain full enforceability and the plaintiffs retain full standing to refile.
US11135265B2, US9993520B2 & US11207372B2 — vasopressin injection formulation patents
The three asserted patents — US11135265B2, US9993520B2, and US11207372B2 — cover formulations of vasopressin for injectable use, anchored to the VASOSTRICT branded product. US9993520B2 was the earliest application in the family (filed via US15/688334), with the later two patents (US16/291915 and US16/291796) extending or refining the protected formulation claims. Vasopressin is a synthetic antidiuretic hormone used as a vasopressor in septic shock and vasodilatory shock, making formulation stability and concentration precision clinically critical. These patents protect specific concentration, excipient, and stability parameters that define the commercial product.
This patent family sits at the intersection of critical care pharmaceuticals and generic drug market entry — a particularly contested IP space. VASOSTRICT has faced multiple generic challenges, and the three-patent stack represents a layered exclusivity structure designed to sustain protection across overlapping claim scopes. For companies developing vasopressin injection generics or biosimilar vasopressors, each patent in this stack must be independently assessed. The without-prejudice dismissal of this case means no claim has been invalidated through litigation, leaving the full exclusionary potential of each patent intact.
Should you run an FTO against US11135265B2, US9993520B2, and US11207372B2?
Any company developing, manufacturing, or commercialising vasopressin injection products — particularly in 0.9% sodium chloride at concentrations including 20 units/100 mL or 40 units/100 mL — should treat this three-patent family as a priority FTO target. The dismissal without prejudice in this case means no invalidity finding exists; all three patents are presumptively valid and enforceable. This is directly relevant to generic pharmaceutical developers, contract manufacturers, and hospital procurement teams assessing long-term supply security.
PatSnap Eureka’s FTO Search Agent can map your vasopressin formulation against the claim scope of all three patents simultaneously, flagging overlap risks and identifying prior art relevant to a potential IPR petition. Eureka’s prosecution history analysis also surfaces any file wrapper estoppel or narrowing amendments that may limit enforceability — critical intelligence before a commercial launch or supply contract commitment in the vasopressin critical care segment.
Run a freedom-to-operate analysis on US11135265B2 to assess your product’s exposure
Run FTO in Eureka →Similar vasopressin formulation patent cases in Delaware federal court
Explore related pharmaceutical formulation patent infringement actions filed in the District of Delaware involving vasopressin, injectable drugs, and critical care pharmaceutical IP.
What this case signals for the vasopressin and injectable drug IP landscape
An unresolved dismissal in a multi-patent pharmaceutical infringement case rarely signals the end of the story.
Without-prejudice dismissals preserve plaintiff leverage in drug patent disputes
When branded pharmaceutical plaintiffs dismiss without prejudice, they retain the ability to re-engage if a defendant’s commercial activity continues or expands. For competitors in the vasopressin injection space, this case closing without a merits ruling means the three asserted patents remain live threats. Monitor any Endo or Par re-filing activity against Baxter or other generic entrants closely.
Baxter’s vasopressin product faces unresolved patent risk until FTO is established
No court has ruled on whether Baxter’s vasopressin in 0.9% Sodium Chloride Injection infringes or whether the three patents are valid. Any company — including Baxter — commercially active in this formulation space should conduct or refresh an FTO analysis against US11135265B2, US9993520B2, and US11207372B2 before scaling supply or entering new tender contracts.
Par v Baxter — key questions answered
The dismissal without prejudice means the court entered no judgment on the merits — no finding of infringement, validity, or invalidity. Par Pharmaceutical and the Endo entities retain the legal right to refile the same claims based on US11135265B2, US9993520B2, and US11207372B2 against Baxter or other parties, subject to applicable statutes of limitations. Baxter obtained no declaratory or defensive judgment from this outcome.
The plaintiffs asserted three U.S. patents: US11135265B2 (application US16/291915), US9993520B2 (application US15/688334), and US11207372B2 (application US16/291796). All three cover vasopressin injection formulations associated with the VASOSTRICT branded product, offered in 40 units/100 mL and 20 units/100 mL concentrations, as well as vasopressin in 0.9% Sodium Chloride Injection.
The public record reflects a Stipulation of Dismissal without prejudice filed by the parties on or before 13 February 2025. The record does not confirm whether a confidential settlement agreement accompanied the dismissal. A stipulated dismissal without prejudice is frequently, though not exclusively, associated with a negotiated resolution — but this cannot be confirmed from publicly available docket information alone.
VASOSTRICT is a branded vasopressin injection product used as a vasopressor in critical care settings, particularly for patients in septic shock or vasodilatory shock. It is offered in 20 units/100 mL and 40 units/100 mL concentrations. The three asserted patents cover specific formulation parameters — including concentration and stability characteristics — that define the commercial product and differentiate it from competing injectable vasopressin products.
The case was filed on 29 March 2023 and closed on 13 February 2025, a duration of 687 days — approximately 22.5 months. This is above the median duration for pharmaceutical patent infringement cases that terminate before trial in Delaware, suggesting meaningful litigation activity, potentially including discovery exchanges and claim construction briefing, before the parties agreed to dismiss.
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