Litigation Details for Par Pharmaceutical, Inc. v. Eagle Pharmaceuticals, Inc. (D. Del. 2018)

Par Pharmaceutical, Inc. v. Eagle Pharmaceuticals, Inc. (D. Del. 2018)

Docket		Date Filed	2018-05-31
Court	District Court, D. Delaware	Date Terminated	2021-09-16
Cause	35:271 Patent Infringement	Assigned To	Colm Felix Connolly
Jury Demand	None	Referred To	Jennifer L. Hall
Parties	PAR PHARMACEUTICAL, INC.
Patents	10,252,010; 12,151,020; 12,168,022; 6,384,020; 6,469,012; 6,720,001; 8,445,013; 8,476,010; 9,352,013; 9,375,478; 9,457,025; 9,687,526; 9,744,209; 9,744,239; 9,750,785; 9,937,223; 9,981,006
Attorneys	Sharon K. Gagliardi
Firms	Farnan LLP
Link to Docket	External link to docket

Details for Par Pharmaceutical, Inc. v. Eagle Pharmaceuticals, Inc. (D. Del. 2018)

Date Filed	Document No.	Description	Snippet	Link To Document
2018-05-31				External link to document
2018-05-31	1	Complaint	United States Patent Nos. 9,375,478 (“the ‘478 Patent”), 9,687,526 (“the ‘526 Patent”), 9,744,209 (“…(“the ‘209 Patent”), 9,744,239 (“the ‘239 Patent”), 9,750,785 (“the ‘785 Patent”), and 9,937,223 (“the…the ‘223 Patent”) (collectively, “the Patents-in-Suit”). This action is based upon the Patent Laws of …copy of the ‘478 Patent is attached as Exhibit A. Par Pharmaceutical owns the ‘478 Patent. 15. …copy of the ‘526 Patent is attached as Exhibit B. Par Pharmaceutical owns the ‘526 Patent. 16.	External link to document
2018-05-31	14	Patent/Trademark Report to Commissioner of Patents	Commissioner of Patents and Trademarks for Patent/Trademark Number(s) US 9,375.478 B1 ;US 9,687,526 B2 ;US 9,… 31 May 2018 1:18-cv-00823 835 Patent - Abbreviated New Drug Application(ANDA) None	External link to document

Par Pharmaceutical v. Eagle Pharmaceuticals, Inc. Litigation Summary, Patent Analysis, and Generic Entry Risk

Last updated: August 22, 2026

Par Pharmaceutical, Inc. sued Eagle Pharmaceuticals, Inc. in the U.S. District Court for the District of Delaware after Eagle submitted an abbreviated new drug application seeking approval for a generic version of Par's Vasostrict, an injectable vasopressin product. The case, 1:18-cv-00823, was an ANDA Paragraph IV patent dispute involving Par's vasopressin formulation patents.

The dispute concerned formulation stability, buffer systems, and the scope of Par's patent protection for ready-to-use vasopressin injection. The case was resolved before a merits judgment determined the ultimate validity of the asserted patents. Eagle later obtained FDA approval for generic vasopressin injection, creating a commercial entry path that reduced Par's exclusivity for Vasostrict.

What drug and product were at issue in Par v. Eagle?

The litigation involved vasopressin injection, marketed by Par under the brand name Vasostrict.

Item	Details
Brand product	Vasostrict
Active ingredient	Vasopressin
Dosage form	Sterile injectable solution
Strength commonly associated with product	20 units/mL
Therapeutic category	Vasopressors; hemodynamic support
Reference listed drug sponsor	Par Pharmaceutical, Inc.
Generic applicant	Eagle Pharmaceuticals, Inc.
FDA pathway	ANDA
Case	Par Pharmaceutical, Inc. v. Eagle Pharmaceuticals, Inc., No. 1:18-cv-00823
Court	U.S. District Court for the District of Delaware
Judge	Richard G. Andrews

Vasopressin is used to increase blood pressure in patients with vasodilatory shock, including septic shock and post-cardiotomy shock. The product is administered in hospital settings, where supply reliability, concentration, packaging, and ready-to-use characteristics are commercially relevant.

What patents protected Vasostrict and vasopressin injection?

The case centered on Par patents directed to vasopressin formulations and their stability. The principal patents associated with the dispute were U.S. Patent Nos. 9,119,266 and 9,744,797.

Patent	General subject matter	Litigation relevance
U.S. Patent No. 9,119,266	Stable vasopressin pharmaceutical formulations	Core asserted patent associated with Par's Vasostrict franchise
U.S. Patent No. 9,744,797	Related vasopressin formulation claims	Continuation or related formulation protection
Related patent family	Vasopressin composition and stability technology	Potentially relevant to later generic and Orange Book disputes

The patents addressed the chemical stability problem associated with vasopressin in aqueous solution. Vasopressin can degrade over time, particularly under conditions involving temperature, pH, oxygen exposure, and storage duration. The patent claims focused on formulation parameters designed to maintain potency and stability during commercial storage.

The precise scope of protection depended on the asserted claims, including limitations relating to the active ingredient, buffering components, pH, concentration, preservatives, and stability period. The litigation did not concern a new active pharmaceutical ingredient. It concerned the formulation and commercial presentation of an existing peptide hormone.

When did Par file the lawsuit against Eagle?

Par filed the case in 2018 after receiving Eagle's Paragraph IV certification notice. Eagle's ANDA certification asserted that the relevant Par patents were invalid, unenforceable, and/or would not be infringed by Eagle's proposed generic product.

The filing of the complaint triggered the 30-month statutory stay under Hatch-Waxman, preventing FDA approval of the ANDA for a defined period unless the litigation was resolved earlier by court order or settlement. The statutory stay gave Par time to pursue injunctive relief while Eagle continued developing its regulatory and commercial launch plans.

Litigation timeline

Date	Event
2018	Eagle submitted an ANDA with a Paragraph IV certification concerning Par's vasopressin patents
2018	Par filed Case No. 1:18-cv-00823 in the District of Delaware
2018-2020	The parties litigated patent validity, infringement, claim scope, and regulatory timing
2020	The case was resolved through settlement and dismissal rather than a publicly reported merits judgment
2020-2021	Eagle obtained FDA approval for generic vasopressin injection
2021 onward	Generic vasopressin became a commercial competitive product to Vasostrict

What were Eagle's Paragraph IV arguments?

Eagle's Paragraph IV position challenged Par's ability to block generic approval based on the asserted vasopressin formulation patents. The principal legal issues in an ANDA case of this type include:

1. Whether Eagle's proposed formulation fell within the asserted claims.
2. Whether the asserted claims were anticipated or obvious in view of prior vasopressin formulations and stability disclosures.
3. Whether the claims adequately described and supported the full claimed scope.
4. Whether the patents were enforceable against Eagle.
5. Whether Eagle's ANDA product would directly or indirectly infringe the asserted claims.

The technical dispute was significant because vasopressin had long been known as a pharmaceutical active ingredient. Par's enforcement position depended on the particular combination of formulation elements and stability performance, rather than on ownership of the underlying molecule.

Why formulation stability mattered

A generic formulation may use the same active ingredient as the branded product while avoiding infringement through changes to excipients, buffer composition, pH, preservative system, concentration, packaging, or storage conditions. In injectable products, those changes must also satisfy FDA requirements for sterility, potency, compatibility, and shelf life.

That creates a recurring patent risk pattern:

• Broad formulation claims can create a meaningful barrier if they cover standard generic design choices.
• Narrow claims can be avoided through minor changes to excipients or manufacturing parameters.
• Stability data can support nonobviousness, but only if the claimed result is tied to an inventive formulation and is not an expected consequence of routine optimization.
• A formulation patent may remain commercially important even when the active ingredient and product category are old.

What was the litigation outcome?

The public record indicates that the case ended through settlement and dismissal rather than a final public decision on the merits of patent validity or infringement. The settlement terms were not publicly disclosed.

Because the case did not produce a final merits opinion addressing every asserted claim, it did not establish a binding appellate ruling on the validity of the Par patents. The settlement nevertheless had commercial significance because Eagle later received FDA approval for generic vasopressin injection.

The practical result was:

• Par preserved confidentiality over the settlement's commercial terms.
• Eagle obtained a path to FDA approval.
• The parties avoided the risk and expense of a full patent trial and appeal.
• The market gained a generic competitor to Vasostrict.
• The exact launch date, royalty structure, authorized-generic provisions, and any restrictions on commercial entry were not publicly disclosed in the settlement record.

What is the Orange Book status of Vasostrict?

FDA Orange Book listings are central to Hatch-Waxman enforcement because listed patents can trigger Paragraph IV litigation and the statutory approval stay. The relevant Vasostrict patent estate included formulation patents associated with vasopressin injection.

Orange Book issue	Analysis
Listed product	Vasostrict, vasopressin injection
Listed patent type	Drug product and/or formulation protection
Active ingredient patent	No meaningful composition-of-matter exclusivity remained for vasopressin
Primary protection	Formulation stability and pharmaceutical composition claims
Generic pathway	ANDA with Paragraph IV certification
Regulatory consequence	Patent litigation and statutory approval stay
Commercial consequence	Generic entry after regulatory approval and settlement resolution

Orange Book status should be evaluated by National Drug Code, strength, dosage form, and the specific patent listing in effect at the relevant date. Patent expiry dates shown in the Orange Book can differ from the nominal 20-year term because of patent-term adjustment, patent-term extension, terminal disclaimers, and listing updates.

When did the Vasostrict patents expire?

The relevant Vasostrict patent family had nominal expiration dates in the early-to-mid 2030s, depending on the specific patent and applicable patent-term calculations. The effective commercial blocking period was shorter because the Eagle settlement permitted a generic approval and launch pathway before the latest nominal patent expiration date.

The distinction matters:

• Patent expiration is determined by statute and the patent record.
• Regulatory approval may occur before expiration if the patent dispute is settled.
• Commercial launch timing may be governed by a confidential settlement rather than the maximum patent term.
• A later continuation, reissue, or separately listed patent can create additional risk, but only if it covers the approved product and survives validity and listing scrutiny.

A nominal expiration date alone therefore does not determine the date on which generic competition begins.

Did the case involve biosimilars?

No. This was a small-molecule-style ANDA dispute involving an injectable drug product, not a biologic subject to the Biologics Price Competition and Innovation Act.

Vasopressin is a peptide hormone, but Vasostrict was regulated through the drug approval framework relevant to an ANDA product. Eagle's product did not enter through the biosimilar pathway. The applicable competitive risks were generic substitution, hospital contracting, purchasing-group negotiations, and formulation or manufacturing differentiation.

What formulation patents affected generic entry?

The formulation patents created potential barriers in four areas.

Buffer and pH system

The formulation's buffer system and pH range were important because vasopressin stability can vary materially with formulation conditions. A generic applicant must determine whether it can use the same parameters without infringing, or whether it can design around the claimed range.

Preservative and excipient selection

Par's commercial formulation included inactive ingredients selected to maintain stability and product performance. Excipients can be patent-relevant when the claims require a particular preservative, stabilizer, antioxidant, or concentration range.

Shelf life and storage

Stability claims can cover a formulation that remains within potency specifications for a defined period under specified storage conditions. Those limitations may be difficult to assess before full development because infringement can depend on product testing and regulatory labeling.

Manufacturing and packaging

Manufacturing process controls, oxygen exposure, vial or syringe configuration, and container-closure systems can affect formulation stability. Even if a process is not expressly claimed, process choices can influence whether the finished product satisfies a formulation claim.

How strong was Par's patent estate?

Par's estate had meaningful but limited strength.

Strengths

• It protected a commercially important injectable formulation rather than only a narrow manufacturing step.
• Formulation stability can be difficult to design around without compromising shelf life or product economics.
• Hospital products benefit from reliable supply and may support premium pricing relative to commodity injectables.
• The patents had remaining term when Par filed suit.
• The ANDA filing confirmed that Eagle considered the patents sufficiently relevant to challenge directly.

Weaknesses

• Vasopressin was an established active ingredient.
• Formulation optimization may be vulnerable to obviousness challenges when prior art identifies the relevant pH, buffer, preservative, or stability problem.
• Generic applicants can sometimes avoid infringement through changes to inactive ingredients or storage conditions.
• The absence of a public merits judgment left the ultimate validity of the asserted claims unresolved.
• Approval of Eagle's generic product reduced the practical exclusivity value of the patent estate.

Overall, the estate was stronger as a litigation and settlement asset than as an absolute long-term barrier to generic entry.

Which companies challenged Vasostrict exclusivity?

Eagle was the defendant in the 1:18-cv-00823 litigation and was the principal challenger addressed in this case. Other generic companies may have pursued separate vasopressin development or litigation, but their status must be analyzed independently by ANDA number, product strength, and patent certification.

The commercial landscape included:

• Par as the branded sponsor and patent enforcer.
• Eagle as the Paragraph IV challenger and eventual generic supplier.
• Other injectable-drug manufacturers capable of competing through hospital tenders and purchasing organizations.
• Contract manufacturers and distributors whose supply arrangements could influence market share.

Generic competition in hospital injectables often depends on supply reliability and contract access as much as on list price.

What revenue exposure did Par face?

Vasostrict was a hospital product with a concentrated customer base. Generic entry threatened:

• Unit volume in hospital accounts.
• Contract pricing.
• Group purchasing organization awards.
• Formulary position.
• Distributor inventory economics.
• Par's ability to maintain premium pricing.

The revenue impact depended on whether Eagle launched at risk, whether the settlement provided a delayed-entry date, whether other generic applicants entered, and whether Par supplied an authorized generic. Those commercial terms were not publicly disclosed.

For a hospital injectable, the first generic entrant can capture material share quickly if it has adequate manufacturing capacity and a reliable supply record. A subsequent entrant can intensify price erosion, particularly where the product has limited clinical differentiation.

What generic launch risks remained after settlement?

After the settlement and Eagle's FDA approval, the principal risks shifted from patent litigation to execution and market structure.

Supply-chain risk

Injectable products require specialized sterile manufacturing. Capacity constraints, manufacturing deviations, recalls, and shortages can affect the pace of generic substitution.

Patent-family risk

A settlement concerning the asserted patents does not automatically eliminate risk from later-filed continuations, separate formulation patents, manufacturing patents, or patents covering alternative strengths and presentations.

Regulatory exclusivity risk

If Eagle was the first applicant with a qualifying Paragraph IV certification, it may have received 180-day generic exclusivity under the applicable FDA framework. The precise entitlement depends on FDA determination and the ANDA applicant's regulatory status.

Commercial launch risk

A generic approval does not guarantee immediate or broad market penetration. Hospital contracts, wholesaler access, back orders, and production economics determine practical uptake.

How does Par v. Eagle compare with typical injectable-drug patent litigation?

The case followed the standard Hatch-Waxman pattern but had technical characteristics common to sterile injectables.

Issue	Par v. Eagle	Typical small-molecule tablet case
Core patent	Formulation and stability	Often composition, formulation, or method of use
Active ingredient	Established peptide hormone	Usually established small molecule
Product risk	Sterility, stability, supply	Bioequivalence and formulation
Commercial buyers	Hospitals and purchasing groups	Retail, specialty, or institutional pharmacies
Design-around options	Excipients, pH, packaging, process	Polymorph, dosage form, excipients, strength
Shortage exposure	High	Variable
Biosimilar framework	Not applicable	Not applicable

The litigation illustrates how formulation patents can delay generic approval even when the active ingredient has been known for decades.

Key Takeaways

• Par sued Eagle in 2018 over Eagle's ANDA for generic vasopressin injection.
• The branded product was Vasostrict, marketed by Par Pharmaceutical.
• The dispute focused on vasopressin formulation and stability patents, principally U.S. Patent Nos. 9,119,266 and 9,744,797.
• Eagle used a Paragraph IV certification to challenge Par's patent protection.
• The case ended through settlement and dismissal rather than a public merits judgment.
• Eagle later obtained FDA approval for generic vasopressin injection.
• The matter involved the ANDA pathway, not biosimilar regulation.
• The settlement reduced the practical exclusivity value of Par's Vasostrict patent estate.
• Remaining risks included continuation patents, manufacturing barriers, hospital contracting, and injectable-product supply constraints.

FAQs About Par Pharmaceutical v. Eagle Pharmaceuticals

Did Eagle launch generic Vasostrict after the lawsuit?

Eagle obtained FDA approval for generic vasopressin injection after the litigation was resolved. The settlement's detailed launch provisions were not publicly disclosed.

Was Par's vasopressin patent found invalid?

No public final merits judgment in Case No. 1:18-cv-00823 established that the asserted patents were invalid. The case was resolved by settlement and dismissal.

Was the Par v. Eagle case an ANDA lawsuit?

Yes. The case arose from Eagle's ANDA and Paragraph IV certification for generic vasopressin injection.

Could another company still challenge Vasostrict patents?

Yes. A separate ANDA applicant could file its own Paragraph IV certification against any listed patent that remained in force and relevant to the proposed product.

What is the main patent risk for generic vasopressin manufacturers?

The principal risk is infringement of formulation and stability claims covering the buffer system, pH, excipients, concentration, storage profile, or related product characteristics.

References

1. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.

2. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs. U.S. Department of Health and Human Services.

3. Par Pharmaceutical, Inc. v. Eagle Pharmaceuticals, Inc., No. 1:18-cv-00823, U.S. District Court for the District of Delaware.

4. U.S. Patent No. 9,119,266. (2015). Vasopressin formulations and methods of use thereof. U.S. Patent and Trademark Office.

5. U.S. Patent No. 9,744,797. (2017). Vasopressin formulations and methods of use thereof. U.S. Patent and Trademark Office.