DCT
1:25-cv-00075
Eagle Pharma Inc v. Slayback Pharma LLC
I. Executive Summary and Procedural Information
- Parties & Counsel:
- Plaintiff: Eagle Pharmaceuticals, Inc. (Delaware)
- Defendant: Slayback Pharma LLC (Delaware)
- Plaintiff’s Counsel: McCarter & English, LLP
- Case Identification: 1:25-cv-00075, D. Del., 01/17/2025
- Venue Allegations: Venue is alleged to be proper as Defendant is incorporated in Delaware and therefore resides in the district for venue purposes.
- Core Dispute: Plaintiff alleges that Defendant’s VIVIMUSTA® injectable drug product infringes a patent related to stable, liquid formulations of the chemotherapy agent bendamustine.
- Technical Context: The case concerns pharmaceutical formulations designed to improve the shelf-life of bendamustine, an active ingredient that is known to degrade rapidly in aqueous solutions, thereby avoiding the need for inconvenient on-site reconstitution of a lyophilized powder.
- Key Procedural History: The complaint notes extensive prior litigation between the parties concerning other patents in the same family as the patent-in-suit. Plaintiff also alleges sending a notice letter to Defendant on the day the patent-in-suit issued. These allegations may be used to support claims of willful infringement.
Case Timeline
| Date | Event |
|---|---|
| 2010-01-28 | Earliest Priority Date for U.S. Patent No. 12,138,248 |
| 2022-12-07 | Slayback’s VIVIMUSTA® receives FDA approval |
| 2024-11-12 | U.S. Patent No. 12,138,248 Issues |
| 2024-11-12 | Plaintiff sends notice letter to Defendant regarding '248 Patent |
| 2025-01-17 | Complaint Filed |
II. Technology and Patent(s)-in-Suit Analysis
U.S. Patent No. 12,138,248 - Formulations of Bendamustine, Issued November 12, 2024
The Invention Explained
- Problem Addressed: The patent’s background section states that bendamustine, the active ingredient in the commercial product Treanda®, "exhibits rapid degradation upon reconstitution of the lyophilized product" and is "not suitable for long-term storage in liquid form" (’248 Patent, col. 1:49-61). This creates a need for a "ready to use (RTU) bendamustine formulation having enhanced stability" (’248 Patent, col. 1:64-65).
- The Patented Solution: The patent describes long-term storage stable liquid compositions of bendamustine that avoid the need for reconstitution. The solution involves formulating bendamustine in a specific "pharmaceutically acceptable fluid," such as one containing polyethylene glycol (PEG), and including a "stabilizing amount of an antioxidant," such as thioglycerol (’248 Patent, Abstract; col. 3:1-9). This combination is described as yielding a composition with less than 5% total impurities after storage for at least 15 months at 5°C to 25°C (’248 Patent, col. 1:41-51).
- Technical Importance: By creating a stable, ready-to-use liquid formulation, the invention aims to provide a more convenient and potentially safer alternative to lyophilized powders that require reconstitution in a clinical setting, a process which can introduce variability and risk chemical instability (’248 Patent, col. 1:61-63).
Key Claims at a Glance
- The complaint asserts at least independent claim 1 (Compl. ¶41).
- The essential elements of independent claim 1 are:
- A sterile container containing a liquid bendamustine-containing composition comprising bendamustine, or a pharmaceutically acceptable salt thereof, wherein the bendamustine concentration in the composition is about 25 mg/mL;
- a pharmaceutically acceptable fluid consisting of polyethylene glycol and optionally one or more of propylene glycol, ethanol, benzyl alcohol and glycofurol; and
- a stabilizing amount of an antioxidant,
- wherein the total impurities resulting from the degradation of the bendamustine is less than about 5% peak area response, as determined by HPLC at a wavelength of 223 nm after at least about 15 months at a temperature of about 5 °C to about 25 °C.
- The complaint reserves the right to assert other claims (Compl. ¶41).
III. The Accused Instrumentality
Product Identification
- The accused product is Slayback’s VIVIMUSTA® (bendamustine hydrochloride injection), 100 mg/4 mL (25 mg/mL) (Compl. ¶3).
Functionality and Market Context
- VIVIMUSTA® is an alkylating drug indicated for treating certain types of leukemia and lymphoma (Compl. ¶16, ¶35). The complaint alleges, based on the product’s Approved Labeling, that each milliliter of VIVIMUSTA® contains 25 mg of bendamustine hydrochloride, polyethylene glycol 400, "absolute alcohol" (ethanol), and 5 mg of monothioglycerol (Compl. ¶27-29, ¶36, ¶42). The complaint states that the product relies on bioavailability and bioequivalence data from Plaintiff's own BELRAPZO® product and has an FDA-approved 24-month shelf life (Compl. ¶24, ¶25). No probative visual evidence provided in complaint.
IV. Analysis of Infringement Allegations
'248 Patent Infringement Allegations
| Claim Element (from Independent Claim 1) | Alleged Infringing Functionality | Complaint Citation | Patent Citation |
|---|---|---|---|
| A sterile container containing a liquid bendamustine-containing composition comprising bendamustine, or a pharmaceutically acceptable salt thereof, wherein the bendamustine concentration in the composition is about 25 mg/mL; | VIVIMUSTA® is marketed in a 100 mg/4 mL vial and its Approved Labeling states it contains 25 mg/mL of bendamustine hydrochloride. | ¶27, ¶42 | col. 15:20-24, 25-28 |
| a pharmaceutically acceptable fluid consisting of polyethylene glycol and optionally one or more of propylene glycol, ethanol, benzyl alcohol and glycofurol; and | The Approved Labeling for VIVIMUSTA® states that it contains polyethylene glycol ("PEG") and "absolute alcohol" (ethanol), which are among the components listed in the claim. The complaint argues that sodium hydroxide, mentioned in the labeling as a pH adjuster, is not a component of the final fluid and thus does not take the product outside the scope of the "consisting of" limitation. | ¶28, ¶29, ¶30, ¶34 | col. 15:30-32 |
| a stabilizing amount of an antioxidant, | The Approved Labeling for VIVIMUSTA® recites that it contains 5 mg/mL of monothioglycerol. The patent specification identifies monothioglycerol as an antioxidant and provides examples where 5 mg/mL is a stabilizing amount. | ¶29, ¶36 | col. 4:5-14, 18-25 |
| wherein the total impurities...is less than about 5% peak area response...after at least about 15 months at a temperature of about 5 °C to about 25 °C. | On information and belief, VIVIMUSTA® has a 24-month expiration period and has the same or substantially similar stability as recited in the claims, based on FDA review documents and alleged concessions by Slayback in prior litigation involving a related patent. | ¶24, ¶25, ¶37 | col. 15:33-38 |
- Identified Points of Contention:
- Scope Questions: The complaint anticipates a dispute over the claim term "consisting of." A primary question will be whether the use of sodium hydroxide as a pH adjuster during manufacturing (Compl. ¶29) means the final VIVIMUSTA® fluid contains an unlisted ingredient, thereby placing it outside the literal scope of a fluid "consisting of" the recited components. The complaint argues that sodium hydroxide is a manufacturing processing aid that is consumed or otherwise not present in the final product (Compl. ¶34).
- Technical Questions: A key evidentiary question will be whether Plaintiff can prove that VIVIMUSTA® meets the stability limitation (less than 5% impurities after 15 months). The complaint’s allegations for this element rely on "information and belief," an FDA-approved 24-month expiry, and alleged concessions Slayback made regarding a different patent in prior litigation (Compl. ¶25, ¶37). The defense may challenge the sufficiency of this evidence to meet the specific quantitative and time-based requirements of the claim.
V. Key Claim Terms for Construction
The Term: "a pharmaceutically acceptable fluid consisting of..."
- Context and Importance: The transitional phrase "consisting of" is a term of art that typically closes a claim to any elements not specified. Its construction is critical because Defendant’s product labeling notes that "Sodium hydroxide is used to adjust [the] pH of polyethylene glycol 400" (Compl. ¶29). The case may turn on whether this use of sodium hydroxide means it is part of the "pharmaceutically acceptable fluid" in the final product.
- Intrinsic Evidence for Interpretation:
- Evidence for a Broader Interpretation: The complaint argues that a person of ordinary skill would understand that processing aids, such as pH adjusters, are not considered components of the final formulation if they are consumed or removed during manufacturing (Compl. ¶34-35). The patent’s focus on long-term stability of the final stored product (’248 Patent, col. 2:19-26) may support an interpretation that only components present during that storage period are relevant.
- Evidence for a Narrower Interpretation: The plain language of "consisting of" is highly limiting. The patent does not explicitly mention pH adjusters or other processing aids, which could support an argument that their presence, even in trace amounts, would place a product outside the claim scope.
The Term: "stabilizing amount"
- Context and Importance: This term appears to impart a functional requirement on the antioxidant. Practitioners may focus on this term because infringement requires not just the presence of an antioxidant, but its presence in an amount that actually performs a stabilizing function. The dispute will be whether simply matching an exemplary concentration from the specification is sufficient, or if a functional effect must be proven.
- Intrinsic Evidence for Interpretation:
- Evidence for a Broader Interpretation: The patent specification provides explicit concentration ranges for antioxidants that are considered a "stabilizing amount," for example, "from about 2.5 mg/mL to about 35 mg/mL," and specifically notes that "the concentration of the antioxidant...is about 5 mg/mL" in some embodiments (’248 Patent, col. 4:8-14). Plaintiff may argue that falling within this disclosed range is sufficient.
- Evidence for a Narrower Interpretation: The term itself—"stabilizing"—suggests a functional outcome. The patent’s objective is to achieve long-term stability and reduce degradation (’248 Patent, col. 2:19-23). A defendant might argue that Plaintiff must prove the antioxidant in the accused product actually causes a material increase in stability compared to a formulation without it, beyond merely being present at a certain concentration.
VI. Other Allegations
- Indirect Infringement: The complaint alleges Slayback induces infringement by "actively induc[ing] or contribut[ing] to the inducement" of infringement (Compl. ¶41). This is based on the Approved Labeling for VIVIMUSTA®, which allegedly "encourages, recommends, instructs, and/or promotes administration to patients" (Compl. ¶38).
- Willful Infringement: The complaint alleges willful infringement based on two main facts: (1) Slayback’s alleged awareness of Eagle’s patent portfolio due to extensive prior litigation over related patents, and (2) Eagle having sent a letter to Slayback on November 12, 2024—the issue date of the ’248 patent—notifying Slayback of the patent and its alleged infringement (Compl. ¶44). This alleges both pre-existing knowledge of the patent family and specific, post-issuance knowledge of the patent-in-suit.
VII. Analyst’s Conclusion: Key Questions for the Case
The resolution of this dispute may depend on the court's determination of the following open questions:
- A core issue will be one of claim scope: does the claim term "consisting of" foreclose infringement if a substance not listed in the claim (sodium hydroxide) is used as a processing aid during manufacturing, or is the term limited to only those components present in the final, stable formulation?
- A key evidentiary question will be one of proving infringement: can the Plaintiff demonstrate, beyond allegations based on "information and belief" and regulatory approvals, that the accused VIVIMUSTA® product factually meets the quantitative stability limitation of having "less than about 5% total impurities...after at least about 15 months"?
- A central question for damages will be one of willfulness: did Slayback's history of litigation with Eagle over related patents, combined with receiving a notice letter on the day the patent issued, constitute the "egregious" conduct necessary to support a finding of willful infringement?