Bow River LLC v. Zydus Lifesciences Global FZE

I. Executive Summary and Procedural Information

• Parties & Counsel:
  • Plaintiff: Bow River LLC (Wyoming)
  • Defendant: Zydus Lifesciences Global FZE (Dubai, United Arab Emirates); Zydus Pharmaceuticals (USA) Inc. (New Jersey); Zydus Lifesciences Limited (India)
  • Plaintiff's Counsel: POTTER ANDERSON & CORROON LLP
• Case Identification: 1:26-cv-00535, D. Del., 05/07/2026
• Venue Allegations: Venue is alleged to be proper in the District of Delaware because the foreign-domiciled defendants (Zydus Lifesciences and Zydus FZE) may be sued in any judicial district, and because Defendant Zydus USA allegedly has persistent and continuous contacts with Delaware, including deriving substantial revenue from the state and regularly engaging in patent litigation in the district.
• Core Dispute: Plaintiff alleges that Defendants' submission of an Abbreviated New Drug Application (ANDA) to the FDA, seeking to market a generic version of the cancer drug VITRAKVI® (larotrectinib), constitutes an act of infringement of two patents covering methods of safely administering the drug.
• Technical Context: The lawsuit concerns the field of pharmacokinetics, specifically methods to manage potentially dangerous drug-drug interactions (DDIs) that can occur when a drug metabolized by the CYP3A4 enzyme is administered after treatment with a strong CYP3A4 inhibitor.
• Key Procedural History: The action was triggered by a notice letter dated March 26, 2026, in which Zydus informed Bow River of its ANDA No. 220875 filing. The asserted patents are listed in the FDA's Approved Drug Products with Therapeutic Equivalence Evaluations (the "Orange Book") for the VITRAKVI® capsule products, which provides a basis for alleging knowledge of the patents.

Case Timeline

Date	Event
2017-05-16	Earliest Priority Date for '967 Patent and '998 Patent
2022-05-24	'967 Patent Issued
2024-05-07	'998 Patent Issued
2026-03-26	Zydus sends ANDA Notice Letter to Bow River
2026-05-07	Complaint Filed

II. Technology and Patent(s)-in-Suit Analysis

U.S. Patent No. 11,337,967: "Methods of Treatment"

• Patent Identification: U.S. Patent No. 11,337,967 (the "'967 Patent"), "Methods of Treatment," issued May 24, 2022 Compl. ¶41

The Invention Explained

• Problem Addressed: The patent addresses the dangerous side effects that can occur when administering a drug that is a CYP3A4 substrate (a drug metabolized by the CYP3A4 enzyme) to a patient who has recently been treated with posaconazole, a strong inhibitor of that same enzyme '967 Patent, col. 1:40-51 The inhibition of the enzyme can lead to a toxic accumulation of the substrate drug '967 Patent, col. 1:52-67
• The Patented Solution: The patent discloses methods to avoid this adverse interaction by requiring a "washout" or delay period after the patient stops taking posaconazole and before starting the CYP3A4 substrate drug '967 Patent, abstract The inventors discovered that this required delay period is longer than previously understood, particularly in certain patient populations, and that an alternative is to administer a reduced dose of the substrate drug for a specified time '967 Patent, col. 2:12-41
• Technical Importance: The invention provides a dosing protocol that allows for the safe administration of critical medications to patients, including cancer patients, who may also require antifungal treatments like posaconazole, thereby reducing the risk of life-threatening DDIs Compl. ¶¶38-39

Key Claims at a Glance

• The complaint does not specify which claims it asserts, stating infringement of "one or more claims" Compl. ¶58 Independent claim 1 is representative of the patented method.
• Independent Claim 1 requires:
  • A method of treating a patient with a disease or condition with a CYP3A4 substrate drug, wherein the patient was previously administered posaconazole.
  • The method comprises: (a) ceasing a posaconazole regimen administered to the patient.
  • (b) waiting for at least about 2-42 days after ceasing the posaconazole regimen.
  • (c) administering a dose of a CYP3A4 substrate drug.

U.S. Patent No. 11,974,998: "Methods of Treatment"

• Patent Identification: U.S. Patent No. 11,974,998 (the "'998 Patent"), "Methods of Treatment," issued May 7, 2024 Compl. ¶44

The Invention Explained

• Problem Addressed: The '998 Patent, a continuation of the family that includes the '967 Patent, addresses the same problem of DDIs between posaconazole and CYP3A4 substrate drugs '998 Patent, col. 1:53-67 It notes that posaconazole accumulation can be particularly significant in specific patient populations, making the DDI risk more acute '998 Patent, col. 2:16-24
• The Patented Solution: The patent discloses that specific patient populations, such as obese patients, require a substantially longer "washout" period or a reduced-dose treatment period for the CYP3A4 substrate drug after stopping posaconazole to avoid dangerous side effects '998 Patent, abstract '998 Patent, col. 3:5-10 The claims are directed to methods of treatment that account for these specific patient characteristics.
• Technical Importance: This invention refines safety protocols for drug administration by tailoring them to specific patient populations (e.g., obese patients) who are at a higher risk for dangerous DDIs, providing more precise guidance to clinicians Compl. ¶¶6-7

Key Claims at a Glance

• The complaint alleges infringement of "one or more claims" Compl. ¶64 Independent claim 1 is representative.
• Independent Claim 1 requires:
  • A method of treating a patient who is obese and has an unresectable or metastatic solid tumor characterized by a gene fusion with a tyrosine kinase.
  • The method comprises: (a) stopping a posaconazole treatment that was administered to the patient.
  • (b) delaying administering, for at least about 3 days after stopping the posaconazole treatment, a dose of a tyrosine kinase inhibitor.

III. The Accused Instrumentality

• Product Identification: The accused products are Defendants' generic versions of VITRAKVI® (larotrectinib) 25 mg and 100 mg capsule products, for which Zydus has filed ANDA No. 220875 ("Zydus ANDA Products") Compl. ¶2
• Functionality and Market Context: Larotrectinib, the active ingredient, is a "first-in-class cancer drug" for treating adult and pediatric patients with certain solid tumors Compl. ¶¶34-36 The infringement allegation is not based on the composition of the drug itself, but on the instructions for its use that will be included in its proposed prescribing information (label) Compl. ¶58 The complaint alleges that the proposed label for the Zydus ANDA Products is "substantially identical" to the label for the brand-name VITRAKVI® Capsules and that this label instructs medical professionals and patients to perform the methods claimed in the asserted patents (Compl. ¶¶43; Compl. ¶46; Compl. ¶51).

IV. Analysis of Infringement Allegations

The complaint does not provide a claim chart or the text of the accused product label. The infringement theory is based on inducement under 35 U.S.C. § 271(e)(2)(A), where the act of infringement is the filing of an ANDA for a drug whose proposed label will instruct others to perform the patented methods. The following tables summarize the allegations as inferred from the complaint's narrative.

No probative visual evidence provided in complaint.

'967 Patent Infringement Allegations

Claim Element (from Independent Claim 1)	Alleged Infringing Functionality	Complaint Citation	Patent Citation
A method of treating a patient...with a CYP3A4 substrate drug, wherein the patient was previously administered posaconazole...	The proposed Zydus ANDA product label is alleged to instruct the administration of larotrectinib (a CYP3A4 substrate drug) to cancer patients, who are often immunocompromised and may have been previously treated with antifungals like posaconazole (Compl. ¶37).	¶58	col. 2:7-11
comprising: (a) ceasing a posaconazole regimen administered to the patient;	The proposed label allegedly provides instructions for administering larotrectinib to patients who are ceasing treatment with posaconazole, a strong CYP3A inhibitor (Compl. ¶¶38-40; Compl. ¶51).	¶51; ¶58	col. 2:25-31
(b) waiting for at least about 2-42 days after ceasing the posaconazole regimen; and	The proposed label is alleged to instruct a "washout" period after stopping posaconazole before starting or resuming a normal dose of larotrectinib, which the patent claims as a novel method (Compl. ¶¶39-40).	¶39; ¶51; ¶58	col. 2:31-34
(c) administering a dose of a CYP3A4 substrate drug.	The proposed label allegedly instructs the administration of the Zydus ANDA product (larotrectinib) after the specified waiting period Compl. ¶58	¶58	col. 2:34-41

'998 Patent Infringement Allegations

Claim Element (from Independent Claim 1)	Alleged Infringing Functionality	Complaint Citation	Patent Citation
A method of treating a patient who is obese and has an unresectable or metastatic solid tumor characterized by a gene fusion with a tyrosine kinase...	The proposed label is alleged to contain instructions for administering larotrectinib (a tyrosine kinase inhibitor) to patients with specific tumors, with the patent specifically identifying obese patients as a key population (Compl. ¶35).	¶35; ¶51; ¶64	col. 3:5-10
comprising: (a) stopping a posaconazole treatment that was administered to the patient; and	The proposed label allegedly instructs a specific dosing regimen for patients who are stopping treatment with posaconazole (Compl. ¶¶38-40; Compl. ¶51).	¶51; ¶64	col. 3:20-22
(b) delaying administering, for at least about 3 days after stopping the posaconazole treatment, a dose of a tyrosine kinase inhibitor.	The proposed label allegedly instructs a delay of at least 3 days after stopping posaconazole before administering larotrectinib, which falls within the method claimed by the patent (Compl. ¶¶39-40).	¶39; ¶51; ¶64	col. 3:23-26

• Identified Points of Contention:
  • Scope Questions: A central question for the court will be whether the language in Zydus's proposed label directs, encourages, or requires physicians to perform all steps of the asserted method claims. The analysis will depend on the precise wording of the label, which is not included in the complaint.
  • Factual Questions: A key factual dispute will be the degree of similarity between the Zydus proposed label and the brand-name VITRAKVI® label. The complaint's allegation that they are "substantially identical" will be a focal point of discovery and argument Compl. ¶51

V. Key Claim Terms for Construction

• Term: "waiting for at least about 2-42 days" ('967 Patent, Claim 1)

• Context and Importance: The temporal limitation defines the core of the patented "washout" method. The scope of "about" will be critical to determining infringement, as it defines the required length of the delay period. Practitioners may focus on this term because the extent of flexibility imparted by "about" could determine whether a label's instructions, which might specify a particular number of days, fall within the claim's scope.

• Intrinsic Evidence for Interpretation:

  • Evidence for a Broader Interpretation: The specification repeatedly uses "about" in relation to time periods and dosages, suggesting the patentee intended a degree of numerical flexibility and did not intend to be limited to the exact ranges recited '967 Patent, col. 2:25-41
  • Evidence for a Narrower Interpretation: The patent discloses specific time intervals based on clinical data, such as "about 2-21 days" '967 Patent, col. 2:32-34 A defendant may argue that "about" should be construed narrowly in light of these specific examples and the pharmacokinetic data presented in the patent's figures '967 Patent, Figs. 1-14

• Term: "a patient who is obese" ('998 Patent, Claim 1)

• Context and Importance: This term defines the specific patient population for the method claimed in the '998 Patent. The definition of "obese" is critical because infringement will depend on whether Zydus's label provides instructions specifically for patients meeting this definition.

• Intrinsic Evidence for Interpretation:

  • Evidence for a Broader Interpretation: The patent specification provides multiple, non-limiting examples of how obesity can be characterized, including BMI, percent ideal body weight, and waist size, which may support a flexible, multi-faceted definition rather than a single rigid cutoff '998 Patent, col. 39:6-14 '998 Patent, col. 40:22-45
  • Evidence for a Narrower Interpretation: The specification provides very specific numerical thresholds, such as "a BMI of at least about 35" or a "waist size greater than about 42 inches" '998 Patent, col. 39:8-10 A party could argue that the term "obese" should be limited to patients who meet at least one of these explicit quantitative criteria.

VI. Other Allegations

• Indirect Infringement: The complaint alleges inducement of infringement, asserting that Zydus's proposed product label will actively encourage and instruct medical practitioners and patients to perform the steps of the patented methods Compl. ¶58 Compl. ¶64 Knowledge and intent are alleged to be based on Zydus's actual and constructive knowledge of the Orange Book-listed patents prior to its ANDA filing Compl. ¶60 Compl. ¶66
• Willful Infringement: Willfulness is alleged based on Zydus having "specific intent to infringe" the patents at the time it filed its ANDA, allegedly with pre-suit knowledge of the patents and the infringing nature of its actions Compl. ¶60 Compl. ¶66

VII. Analyst's Conclusion: Key Questions for the Case

1. Label-Induced Infringement: A central issue will be whether the specific instructions in Zydus's proposed product label will be found by the court to meet all the limitations of the asserted method claims. The case will likely hinge on whether the label directs, rather than merely informs of a possibility, the performance of the patented "washout" or dose-reduction methods.
2. Claim Construction: The dispute may turn on the construction of key claim terms. A primary question will be one of definitional scope: how broadly will the court construe the term "about" in the temporal limitations of the '967 Patent, and will the definition of "a patient who is obese" in the '998 Patent be interpreted to require specific clinical metrics that must be reflected in the accused label?
3. Patent Validity: An underlying question for the court will be whether the asserted claims are valid over the prior art. Defendants may argue that determining a safe dosing regimen by observing drug-drug interactions and establishing a washout period is a conventional and obvious practice in the field of pharmacokinetics, potentially rendering the claims invalid.