DCT

1:25-cv-17780

Salix Pharma Inc v. Ajanta Pharma Ltd

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Key Events
Complaint

I. Executive Summary and Procedural Information

  • Parties & Counsel:
  • Case Identification: 3:25-cv-17780, D.N.J., 11/20/2025
  • Venue Allegations: Venue is alleged to be proper in the District of New Jersey as Defendant Ajanta Pharma USA Inc. has its principal place of business in the district, and Defendant Ajanta Pharma Ltd., a foreign corporation, is subject to personal jurisdiction there.
  • Core Dispute: Plaintiffs allege that Defendants’ submission of an Abbreviated New Drug Application (ANDA) to the FDA for a generic version of Xifaxan® (rifaximin) constitutes an act of infringement of three patents covering methods of use and polymorphic forms of the drug.
  • Technical Context: The technology relates to the antibiotic rifaximin, a widely used treatment for gastrointestinal conditions, particularly irritable bowel syndrome with diarrhea (IBS-D).
  • Key Procedural History: This action was filed under the Hatch-Waxman Act following Plaintiffs’ receipt of a Paragraph IV certification notice letter from Defendants, dated October 6, 2025. The notice letter informed Plaintiffs of Defendants' ANDA submission seeking to market a generic rifaximin product prior to the expiration of the patents-in-suit, which are listed in the FDA's "Orange Book" for Xifaxan®.

Case Timeline

Date Event
2005-03-03 ’196 Patent Priority Date
2008-02-26 ’571 and ’912 Patents Priority Date
2012-06-05 U.S. Patent No. 8,193,196 Issued
2023-01-31 U.S. Patent No. 11,564,912 Issued
2023-10-10 U.S. Patent No. 11,779,571 Issued
2025-10-06 Defendants' Paragraph IV Notice Letter
2025-11-20 Complaint Filing Date

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

U.S. Patent No. 11,779,571 - "Methods for Treating Irritable Bowel Syndrome (IBS)"

  • The Invention Explained:
    • Problem Addressed: The patent background describes the need for effective methods of "preventing, ameliorating and/or treating bowel diseases (BDs)," including irritable bowel syndrome (IBS) and its variants (’571 Patent, col. 2:40-42).
    • The Patented Solution: The invention provides methods for treating IBS by administering a specific dosage of the antibiotic rifaximin. A key aspect of the described solution is achieving a "durability of response," wherein a patient who responds to an initial course of treatment continues to experience relief from symptoms even after the treatment has been removed (’571 Patent, col. 2:56-62).
    • Technical Importance: Rifaximin is described as an antibiotic characterized by "negligible systemic absorption," making it suitable for treating localized gastrointestinal bacteria that cause conditions like IBS, while potentially minimizing systemic side effects (’571 Patent, col. 1:24-37).
  • Key Claims at a Glance:
    • The complaint asserts infringement of "one or more claims" without specifying which ones (Compl. ¶42). Independent claim 1 is representative:
    • A method of treating bloating associated with diarrhea-predominant irritable bowel syndrome (dIBS) in a female subject,
    • said method comprising administering 550 mg of rifaximin three times a day (TID) for 14 days to the female subject,
    • thereby treating bloating associated with dIBS in the female subject.

U.S. Patent No. 11,564,912 - "Methods for Treating Irritable Bowel Syndrome (IBS)"

  • The Invention Explained:
    • Problem Addressed: Similar to the ’571 Patent, this patent addresses the need for methods to treat bowel diseases like IBS, which can manifest as symptoms including "cramping, pain, diarrhea, constipation, lumpy stool, watery stool," and others (’912 Patent, col. 2:65-67).
    • The Patented Solution: The invention is a method of treating IBS symptoms through the administration of rifaximin. The patent describes that after an initial treatment period, subjects who respond may be removed from treatment and experience a "durability of antibiotic response" where symptoms remain relieved (’912 Patent, col. 2:56-62).
    • Technical Importance: The use of a minimally absorbed antibiotic like rifaximin for a gastrointestinal condition provides a targeted therapeutic approach (’912 Patent, col. 1:24-34).
  • Key Claims at a Glance:
    • The complaint asserts infringement of "one or more claims" (Compl. ¶54). Independent claim 1 is representative:
    • A method of treating one or more symptoms of irritable bowel syndrome (IBS) in a female subject,
    • said method comprising administering 550 mg of rifaximin TID for 14 days to the female subject,
    • thereby treating one or more symptoms of IBS in the female subject.

U.S. Patent No. 8,193,196 - "Polymorphous Forms of Rifaximin, Processes for their Production and Use thereof in the Medicinal Preparations"

  • Technology Synopsis: This patent addresses the technical issue that different crystalline forms, or polymorphs, of a drug can alter its physical properties, such as systemic absorption and bioavailability (’196 Patent, col. 3:4-14). The invention claims specific polymorphous forms of rifaximin, designated as forms δ and ε, as well as processes for their production. This allows for the selection of a form with a desired level of absorption, which is particularly relevant for an antibiotic intended for localized gastrointestinal activity (’196 Patent, Abstract).
  • Asserted Claims: The complaint alleges infringement of "one or more claims of the ’196 Patent" (Compl. ¶66).
  • Accused Features: The complaint alleges that Defendants' proposed generic product comprises a polymorphic form of rifaximin used for treating bacterial activity in the gastrointestinal tract, thereby infringing the patent (Compl. ¶65).

III. The Accused Instrumentality

Product Identification

  • Defendants' proposed generic rifaximin 550 mg tablets, for which they submitted ANDA No. 220990 to the FDA (the "ANDA Product") (Compl. ¶1-2).

Functionality and Market Context

  • The ANDA Product is a generic version of Plaintiffs' Xifaxan® 550 mg tablets (Compl. ¶1). The complaint alleges that the ANDA seeks FDA approval for the product to be used for the treatment of IBS-D in adults (Compl. ¶34). The filing of the ANDA signifies Defendants' intent to commercially manufacture and sell a lower-cost generic equivalent to the branded Xifaxan® product upon FDA approval (Compl. ¶1).

No probative visual evidence provided in complaint.

IV. Analysis of Infringement Allegations

The complaint does not contain a detailed claim chart. The infringement allegations are based on the statutory act of infringement under 35 U.S.C. § 271(e)(2)(A), which defines the submission of an ANDA seeking approval for a generic drug for a patented use as an act of infringement (Compl. ¶40, 52, 64). The following tables summarize the infringement theory for the representative independent claims.

’571 Patent Infringement Allegations

Claim Element (from Independent Claim 1) Alleged Infringing Functionality Complaint Citation Patent Citation
A method of treating bloating associated with diarrhea-predominant irritable bowel syndrome (dIBS) in a female subject... The ANDA Product is a 550 mg rifaximin tablet for which Defendants seek approval for the treatment of IBS-D in adults, which would include female patients. ¶34, 43 col. 4:4-6
...said method comprising administering, 550 mg of rifaximin TID for 14 days to the female subject... The ANDA Product is a generic equivalent to Xifaxan® 550 mg tablets. The complaint alleges that upon approval, the product would be prescribed and administered to patients, including females, which would constitute direct infringement of the claimed method. ¶43 col. 46:7-10
...thereby treating bloating associated with dIBS in the female subject. The alleged purpose of administering the ANDA Product is to relieve the signs and symptoms of IBS-D, which includes bloating. ¶43 col. 46:7-10

’912 Patent Infringement Allegations

Claim Element (from Independent Claim 1) Alleged Infringing Functionality Complaint Citation Patent Citation
A method of treating one or more symptoms of irritable bowel syndrome (IBS) in a female subject... The ANDA Product is intended for the treatment of IBS-D, and upon approval would allegedly be prescribed and administered to patients, including females, to relieve the symptoms of IBS. ¶55 col. 46:1-5
...said method comprising administering, 550 mg of rifaximin TID for 14 days to the female subject... The ANDA Product is a 550 mg rifaximin tablet. The complaint alleges that its proposed use would involve administration to patients in a manner that directly infringes the claimed method. ¶55 col. 46:6-10
...thereby treating one or more symptoms of IBS in the female subject. The alleged intended use of the ANDA Product is to relieve the signs and symptoms of IBS in patients. ¶55 col. 46:6-10

Identified Points of Contention

  • Scope Questions: For the ’571 and ’912 Patents, a central issue may be whether Defendants' proposed product label will induce infringement. The claims are directed to treating a "female subject." Questions may arise as to whether a product label for a general adult population, which will inevitably be used by females, is sufficient to meet the intent standard for induced infringement.
  • Technical Questions: For the ’196 Patent, the primary dispute will likely be factual and scientific: does the Defendants' ANDA Product actually contain one of the specific rifaximin polymorphs (δ or ε) claimed in the patent? The complaint does not provide sufficient detail for analysis of this element, as this determination would require physical testing of the ANDA product.

V. Key Claim Terms for Construction

The Term

  • "female subject" (’571 Patent, Claim 1; ’912 Patent, Claim 1)

Context and Importance

  • Both representative independent claims of the method-of-use patents are expressly limited to treating a "female subject." The construction of this term is critical because if Defendants' proposed labeling and marketing materials are not directed specifically to females, they may argue they do not induce infringement of these claims. Practitioners may focus on this term because it presents a potential avenue to design around the patents or argue against the specific intent required for inducement.

Intrinsic Evidence for Interpretation

  • Evidence for a Broader Interpretation: The specifications of the ’571 and ’912 patents discuss the treatment of bowel diseases in subjects generally, without consistently limiting the invention to females, which could support an argument that the term should be given its plain and ordinary meaning without special limitations (’912 Patent, col. 2:41-42).
  • Evidence for a Narrower Interpretation: The explicit inclusion of "female subject" in the claims themselves is strong evidence for a narrower scope. The patentee’s choice to include this limitation suggests it is a material part of the claimed invention, potentially to distinguish it from prior art or to claim a specific discovery related to efficacy in a particular sub-population. The abstracts of both patents also explicitly mention treating IBS in females (’571 Patent, Abstract; ’912 Patent, Abstract).

VI. Other Allegations

  • Indirect Infringement: The complaint alleges that Defendants would actively induce infringement by encouraging, aiding, and abetting the prescription and administration of the ANDA Product for the patented uses (Compl. ¶46, 58, 69). This inducement is allegedly based on the knowledge and specific intent that such uses would infringe Plaintiffs' patent rights (Compl. ¶44, 56, 68).
  • Willful Infringement: The complaint alleges willful infringement based on Defendants' knowledge of the patents-in-suit (Compl. ¶45, 57, 70). This knowledge is allegedly evidenced by Defendants' reference to the patents in their Paragraph IV Notice Letter and the patents' listing in the FDA's Orange Book (Compl. ¶49, 61, 73).

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

  1. A central evidentiary question will be one of compositional identity: Does the Defendants' proposed generic rifaximin product contain one of the specific crystalline polymorphs protected by the claims of the ’196 Patent? The outcome of this largely factual inquiry will be critical to the infringement analysis for that patent.
  2. A key legal issue will be one of induced infringement: Will the language of the Defendants' proposed product label be found to specifically encourage or instruct physicians to prescribe the 550 mg rifaximin tablets in a manner that directly corresponds to the methods claimed in the ’571 and ’912 Patents, particularly with respect to the "female subject" limitation?
  3. Underlying the entire case will be the question of patent validity: Although not detailed in the complaint, Defendants have asserted in their Paragraph IV notice that the patents-in-suit are invalid (Compl. ¶35). A determinative issue for the court will be whether Defendants can meet their burden of proving, by clear and convincing evidence, that the asserted claims are invalid on grounds such as obviousness or lack of adequate written description.