Salix v. Carnegie Pharmaceuticals: Xifaxan Rifaximin Patent Settlement
Salix Pharmaceuticals, Bausch Health Ireland, and Alfasigma filed a Hatch-Waxman infringement action in New Jersey District Court against Carnegie Pharmaceuticals over six rifaximin patents protecting Xifaxan 550 mg. The parties reached a confidential settlement after 228 days, terminating the 30-month ANDA stay and leaving Carnegie’s Paragraph IV certifications intact.
Hatch-Waxman rifaximin battle ends in confidential license deal
Filed on 7 November 2024 in the District of New Jersey, this Hatch-Waxman patent infringement action was brought by Salix Pharmaceuticals, Inc., Salix Pharmaceuticals, Ltd., Bausch Health Ireland Limited, and Alfasigma S.p.A. (collectively the brand-side plaintiffs) against Carnegie Pharmaceuticals LLC and Carnegie Pharma Limited. The suit arose from Carnegie’s ANDA filing with Paragraph IV certifications challenging six rifaximin patents, including US8193196B2, US11564912B2, and US11779571B2, all protecting Xifaxan (rifaximin tablets, 550 mg).
The case closed on 23 June 2025 — just 228 days after filing — pursuant to a Confidential Settlement and License Agreement. All complaints, counterclaims, and affirmative defenses were dismissed without prejudice, with no costs awarded to either side. Critically, the 30-month ANDA stay under 21 U.S.C. § 355(j)(5)(B)(iii) was explicitly terminated by stipulation, signalling that Carnegie received a negotiated entry date rather than continued blocking.
A resolution in under eight months is notably swift for a multi-patent Hatch-Waxman case, suggesting the parties found a commercially workable licence structure early in discovery. The confidential nature of the settlement means the specific launch date granted to Carnegie, royalty terms, and any co-promotion arrangements remain unknown from the public record. The court’s retained jurisdiction to enforce the settlement agreement suggests ongoing compliance obligations for both parties.
Filing to Dismissed without Prejudice in 228 days
228 days — faster than the typical Hatch-Waxman district court median of ~2–3 years
Dismissed without prejudice: what the settlement means for both parties
Dismissed without prejudice under a confidential licence
A dismissal without prejudice means claims are withdrawn without a final merits ruling, preserving the theoretical right to refile. Here the dismissal is paired with a Confidential Settlement and License Agreement, so in practice the parties have resolved the dispute contractually. The court’s retained jurisdiction to enforce the agreement gives plaintiffs an enforcement lever without requiring a new lawsuit if Carnegie breaches the settlement terms.
No merits adjudicationBrand side secures licence terms without litigating validity
Salix and co-plaintiffs avoided the risk of an adverse validity or non-infringement ruling on six rifaximin patents. A negotiated licence preserves royalty income and controls the timing of any generic entry. The without-prejudice dismissal technically leaves the patents unchallenged on the merits, though Carnegie retains its Paragraph IV certifications — meaning the patents remain open to future challenge by other ANDA filers.
Patents unchallenged on meritsCarnegie retains Paragraph IV certifications and gains a negotiated entry date
Carnegie’s right to maintain its Paragraph IV certifications to all six patents is explicitly preserved in the stipulation, a standard provision that allows the generic to market under the licence without withdrawing its patent challenge posture. The termination of the 30-month ANDA stay strongly suggests Carnegie secured an agreed-upon launch date, a commercially significant concession from the brand side. Specific launch timing remains confidential.
30-month stay terminatedRifaximin IP landscape remains contested for future ANDA filers
Because no court ruled on the validity or scope of US8193196B2, US11564912B2, or US11779571B2, the patents retain their presumption of validity against subsequent generic challengers. Other ANDA filers for rifaximin 550 mg cannot rely on this case as precedent. The settlement also suggests the brand coalition views the patent estate as defensible enough to licence rather than litigate to judgment — a signal that may deter near-term generic competition from other parties.
Patents presumed validFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Salix Pharmaceuticals, Inc. | Company | Pharmaceutical brand and licensing group — holder of US8193196B2 (rifaximin, Xifaxan 550 mg)Search in Eureka ↗ |
| Co-Plaintiff | Bausch Health Ireland, Ltd. | Company | Search in Eureka ↗ |
| Co-Plaintiff | Salix Pharmaceuticals, Ltd. | Company | Search in Eureka ↗ |
| Co-Plaintiff | Alfasigma, S.p.A. | Individual | Search in Eureka ↗ |
| Defendant | CARNEGIE PHARMACEUTICALS, LLC | Company | Generic pharmaceutical company pursuing ANDA approval for rifaximin 550 mg tabletsSearch in Eureka ↗ |
| Co-Defendant | CARNEGIE PHARMA LIMITED | Individual | Search in Eureka ↗ |
| Plaintiff counsel | Harvey Bartle , IV | Attorney | Counsel for Salix Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Morgan, Lewis & Bockius, LLP | Law Firm | Representing Salix Pharmaceuticals, Inc.Search in Eureka ↗ |
| Defendant counsel | Dmitry V. Shelhoff | Attorney | Counsel for CARNEGIE PHARMACEUTICALS, LLCSearch in Eureka ↗ |
| Defendant counsel | KENNETH CANFIELD | Attorney | Counsel for CARNEGIE PHARMACEUTICALS, LLCSearch in Eureka ↗ |
| Defendant law firm | SHELHOFF CANFIELD & CHIN LLC | Law Firm | Representing CARNEGIE PHARMACEUTICALS, LLCSearch in Eureka ↗ |
| Presiding judge | Judge John F. Murphy (EDPA) | Judge | New Jersey District CourtSearch in Eureka ↗ |
Official order — verbatim text
The stipulated dismissal without prejudice is explicitly conditioned on a Confidential Settlement and License Agreement, distinguishing it from a simple abandonment. The preservation of Carnegie’s Paragraph IV certifications across all six patents — combined with termination of the 30-month ANDA stay — indicates a structured commercial resolution rather than a concession of infringement. No court assessed the validity or enforceability of the rifaximin patents, leaving the brand-side portfolio legally intact against future challengers.
US8193196B2 — rifaximin polymorph formulations for Xifaxan 550 mg
US8193196B2, filed under application US11/658702, protects rifaximin polymorph compositions central to Xifaxan (rifaximin tablets, 550 mg) — a minimally absorbed oral antibiotic approved for hepatic encephalopathy reduction and irritable bowel syndrome with diarrhea. The patent covers specific crystalline forms of rifaximin that underpin the commercial product’s bioavailability and stability profile. Co-asserted patents US11564912B2 (appl. US17/892982) and US11779571B2 (appl. US17/197561) represent later-filing portfolio extensions, suggesting a layered exclusivity strategy across formulation, method, and composition claims.
Rifaximin is a high-revenue gastrointestinal antibiotic with significant generic competition risk. The multi-plaintiff structure — Salix, Bausch Health Ireland, and Alfasigma as originator — reflects a complex licensing and co-ownership arrangement that is common where a compound has been sublicensed across jurisdictions. The breadth of the six-patent portfolio asserted against Carnegie’s single ANDA signals that the brand coalition is willing to deploy its full patent estate to negotiate favourable licence terms, raising the cost of generic entry for any filer that cannot reach a settlement.
Should you run an FTO against US8193196B2 and the Xifaxan rifaximin portfolio?
Any company developing rifaximin formulations, generic Xifaxan tablets, or related minimally-absorbed oral antibiotic compositions should treat this patent family as a primary FTO priority. The six patents named in this case span polymorph, formulation, and method-of-use claims, creating overlapping exclusivity that is difficult to design around without a freedom-to-operate analysis. ANDA filers, API manufacturers supplying rifaximin, and companies developing next-generation gut-selective antibiotics are all within the potential enforcement perimeter.
PatSnap Eureka’s FTO Search Agent can map the full claim scope of US8193196B2, US11564912B2, and US11779571B2 against your product pipeline, identify prior art relevant to validity challenges, and flag related applications still in prosecution. Given the retained Paragraph IV certifications and the confidential licence in this case, understanding which claims remain commercially uncontested is essential before filing an ANDA or committing R&D resources to rifaximin-adjacent products.
Run a freedom-to-operate analysis on US8193196B2 to assess your product’s exposure
Run FTO in Eureka →Similar Hatch-Waxman rifaximin and GI antibiotic patent cases
Explore Hatch-Waxman ANDA infringement cases involving rifaximin and gastrointestinal antibiotic formulation patents in New Jersey District Court and comparable venues.
What this case signals for the Hatch-Waxman rifaximin IP landscape
Early settlement with retained Paragraph IV certifications is a recurring pattern in Hatch-Waxman cases where brand portfolios are deep and both sides face litigation risk.
Early settlement signals brand confidence in the rifaximin patent estate
Resolving in 228 days — before significant claim construction or expert discovery — suggests Salix and co-plaintiffs assessed their portfolio as strong enough to offer a licence on acceptable terms rather than risk an adverse ruling. Competitors planning ANDA filings should not interpret this settlement as a vulnerability signal; no validity finding was made.
30-month stay termination is the key commercial tell
The explicit termination of the 30-month ANDA stay is the clearest indicator that Carnegie received a negotiated entry date. For brand-side companies, this underscores that ANDA settlements routinely trade stay duration for royalty certainty. For generics, it confirms that early settlement can unlock ANDA approval timelines blocked by automatic stays.
Salix v CARNEGIE — key questions answered
The complaint asserted US8193196B2, US11779571B2, and US11564912B2 as the three patents identified in the case record. The stipulated dismissal references six patents total — also including US8309569, US10456384, and US10765667 — across which Carnegie maintained Paragraph IV certifications.
Dismissal without prejudice means no court ruled on the validity or infringement of the rifaximin patents. They retain their presumption of validity and can be asserted against future ANDA filers. The patents are not weakened by this outcome — the dismissal reflects a negotiated licence, not a concession by either side on the merits.
Yes. The stipulation of dismissal explicitly terminates the 30-month stay under 21 U.S.C. § 355(j)(5)(B)(iii) with respect to Carnegie’s ANDA. This is a significant commercial term, typically indicating that the parties agreed on a specific future launch date for Carnegie’s generic rifaximin product, though the exact date is confidential.
The multi-plaintiff structure reflects the complex licensing and co-ownership arrangements common in branded pharmaceutical products with international origins. Alfasigma S.p.A. is the Italian originator of rifaximin; Salix holds US commercialisation rights; Bausch Health Ireland is a related licensing entity. All rights-holders typically join Hatch-Waxman actions to establish standing across all asserted patents.
Carnegie’s retention of Paragraph IV certifications to all six patents means those patents remain formally challenged. However, because the case settled without a court ruling, no other generic filer can rely on Carnegie’s certifications as precedent or claim a first-filer exclusivity benefit from this action. Each future ANDA challenger must independently litigate or negotiate around the same patent estate.
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