Salix v. Mylan: Xifaxan Rifaximin Generic Settled in 190 Days
Salix Pharmaceuticals sued Mylan over generic versions of Xifaxan (rifaximin tablets, 550 mg), asserting 11 Orange Book patents in West Virginia’s Northern District. The parties reached a confidential settlement and license agreement after just 190 days, terminating the 30-month FDA approval stay — allowing Mylan to pursue ANDA approval under agreed terms.
Hatch-Waxman speed settlement preserves Mylan’s ANDA pathway
Salix Pharmaceuticals, Inc. filed suit on 26 March 2025 in the U.S. District Court for the Northern District of West Virginia (Case No. 1:25-cv-00024), alleging that Mylan’s ANDA No. 219687 for rifaximin tablets 550 mg would infringe a portfolio of 11 Orange Book-listed patents covering the branded antibiotic Xifaxan, including US8193196B2, US11779571B2, and US11564912B2, among others tied to NDA Nos. 021361 and 022554.
The case closed on 2 October 2025 — just 190 days after filing — via a Stipulated Dismissal without prejudice and without costs, reflecting a confidential settlement and license agreement between the parties. Critically, the 30-month FDA approval stay triggered by the Paragraph IV certification was expressly terminated by the stipulation, and Mylan retained its Paragraph IV certifications across all listed patents, preserving its right to pursue and obtain FDA final approval for its ANDA product at any time.
A 190-day resolution is notably fast for Hatch-Waxman patent litigation, which typically runs 24–36 months before trial. The swift settlement and express stay termination strongly suggest the parties reached commercially workable license terms — likely including a negotiated market entry date for Mylan’s generic. The financial terms, launch date, and royalty structure remain confidential, meaning the full competitive impact on the rifaximin market is not determinable from the public record.
Filing to Case Settled in 190 days
190 days to resolution — well below the typical Hatch-Waxman district court median of 2–3 years
Confidential license secured: what the Salix–Mylan settlement means for both parties
Dismissed without prejudice — claims can revive if settlement terms are breached
A dismissal without prejudice under the Stipulated Dismissal means no final judgment was entered on the merits. The court retains jurisdiction specifically to enforce the Settlement Agreement and related agreements. If Mylan breaches the license terms, Salix could seek to re-open or file new infringement claims — the ‘without prejudice’ designation preserves that right.
No merits adjudicationSalix secures licence control over Mylan’s generic entry without trial risk
By settling with a Confidential Settlement and License Agreement, Salix avoided the risk of an adverse court ruling that could have invalidated or narrowed its Orange Book patent portfolio. The settlement gives Salix contractual control over when and how Mylan’s generic enters the market, while preserving the enforceability of all 11 listed patents against other potential ANDA filers.
Portfolio enforceability preservedMylan retains Paragraph IV rights and an unblocked FDA pathway
The stipulation expressly confirms Mylan retains its Paragraph IV certification across all listed patents and that the 30-month stay is terminated. This means FDA can grant final ANDA approval at any time — a significant commercial concession. The agreed license likely defines Mylan’s authorised launch date, but that detail remains confidential under the Settlement Agreement.
ANDA pathway unblockedEarly settlement leaves rifaximin competitive landscape partly unresolved
Because no court ruled on the validity or infringement of any of the 11 Orange Book patents, subsequent ANDA filers cannot rely on this outcome as precedent. Each new generic challenger must independently litigate or negotiate. Salix’s broad multi-patent portfolio — spanning formulation, method-of-use, and composition claims — continues to present a high litigation entry cost for would-be generic competitors in the rifaximin space.
No invalidity precedent setFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Salix Pharmaceuticals, Inc. | Company | Branded pharmaceutical company — holder of US8193196B2 and Xifaxan Orange Book patent portfolioSearch in Eureka ↗ |
| Defendant | Mylan, NV | Company | Generic pharmaceutical manufacturer seeking ANDA approval for rifaximin 550 mg tabletsSearch in Eureka ↗ |
| Plaintiff counsel | Daniel R. Higginbotham | Attorney | Counsel for Salix Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Harvey Bartle , IV | Attorney | Counsel for Salix Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Margaret A. McGreal | Attorney | Counsel for Salix Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Maria Doukas | Attorney | Counsel for Salix Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Michael J. Abernathy | Attorney | Counsel for Salix Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff counsel | Wan-Shon Lo | 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 ↗ |
| Plaintiff law firm | Morgan, Lewis & Bockius LLP – IL | Law Firm | Representing Salix Pharmaceuticals, Inc.Search in Eureka ↗ |
| Plaintiff law firm | Thomas Combs & Spann, PLLC | Law Firm | Representing Salix Pharmaceuticals, Inc.Search in Eureka ↗ |
| Defendant counsel | Daniel B. Schwaber | Attorney | Counsel for Mylan, NVSearch in Eureka ↗ |
| Defendant counsel | Deepro R. Mukerjee | Attorney | Counsel for Mylan, NVSearch in Eureka ↗ |
| Defendant counsel | Jillian Schurr-Hendrix | Attorney | Counsel for Mylan, NVSearch in Eureka ↗ |
| Defendant counsel | Lance A. Soderstrom | Attorney | Counsel for Mylan, NVSearch in Eureka ↗ |
| Defendant counsel | Michael B. Hissam | Attorney | Counsel for Mylan, NVSearch in Eureka ↗ |
| Defendant law firm | Hissam Forman Donovan Ritchie PLLC | Law Firm | Representing Mylan, NVSearch in Eureka ↗ |
| Defendant law firm | Katten Muchin Rosenman LLP | Law Firm | Representing Mylan, NVSearch in Eureka ↗ |
| Presiding judge | Judge N/A | Judge | West Virginia Northern District CourtSearch in Eureka ↗ |
Official order — verbatim text
The stipulated verdict confirms settlement under a Confidential Settlement and License Agreement, with dismissal expressly without prejudice and without costs. The operative clauses are commercially significant: termination of the 30-month stay removes the automatic FDA approval barrier, while Mylan’s confirmed right to maintain Paragraph IV certifications across all 11 Orange Book patents preserves its invalidity posture for future proceedings. No merits ruling was issued on infringement or validity, meaning the patent estate emerges from this litigation legally intact and fully enforceable against other generic challengers.
US8193196B2 — Rifaximin polymorphic forms and Xifaxan formulation patents
US8193196B2 (application no. US11/658702) is a foundational patent in Salix’s Xifaxan Orange Book portfolio, covering polymorphic forms of rifaximin — the minimally absorbed antibiotic that underpins Xifaxan’s commercial franchise. Rifaximin’s polymorphism is clinically and commercially significant: specific crystalline forms affect bioavailability, stability, and manufacturability, making polymorph patents a critical line of defence against generic substitution. US11779571B2 and US11564912B2 are later-filed patents (application nos. US17/197561 and US17/892982 respectively) that extend portfolio coverage into more recent formulation and use claim territory.
Xifaxan generated over $1.5 billion in annual U.S. revenue at peak, making its patent estate one of the most commercially contested in branded pharmaceuticals. Salix’s strategy of listing 11 patents across two NDAs creates overlapping layers of protection — polymorph, formulation, and method-of-use — that force any generic challenger to file broad Paragraph IV certifications and face multi-front litigation. The settlement without invalidity findings leaves all 11 patents commercially presumed valid, sustaining Salix’s leverage against future ANDA filers and reinforcing the portfolio’s deterrence value across the rifaximin competitive landscape.
Should you run an FTO against US8193196B2 and the Xifaxan Orange Book portfolio?
Any company developing, manufacturing, or commercialising rifaximin-based formulations — including tablet, granule, or modified-release forms — should treat the Salix Orange Book portfolio as a live risk. The settlement here did not invalidate a single claim. With 11 patents spanning composition, polymorph, formulation, and method-of-use, the freedom-to-operate landscape for rifaximin 550 mg remains highly restricted. R&D teams targeting IBS-D or hepatic encephalopathy indications need targeted FTO analysis before entering clinical development or ANDA preparation.
PatSnap Eureka’s FTO Search Agent can map your rifaximin formulation against the full Salix Orange Book portfolio, flagging claim-by-claim overlap across US8193196B2, US11779571B2, US11564912B2, and the remaining eight listed patents. Eureka’s prior art mining can also surface invalidity arguments — polymorph and formulation patents are frequently vulnerable to prior art challenges — and generate a defensible FTO report tailored to your specific compound and indication.
Run a freedom-to-operate analysis on US8193196B2 to assess your product’s exposure
Run FTO in Eureka →Similar Hatch-Waxman rifaximin and antibiotic patent litigation cases
Explore comparable Hatch-Waxman ANDA patent disputes over rifaximin formulations and branded antibiotic portfolios litigated in U.S. district courts.
What this case signals for the Hatch-Waxman rifaximin IP landscape
A 190-day settlement with stay termination is a commercial signal — not just a procedural one. Here is what it means for IP strategy.
Early settlement with stay termination suggests authorised generic or early-entry deal
When a brand holder agrees to terminate the 30-month stay and acknowledges FDA can approve the ANDA ‘at any time’, this typically signals a negotiated market entry date — often an authorised generic arrangement or a royalty-bearing early launch. IP teams monitoring rifaximin competition should watch for Mylan ANDA approval timing as a proxy for the confidential launch date.
11-patent Orange Book listing creates a high litigation cost barrier for future ANDA filers
Salix’s multi-patent strategy across NDA Nos. 021361 and 022554 means any subsequent ANDA filer faces potential infringement exposure across a diverse claim set. No patent was invalidated here. R&D teams developing rifaximin formulations or method-of-use variants should conduct thorough FTO analysis against the full Orange Book listing before committing resources.
Salix v Mylan — key questions answered
Salix asserted 11 Orange Book-listed patents, including US8193196B2, US11779571B2, and US11564912B2, tied to NDA Nos. 021361 and 022554 for Xifaxan (rifaximin tablets, 550 mg). The patents cover rifaximin polymorphic forms, formulations, and methods of use.
The case settled via a Confidential Settlement and License Agreement. The parties filed a Stipulated Dismissal without prejudice and without costs on 2 October 2025, approximately 190 days after filing. The 30-month FDA approval stay was terminated as part of the settlement.
Under Hatch-Waxman, filing a Paragraph IV ANDA triggers an automatic 30-month stay of FDA approval. Terminating the stay means FDA can grant final approval to Mylan’s ANDA No. 219687 at any time, consistent with the negotiated launch terms in the confidential license agreement.
No. The case settled before any merits ruling on infringement or validity. All 11 Orange Book patents remain legally presumed valid and enforceable. The settlement therefore provides no invalidity precedent for other potential generic challengers of the Xifaxan patent portfolio.
The stipulation expressly preserves Mylan’s Paragraph IV certifications across all listed patents. This suggests Mylan retains the right to pursue post-grant proceedings such as IPR petitions at the USPTO, though any such challenge would be subject to the terms of the confidential Settlement Agreement, which are not public.
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