Salix v. Alkem: Xifaxan® Rifaximin ANDA Settled in 65 Days
Salix Pharmaceuticals and co-plaintiffs sued Alkem Laboratories in the District of New Jersey over Paragraph IV ANDA filings challenging six rifaximin 550 mg patents, including US8193196, US11779571, and US11564912. The parties reached a confidential settlement and license agreement, terminating the 30-month regulatory stay, in just 65 days.
Rifaximin ANDA dispute resolves swiftly under confidential licence
Salix Pharmaceuticals, Inc., together with Salix Pharmaceuticals Ltd., Alfasigma S.p.A., and Bausch Health Ireland Limited, filed suit on 10 June 2025 in the District of New Jersey against Alkem Laboratories Ltd., a major Indian generics manufacturer. The complaint alleged infringement of six patents covering Xifaxan® (rifaximin tablets, 550 mg) arising from Alkem’s Paragraph IV ANDA certification — asserting that Alkem’s proposed generic rifaximin 550 mg tablets would infringe US8193196, US8309569, US10456384, US10765667, US11564912, and US11779571.
The case closed on 14 August 2025, just 65 days after filing, via a stipulated dismissal without prejudice anchored to a Confidential Settlement and License Agreement. The court retained jurisdiction to enforce the settlement terms. Notably, the stipulation expressly acknowledges Alkem’s right to maintain its Paragraph IV certifications to all six patents, and the 30-month regulatory stay blocking FDA approval of Alkem’s ANDA was terminated — terms that together strongly suggest a negotiated market-entry date was central to the deal.
The speed of resolution — under three months — is consistent with ANDA litigation patterns in which the economic calculus of a licence often outweighs the cost and risk of full patent adjudication. The financial terms, royalty structure, and any agreed launch date remain entirely confidential. What the public record cannot reveal is whether Alkem secured a near-term launch window or a far-future date, nor the royalty rate — factors that will ultimately determine the competitive significance of this settlement for the rifaximin market.
Filing to Dismissed without Prejudice in 65 days
65 days — substantially faster than the median ANDA patent case, which typically exceeds 2 years at trial
Dismissed without prejudice: what the settlement structure means for both parties
Dismissal without prejudice anchored to a licence
A dismissal without prejudice means neither party obtained a final merits adjudication — claims can theoretically be refiled. In ANDA litigation, however, this structure almost always signals a settlement that is effectively final: the accompanying Confidential Settlement and License Agreement governs future rights, and the court’s retained jurisdiction provides an enforcement backstop. The dismissal format preserves flexibility without indicating litigation weakness by either side.
No merits ruling; licence governsSalix secures confidential licence terms without trial risk
By settling, Salix and its co-plaintiffs avoided the risk of patent invalidity findings across six rifaximin patents — an outcome that would have opened the market to all generic competitors simultaneously. The confidential licence likely provides a controlled entry date for Alkem, preserving Xifaxan® revenue during the exclusivity window. Salix retains all six patents intact, with Paragraph IV certifications acknowledged but not adjudicated as invalid or non-infringed.
Patents intact; controlled generic entryAlkem gains licence and ANDA pathway with stay lifted
The termination of the 30-month regulatory stay is commercially significant for Alkem: FDA can now act on the ANDA without the automatic hold. Alkem also retains its Paragraph IV certifications to all six patents, preserving optionality. The confidential licence grants authorised market entry on agreed terms — avoiding years of costly litigation while securing a defined path to the U.S. rifaximin market, the precise timing of which remains undisclosed.
ANDA stay lifted; authorised entry securedSettlement pattern reinforces Xifaxan® patent fortification strategy
This settlement is consistent with a broader Salix/Bausch Health strategy of resolving Xifaxan® ANDA challenges through negotiated licences rather than full adjudication — preserving the patent estate and managing generic entry timing. For the rifaximin sector, the outcome suggests the six-patent cluster presents sufficient litigation risk to prompt early settlement. Other ANDA filers in the rifaximin space should anticipate a similar enforcement posture from plaintiffs.
Controlled generic entry modelFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Salix Pharmaceuticals, Inc. | Company | Specialty pharma group — holder of Xifaxan® (rifaximin) formulation patents including US8193196Search in Eureka ↗ |
| Defendant | Alkem Laboratories, Ltd. | Company | Alkem Laboratories Ltd. — Indian generics manufacturer seeking FDA ANDA approval for rifaximin 550 mg tabletsSearch 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 | R. Touhey Myer | Attorney | Counsel for Alkem Laboratories, Ltd.Search in Eureka ↗ |
| Defendant law firm | Kratz & Barry, LLP | Law Firm | Representing Alkem Laboratories, Ltd.Search in Eureka ↗ |
| Presiding judge | Judge John F. Murphy (EDPA) | Judge | New Jersey District CourtSearch in Eureka ↗ |
Official order — verbatim text
The stipulated dismissal language is carefully constructed: by preserving Alkem’s Paragraph IV certifications rather than withdrawing them, and by expressly terminating the 30-month stay rather than allowing it to expire, the settlement reflects active negotiation of regulatory mechanics rather than a simple walkaway. The court’s retained jurisdiction to enforce ‘this Stipulation and the parties’ related agreements’ suggests the Settlement Agreement contains substantive ongoing obligations — likely including a licensed launch date — that may require judicial intervention if breached. No merits determination was made on infringement or validity of any of the six patents.
US8193196, US11779571 & US11564912 — rifaximin 550 mg tablet formulations
US8193196B2 (application US11/658702) is among the foundational Xifaxan® formulation patents, covering rifaximin compositions and polymorphic forms that underpin the 550 mg tablet product. US11779571B2 and US11564912B2 represent later-filed continuation-family patents with application dates in 2021 and 2022 respectively, suggesting active patent prosecution to extend exclusivity over rifaximin formulations and dosing methods into the late 2030s. Together with the three additional asserted patents, this cluster spans composition, method-of-use, and formulation domains.
The breadth of six asserted patents across multiple patent families creates a formidable clearance challenge for any rifaximin ANDA filer. Alkem’s decision to settle — preserving rather than litigating the Paragraph IV certifications — is consistent with the litigation economics: invalidating even one patent in a six-patent cluster is insufficient if the remaining patents block market entry independently. For competitors in the antibacterial and gastrointestinal drug space, the Xifaxan® patent estate remains a high-risk area requiring comprehensive FTO analysis before ANDA submission.
Should your team run an FTO against the Xifaxan® rifaximin patent cluster?
Any pharmaceutical company developing or commercialising rifaximin-based formulations — particularly 550 mg oral tablet presentations — must treat the Salix/Alfasigma/Bausch Health patent estate as a priority FTO target. This litigation involved six active U.S. patents, three of which have application dates from 2021–2022, meaning their terms extend well into the 2040s. Generic manufacturers, contract development organisations, and API suppliers to ANDA filers all face potential exposure and should conduct clearance analysis before advancing IND or ANDA filings.
PatSnap Eureka’s FTO Search Agent can map the full rifaximin patent landscape across composition, formulation, polymorphic form, and method-of-use claim dimensions — identifying not only the six patents asserted in this case but the broader continuation families from which future assertions may arise. Eureka’s litigation overlay surfaces prior ANDA enforcement patterns from Salix, Alfasigma, and Bausch Health, enabling your team to model assertion probability and claim scope before committing to a development programme.
Run a freedom-to-operate analysis on US8193196B2 to assess your product’s exposure
Run FTO in Eureka →Related ANDA rifaximin and specialty pharma patent disputes in D.N.J.
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What this case signals for the rifaximin and ANDA patent IP landscape
A 65-day ANDA settlement with a licence and lifted stay reveals a calculated enforcement strategy — not a weak patent position.
Speed of settlement signals strong plaintiff leverage, not weak patents
When ANDA litigation settles in under three months, it typically indicates that the generic challenger assessed the patent cluster as difficult to invalidate quickly — or that the economic terms of a licence were superior to years of uncertainty. Six patents across multiple families raises the invalidity challenge bar considerably.
The lifted 30-month stay resets the FDA approval timeline for Alkem
With the regulatory stay terminated, FDA can now approve Alkem’s rifaximin ANDA on its own scientific timeline. This is a material commercial event: other rifaximin ANDA filers and Salix’s commercial team should model the realistic approval window and its market share implications.
Salix v Alkem — key questions answered
Salix and co-plaintiffs asserted six U.S. patents: US8193196, US8309569, US10456384, US10765667, US11564912, and US11779571 — all covering Xifaxan® (rifaximin tablets, 550 mg) formulations and methods. Three of these (US8193196, US11779571, US11564912) are identified in the court record as the primary asserted patents.
The case settled via a stipulated dismissal without prejudice filed 14 August 2025, anchored to a Confidential Settlement and License Agreement. Key public terms include: (1) no costs or fees awarded; (2) Alkem’s Paragraph IV certifications to all six patents are maintained; (3) the 30-month ANDA regulatory stay is terminated; and (4) the court retains enforcement jurisdiction. Financial terms and any agreed launch date remain confidential.
The 30-month stay under 21 U.S.C. § 355(j)(5)(B)(iii) automatically delays FDA approval of an ANDA when a patent infringement suit is filed. Its termination means FDA can now act on Alkem’s rifaximin 550 mg ANDA on its own regulatory timeline, without waiting for the stay period to expire. This is a prerequisite to any commercial launch and represents a materially positive outcome for Alkem.
Retention of Paragraph IV certifications after settlement is commercially significant: it preserves Alkem’s ANDA status and regulatory pathway without requiring it to convert to a Paragraph III (wait-for-expiry) certification. This structure is consistent with a licence allowing entry on an agreed future date, while keeping the certifications active in case of any future dispute over launch timing or agreement performance.
Salix and co-plaintiffs were represented by Morgan, Lewis & Bockius LLP (attorney Harvey Bartle IV). Alkem Laboratories was represented by Kratz & Barry LLP (attorney R. Touhey Myer). The case was assigned to Judge John F. Murphy (sitting by designation from the Eastern District of Pennsylvania) in the District of New Jersey.
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