Salix v. Norwich: Supreme Court Denies Certiorari on Xifaxan Rifaximin Patents
Salix Pharmaceuticals sought U.S. Supreme Court review of invalidity rulings against two patents covering rifaximin 550 mg tablets — the active ingredient in blockbuster gastrointestinal drug Xifaxan. The Court denied the petition in just 96 days, leaving the lower court’s invalidity findings intact.
Xifaxan’s Patent Shield Falls as Supreme Court Refuses to Intervene
Salix Pharmaceuticals, Ltd. filed a petition for a writ of certiorari with the U.S. Supreme Court on September 11, 2024, seeking review of invalidity determinations affecting two patents — US8309569B2 and US10765667B2 — covering rifaximin 550 mg tablets marketed under the brand name Xifaxan. Norwich Pharmaceuticals, a generic drug challenger, had successfully argued invalidity of these patents before the lower tribunals. The case arose from an Abbreviated New Drug Application (ANDA) dispute, a standard mechanism through which generic manufacturers challenge branded pharmaceutical patents.
The Supreme Court denied the petition on December 16, 2024, terminating the case in 96 days. A denial of certiorari carries no precedential weight on the merits — the Court offers no reasoning and does not endorse the lower court’s analysis — but it is conclusive in practical effect: Salix exhausted its appellate options at this level, and the invalidity findings against both patents remain operative. Norwich’s path toward a generic rifaximin 550 mg product is materially clearer as a result.
The sub-100-day resolution is consistent with standard Supreme Court cert petition timelines and does not suggest any unusual procedural complexity. What remains unknown from the public record is whether Salix retains any remaining Orange Book-listed patents capable of blocking Norwich’s ANDA approval, or whether settlement discussions accompanied the petition. The denial effectively forecloses further federal appellate review of the invalidity question as litigated in this proceeding.
Filing to Petition Dismissed in 96 days
96-day petition lifecycle — Supreme Court cert petitions typically resolve within 90–120 days
Supreme Court denies cert: what the ruling means for both parties
Certiorari denied: no merits ruling, but finality achieved
A denial of certiorari means the Supreme Court declined to hear the case — it is not an endorsement or rejection of the lower court’s reasoning. The Court grants cert in fewer than 2% of petitions. However, denial is final at the federal level: Salix cannot re-appeal the invalidity findings from this proceeding. The lower tribunal’s patent invalidity determination stands as the operative legal outcome.
Petition denied — lower ruling intactSalix loses its last federal appellate avenue for these patents
With certiorari denied, Salix can no longer challenge the invalidity of US8309569B2 and US10765667B2 through federal courts in this proceeding. The commercial significance is substantial: Xifaxan has historically been among Salix’s highest-revenue products. Loss of patent protection on these formulation patents typically accelerates generic market entry and compresses branded pricing power significantly.
Appellate options exhaustedNorwich clears a critical patent hurdle toward generic market entry
For Norwich Pharmaceuticals, the denial removes a significant legal obstacle. With the invalidity findings on both asserted patents now undisturbed, Norwich’s ANDA for a rifaximin 550 mg generic is no longer blocked by these two patents. Regulatory approval from the FDA and any remaining Orange Book patent barriers would determine the precise timing of market entry, but the litigation risk from US8309569B2 and US10765667B2 is effectively extinguished.
Generic pathway materially clearerRifaximin generic competition now closer — sector watches carefully
The denial signals to the pharmaceutical sector that these rifaximin formulation patents will not receive Supreme Court rescue. Brand-side competitors and generic manufacturers in the gastrointestinal drug space should monitor FDA approval timelines for Norwich’s ANDA and any surviving Orange Book listings. The outcome may also embolden other generic challengers to mount ANDA-based invalidity actions against Salix’s remaining rifaximin IP estate.
Generic GI drug competition acceleratesFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Salix Pharmaceuticals, Ltd | Company | Branded pharmaceutical company — holder of US8309569B2 and US10765667B2 (Xifaxan/rifaximin)Search in Eureka ↗ |
| Defendant | Norwich Pharmaceuticals | Individual | Generic pharmaceutical manufacturer challenging Xifaxan rifaximin 550 mg tablet patents via ANDASearch in Eureka ↗ |
| Plaintiff counsel | William Robert Peterson | Attorney | Counsel for Salix Pharmaceuticals, LtdSearch in Eureka ↗ |
| Plaintiff law firm | Morgan, Lewis & Bockius, LLP | Law Firm | Representing Salix Pharmaceuticals, LtdSearch in Eureka ↗ |
| Defendant counsel | Thomas Knut Hedemann | Attorney | Counsel for Norwich PharmaceuticalsSearch in Eureka ↗ |
| Defendant law firm | Axinn Veltrop & Harkrider, LLP | Law Firm | Representing Norwich PharmaceuticalsSearch in Eureka ↗ |
| Presiding judge | Judge N/A | Judge | U.S. Supreme CourtSearch in Eureka ↗ |
Official order — verbatim text
The Supreme Court’s ‘Petition DENIED’ disposition carries no articulated reasoning and establishes no precedent on the validity of the rifaximin patents at issue. At the certiorari stage, the Court applies a discretionary standard — typically reserving review for circuit splits or questions of exceptional national importance. The denial suggests the Court did not find either criterion met here. For the parties, the practical effect is equivalent to affirmance: the invalidity findings below are final and binding in this proceeding.
US8309569B2 & US10765667B2 — Rifaximin 550 mg Tablet Formulations (Xifaxan)
US8309569B2 (application US12/393979) and US10765667B2 (application US16/738392) both protect aspects of rifaximin 550 mg tablet technology underlying Xifaxan, a broad-spectrum gastrointestinal antibiotic used to treat irritable bowel syndrome with diarrhea (IBS-D) and hepatic encephalopathy. The patents sit within a broader Salix rifaximin IP estate designed to extend market exclusivity beyond the core compound patent through formulation and method-of-use claims — a common lifecycle management strategy in branded pharmaceuticals.
The strategic significance of these two patents lies in their role as ANDA-blocking assets in the Orange Book. Xifaxan has been a multi-billion-dollar revenue contributor for Salix and its parent Bausch Health. Invalidation removes what were likely among the later-expiring barriers to generic rifaximin entry, compressing the effective exclusivity window. For competitors in the GI antibiotic and microbiome therapy space, the outcome suggests that rifaximin formulation claims of this type face elevated invalidity risk under current Federal Circuit doctrine.
Should you run an FTO analysis against US8309569B2 and US10765667B2?
Any company developing, manufacturing, or commercialising rifaximin 550 mg oral tablet products — including generic ANDA applicants, 505(b)(2) applicants, or novel formulation developers — should conduct a freedom-to-operate analysis against Salix’s full rifaximin patent portfolio. While US8309569B2 and US10765667B2 have been found invalid in proceedings involving Norwich, that finding binds only the parties to that litigation. Third parties are not automatically shielded and must independently assess their exposure.
PatSnap Eureka’s FTO Search Agent enables R&D and IP teams to map the entire Salix rifaximin patent landscape in minutes — identifying surviving Orange Book listings, continuation applications, and method-of-use claims that may still pose enforcement risk. Eureka cross-references invalidation history and litigation outcomes to flag patents with heightened or reduced risk profiles, giving your team a defensible, evidence-based FTO foundation before filing or commercial launch.
Run a freedom-to-operate analysis on US8309569B2 to assess your product’s exposure
Run FTO in Eureka →Similar pharmaceutical patent invalidity cases at the Supreme Court
Explore comparable ANDA-driven pharmaceutical patent invalidity cases where certiorari was sought before the U.S. Supreme Court in the District of Columbia.
What this case signals for the pharmaceutical patent IP landscape
The Supreme Court’s swift denial crystallises the litigation risk profile for branded rifaximin patents and sets a marker for ANDA challengers sector-wide.
Cert denial does not kill the patent — but it ends this fight
Practitioners should note that a cert denial leaves US8309569B2 and US10765667B2 technically listed as issued patents, but the invalidity findings are binding on the parties. Salix cannot enforce these patents against Norwich in a subsequent action on the same invalidity grounds. Monitor whether Salix holds additional Orange Book-listed patents not reached in this proceeding.
ANDA litigation remains the primary battleground for blockbuster GI drugs
This case reinforces that Hatch-Waxman ANDA challenges continue to be the dominant mechanism for dismantling branded pharmaceutical patent portfolios. Generic challengers willing to invest in invalidity litigation through the Federal Circuit and into certiorari petitions extract maximum leverage. Brand holders must ensure their patent estates are layered with method-of-use and formulation claims across multiple patents.
Salix v Norwich — key questions answered
The cert denial in Case No. 24-292 means the Supreme Court declined to review the invalidity findings against US8309569B2 and US10765667B2. It carries no merits reasoning but is final: Salix cannot re-litigate those invalidity determinations against Norwich in federal court. The patents remain issued but are unenforceable against Norwich based on the binding invalidity findings.
Salix’s petition involved two patents: US8309569B2 (application no. US12/393979) and US10765667B2 (application no. US16/738392), both covering rifaximin 550 mg tablet formulations sold under the brand name Xifaxan. The patents are Orange Book-listed assets that Salix used to block Norwich’s ANDA for a generic rifaximin 550 mg product.
Not directly. A cert denial binds only the parties — Salix and Norwich. Other generic manufacturers must independently assess their exposure to US8309569B2 and US10765667B2, as the invalidity finding does not automatically invalidate the patents as to third parties. However, the reasoning from the lower tribunal may be persuasive in subsequent ANDA litigations involving the same patents.
The petition was filed on September 11, 2024, and denied on December 16, 2024 — a period of 96 days. This is consistent with typical Supreme Court cert petition timelines, which generally fall within a 90–120 day window. The speed of resolution does not suggest any unusual procedural treatment of the petition.
With invalidity findings intact on both asserted patents, Norwich’s ANDA for a generic rifaximin 550 mg tablet faces reduced patent litigation risk. For Salix and its parent Bausch Health, this outcome narrows the IP barriers protecting Xifaxan’s market exclusivity, potentially accelerating generic competition. The full commercial impact depends on remaining Orange Book-listed patents and FDA approval timing for Norwich’s ANDA.
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