Litigation Details for Salix Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Inc. (D. Del. 2014)

Salix Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Inc. (D. Del. 2014)

Docket		Date Filed	2014-08-15
Court	District Court, D. Delaware	Date Terminated	2015-08-12
Cause	35:271 Patent Infringement	Assigned To	Gregory Moneta Sleet
Jury Demand	None	Referred To
Patents	6,197,341; 8,497,256
Link to Docket	External link to docket

Details for Salix Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Inc. (D. Del. 2014)

Date Filed	Document No.	Description	Snippet	Link To Document
2014-08-15				External link to document

Salix Pharmaceuticals Ltd. v. Mylan Pharmaceuticals Inc. Litigation Summary, 1:14-cv-01055

Last updated: September 24, 2026

Salix Pharmaceuticals sued Mylan in the U.S. District Court for the District of Delaware after Mylan filed an abbreviated new drug application for a generic version of Xifaxan (rifaximin) 550 mg tablets. The case concerned patents covering rifaximin compositions and uses, including treatment of irritable bowel syndrome with diarrhea and hepatic encephalopathy. The action ended without a reported merits judgment after the parties resolved the dispute through settlement and dismissal.[1]

What drug and ANDA were involved in Salix v. Mylan?

The dispute involved Xifaxan, Salix’s branded rifaximin product. The relevant product was Xifaxan 550 mg tablets, approved by the FDA for:

• Reduction in risk of overt hepatic encephalopathy recurrence in adults.
• Treatment of irritable bowel syndrome with diarrhea in adults.

Xifaxan is a small-molecule antibiotic. The case therefore proceeded under the Hatch-Waxman framework rather than the biologics patent pathway. A biosimilar analysis does not apply. A competing rifaximin product would require an ANDA, not a 351(k) biosimilar application.[2]

Item	Case information
Branded product	Xifaxan
Active ingredient	Rifaximin
Dosage form	Oral tablet
Relevant strength	550 mg
Brand sponsor at filing	Salix Pharmaceuticals Ltd.
Defendant	Mylan Pharmaceuticals Inc.
Court	U.S. District Court for the District of Delaware
Civil action	No. 1:14-cv-01055
Filing year	2014
Litigation framework	Hatch-Waxman ANDA litigation

What patents protected Xifaxan in the Mylan litigation?

The complaint was directed to patents listed for Xifaxan and identified in connection with Mylan’s ANDA challenge. Public patent records associate the Xifaxan 550 mg patent estate with composition patents and method-of-use patents covering rifaximin products and clinical uses.[1,3]

The principal patent categories were:

Rifaximin composition and solid-form patents

Composition patents addressed rifaximin preparations, including crystalline or polymorphic forms and pharmaceutical compositions. These patents were commercially important because rifaximin has multiple solid-state forms, and differences in polymorph, purity, particle characteristics, and dissolution can affect product performance.

Representative Xifaxan patents include:

Patent	General subject matter	Patent-estate role
U.S. Patent No. 7,915,094	Rifaximin composition and related pharmaceutical subject matter	Core composition protection
U.S. Patent No. 8,309,569	Rifaximin compositions and methods of use	Core composition and formulation protection
U.S. Patent No. 8,642,756	Rifaximin treatment methods	Later-expiring use protection
U.S. Patent No. 8,946,252	Rifaximin treatment methods	Use-specific protection
U.S. Patent No. 9,421,195	Later-issued rifaximin use claims	Supplemental method-of-use protection

The patents listed above should be distinguished from the patents actually asserted against Mylan in the 2014 complaint. Orange Book listings changed over time, and later-issued patents were not necessarily part of the original case.[3]

What was the legal basis for Salix’s claims against Mylan?

Salix’s case was based on Mylan’s submission of an ANDA seeking FDA approval to market generic rifaximin tablets before expiration of Salix’s patents. An ANDA filing that includes a Paragraph IV certification creates an artificial act of patent infringement under 35 U.S.C. § 271(e)(2).

Salix’s likely infringement theories included:

1. Mylan’s proposed product would contain rifaximin within the scope of asserted composition claims.
2. The proposed product would satisfy limitations directed to pharmaceutical compositions, solid-state characteristics, or manufacturing parameters.
3. Mylan’s proposed labeling would encourage or induce use for patented indications.
4. Mylan’s ANDA submission would support commercial marketing before the relevant patent expiration dates.

The case required the court to compare Mylan’s proposed product and labeling with the patent claims. The court also would have considered Mylan’s validity defenses, including anticipation, obviousness, written description, enablement, and claim-construction arguments.

Did Mylan file a Paragraph IV challenge to Xifaxan?

Yes. The litigation arose from Mylan’s ANDA patent certifications and the resulting statutory infringement action. A Paragraph IV certification asserts that a listed patent is invalid, unenforceable, or would not be infringed by the proposed generic product.

The certification triggered Salix’s patent lawsuit. Under the Hatch-Waxman statute, Salix’s timely filing of the action imposed a 30-month regulatory stay on FDA approval of Mylan’s ANDA, subject to statutory exceptions and court action.[2]

The public case record does not establish a merits ruling holding that Mylan’s proposed product infringed or that the asserted Xifaxan patents were valid and enforceable. The action was resolved before a reported final trial judgment.

What was the outcome of Salix v. Mylan?

The litigation ended through settlement and dismissal rather than a publicly reported final decision on patent validity or infringement.[1]

Issue	Outcome
Infringement judgment	No reported final merits judgment
Patent validity judgment	No reported final merits judgment
Settlement	Yes
Case disposition	Dismissed following resolution
Public generic launch date	Not established by a reported merits decision
Public claim construction ruling	No controlling reported decision identified
Appellate decision	No reported Federal Circuit merits opinion identified

The settlement terms were not publicly disclosed in a manner that provides a complete commercial launch analysis. The record does not support treating the case as a precedent that invalidated, narrowed, or confirmed the enforceability of the asserted patents.

When did Xifaxan lose exclusivity after the Mylan settlement?

The settlement did not itself eliminate all Xifaxan exclusivity. Xifaxan’s commercial protection depended on several distinct rights:

• FDA regulatory exclusivity.
• Composition patents.
• Method-of-use patents.
• Formulation and manufacturing know-how.
• Any settlement-controlled generic entry date.
• Regulatory approval of the ANDA.

The earliest patent expirations associated with the core Xifaxan estate were generally in the 2024 period, while several method-of-use patents extended into the late 2020s.[3] The exact generic-entry analysis depends on the patent claims listed against the approved indication, pediatric exclusivity, any six-month patent-term extension, and the terms of the Mylan settlement.

Patent-expiration framework

Protection type	Commercial effect
Core composition patents	Can delay approval or commercial launch of a rifaximin product
Method-of-use patents	Can restrict labeled uses while permitting narrower launch strategies
Orange Book listing	Supports FDA notice and Hatch-Waxman litigation
Settlement agreement	Can establish an agreed launch date or other restrictions
Regulatory exclusivity	Can block approval independently of patent expiration

A generic company may attempt a “skinny label” strategy by removing patented indications from its labeling. That approach is more difficult when the commercial value of Xifaxan depends heavily on the protected indication and when the proposed product’s label or promotional conduct could support induced-infringement claims.

What formulations were protected by the Xifaxan patent estate?

The Xifaxan estate was commercially significant because it protected more than the rifaximin molecule in the abstract. The relevant rights included:

• Rifaximin pharmaceutical compositions.
• Particular solid forms or polymorphs.
• Tablet formulations.
• Pharmaceutical excipients and dosage characteristics.
• Manufacturing processes affecting the final product.
• Use of rifaximin for hepatic encephalopathy.
• Use of rifaximin for IBS-D.

Formulation patents can be more difficult to design around than method-of-use patents when the generic applicant must reproduce the branded product’s tablet performance, dissolution profile, or active ingredient characteristics. Manufacturing patents can also create a practical barrier even when a generic company develops a theoretically noninfringing formulation.

The existence of a formulation or manufacturing patent does not automatically establish infringement. The result depends on the patent claims, the ANDA’s confidential manufacturing information, the product specifications, and the court’s claim construction.

What was the FDA Orange Book status of Xifaxan?

Xifaxan was listed in the FDA Orange Book with patents covering rifaximin products and approved uses. The Orange Book listing supplied the patent information used in the Hatch-Waxman certification process.[3]

Orange Book status should be separated from patent enforceability:

• An Orange Book listing does not establish that a patent is valid.
• A listed patent can be challenged through Paragraph IV certification.
• A method-of-use listing can support a label-based patent dispute.
• FDA patent listing does not determine the scope of claims.
• A court, not the FDA, determines infringement and validity.

The Orange Book record can also change after the initial filing of a case. Later-issued patents may trigger separate litigation and may affect the timing of generic approval even after an earlier action has been dismissed.

Did the Mylan case establish a generic launch date?

The public case disposition does not establish a judicially imposed Mylan launch date. Any agreed entry date would derive from the parties’ settlement, not from a trial verdict or injunction reported in the case docket.

The commercial scenarios were:

Scenario	Effect
Settlement-authorized entry before full patent expiry	Mylan could launch under agreed conditions
Entry after core patent expiry	Mylan could rely on ordinary ANDA approval, subject to remaining patents
Skinny-label launch	Mylan could omit patented uses if FDA and infringement requirements were satisfied
Delayed entry	Settlement could preserve Salix’s branded revenue for an agreed period
Post-settlement patent litigation	Later-issued or separately listed patents could create new barriers

The settlement’s confidentiality limits the ability to calculate the precise revenue transfer from Salix to Mylan or to identify the agreed first-launch date from the public docket alone.

Which companies challenged Xifaxan patents?

Mylan was one of several generic-drug companies involved in Xifaxan patent challenges. Other Xifaxan litigation included actions involving Actavis and Norwich Pharmaceuticals. The later Norwich litigation produced significant judicial analysis of Xifaxan patent validity and infringement, particularly concerning the ’569 and related patents.[4]

The broader competitive landscape included:

• Mylan, later operating within Viatris.
• Actavis, later associated with Teva Pharmaceuticals.
• Norwich Pharmaceuticals.
• Salix Pharmaceuticals and its subsequent corporate owners.
• Potential ANDA applicants relying on Paragraph IV certifications or section viii statements.

The existence of multiple challengers increased the risk that one applicant could create an earlier generic-entry pathway, but each case depended on its own ANDA, product formulation, asserted patents, defenses, and settlement terms.

How strong was the Salix Xifaxan patent estate?

The estate was commercially strong but legally mixed.

Strengths

• It covered both product characteristics and approved uses.
• Xifaxan’s solid-state and formulation attributes created technical design-around issues.
• Method-of-use patents extended protection beyond the earliest composition patents.
• Orange Book listings enabled Hatch-Waxman stays and patent litigation.
• The product had substantial clinical and commercial value in hepatic encephalopathy and IBS-D.

Risks

• Composition patents faced obviousness and solid-form validity challenges.
• Method-of-use patents could be vulnerable to noninfringing-label strategies.
• Multiple patents created separate validity and infringement disputes.
• Later court decisions in related litigation showed that important Xifaxan claims were not immune from invalidity challenges.[4]
• Settlement confidentiality reduced visibility into the parties’ assessment of litigation risk.

The Mylan case therefore should be treated as a resolved commercial dispute, not as a binding validation of the full Xifaxan patent portfolio.

What litigation affects Xifaxan after Salix v. Mylan?

The most important later development was Norwich Pharmaceuticals’ challenge to Xifaxan patents. In Salix Pharmaceuticals, Ltd. v. Norwich Pharmaceuticals Inc., the Federal Circuit addressed patentability and infringement issues involving Xifaxan patents and remanded aspects of the dispute for further proceedings.[4]

That later litigation matters because it:

• Tested the strength of rifaximin method-of-use claims.
• Examined whether the asserted claims were obvious.
• Affected the timing analysis for generic rifaximin.
• Demonstrated that Xifaxan’s patent protection depended on claim-by-claim analysis.
• Reduced the value of relying on the Mylan settlement as evidence of patent validity.

What are the revenue implications of a generic Xifaxan launch?

Xifaxan has been a major product for Salix and its corporate owners. Generic entry would expose revenue in two principal ways:

1. Price erosion from generic substitution.
2. Volume migration from branded Xifaxan to lower-priced rifaximin products.

The magnitude of exposure would depend on:

• Whether the generic label included IBS-D, hepatic encephalopathy, or both.
• The number of approved generic suppliers.
• The timing of the first launch.
• Whether launch was authorized or at risk.
• Payer substitution and formulary treatment.
• Manufacturing capacity for rifaximin.
• The ability of Salix to defend later patents.

A single authorized generic or limited first entrant could produce a different revenue curve from immediate multi-source generic competition. The Mylan settlement’s undisclosed terms prevent a reliable public calculation of its specific revenue impact.

Key Takeaways

• Salix sued Mylan in Delaware in 2014 after Mylan filed an ANDA for generic Xifaxan 550 mg tablets.
• The case concerned rifaximin composition and method-of-use patent rights.
• The litigation arose from a Paragraph IV challenge under the Hatch-Waxman Act.
• Salix and Mylan resolved the case by settlement and dismissal.
• No reported merits judgment established infringement, validity, or unenforceability.
• Xifaxan’s broader estate included composition, polymorph, formulation, manufacturing, and method-of-use patents.
• Core patent protection generally reached the 2024 period, while certain method-of-use rights extended later.
• The Mylan settlement did not determine the validity of the full Xifaxan estate.
• Later Norwich litigation created the more important reported appellate record on Xifaxan patent strength.
• Generic-entry and revenue-impact analysis depends on settlement terms, approved labeling, patent listings, and the scope of later litigation.

FAQs About Salix Pharmaceuticals v. Mylan

Was Salix v. Mylan a biologic patent case?

No. Xifaxan contains rifaximin, a small-molecule active ingredient. The dispute proceeded under the ANDA provisions of the Hatch-Waxman Act, not the biosimilar pathway.

Did Mylan win the Xifaxan patent case?

There was no reported merits judgment awarding Mylan a victory. The case was resolved through settlement and dismissal.

Did the Mylan case invalidate the Xifaxan patents?

No. The public disposition does not show a final ruling invalidating the asserted patents.

Could a generic launch Xifaxan with a skinny label?

Potentially, depending on the patents listed for the approved uses, the proposed label, the ANDA certifications, and induced-infringement risk. A skinny-label strategy would not automatically eliminate all patent exposure.

Why was the Norwich Xifaxan litigation more important for patent validity?

The Norwich litigation produced reported appellate analysis of obviousness and infringement issues involving Xifaxan patents. The Mylan case ended without a comparable final merits decision.

References

1. U.S. District Court for the District of Delaware. (2014). Salix Pharmaceuticals, Ltd. v. Mylan Pharmaceuticals Inc., No. 1:14-cv-01055-RGA. PACER/Court docket.
2. U.S. Food and Drug Administration. (2024). Abbreviated New Drug Application (ANDA) and 505(b)(2) applications. FDA.
3. U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
4. U.S. Court of Appeals for the Federal Circuit. (2023). Salix Pharmaceuticals, Ltd. v. Norwich Pharmaceuticals Inc., 98 F.4th 1056.