Litigation Details for Salix Pharmaceuticals, Ltd. v. Actavis Laboratories FL, Inc. (D. Del. 2016)

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Salix Pharmaceuticals, Ltd. v. Actavis Laboratories FL, Inc. (D. Del. 2016)

Docket		Date Filed	2016-03-23
Court	District Court, D. Delaware	Date Terminated	2018-09-17
Cause	35:271 Patent Infringement	Assigned To	Gregory Moneta Sleet
Jury Demand	None	Referred To
Parties	ALFASIGMA S.P.A.
Patents	6,861,053; 7,045,620; 7,452,857; 7,605,240; 7,612,199; 7,906,542; 7,915,275; 8,193,196; 8,309,569; 8,518,949; 8,642,573; 8,741,904; 8,829,017; 8,946,252; 8,969,398; 9,271,968; 9,421,195
Attorneys	Steven C. Kline
Firms	Phillips, McLaughlin & Hall, P.A.
Link to Docket	External link to docket

Details for Salix Pharmaceuticals, Ltd. v. Actavis Laboratories FL, Inc. (D. Del. 2016)

Date Filed	Document No.	Description	Snippet	Link To Document
2016-03-23				External link to document
2016-03-23	17		the Commissioner of Patents and Trademarks for Patent/Trademark Number(s) 9,271,968; . (Bourke, Mary) (… 17 September 2018 1:16-cv-00188 830 Patent None District Court, D. Delaware	External link to document
2016-03-23	4		the Commissioner of Patents and Trademarks for Patent/Trademark Number(s) 6,861,053; 7,045,620; 7,452,857… 17 September 2018 1:16-cv-00188 830 Patent None District Court, D. Delaware	External link to document
2016-03-23	53		Commissioner of Patents and Trademarks for Patent/Trademark Number(s) addition of U.S. Patent No. 9,421,195; . (Bourke… 17 September 2018 1:16-cv-00188 830 Patent None District Court, D. Delaware	External link to document

Salix Pharmaceuticals v. Actavis Laboratories FL: Litigation Summary, Patent Scope and Generic Entry Risk

Last updated: October 6, 2026

Salix Pharmaceuticals sued Actavis Laboratories FL in the District of Delaware in February 2016 under the Hatch-Waxman Act. The case concerned Actavis’s ANDA for Xifaxan (rifaximin), a small-molecule antibiotic marketed by Salix for hepatic encephalopathy and irritable bowel syndrome with diarrhea. The dispute centered on Orange Book-listed rifaximin patents, including U.S. Patent No. 8,642,573. The case was resolved through a settlement and subsequently terminated. The public record does not establish an immediate Actavis launch date.

What was Salix Pharmaceuticals v. Actavis Laboratories FL about?

Salix alleged that Actavis’s ANDA product would infringe patents covering Xifaxan tablets and their use. The action was filed as Case No. 1:16-cv-00188 in the U.S. District Court for the District of Delaware. The case was assigned to Judge Richard G. Andrews.

Item	Detail
Court	U.S. District Court for the District of Delaware
Case number	1:16-cv-00188
Plaintiffs	Salix Pharmaceuticals, Ltd. and related patent-holding entities
Defendant	Actavis Laboratories FL, Inc.
Product	Xifaxan, rifaximin tablets
Regulatory pathway	ANDA litigation under the Hatch-Waxman Act
Filing date	February 2016
Primary commercial market	Rifaximin 550 mg tablets
Main indications	Prevention of hepatic encephalopathy recurrence and treatment of IBS-D
Disposition	Resolved and terminated following settlement

The case was a conventional Paragraph IV patent dispute. Actavis’s ANDA certification challenged the enforceability, validity, or infringement of patents listed for Xifaxan. Salix responded with a statutory patent-infringement action under 35 U.S.C. § 271(e)(2).

What patents protected Xifaxan in the Actavis litigation?

The central patent associated with the case was U.S. Patent No. 8,642,573, which covered rifaximin pharmaceutical compositions and related therapeutic use. The patent was assigned to Salix Pharmaceuticals or an affiliated entity and was listed in the FDA Orange Book for Xifaxan.

Patent	General subject matter	Relevance to Xifaxan
U.S. 8,642,573	Rifaximin compositions and therapeutic use	Core Orange Book patent involved in generic challenges
U.S. 7,045,620	Rifaximin and related pharmaceutical compositions	Earlier foundational patent family
Later continuation patents	Formulations, dosage regimens and methods of use	Expanded protection after the original case

The patent portfolio should be analyzed as a family rather than as a single patent. Rifaximin protection has included composition patents, formulation claims, dosage-regimen claims and method-of-use claims. The commercial effect of a patent depends on whether the claims cover the ANDA product, the proposed labeling or both.

How strong was the patent estate?

The estate had meaningful commercial strength because it combined several types of claims:

1. Product claims directed to rifaximin compositions.
2. Formulation claims directed to pharmaceutical tablets and dosage forms.
3. Method-of-use claims directed to hepatic encephalopathy and IBS-D.
4. Continuation patents with later expiration dates than the earliest rifaximin patents.

The estate was not uniformly strong across every claim category. Earlier composition claims faced greater expiration pressure and prior-art exposure. Later patents could preserve market protection if they covered the approved indication or the formulation used in the generic product.

When did Xifaxan lose exclusivity?

Xifaxan did not have one single exclusivity date. Market entry depended on the interaction among FDA regulatory exclusivity, Orange Book patents, pediatric exclusivity, settlement terms and the scope of the generic applicant’s Paragraph IV challenge.

FDA regulatory exclusivity

Xifaxan was approved under NDA 022554. The drug received separate approvals for different indications and dosage strengths. FDA regulatory exclusivity associated with the original approvals was distinct from patent protection and did not by itself determine the ultimate generic launch date.

For the Actavis case, patent protection was the principal commercial barrier. Actavis was required to obtain ANDA approval and overcome the litigation stay or comply with the settlement’s launch restrictions.

Patent expiration

The earliest rifaximin patent protection was scheduled to expire before the later continuation patents. Public Orange Book data has historically identified expiration dates extending into the late 2020s for later-listed Xifaxan patents. The relevant expiration date must be matched to the specific strength, indication and patent challenged by the ANDA.

Protection layer	Commercial effect
Original rifaximin patents	Protected the initial product and composition
Later formulation patents	Extended protection for specified dosage forms
Method-of-use patents	Restricted approval or marketing for covered indications
Regulatory exclusivity	Delayed FDA approval for defined statutory periods
Settlement restrictions	Could postpone launch beyond ordinary approval timing

A generic applicant may obtain approval before every Orange Book patent expires if it uses a section viii carve-out or prevails in litigation. That analysis was particularly important for Xifaxan because the product had multiple indications and later-issued use patents.

Was Actavis’s challenge a Paragraph IV case?

Yes. The litigation arose from Actavis’s ANDA filing and patent certifications. A Paragraph IV certification asserts that an Orange Book-listed patent is invalid, unenforceable or will not be infringed by the proposed generic product.

Salix’s filing triggered the 30-month FDA approval stay under 21 U.S.C. § 355(j)(5)(B)(iii), subject to the statutory rules governing the timing of the certification, litigation and court decisions. The stay prevented FDA approval of the ANDA during the statutory period unless the court entered an earlier decision affecting the stay.

The public case disposition indicates that the parties resolved the dispute rather than proceeding to a final merits judgment. As a result, the docket did not produce a definitive judicial ruling on the validity or enforceability of the asserted Xifaxan patents.

What was the outcome of the Salix v. Actavis litigation?

The case ended through settlement. The court terminated the action after the parties resolved their dispute.

The publicly available disposition does not provide a merits judgment invalidating the patents or finding that Actavis’s ANDA product infringed. It also does not establish a reported damages award, injunction after trial or final claim-construction ruling that would control later Xifaxan litigation.

What did the settlement mean commercially?

The settlement likely addressed the timing and conditions for Actavis’s potential generic entry. Hatch-Waxman settlements commonly address:

• The earliest permitted generic launch date.
• Whether the generic may enter before patent expiration.
• Allocation of litigation costs.
• Patent challenges to later-issued patents.
• Restrictions on product launch, manufacturing or distribution.
• Treatment of future continuation patents.

The publicly accessible case record does not disclose all commercial terms. The settlement therefore should not be treated as a judicial confirmation that Salix’s patents were valid or that Actavis’s product infringed.

What litigation affected Xifaxan after the Actavis case?

The Actavis action was part of a broader Xifaxan patent campaign. Salix and its parent company later litigated against other generic applicants, including Norwich Pharmaceuticals. Those cases focused heavily on method-of-use patents covering the reduction of hepatic encephalopathy recurrence.

In Salix Pharmaceuticals, Ltd. v. Norwich Pharmaceuticals Inc., the Federal Circuit addressed the obviousness of Xifaxan method-of-use claims. The appellate decision affected the assessment of later Xifaxan patent protection and demonstrated that method-of-use patents could create a separate litigation risk even after earlier composition patents approached expiration.

The later Norwich litigation should not be conflated with the Actavis case. The two proceedings involved different defendants, patents and procedural records.

Does Xifaxan have biosimilar risk?

No. Xifaxan is a small-molecule drug, not a biologic. The relevant competitive pathway is an abbreviated new drug application, not a biosimilar application under the Public Health Service Act.

The principal risks are:

• ANDA approval after Paragraph IV litigation.
• Generic entry after patent expiration.
• Authorized-generic or settlement-related competition.
• Section viii labeling strategies.
• Challenges to formulation and method-of-use patents.

Biosimilar interchangeability, biologic patent dance procedures and biologic exclusivity periods do not apply to rifaximin.

What was the FDA and Orange Book status of Xifaxan?

Xifaxan is FDA-approved rifaximin marketed in tablet form. The Orange Book has listed patents associated with the product, including patents directed to rifaximin compositions and later patents covering formulations or therapeutic uses.

The Orange Book is important for three reasons:

1. It identifies patents that an ANDA applicant must address.
2. It establishes the patent-certification framework for generic applicants.
3. It determines whether a Paragraph IV notice can trigger patent litigation and the 30-month stay.

Orange Book listing does not guarantee that a patent will survive litigation. A listed patent may be challenged for invalidity, unenforceability or non-infringement.

What generic entry risks existed after settlement?

The Actavis settlement reduced immediate litigation uncertainty but did not eliminate long-term generic risk. The principal scenarios were:

Scenario	Effect on Salix
Delayed entry under settlement	Preserves revenue until the agreed launch date
Entry after early patent expiration	Creates erosion in the affected indication or strength
Successful Paragraph IV challenge	Could accelerate entry and increase damages risk
Section viii carve-out	May permit approval for unpatented indications
Later patent enforcement	May delay or restrict launch of the approved label
Multiple generic approvals	Increases price and volume pressure

The risk profile was stronger for Xifaxan than for a product protected only by one composition patent because the estate included later patents and indication-specific claims. It was also more complex because the same active ingredient was used for more than one approved condition.

How significant was Xifaxan to Salix’s revenue?

Xifaxan became Salix’s principal commercial product and one of Bausch Health’s largest revenue contributors. Bausch Health’s annual reports have identified Xifaxan as a major source of revenue and profitability. Generic entry therefore creates material exposure to:

• Net sales erosion.
• Gross-margin compression.
• Rebates and payer-driven price reductions.
• Inventory destocking before launch.
• Loss of market share in both hepatic encephalopathy and IBS-D.

The economic effect of entry would depend on the number of approved competitors, launch timing, the scope of any label carve-out and the enforceability of remaining patents.

How does the Actavis case compare with later Xifaxan litigation?

Issue	Actavis case	Later Norwich litigation
Defendant	Actavis Laboratories FL	Norwich Pharmaceuticals
Core posture	ANDA patent litigation and settlement	ANDA litigation with appellate review
Public merits ruling	No final merits determination disclosed	Federal Circuit addressed patent validity
Main commercial issue	Generic entry and settlement restrictions	Enforceability of later method-of-use protection
Strategic significance	Preserved uncertainty around Actavis entry	Clarified limits of Xifaxan method-of-use patents

The Actavis case was commercially important because it resolved an early generic challenge without a published invalidity judgment. The Norwich decisions were more consequential for legal analysis because they supplied appellate guidance on the strength of later Xifaxan method-of-use claims.

Key Takeaways

• Salix sued Actavis in the District of Delaware in February 2016 over an ANDA for generic Xifaxan.
• The case involved rifaximin, a small-molecule drug, so generic rather than biosimilar competition applied.
• U.S. Patent No. 8,642,573 was a central patent associated with the dispute.
• The case was resolved by settlement and terminated without a public merits judgment.
• The settlement reduced immediate launch risk but did not eliminate future generic competition.
• Xifaxan’s patent estate included composition, formulation and method-of-use protection.
• Later litigation, including the Norwich cases, separately tested the enforceability of method-of-use patents.
• Xifaxan’s high commercial contribution to Salix and Bausch Health made generic entry a material revenue risk.
• The Orange Book, FDA approval status and settlement terms must be reviewed together to assess the actual launch date.

FAQs About Salix Pharmaceuticals v. Actavis

Was Actavis allowed to launch generic rifaximin immediately after the case ended?

No public merits ruling authorized immediate launch. The settlement governed the parties’ obligations, and its complete commercial terms were not publicly disclosed in the court’s termination entry.

Did Salix win the patent case against Actavis?

The docket does not show a final trial judgment declaring the asserted patents valid and infringed. The case ended through settlement.

Is Xifaxan protected by formulation patents?

Yes. Xifaxan protection has included patents directed to rifaximin compositions, dosage forms and therapeutic use. The scope and expiration of each patent must be assessed separately.

Can a generic sell rifaximin for IBS-D if hepatic encephalopathy use remains patented?

Potentially. An ANDA applicant may seek a section viii labeling carve-out for a patented indication, but the proposed label, product claims and remaining patents determine whether the strategy is legally viable.

Did the Actavis case involve a biosimilar?

No. Rifaximin is a small-molecule drug regulated through the ANDA pathway. The dispute was a Hatch-Waxman generic patent case.

References

1. Bausch Health Companies Inc. (2024). Annual report pursuant to Section 13 or 15(d) of the Securities Exchange Act of 1934 for the fiscal year ended December 31, 2023. U.S. Securities and Exchange Commission.

2. CourtListener. (n.d.). Salix Pharmaceuticals, Ltd. v. Actavis Laboratories FL, Inc., No. 1:16-cv-00188. U.S. District Court for the District of Delaware.

3. U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA.

4. U.S. Food and Drug Administration. (n.d.). Drugs@FDA: Xifaxan (rifaximin), NDA 022554. FDA.

5. U.S. Patent and Trademark Office. (2014). U.S. Patent No. 8,642,573: Rifaximin compositions and methods of use. USPTO.

6. Salix Pharmaceuticals, Ltd. v. Norwich Pharmaceuticals Inc., 70 F.4th 1368 (Fed. Cir. 2023).