United States Drug Patent 9,629,828: Rifaximin Hepatic Encephalopathy Claims and Patent Landscape

U.S. Patent No. 9,629,828 protects a patient-selection and dosing method for reducing recurrence of overt hepatic encephalopathy in patients with chronic liver disease. The independent claim is limited to patients in remission who experienced at least two hepatic encephalopathy episodes during the preceding six months and requires daily rifaximin dosing of 1,000 to 1,200 mg. The commercially relevant embodiment is Xifaxan 550 mg administered twice daily.

The patent is a method-of-use patent, not a composition-of-matter patent. Its commercial value depends on the enforceability of the hepatic encephalopathy indication, Orange Book listing, patent-term status, and the ability of a generic applicant to launch without infringing the claimed method.

What does U.S. Patent 9,629,828 cover?

U.S. Patent 9,629,828 covers administration of rifaximin to a narrowly defined high-risk hepatic encephalopathy population. The claimed method requires all of the following elements:

Required element	Claim limitation
Patient identification	Subject has “TD” and chronic liver disease
Disease state	Subject is in remission from hepatic encephalopathy
Recurrence history	At least two hepatic encephalopathy episodes in the prior six months
Dose	1,000 to 1,200 mg rifaximin daily
Preferred dose	1,100 mg daily
Commercial regimen	550 mg twice daily
Disease duration	Chronic liver disease, including cirrhosis
Treatment duration	More than 28 days; preferably six months or longer; more preferably one year or longer
Patient type	Human
Severity stratification	Child-Pugh Class A, B, or C
Formulation	Oral tablet containing specified excipients or combinations of those excipients

The claim set is directed to secondary prevention. It does not broadly cover treatment of all hepatic encephalopathy patients, treatment of an acute episode, or use of rifaximin at any dose for any chronic liver disease.

The term “TD” appears in the supplied version of claim 1. Its scope depends on the patent specification’s definition and prosecution history. If “TD” is not expressly defined in the issued patent or is an apparent transcription error, that language creates a potential claim-construction issue.

How broad is claim 1 of Patent 9,629,828?

Claim 1 is narrow in patient selection but broad in several operational respects.

It requires a patient who:

Has chronic liver disease;
Is currently in remission from hepatic encephalopathy;
Had at least two hepatic encephalopathy episodes during the prior six months; and
Receives between 1,000 and 1,200 mg of rifaximin daily.

The dose range captures the approved 550 mg twice-daily regimen. It also captures other daily dosing schedules, provided the total daily dose falls within the claimed range.

The claim does not expressly require:

Concomitant lactulose;
A specific rifaximin polymorph;
A particular treatment setting;
A particular route other than the method’s implied administration route;
A particular age;
A specific Child-Pugh class; or
A specific cause of cirrhosis.

A generic company could face infringement risk if its label instructs use of rifaximin for reduction of recurrent overt hepatic encephalopathy in the same patient population. Direct infringement would generally depend on practicing the claimed method, while inducement risk could arise from the generic label, promotional materials, dosing instructions, or other evidence showing intent to encourage the patented use.

What do claims 2 through 12 add?

Dose and administration schedule

Claims 2 and 3 narrow the daily dose to 1,100 mg and specify 550 mg twice daily. Claim 3 tracks the marketed Xifaxan hepatic encephalopathy regimen.

The practical importance of claim 3 is high because it maps directly onto the FDA-approved dosage for reduction in the risk of overt hepatic encephalopathy recurrence. A generic applicant seeking approval for the same indication would have difficulty avoiding the literal dosing limitation without using a different dose or a different labeling strategy.[2]

Human patients

Claim 4 limits claim 1 to human treatment. This has little commercial significance because the relevant FDA indication is human therapy. It excludes veterinary applications but does not narrow the human-use market materially.

Tablet formulation

Claim 5 requires tablets containing one or more listed excipients, including:

Colloidal silicon dioxide;
Disodium edetate;
Glycerol palmitostearate;
Hypromellose;
Microcrystalline cellulose;
Propylene glycol;
Red iron oxide;
Sodium starch glycolate;
Talc; or
Titanium dioxide.

The use of “one or more” makes this limitation relatively broad. A tablet containing only one listed excipient could satisfy the literal wording, assuming the remaining limitations are met.

The claim does not appear to require the full commercial excipient combination unless the specification or prosecution history imposes a narrower construction. The formulation limitation is therefore more significant for product-level enforcement than for the basic indication claim. A generic manufacturer could attempt to design around claim 5 by using a non-tablet dosage form or a tablet containing none of the listed excipients. That strategy would not avoid claims 1 through 4 or 6 through 12.

Treatment duration

Claims 6 through 8 impose progressively longer treatment periods:

Claim	Duration
Claim 6	More than 28 days
Claim 7	Six months or longer
Claim 8	One year or longer

These limitations may complicate proof of infringement because the relevant course of treatment must continue for the specified period. They also create potential distinctions between a label that merely recommends chronic therapy and actual patient use.

A product label that recommends indefinite or long-term administration could support inducement allegations for the longer-duration claims. Claims 1 through 5 remain the more important claims because they do not require six months or one year of treatment.

Chronic liver disease and cirrhosis

Claim 9 specifies cirrhosis. Since cirrhosis is a major cause of recurrent hepatic encephalopathy, this claim is commercially relevant but narrower than claim 1.

Child-Pugh classification

Claims 10, 11, and 12 cover administration to patients classified as Child-Pugh Class A, B, and C, respectively. The claims require determining the patient’s Child-Pugh class and administering rifaximin if the patient falls within the specified class.

Together, the three claims cover all standard Child-Pugh classes. They do not appear to require dose adjustment by class. The same 1,000-to-1,200 mg daily range applies to Class A, B, and C patients.

These claims raise two enforcement issues:

Whether a physician must actually calculate or document the Child-Pugh score; and
Whether a generic label instructs physicians to use rifaximin across the relevant disease-severity population.

What is the approved FDA use of rifaximin relevant to Patent 9,629,828?

Xifaxan is FDA-approved for reduction in the risk of overt hepatic encephalopathy recurrence in adults. The approved regimen is 550 mg twice daily, equivalent to 1,100 mg daily.[2]

The FDA-approved indication closely tracks claims 1 through 4 and claim 9. The approved labeling also supports the chronic-use limitations in claims 6 through 8 because hepatic encephalopathy prevention is intended as continuing therapy rather than short-course treatment.

FDA and commercial parameter	Xifaxan
Active ingredient	Rifaximin
Brand	Xifaxan
Sponsor	Salix Pharmaceuticals, a Bausch Health company
Relevant indication	Reduction in risk of overt hepatic encephalopathy recurrence
Dose	550 mg orally twice daily
Daily total	1,100 mg
Product type	Oral tablets
Therapeutic category	Gastrointestinal and hepatic disease
Regulatory pathway	New Drug Application
Biosimilar pathway	Not applicable

Rifaximin is a small-molecule drug. Biosimilar litigation and biosimilar substitution rules do not apply. Competitive entry would proceed through an abbreviated new drug application, subject to patent certifications and regulatory exclusivity.

What patents protect Xifaxan’s hepatic encephalopathy indication?

The Xifaxan patent estate has included composition, formulation, dosing, and method-of-use patents. Patent 9,629,828 is one part of the method-of-use estate.

Patent	General subject matter	Commercial relevance
U.S. 7,045,620	Rifaximin composition and related pharmaceutical protection	Foundational product protection
U.S. 8,309,569	Hepatic encephalopathy recurrence prevention	Core method-of-use protection
U.S. 9,629,828	Patient selection, dose, duration, formulation, and Child-Pugh limitations	Continuation method-of-use protection
U.S. 10,583,138	Later Xifaxan method-of-use protection	Extended indication protection
U.S. 11,020,361	Additional later-issued Xifaxan protection	Potential post-expiration enforcement barrier

The expiration analysis must distinguish statutory patent term, patent-term adjustment, patent-term extension, terminal disclaimers, and any pediatric exclusivity. Patent 9,629,828 is associated with the later-expiring hepatic encephalopathy patent family rather than the original rifaximin composition patent. Public patent databases and Orange Book records should be read together because a continuation patent may have a different nominal expiration date but remain subject to a terminal disclaimer or other term limitation.[1][3]

When does Patent 9,629,828 lose exclusivity?

The practical exclusivity date for Patent 9,629,828 depends on the patent’s term record and any applicable terminal disclaimer or regulatory extension. The patent issued on April 25, 2017. Its relevant protection is tied to the Xifaxan hepatic encephalopathy patent family, which has been used to delay unrestricted generic entry beyond the original rifaximin composition term.[1][3]

For commercial planning, the key date is not only the expiration date of Patent 9,629,828. A generic entrant must assess:

Every Orange Book-listed Xifaxan patent;
Patent claims covering hepatic encephalopathy;
Patent claims covering the 550 mg tablet;
Any later-issued continuation patents;
Pediatric exclusivity;
Patent-term extension;
Pending Paragraph IV litigation; and
Settlement restrictions on launch timing.

A generic applicant that defeats or avoids Patent 9,629,828 may still face other listed patents. Conversely, an applicant may obtain approval for an indication carved out of the protected hepatic encephalopathy use while retaining a non-infringing label.

What is the Orange Book status of Patent 9,629,828?

Patent 9,629,828 has been associated with the Xifaxan 550 mg product and the hepatic encephalopathy recurrence indication in FDA Orange Book patent listings. The relevant Orange Book use code identifies the use of rifaximin to reduce the risk of overt hepatic encephalopathy recurrence in adults.[3]

Orange Book listing does not establish validity or infringement. It triggers the statutory patent-certification framework for an ANDA applicant. A generic applicant generally must certify that:

No listed patent exists;
The patent has expired;
The applicant will not market before patent expiration; or
The listed patent is invalid, unenforceable, or will not be infringed.

A Paragraph IV certification can trigger a 30-month stay of approval when the patent holder files suit within the statutory period.[4]

Which companies have challenged Xifaxan patents?

Norwich Pharmaceuticals challenged Xifaxan patents in ANDA litigation against Salix Pharmaceuticals. The dispute involved patents covering rifaximin use for hepatic encephalopathy and related indications. The litigation reached the U.S. Court of Appeals for the Federal Circuit in Salix Pharmaceuticals, Ltd. v. Norwich Pharmaceuticals Inc.[5]

The litigation demonstrates the principal generic-entry vulnerability of the Xifaxan estate: obviousness challenges to method-of-use claims based on the known use of rifaximin, prior clinical data, and the motivation to apply an established dosing regimen to recurrent hepatic encephalopathy.

The existence of a Federal Circuit decision does not eliminate risk under Patent 9,629,828. Patent-specific claim language, prosecution history, priority dates, and asserted claims must be analyzed separately. A decision concerning one patent does not automatically invalidate every continuation patent in the family.

What patent litigation affects Xifaxan generic launch timing?

Xifaxan generic launch timing has been affected by ANDA litigation, patent certifications, and settlement arrangements. In litigation involving Norwich, the courts considered whether the asserted Xifaxan method claims were patentable and whether the generic applicant could enter before the relevant patent terms expired.[5]

The principal launch scenarios are:

Scenario	Effect on generic entry
All relevant patents survive	Entry generally waits until the latest enforceable barrier or negotiated date
One core method patent is invalidated	Entry may still be blocked by other listed patents
Carve-out label accepted	Generic may enter for non-protected indications
Settlement permits an agreed date	Entry occurs under contractual restrictions
Patent claims are not infringed	Approval may proceed after statutory litigation obligations are satisfied
Label induces the patented use	Generic faces potential inducement liability

The most important risk for a generic manufacturer is an approved label that reproduces the hepatic encephalopathy indication and the 550 mg twice-daily regimen. A skinny-label strategy may reduce infringement exposure, but its effectiveness depends on the scope of the remaining label, promotional conduct, physician behavior, and the patent claims still in force.

How strong is the patent estate for rifaximin hepatic encephalopathy treatment?

Strengths

Patent 9,629,828 has several enforcement advantages:

Claims 1 and 3 map closely to the FDA-approved indication and commercial dosing regimen.
The patient-selection language targets a clinically identifiable population.
Claims cover both dose range and the specific 550 mg twice-daily schedule.
Claims extend to treatment duration and Child-Pugh classifications.
The formulation claim may cover the commercial tablet composition.
A generic label for the same indication could create inducement exposure.

Vulnerabilities

The estate also has material vulnerabilities:

Rifaximin was already known as a gastrointestinally acting antibiotic.
The 550 mg twice-daily regimen was publicly associated with hepatic encephalopathy prevention.
The disease population and recurrence endpoint may be viewed as clinically predictable.
Patient-selection limitations may be attacked as inherent or obvious.
Duration limitations may be difficult to enforce if the label does not require the full duration.
Claim 5 may be avoided through formulation redesign.
Claims 10 through 12 depend on patient classification and may be less useful if Child-Pugh scoring is not required by the label.
Continuation patents may face double-patenting or terminal-disclaimer constraints.

Overall, the patent is strongest against a generic product that uses the same 550 mg tablet, carries the hepatic encephalopathy indication, and recommends chronic twice-daily administration. It is weaker against a product with a carved-out label, a different formulation, or evidence that the generic sponsor does not encourage the patented use.

What manufacturing and formulation barriers exist?

Patent 9,629,828 does not appear to create a broad manufacturing-process monopoly over rifaximin. Its principal barrier is use-related. Claim 5 adds a tablet-composition limitation, but the listed excipients are conventional pharmaceutical excipients rather than a unique rifaximin manufacturing process.

A generic manufacturer may therefore pursue:

A different excipient system;
A different coating composition;
A non-tablet oral dosage form;
A formulation containing none of the listed excipients; or
A product marketed only for an unprotected indication.

Design-around does not eliminate method-of-use risk if the generic label still directs administration of rifaximin 550 mg twice daily to prevent recurrent overt hepatic encephalopathy.

How does Patent 9,629,828 compare with other Xifaxan protections?

Patent 9,629,828 is narrower than a composition patent but more commercially targeted. Its claims are tied to the approved hepatic encephalopathy use and the precise regimen that generates substantial Xifaxan revenue.

Protection type	Breadth	Generic design-around potential
Composition patent	Broad	Low after expiration
Formulation patent	Medium	Moderate
Hepatic encephalopathy method patent	Indication-specific	Moderate to low for same-label entry
Dosing patent	Narrow but commercially aligned	Moderate
Patient-selection patent	Narrow	Higher, depending on label and proof
Manufacturing patent	Process-specific	Moderate to high

Because the drug is a small molecule, the main competitive threat is an ANDA generic, not a biosimilar. The commercial exposure is concentrated in the hepatic encephalopathy and irritable bowel syndrome with diarrhea indications, with the former being the indication most directly implicated by Patent 9,629,828.[2]

Key Takeaways

Patent 9,629,828 covers rifaximin use in patients in remission from overt hepatic encephalopathy who had at least two episodes during the prior six months.
The principal commercial embodiment is 550 mg twice daily, or 1,100 mg daily.
The patent includes claims covering chronic liver disease, cirrhosis, treatment duration, tablet excipients, and Child-Pugh Classes A, B, and C.
It is a method-of-use patent, not a basic rifaximin composition patent.
The claims most relevant to generic risk are claims 1 and 3 because they closely track the FDA-approved indication and marketed dose.
A generic label carrying the hepatic encephalopathy indication could create direct-use and inducement concerns.
Formulation and patient-selection design-arounds may reduce risk but do not necessarily avoid the core method claims.
Norwich’s litigation against Salix shows that obviousness and generic-entry challenges remain central to the Xifaxan patent estate.
Biosimilar competition is irrelevant because rifaximin is a small-molecule drug.
The Orange Book listing and the full continuation family must be reviewed together before assessing launch timing or valuation exposure.

FAQs

Does Patent 9,629,828 cover rifaximin for irritable bowel syndrome with diarrhea?

No. The supplied claims are directed to reducing recurrence of overt hepatic encephalopathy. They do not expressly cover rifaximin treatment of irritable bowel syndrome with diarrhea.

Does the patent require concurrent lactulose therapy?

No. The supplied claims do not require lactulose. A patient may receive lactulose, but that limitation is not stated in claims 1 through 12.

Can a generic sell rifaximin for another indication before the patent expires?

Potentially. A generic may pursue a label carve-out for an indication outside the patented hepatic encephalopathy use, subject to the remaining Orange Book patents, FDA requirements, and inducement risk.

Does claim 5 require every listed excipient?

No. The claim language states that the tablet comprises one or more of the listed excipients. It does not, on its face, require all listed ingredients.

Is a Child-Pugh score required for every use covered by the patent?

No. Child-Pugh scoring is expressly required only by claims 10 through 12. Claims 1 through 9 do not require assignment to Child-Pugh Class A, B, or C.

References

U.S. Patent No. 9,629,828. (2017). Methods of reducing the risk of hepatic encephalopathy recurrence. U.S. Patent and Trademark Office.
U.S. Food and Drug Administration. (2023). Xifaxan (rifaximin) prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
Food, Drug, and Cosmetic Act, 21 U.S.C. § 355(j).
Salix Pharmaceuticals, Ltd. v. Norwich Pharmaceuticals Inc., 56 F.4th 1378 (Fed. Cir. 2023).

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Salix Pharms	XIFAXAN	rifaximin	TABLET;ORAL	021361-002	Mar 24, 2010	AB	RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial				REDUCTION IN RISK OF OVERT HEPATIC ENCEPHALOPATHY (HE) IN ADULTS	⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Patented / Exclusive Use	>Submissiondate

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	2009298389	⤷ Start Trial
Australia	2010260089	⤷ Start Trial
Australia	2010271070	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 9,629,828

Which drugs does patent 9,629,828 protect, and when does it expire?

Summary for Patent: 9,629,828