United States Drug Patent 7,915,275: Rifaximin Polymorph Claims, Scope, Expiration, and Patent Landscape

US Patent 7,915,275 protected methods of treating bowel-related bacterial disorders with solid rifaximin compositions containing Form alpha, Form beta, or Form gamma polymorphs. Its principal commercial relevance was the physical form of rifaximin and the resulting control of systemic exposure, dissolution, and pharmacokinetic parameters. The patent expired on March 19, 2024, eliminating current exclusion based on this patent alone. Commercial protection for Xifaxan now depends on later patents, regulatory exclusivities, formulation barriers, and the outcome of ANDA litigation involving other patents.

What does US Patent 7,915,275 cover?

The patent covers a treatment method, not a standalone rifaximin compound or an abstract polymorph composition.

Claim 1 requires all of the following:

Treatment of a bacterial infection.
A patient suffering from a bowel-related disorder.
Administration of a solid pharmaceutical composition.
A therapeutically effective amount of Form alpha, Form beta, or Form gamma rifaximin.
A pharmaceutically acceptable excipient or carrier.
The amount of polymorph used must control systemic absorption.
The rifaximin polymorph must satisfy specified X-ray powder diffraction characteristics.

The patent therefore combines three technical limitations:

A disease-treatment limitation.
A pharmaceutical composition limitation.
A polymorph and pharmacokinetic-control limitation.

The claims do not cover every rifaximin product. A potential infringer would need to practice the claimed treatment method using a qualifying solid composition and one of the claimed polymorphic forms.

Claim element	Scope
Active ingredient	Rifaximin
Covered forms	Form alpha, Form beta, Form gamma
Dosage form	Solid pharmaceutical composition
Excipients	Pharmaceutically acceptable excipient or carrier
Route	Oral or topical under dependent claims
Disease setting	Bowel-related bacterial infection
Physical characterization	XRPD peak limitations
Water content	Form-specific limitations in claims 5-7 and dependent claims
Pharmacokinetics	Cmax, Tmax, AUC ranges
Dissolution	Form beta and Form gamma ranges
Claim type	Method of treatment

The patent’s commercial value came from connecting rifaximin’s solid-state form to low systemic absorption. That relationship was relevant to Xifaxan’s gastrointestinal activity and safety profile.

What polymorphs are protected by US 7,915,275?

The patent identifies three rifaximin forms using XRPD peaks and water-content characteristics.

Polymorph	Representative XRPD peaks, 2-theta	Water content	Claimed pharmacokinetic profile
Form alpha	About 7.4°, 19.7°, 21.0°, and 22.1°	Less than 4.5%	Cmax up to about 5.5 ng/mL; AUC0-24h up to about 100 ng·h/mL
Form beta	About 5.4°, 9.0°, and 20.9°	At least 4.5%	Cmax up to about 3.7 ng/mL; AUC0-24h up to about 40 ng·h/mL
Form gamma	About 5.0°, 7.1°, and 8.4°	About 0%-2%	Cmax up to about 5,000 ng/mL; AUC0-24h up to about 22,000 ng·h/mL

The claims use “about” before the XRPD peak positions. That language creates a tolerance question. The scope cannot be determined from the peak labels alone without the specification, claim-construction record, and relevant analytical evidence. In a dispute, the parties would likely contest the acceptable deviation from each listed peak and the effect of XRPD instrument conditions.

Form alpha is the most commercially relevant form because commercial rifaximin products have generally been associated with the alpha polymorph. Form beta and Form gamma are technically covered, but their markedly different water content, dissolution behavior, and systemic exposure make them less obvious commercial substitutes.

How do the claims differ from one another?

Claims 1 through 4 establish the basic treatment framework. Claims 5 through 7 add water-content limitations. Claims 8 through 18 add pharmacokinetic or dissolution limitations. Claims 19 through 30 repeat and combine those limitations.

Independent claim 1

Claim 1 is the broadest claim. It covers a solid composition containing one or more of the three forms, provided the composition controls systemic absorption and is used to treat a bowel-related bacterial infection.

The phrase “one or more” permits a composition containing a single form or a mixture of forms. A formulation containing alpha and beta, for example, could fall within the literal scope if the remaining limitations are met.

Disease limitations

Claim 2 lists:

Irritable bowel syndrome.
Traveler’s diarrhea.
Small intestinal bacterial overgrowth.
Crohn’s disease.
Chronic pancreatitis.
Pancreatic insufficiency.
Colitis.

The claim language does not limit the patent to a single approved indication. It reaches the listed bowel disorders if the treatment is for bacterial infection and the other elements are satisfied.

Route limitations

Claim 3 specifies oral administration. Claim 4 specifies topical administration. The presence of claim 4 is unusual in the context of a bowel-related disorder and could create an issue concerning written description, enablement, or practical claim construction depending on the topical administration scenario.

Pharmacokinetic limitations

The pharmacokinetic claims are narrow in one respect and potentially difficult to enforce in another.

They are narrow because they require measured ranges for:

Cmax.
Tmax.
AUC0-24h.
AUC0-inf.

They may be difficult to enforce because pharmacokinetic values can vary with dose, food intake, patient population, analytical method, sampling schedule, renal or hepatic function, and formulation conditions. A product may produce different exposure values from those stated in the patent without changing its solid-state form.

Form gamma has particularly broad numerical exposure limits. The claimed Cmax range of approximately 0.0 to 5,000 ng/mL and AUC ranges extending to approximately 22,000 ng·h/mL cover exposure profiles materially different from the low-systemic-exposure profile associated with Form alpha and Form beta.

What are the principal claim-construction and validity issues?

The patent had several potential pressure points even before expiration.

“Controls systemic absorption”

Claim 1 requires that the amount of each polymorph be an amount “to control the amount of systemic absorption.” This limitation provides a functional restriction but may raise construction questions.

Possible issues include:

Whether any measurable effect on absorption satisfies the limitation.
Whether the claim requires a predetermined target exposure.
Whether the limitation is judged by formulation design or clinical results.
Whether a mixture of polymorphs must produce a demonstrable absorption-control effect.
Whether the claim is sufficiently definite to identify an infringing composition.

XRPD identification

The polymorph definitions depend on selected XRPD peaks. An accused product could dispute infringement by showing:

The relevant peaks are absent.
Peak positions fall outside the legally effective “about” range.
The product contains a different polymorph.
The tested sample is a hydrate, amorphous material, or polymorph mixture.
Manufacturing or storage changes the solid-state form.

XRPD testing would need controlled sample preparation, instrument calibration, and comparison against the patent’s disclosed patterns.

Water-content limitations

Water content can vary with humidity, packaging, drying conditions, and testing methodology. Form beta is defined in part by water content of at least 4.5%, while Form gamma is described as having approximately 0%-2% water. A manufacturer could face a classification dispute if a product changes water content during storage without changing its underlying crystal structure.

Enablement and written description

The patent claims multiple forms, disease states, routes, exposure ranges, and dissolution ranges. A challenger could argue that the disclosure does not enable the entire breadth of those combinations, particularly:

Form gamma compositions with very high systemic exposure.
Topical administration for bowel-related disorders.
Every listed disorder and treatment context.
Every mixture of the three forms.
The full range of pharmacokinetic outcomes.

The strength of such arguments would depend on the specification, examples, prosecution history, and expert evidence.

Obviousness

Polymorph patents commonly face obviousness attacks based on:

Routine solid-state screening.
Known rifaximin compositions.
Predictable hydration or dehydration procedures.
Expected differences in dissolution and bioavailability.
Prior disclosures of rifaximin formulations.

The patent’s strongest defense would be evidence of unexpected differences in dissolution, absorption, gastrointestinal retention, stability, or clinical performance.

When did US Patent 7,915,275 expire?

US Patent 7,915,275 expired on March 19, 2024, based on the patent-family priority and term records. The patent is therefore no longer an enforceable exclusionary right against current manufacture, sale, or use.

Event	Date or status
Earliest relevant priority	March 19, 2003
US patent issue date	March 29, 2011
Patent term	20-year term measured from the applicable nonprovisional/PCT filing framework
Expiration	March 19, 2024
Current enforceability	Expired
Patent-term extension	No continuing term available under the ordinary record used for this patent

The expiration removes the patent as a current barrier to generic use of the claimed rifaximin polymorphs. It does not invalidate later patents directed to indications, formulations, dosing regimens, manufacturing processes, or other aspects of Xifaxan.

What was the Orange Book status of US 7,915,275?

US 7,915,275 was associated with the Xifaxan patent estate and was relevant to rifaximin products marketed by Salix Pharmaceuticals, later acquired by Valeant Pharmaceuticals and now part of Bausch Health. FDA Orange Book listings must be evaluated by product, strength, dosage form, and listing status.

The patent’s expiration means that it cannot independently support a current Paragraph IV litigation block. A generic applicant can still face other Orange Book-listed patents covering Xifaxan, particularly patents directed to approved indications and dosing regimens.

The Orange Book distinction is important:

A listed patent can trigger a Paragraph IV notice and litigation.
An expired listed patent cannot create a current enforceable patent term.
A patent may remain visible in historical Orange Book records after expiration.
Approval timing can still be affected by other listed patents and statutory stays.

FDA approval history for Xifaxan includes:

Product or indication	FDA milestone
Rifaximin 200 mg for traveler’s diarrhea	Approved in 2004
Rifaximin 550 mg for reduction in hepatic encephalopathy recurrence	Approved in 2010
Rifaximin 550 mg for IBS-D	Approved in 2015

FDA’s current labeling identifies Xifaxan as rifaximin tablets for these gastrointestinal indications. The product is a small molecule, so biosimilar approval is not the relevant pathway. Generic applicants use the abbreviated new drug application, or ANDA, pathway.

Which later patents protect Xifaxan after US 7,915,275?

The post-expiration landscape is dominated by later patents rather than the polymorph patent.

Patent family or subject	Commercial relevance
Rifaximin compound and early use patents	Historical protection for rifaximin and early gastrointestinal uses
Hepatic encephalopathy method patents	Protection for 550 mg dosing and recurrence reduction
IBS-D method patents	Protection for rifaximin treatment of irritable bowel syndrome with diarrhea
Formulation patents	Potential protection for release profile, excipients, particle characteristics, or dosage forms
Manufacturing patents	Potential barriers involving crystallization, purification, polymorph control, or scale-up
Combination or regimen patents	May cover treatment schedules or use with other agents

The most significant Xifaxan litigation has involved later indication patents, particularly patents associated with rifaximin treatment for IBS-D and hepatic encephalopathy. Norwich Pharmaceuticals’ ANDA challenge to Xifaxan led to litigation against Salix and related parties. The Federal Circuit addressed the validity of asserted rifaximin patents in Norwich Pharmaceuticals Inc. v. Salix Pharmaceuticals, Ltd., including obviousness issues involving IBS-D treatment. That litigation did not restore or extend US 7,915,275.

What Paragraph IV challenges affected rifaximin?

Paragraph IV challenges have targeted the broader Xifaxan patent estate. The major commercial question has been whether a generic applicant can launch rifaximin while carving out patented indications or defeating the listed patents in court.

A generic applicant may pursue several strategies:

Paragraph IV certification against listed patents.
A “section viii” statement carving out patented uses from the label.
A skinny label directed to nonprotected indications.
Patent invalidity or noninfringement litigation.
A settlement with the branded sponsor.
A launch after expiration of the remaining enforceable patents.

The risk profile is different for US 7,915,275 because the patent has expired. A current applicant generally would not need to defeat this patent to sell a product containing rifaximin polymorph alpha, beta, or gamma. The applicant may still need to address later patents and FDA’s product-specific requirements.

How strong was the patent estate for the rifaximin polymorphs?

The patent was technically significant but commercially narrower than a compound patent.

Strengths

It claimed three named solid-state forms.
It linked physical form to absorption and dissolution.
It covered mixtures through the “one or more” language.
It included water-content, pharmacokinetic, and dissolution fallbacks.
It could complicate generic solid-form selection and analytical characterization.

Weaknesses

It was a method-of-treatment patent rather than a composition or compound monopoly.
Infringement required proof of use in the claimed disease context.
Several dependent claims repeat limitations without materially expanding the estate.
Pharmacokinetic ranges may be difficult to use as a reliable infringement screen.
The patent term ended before many later Xifaxan indication patents.
Solid-state form can be challenged through analytical testing and alternative manufacturing routes.

The patent was strongest as a historic barrier to an ANDA product using the same commercial rifaximin form during the patent term. It is no longer a live barrier.

What manufacturing and formulation barriers remain?

Patent expiration does not eliminate technical barriers to generic rifaximin.

A generic manufacturer must control:

Polymorph identity.
Hydration state.
Particle-size distribution.
Dissolution behavior.
Chemical purity and degradation products.
Tablet compression and coating.
Batch-to-batch solid-state consistency.
Stability under humidity and temperature stress.
Bioequivalence and comparative dissolution.

Rifaximin’s low aqueous solubility and gastrointestinally localized activity make formulation development more complex than a simple immediate-release tablet substitution. The manufacturer must also ensure that the final product meets FDA’s pharmaceutical equivalence and bioequivalence requirements for the referenced product.

Manufacturing patents may remain relevant if they claim a specific crystallization process, purification method, solvent system, or polymorph-control procedure. Those rights must be analyzed separately from US 7,915,275.

What generic launch scenarios exist for rifaximin?

Launch after polymorph-patent expiration

This is the lowest-risk scenario with respect to US 7,915,275. The generic product can use the same or a different rifaximin solid form, subject to FDA requirements and remaining patents.

Skinny-label launch

A generic applicant may seek approval for nonprotected indications while omitting patented uses from its label. This strategy is difficult when the reference product’s principal commercial market depends on a patented indication or when the proposed labeling and marketing materials induce infringing use.

Launch after later-patent litigation

A manufacturer may challenge later Xifaxan patents and launch if it obtains a favorable judgment, reaches a settlement, or determines that a remaining patent does not cover its product or proposed label.

At-risk launch

A company may launch before all patent disputes are resolved. That exposes it to damages, injunction risk, and possible induced-infringement claims if a court later finds the relevant patents valid and infringed.

How does US 7,915,275 compare with later Xifaxan patents?

Issue	US 7,915,275	Later Xifaxan patents
Main subject	Rifaximin polymorphs and exposure control	Indications, dosing, formulations, or regimens
Claim type	Method of treatment	Often method of treatment or formulation
Main technical issue	Solid-state form and systemic absorption	Clinical use and commercial dosing
Expiration	March 19, 2024	Varies by patent and family
Current status	Expired	Some later rights may remain active
Generic relevance	Form-selection and historical ANDA barrier	Primary source of current launch risk
Biosimilar relevance	None	None, because rifaximin is a small molecule

What licensing deals affect rifaximin commercialization?

Alfa Wassermann developed rifaximin and licensed US commercialization rights to Salix Pharmaceuticals. Salix became part of Valeant Pharmaceuticals in 2015, and Valeant’s pharmaceutical operations were later reorganized under Bausch Health. Those transactions transferred or consolidated commercial rights and patent-estate control but did not extend the term of US 7,915,275.

The key commercial relationship is therefore:

Alfa Wassermann: originator and rifaximin rights holder.
Salix Pharmaceuticals: US commercial partner and Xifaxan marketer.
Valeant Pharmaceuticals: acquirer of Salix.
Bausch Health: current corporate successor for the US Xifaxan business.

Key Takeaways

US 7,915,275 covered treatment of bowel-related bacterial infections using rifaximin Form alpha, beta, or gamma in solid compositions.
The claims relied on XRPD peaks, water content, dissolution rates, and systemic pharmacokinetic ranges.
Form alpha was the principal commercial form associated with low systemic absorption.
Claim 1 was broadest, but infringement required a qualifying treatment method, composition, polymorph, and absorption-control limitation.
The patent expired on March 19, 2024.
It no longer independently blocks generic rifaximin entry.
Current Xifaxan risk is concentrated in later indication, dosing, formulation, and manufacturing patents.
Rifaximin is a small molecule, so biosimilar litigation is not relevant.
Generic applicants must still manage ANDA requirements, Orange Book-listed later patents, formulation development, and potential Paragraph IV litigation.

FAQs About US Patent 7,915,275 and Rifaximin

Does US 7,915,275 cover Xifaxan tablets?

Historically, it covered methods using solid rifaximin compositions containing the claimed polymorphs. It did not operate as a direct composition-of-matter patent covering every Xifaxan tablet.

Can a generic use rifaximin Form alpha after the patent expired?

Yes. The expiration of US 7,915,275 removes that patent as a current barrier to use of Form alpha, subject to any separate unexpired patents covering the indication, formulation, dosing regimen, or manufacturing process.

Is Form gamma commercially equivalent to Form alpha?

Not necessarily. The patent assigns Form gamma substantially higher potential systemic exposure and a faster dissolution range than Forms alpha and beta. Equivalence would depend on the complete formulation, product specifications, and FDA bioequivalence requirements.

Did US 7,915,275 protect rifaximin for hepatic encephalopathy?

It could cover treatment in a bowel-related disorder context if the claim limitations were met, but later patents more specifically addressed rifaximin use for hepatic encephalopathy and the 550 mg dosing regimen.

Does expiration of US 7,915,275 guarantee immediate generic Xifaxan approval?

No. Approval depends on FDA review of an ANDA, product-specific requirements, and any remaining enforceable Orange Book patents or regulatory exclusivities associated with the proposed indication and labeling.

References

United States Patent and Trademark Office. (2011). United States Patent No. 7,915,275: Polymorphic forms of rifaximin. U.S. Department of Commerce.
U.S. Food and Drug Administration. (2024). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/
U.S. Food and Drug Administration. (2024). Xifaxan (rifaximin) prescribing information. Salix Pharmaceuticals.
U.S. Food and Drug Administration. (2004). FDA approval history for Xifaxan (rifaximin). Drugs@FDA.
Norwich Pharmaceuticals Inc. v. Salix Pharmaceuticals, Ltd., 116 F.4th 1366 (Fed. Cir. 2024).
Bausch Health Companies Inc. (2024). Annual report and Xifaxan product disclosures. U.S. Securities and Exchange Commission.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Italy	MI03A2144	Nov 7, 2003

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	043547	⤷ Start Trial
Argentina	081991	⤷ Start Trial
Argentina	081992	⤷ Start Trial
Austria	361927	⤷ Start Trial
Austria	421965	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 7,915,275