US Patent 8,853,231: Rifaximin Polymorph Claims, Scope and Patent Landscape

US Patent 8,853,231 covers pharmaceutical compositions containing specific crystalline polymorphs of rifaximin. Its principal protection is not directed to rifaximin generally, Xifaxan branding, a particular disease indication, or a manufacturing process. The patent claims compositions containing rifaximin Form α, Form β, or Form γ, identified primarily through powder X-ray diffraction peaks and, for Form γ, an intrinsic dissolution-rate limitation.[1]

The patent is most relevant to generic rifaximin products that use the claimed solid form in an oral dosage formulation. It creates a potential composition-patent issue distinct from rifaximin’s broader product, formulation, method-of-use, and regulatory exclusivity rights.

What does US Patent 8,853,231 claim?

The independent claims divide the patent into three polymorph families.

Independent claim	Covered form	Principal identifying limitation	Formulation requirement
Claim 1	Form α	At least one listed combination of three XRPD peaks, including combinations centered on 7.4°, 11.8°, 11.1°, 12.9°, 19.7°, 21.4° or 22.1° 2θ	Rifaximin polymorph plus pharmaceutically acceptable carrier
Claim 7	Form β	At least one listed combination of three XRPD peaks, including combinations centered on 5.4°, 6.4°, 10.4°, 17.9°, 18.3° or 20.9° 2θ	Rifaximin polymorph plus pharmaceutically acceptable carrier
Claim 13	Form γ	XRPD peaks at about 5.0°, 7.1° and 8.4° 2θ, plus intrinsic dissolution rate of about 0.14 mg/min/cm²	Rifaximin polymorph plus pharmaceutically acceptable carrier

Claims 1 and 7 use alternative peak combinations. A composition can fall within the claim if the relevant polymorph exhibits one of the listed combinations, subject to claim construction of terms such as “about,” “comprising,” and “polymorphic form.”

Claim 13 is narrower in one respect and potentially more difficult to design around in another. It requires both a diffraction pattern and a numerical dissolution characteristic. A competing product may avoid literal infringement if it does not meet the XRPD and dissolution limitations, but the result would depend on analytical methodology, test conditions, and the interpretation of “about.”

How broad are the Form α and Form β claims?

Claims 1 and 7 are composition claims with a solid-state identity limitation. They do not require a specific tablet strength, dosage amount, disease indication, release profile, excipient, or named brand.

The claims use “comprising.” That open-ended transition generally permits additional ingredients, coating layers, processing aids, or other formulation components without removing the product from claim scope. A tablet containing the claimed rifaximin form and additional excipients can therefore remain within the claim.

The claims are broad across dosage forms. The dependent claims identify tablets, capsules, sugar-coated pills, lozenges, wafer sheets, pellets, and powders in sealed packets, but those examples do not necessarily limit the independent claims to only those forms.

Form α scope

Form α is identified through alternative combinations of XRPD peaks. The repeated presence of 7.4° and 11.8° in many alternatives indicates that these peaks may function as central identifiers for the claimed form. Other alternatives rely on combinations involving 11.1°, 12.9°, 19.7°, 21.4°, 22.1°, or 19.9°.

A formulation containing Form α can potentially infringe Claim 1 even if it contains other rifaximin forms, because “comprising” does not ordinarily exclude additional polymorphic material. The critical issue would be whether the accused composition contains a polymorphic form meeting the claimed diffraction limitations.

Form β scope

Form β is identified by a separate diffraction profile centered on lower-angle peaks, including 5.4°, 6.4°, 7.0°, 7.8°, 9.0°, 10.4°, 13.1°, 14.4°, 17.1°, 17.9°, 18.3°, and 20.9° 2θ.

The alternative structure gives Claim 7 substantial coverage across possible peak combinations. As with Form α, the patent does not require a specific excipient system or commercial dosage strength in the independent claim.

What additional limitations do the dependent claims add?

The dependent claims add three principal subject-matter groups: systemic exposure, excipients, and oral dosage forms.

Claims	Added limitation	Commercial significance
2, 8	Observed plasma rifaximin concentration is negligible	Targets low-systemic-exposure oral rifaximin products
3, 9, 15	Composition includes an excipient	Captures conventional finished dosage forms
4, 10, 16	Specific excipient categories	Covers standard tablet and capsule formulation components
5, 11, 17	Listed oral dosage forms	Connects the polymorph claims to commercial oral products
6, 12, 18	Specific excipients, including microcrystalline cellulose and sodium starch glycolate	Provides narrower fallback positions for formulation enforcement

The “negligible” plasma limitation is potentially significant but fact-intensive. It requires a post-administration observation, not simply a qualitative statement that rifaximin is locally acting. Infringement analysis would require the claimed composition, administration conditions, patient or study population, assay method, and interpretation of “negligible.”

The Form γ claims are materially different. Claim 14 recites an observed plasma concentration of about 670 ng/ml, which is substantially more specific than the negligible-exposure limitations attached to Forms α and β.

What formulations are protected by US 8,853,231?

The patent can reach oral rifaximin formulations containing a claimed polymorph and ordinary pharmaceutical excipients. The listed excipients include:

Colloidal silicon dioxide
Hydroxypropyl methylcellulose
Cellulose
Microcrystalline cellulose
Propylene glycol
Sodium starch glycolate

These ingredients are common in tablets and capsules. Their presence alone does not create infringement. The formulation must also contain the claimed rifaximin polymorph and satisfy the applicable XRPD, dissolution, or plasma-concentration limitation.

The patent does not, based on the supplied claims, require:

A 200 mg or 550 mg dose
A particular tablet coating
A specific rifaximin particle size
A particular release mechanism
A defined indication such as hepatic encephalopathy, irritable bowel syndrome with diarrhea, or travelers’ diarrhea
A manufacturing process
A specific rifaximin purity level

That distinction limits the patent’s direct reach over products using a different crystalline form, an amorphous form, a salt or derivative, or a formulation in which the accused solid state cannot be established.

How would infringement of the XRPD claims be evaluated?

XRPD testing would be the central technical tool. A typical analysis would compare the accused material’s diffraction pattern with the peak combinations recited in the claims.

Important variables include:

Peak position tolerance. The claims use “about,” requiring interpretation of acceptable deviation from each listed 2θ value.
Instrument calibration. Internal standards, wavelength, sample preparation, and instrument resolution can affect measured positions.
Peak intensity. The supplied claims identify peaks but do not make intensity ratios an express limitation.
Mixtures. A product containing multiple polymorphs may still satisfy a “comprising” claim if one component meets the claimed form.
Manufacturing-stage changes. Milling, granulation, compression, coating, humidity, and storage can alter the solid-state profile.
Formulation interference. Excipients can dilute or obscure the API signal, requiring API isolation or validated analytical methods.

A generic manufacturer’s non-infringement position would be strongest where its API has a reproducibly different XRPD pattern and does not convert into Form α, β, or γ during formulation, storage, or dissolution testing.

Is US 8,853,231 a method-of-use or manufacturing patent?

No. Based on the supplied claims, US 8,853,231 is primarily a composition and solid-state patent.

Patent category	Present in supplied claims?	Relevance
Polymorph composition	Yes	Core protection
Pharmaceutical formulation	Yes	Carrier, excipient, and dosage-form limitations
Method of treatment	No	No patient-treatment step appears
Manufacturing process	No	No crystallization, drying, milling, or isolation process appears
Pharmacokinetic limitation	Yes, in dependent claims	Negligible or approximately 670 ng/ml plasma exposure
Product-by-process limitation	No	Product is defined by physical characteristics, not preparation steps

The absence of a process claim means that the patent does not directly prevent every method of making rifaximin Form α, β, or γ. It can still create commercial exposure if the resulting API is used in a claimed composition.

What is the FDA and Orange Book significance?

FDA approval and patent enforceability are separate issues. The Orange Book identifies patents submitted by NDA sponsors for approved drug products and provides patent-listing information, expiration data, and use codes.[2]

A composition patent covering a rifaximin polymorph may be relevant to an ANDA only if it is properly listed against the relevant NDA and product. If listed, a generic applicant may need to address it through a Paragraph III certification, Paragraph IV certification, or another certification permitted by the Hatch-Waxman framework.[3]

A Paragraph IV certification asserts that the listed patent is invalid, unenforceable, or will not be infringed. The NDA holder may file infringement litigation within the statutory period, potentially triggering a 30-month stay of final ANDA approval under the applicable conditions.[3]

The supplied claim text does not establish whether US 8,853,231 is currently listed in the Orange Book for Xifaxan, whether it has been delisted, or whether FDA has assigned a specific use code. Those questions must be resolved from the current Orange Book record rather than inferred from the issued claims.

When does US 8,853,231 lose exclusivity?

The patent’s enforceable term is determined by the patent’s priority chain, filing date, patent-term adjustment, terminal disclaimers, maintenance-fee status, and any applicable patent-term extension. The issue date alone does not establish the expiration date.[4]

The practical exclusivity analysis should separate four dates:

Date category	What it controls
Statutory patent expiration	End of ordinary enforceable patent term
Patent-term adjustment	Additional term for qualifying USPTO delays
Terminal disclaimer date	Potentially earlier cutoff tied to another patent
FDA regulatory exclusivity	Approval restrictions independent of patent term

For generic planning, the controlling date is the earliest effective barrier applicable to the proposed product, not necessarily the latest rifaximin patent expiration date. A product may face separate listed patents covering rifaximin formulations, indications, dosing regimens, or other solid forms.

Which companies are challenging rifaximin patents?

Rifaximin generic competition has involved ANDA applicants and patent litigation concerning Xifaxan. The relevant defendants and challenged patents can change by dosage strength, indication, ANDA filing date, settlement terms, and later amendments to the Orange Book.

The material distinction is between:

Challenges to broad rifaximin or formulation patents;
Challenges to method-of-use patents;
Challenges to solid-state or polymorph patents;
Commercial launches authorized by settlement;
Paragraph IV disputes that terminate without a launch.

A litigation docket or settlement concerning another Xifaxan patent does not establish that US 8,853,231 was challenged or resolved in the same proceeding. Patent-by-patent docket matching is required.

How strong is the patent estate for a generic rifaximin product?

US 8,853,231 is strongest against a product that uses the claimed polymorph in finished oral dosage form and produces the specified XRPD pattern under validated testing.

Risk factor	Assessment
Use of Form α	High risk if the claimed peak combinations are present
Use of Form β	High risk if the claimed peak combinations are present
Use of Form γ	High risk only if both XRPD and dissolution limitations are met
Different polymorph	Potentially favorable non-infringement position
Amorphous rifaximin	Potentially outside literal scope, subject to conversion or mixture evidence
Different excipients	Usually insufficient by itself to avoid the independent claims
Different indication	Does not avoid the composition claims
Different tablet strength	Does not avoid the composition claims
API-only sale	Claims require a pharmaceutical composition with carrier, not merely isolated API
Polymorph conversion during manufacture	Creates material process and product risk

The principal design-around strategy is solid-state control: select a rifaximin form outside Forms α, β, and γ, demonstrate stability through formulation and storage, and confirm that processing does not generate a claimed form. A formulation change alone is less likely to avoid the independent claims.

How does this patent compare with broader rifaximin patents?

US 8,853,231 has narrower subject-matter breadth than a patent claiming rifaximin generally, but it can be technically stronger against a product using the same crystalline form.

Patent type	Breadth	Typical design-around
Rifaximin compound patent	Broad chemical-product protection	Wait for expiration or challenge validity
Polymorph patent	Narrower, form-specific protection	Use another solid form
Formulation patent	Product-specific protection	Change excipients, coating, release profile
Method-of-use patent	Indication or regimen-specific	Avoid the patented indication or regimen where commercially feasible
Manufacturing patent	Process-specific protection	Use a non-infringing process

The patent’s commercial value depends on whether the approved rifaximin product uses one of the claimed forms and whether the patent is listed against the relevant NDA. A polymorph patent can be a substantial barrier even when a basic compound patent has expired, but it does not automatically block every rifaximin product.

Key Takeaways

US 8,853,231 claims pharmaceutical compositions containing rifaximin Forms α, β, or γ.
Forms α and β are defined primarily by alternative XRPD peak combinations.
Form γ requires both XRPD peaks and an intrinsic dissolution rate of about 0.14 mg/min/cm².
The independent claims are open-ended composition claims and can cover tablets, capsules, powders, and other oral products.
Changing excipients or dosage strength alone is unlikely to avoid Claims 1, 7, or 13.
The strongest design-around is a rigorously controlled rifaximin solid form outside the claimed XRPD profiles.
“Negligible” plasma concentration and approximately 670 ng/ml plasma concentration create additional, fact-dependent limitations.
Orange Book listing, patent expiration, Paragraph IV challenges, and litigation status must be assessed separately from the wording of the issued claims.
The patent is not, based on the supplied claims, a treatment-method or manufacturing-process patent.
Generic launch risk turns on the product’s actual solid-state form, not simply its active ingredient or therapeutic indication.

FAQs About US Patent 8,853,231 and Rifaximin

Does US 8,853,231 cover Xifaxan by brand name?

No. The claims cover compositions containing specified rifaximin polymorphs. They do not claim the Xifaxan trademark or brand identity.

Can a generic use rifaximin without infringing US 8,853,231?

Potentially. A generic may avoid literal infringement if its composition does not contain Form α, β, or γ as claimed and does not meet the applicable XRPD and dissolution limitations. Solid-state conversion during manufacturing or storage could alter that analysis.

Does a different excipient avoid the rifaximin polymorph patent?

Usually not. The independent claims require a rifaximin polymorph and a pharmaceutically acceptable carrier. They do not require the narrower excipient lists in Claims 6, 12, and 18.

Is Form γ protected more narrowly than Forms α and β?

Yes. Form γ requires a defined three-peak XRPD pattern and an intrinsic dissolution rate of about 0.14 mg/min/cm². Forms α and β rely on listed XRPD peak combinations without the same dissolution-rate requirement.

Does an expired basic rifaximin patent eliminate the risk from US 8,853,231?

No. A later-expiring or separately enforceable polymorph patent can create a distinct barrier after broader rifaximin patent protection ends.

References

United States Patent and Trademark Office. (2014). US Patent No. 8,853,231, pharmaceutical compositions comprising polymorphic forms of rifaximin.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
21 U.S.C. § 355(j); 35 U.S.C. § 271(e).
United States Patent and Trademark Office. (2024). Manual of Patent Examining Procedure, Chapter 2700: Patent term.

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	E361927	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 8,853,231

Summary for Patent: 8,853,231