United States Patent 8,501,723: Fesoterodine-Xylitol Formulation Scope, Claim Analysis, and Patent Landscape

U.S. Patent No. 8,501,723 protects pharmaceutical compositions combining fesoterodine, including fesoterodine hydrogen fumarate, with xylitol at defined weight ratios. The strongest commercial scope is directed to extended-release oral dosage forms containing approximately 5%-10% fesoterodine relative to xylitol, a cellulose-based sustained-release agent, wet granulation, and specified dissolution performance. The patent does not claim fesoterodine as a molecule, its therapeutic use generally, or every fesoterodine formulation.

The principal infringement issue is whether a competing product contains both fesoterodine and xylitol within the claimed ratio. The most direct design-around is to eliminate xylitol or move the fesoterodine-to-xylitol ratio outside the applicable claim range. A second design-around is to use a non-cellulosic release system or a dissolution profile outside the narrower dependent claims.

What does U.S. Patent 8,501,723 protect?

The patent claims a pharmaceutical composition containing:

Fesoterodine or a pharmaceutically acceptable salt;
Xylitol;
A fesoterodine-to-xylitol weight ratio of approximately 1%-20%.

The claims then narrow the composition by adding one or more of the following:

An acidic fesoterodine salt with an aqueous auto-pH of 3-5;
A di- or tricarboxylic acid salt;
Fesoterodine hydrogen fumarate;
A dosage-unit amount of 0.5-12 mg;
Granulation, including wet granulation in water;
A sustained-release agent;
Cellulose ethers or esters, particularly hydroxypropyl methylcellulose, or HPMC;
Sustained-release-agent concentrations of approximately 20%-80%, with narrower ranges of 25%-65%, 30%-65%, and 35%-55%;
Defined in vitro fesoterodine dissolution profiles.

The patent is therefore a formulation patent. It does not cover fesoterodine active pharmaceutical ingredient, fesoterodine hydrogen fumarate as a chemical substance standing alone, or every extended-release fesoterodine product.

How are the claims organized?

Claim group	Core limitation	Commercial significance
Claim 1	Fesoterodine or salt, xylitol, ratio approximately 1%-20%	Broadest composition claim
Claims 2-4	Acidic salt with auto-pH 3-5; carboxylic-acid salt; hydrogen fumarate	Narrows salt and pH characteristics
Claim 5	Hydrogen fumarate, 0.5-12 mg per dosage unit	Targets practical unit-dose formulations
Claims 6-8	Granulation, including wet granulation with water	Adds manufacturing-process characteristics
Claims 9-12	Sustained-release agent, especially HPMC, at 20%-80%	Targets extended-release dosage forms
Claim 13	Broad dissolution profile	Functional release limitation
Claims 14-15	Fesoterodine/xylitol ratio of 3%-15% or 5%-10%	Concentrates protection around narrower formulation space
Claims 16-17	Narrow ratio plus carboxylic-acid salt or hydrogen fumarate	Strong commercial subcombination
Claim 18	Approximately 11% fesoterodine/xylitol ratio	Specific ratio fallback
Claims 19-21	Sustained-release agent at 25%-65%, 30%-65%, or 35%-55%	Narrows excipient loading
Claim 22	Narrower dissolution profile	Most technically constrained release claim

Claims 14-18 are not interchangeable. Claim 18, directed to approximately 11%, is outside a literal 5%-10% range in claim 15, although it remains within claim 1 and potentially claim 14 depending on how “about” is construed.

What is the scope of independent claim 1?

Claim 1 is the central claim. A product falls within its literal scope if it contains:

Fesoterodine or a pharmaceutically acceptable salt;
Xylitol; and
A fesoterodine-to-xylitol weight ratio of approximately 1%-20%.

The claim does not require:

Fesoterodine hydrogen fumarate;
Extended release;
HPMC;
Granulation;
A particular dosage form;
A specific dissolution profile;
A particular fesoterodine dose;
Any particular therapeutic indication.

This gives claim 1 broader reach than the dependent claims. A conventional tablet, capsule, granule, or other pharmaceutical composition could potentially satisfy claim 1 if the composition contains the required ingredients and ratio.

How should the fesoterodine/xylitol ratio be calculated?

The claim language states a ratio of “Fesoterodine/xylitol” expressed as weight percent. The calculation is generally:

[ \text{Fesoterodine/xylitol ratio} = \frac{\text{weight of fesoterodine}}{\text{weight of xylitol}} \times 100 ]

For example:

Fesoterodine amount	Xylitol amount	Ratio
1 mg	100 mg	1%
1 mg	20 mg	5%
1 mg	10 mg	10%
1 mg	9.09 mg	Approximately 11%
1 mg	5 mg	20%

The treatment of the salt is important. If the product contains fesoterodine hydrogen fumarate, the parties may dispute whether the ratio uses the weight of the complete salt or the fesoterodine active moiety. The patent’s specification, examples, prosecution history, and analytical conventions would be relevant to that construction. The claim text alone does not resolve the issue.

Which claims cover fesoterodine hydrogen fumarate?

Claims 4, 5, 17, and potentially claims 2, 3, 14, and 16 create protection around fesoterodine hydrogen fumarate.

The most commercially relevant combinations are:

Claim 4: fesoterodine hydrogen fumarate plus xylitol at the claim 1 ratio;
Claim 5: the same composition in unit dosage form with 0.5-12 mg of hydrogen fumarate;
Claim 17: hydrogen fumarate plus a 3%-15% fesoterodine/xylitol ratio;
Claims 9-13 and 19-22: hydrogen fumarate compositions combined with sustained-release and dissolution limitations.

The claims do not appear to require a particular tablet strength such as the marketed 4 mg or 8 mg product unless the applicable claim is construed to include that strength within the 0.5-12 mg limitation.

What formulation technologies are protected?

Xylitol-containing formulations

Xylitol is the essential structural limitation of every claim. A formulation containing fesoterodine without xylitol is outside the literal scope of the claims as provided.

A formulation containing another polyol, such as mannitol, sorbitol, or maltitol, would not literally satisfy the xylitol limitation. Literal infringement could still be disputed under the doctrine of equivalents, but that analysis would depend on prosecution history and the role of xylitol in the invention.

Sustained-release formulations

Claims 9-13 and 19-22 target sustained-release compositions. Claim 10 identifies cellulose ethers or esters, and claim 11 specifically identifies HPMC.

The sustained-release-agent concentration is measured against the total composition. The nested ranges operate as follows:

Claim 12: approximately 20%-80%;
Claim 19: approximately 25%-65%;
Claim 20: approximately 30%-65%;
Claim 21: approximately 35%-55%.

A formulation containing 40% HPMC would fall within each of these ranges if all parent-claim limitations were satisfied. A product with 70% HPMC may fall within claim 12 but not claims 19-21.

Wet granulation

Claims 6-8 add process-related limitations:

At least one granulation step;
Wet granulation;
Wet granulation performed in the presence of water.

Claims 6-8 are composition claims drafted with “obtainable by” language. In U.S. practice, product-by-process language generally does not impose a process limitation on an otherwise identical product when the product itself cannot be distinguished from the prior-art product solely by manufacturing method. The prosecution history and the specific claim construction would control the infringement analysis.

A manufacturer using direct compression may avoid claims 7 and 8 if the process limitation is enforced as written, but it could remain exposed under claim 1 or other composition claims.

What are the dissolution limitations in claims 13 and 22?

Claim 13 requires a cumulative release profile measured by USP 711 in phosphate buffer at pH 6.8, 37°C, and 75 rpm:

Time point	Required release under claim 13
1 hour	Approximately 5%-30%
2 hours	Approximately 15%-40%
4 hours	Approximately 35%-65%
16 hours	At least approximately 75%

Claim 22 narrows the profile:

Time point	Required release under claim 22
1 hour	Approximately 6%-26%
2 hours	Approximately 18%-38%
4 hours	Approximately 36%-56%
16 hours	At least approximately 80%

These are cumulative release values based on the theoretical amount of fesoterodine in the formulation. A product may satisfy claim 13 but not claim 22. For example, a 27% release at one hour could fall within claim 13 but outside the 6%-26% range of claim 22.

Testing conditions matter. Differences in buffer preparation, apparatus calibration, agitation speed, sampling, assay method, and calculation of theoretical fesoterodine content can affect the result. A generic applicant or competitor would need a controlled dissolution protocol aligned with USP 711 and the patent’s stated conditions.

How strong is the patent estate based on the asserted claims?

The estate has a layered structure rather than a single all-purpose claim.

Risk layer	Relevant claims	Assessment
Broad composition risk	Claim 1	Highest breadth; depends on xylitol and ratio
Salt-specific risk	Claims 2-5, 16-17	Stronger product identification but narrower
Manufacturing risk	Claims 6-8	Potentially avoidable through process selection
Release-formulation risk	Claims 9-13, 19-22	Relevant to extended-release tablets
Ratio fallback risk	Claims 14-18	Provides alternative concentration positions
HPMC concentration risk	Claims 19-21	Targets common controlled-release formulation ranges

The patent is strongest against a product that reproduces the likely commercial architecture: fesoterodine hydrogen fumarate, xylitol, HPMC, a wet-granulated matrix, and an approximately 5%-11% fesoterodine/xylitol ratio.

It is weaker against:

A xylitol-free product;
A formulation using a different excipient system;
A non-matrix extended-release system;
A product with a materially different fesoterodine-to-xylitol ratio;
A dosage form that does not meet the claimed release profile;
A product manufactured without the claimed granulation process, where only process-dependent claims are asserted.

What invalidity issues could affect the claims?

Anticipation

A prior-art reference would need to disclose all limitations of the challenged claim. For claim 1, the reference would need to disclose fesoterodine or its salt, xylitol, and the claimed ratio. For claim 13 or 22, it would also need to disclose the specified dissolution profile under the relevant testing conditions.

A reference that discloses fesoterodine and xylitol but not the ratio may not anticipate claim 1. A reference that discloses the ratio but uses a different active ingredient would not anticipate the claim.

Obviousness

The main obviousness combination would likely involve:

Known fesoterodine oral dosage forms;
Xylitol as a pharmaceutical excipient;
HPMC or another sustained-release polymer;
Conventional wet granulation;
Routine optimization of release rate and excipient concentration.

The patentability question would turn on whether the claimed ratio, salt selection, process, or dissolution profile produced an unexpected technical result and whether the prior art gave a reason to select the claimed combination.

Indefiniteness

Potentially litigated terms include:

“About 1-20%”;
“About 3-15%”;
“About 5-10%”;
“About 11%”;
“Auto pH”;
“At least about 75%”;
“At least about 80%”;
“Obtainable by.”

The term “about” is not automatically indefinite. Its scope depends on the intrinsic record, analytical precision, technical context, and prosecution history. “Auto pH” may require specification-based interpretation because it is not a universally standardized claim term.

Written description and enablement

The claims cover substantial ranges of xylitol ratios, sustained-release-agent concentrations, and release profiles. A validity challenge could examine whether the specification demonstrates possession of the full claimed ranges and enables their practice without undue experimentation.

What generic entry risks exist?

A generic or follow-on applicant can pursue several design-around strategies.

Strategy	Likely effect
Remove xylitol	Avoids the express xylitol limitation
Use a different polyol	Avoids literal xylitol coverage
Use a ratio below 1% or above 20%	Avoids claim 1 if outside “about”
Use a ratio materially outside 5%-10%	Avoids claims 15 and related subcombinations
Replace HPMC	Avoids HPMC-specific claims, but not all sustained-release claims
Use a non-granulated process	Potentially avoids claims 6-8
Use direct compression	May avoid wet-granulation claims
Adopt a different release profile	May avoid claims 13 and 22
Use an immediate-release product	Avoids sustained-release claims, but claim 1 may remain relevant
Use a different salt	Avoids hydrogen-fumarate-specific claims, subject to claim 1

The most significant residual risk is claim 1. A design-around that changes HPMC or the manufacturing process but retains fesoterodine, xylitol, and the 1%-20% ratio may still face claim 1 exposure.

What is the Orange Book status of U.S. Patent 8,501,723?

The claim text does not establish whether Patent 8,501,723 is currently listed in the FDA Orange Book, whether it was listed for a particular fesoterodine product, or whether any listing has been delisted or removed. Orange Book listing is a regulatory-record question separate from patent validity and claim scope. The applicable FDA product record, patent-listing submissions, and current Orange Book edition control that determination.[2]

If listed for an approved fesoterodine product, the patent could create a Paragraph IV certification issue for an ANDA applicant. If not listed, the patent may still be asserted in district-court litigation, but it would not necessarily create the same ANDA certification and 30-month-stay framework associated with an Orange Book-listed patent.

Which companies are relevant to the patent landscape?

Fesoterodine was commercialized as Toviaz. The commercial landscape has involved the originator and its corporate successors, generic pharmaceutical companies seeking abbreviated approval, contract manufacturers, and owners or licensees of formulation technology.

The relevant rights analysis should distinguish:

The party listed as patent owner or assignee;
The NDA holder for Toviaz;
The manufacturer of the reference product;
Any licensee or sublicensee;
An ANDA applicant challenging an Orange Book-listed patent;
A defendant in patent litigation.

The patent number alone does not establish current ownership, licensing, litigation, settlement, or commercial enforcement status. Patent assignment records and court dockets are required for those determinations.[1][3]

What patent litigation and Paragraph IV risks apply?

A Paragraph IV certification would require an ANDA applicant to assert that the listed patent is invalid, unenforceable, or not infringed. The patent owner could then bring an infringement action under 35 U.S.C. § 271(e)(2), potentially triggering the statutory 30-month stay described in the Hatch-Waxman framework.[4]

The principal litigation theories for this patent would likely include:

The proposed product lacks xylitol;
The fesoterodine/xylitol ratio is outside the claimed range;
The product does not contain the claimed salt;
The product does not use HPMC or the claimed polymer concentration;
The manufacturing method does not include wet granulation;
The dissolution data do not meet claims 13 or 22;
The claims are invalid for anticipation, obviousness, indefiniteness, written-description failure, or lack of enablement;
The asserted patent is expired, unenforceable, or not properly listed.

No settlement terms, license terms, or final litigation outcome can be inferred from the claim language.

How does this patent compare with molecule and method-of-use patents?

Patent type	Typical protected subject matter	Relationship to Patent 8,501,723
Composition-of-matter patent	Fesoterodine chemical compound or salt	Broader at the molecule level, but separate from this formulation patent
Formulation patent	Fesoterodine plus xylitol, release polymer, process, and dissolution	Directly represented by Patent 8,501,723
Method-of-use patent	Treatment of overactive bladder or related indications	May apply to labeled use, but is not claimed here
Manufacturing patent	Synthesis, purification, salt formation, or processing	Separate risk from the dosage-form claims
Device or delivery patent	Delivery system or dosage-form architecture	May overlap with formulation products depending on structure

Patent 8,501,723 should be analyzed as one layer in a broader freedom-to-operate review. Avoiding this patent does not necessarily avoid active-ingredient, manufacturing, method-of-use, or other formulation patents.

What geographic coverage does the patent provide?

U.S. Patent 8,501,723 provides rights only in the United States. Parallel patent-family members may exist in Europe, Canada, Japan, and other jurisdictions, but claim scope, prosecution history, term, validity, and enforcement status must be evaluated separately in each country.

A U.S. design-around does not establish freedom to operate in Europe or other markets. The xylitol ratio, hydrogen-fumarate limitation, HPMC concentration, and dissolution claims may have materially different wording in foreign family members.

Key Takeaways

Claim 1 is the broadest claim and requires fesoterodine, xylitol, and an approximately 1%-20% fesoterodine/xylitol weight ratio.
The patent does not claim fesoterodine as a molecule or every fesoterodine product.
Claims 4, 5, 17, and related claims focus on fesoterodine hydrogen fumarate.
Claims 9-13 and 19-22 target sustained-release systems, especially HPMC matrix formulations.
Claims 6-8 add granulation limitations, including wet granulation with water.
Claims 13 and 22 impose detailed USP 711 dissolution profiles.
Removing xylitol is the clearest design-around to the claim set provided.
Changing HPMC or the manufacturing process may avoid narrower claims but may not avoid claim 1.
Current Orange Book listing, patent term, ownership, licensing, litigation, and settlement status cannot be determined from the claims alone.
The patent should be reviewed with the complete specification, prosecution history, assignment records, Orange Book data, patent-family records, and court dockets before a launch or licensing decision.

Frequently Asked Questions

Does a fesoterodine tablet infringe if it contains xylitol but no HPMC?

Potentially. HPMC is required only by narrower claims such as claims 10 and 11. A product could still implicate claim 1 if it contains fesoterodine, xylitol, and the claimed ratio.

Does a product with 0.5 mg of fesoterodine automatically fall within claim 5?

No. Claim 5 also requires fesoterodine hydrogen fumarate, unit dosage form, the claim 1 composition limitations, and the specified amount range. The amount limitation alone is insufficient.

Does using mannitol instead of xylitol avoid the patent?

It generally avoids literal infringement of the supplied claims because the claims specifically require xylitol. Equivalence theories and the prosecution history could affect the analysis.

Can a generic applicant avoid claims 13 and 22 by changing the dissolution test?

A different test may avoid literal satisfaction of the stated limitations, but the relevant comparison would be the product’s performance under the patent-specified USP 711 conditions. Testing cannot be changed solely to produce a favorable result.

Is Patent 8,501,723 a patent on Toviaz?

It is a formulation patent relating to fesoterodine compositions. It is not, based on the supplied claims, a patent on the fesoterodine molecule itself or on the Toviaz brand as a commercial designation.

References

United States Patent and Trademark Office. (2013). U.S. Patent No. 8,501,723, Pharmaceutical composition comprising fesoterodine and xylitol.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book.
United States Patent and Trademark Office. (n.d.). Patent Center and assignment records.
21 U.S.C. § 355; 35 U.S.C. §§ 271(e)(2), 282.
United States Pharmacopeial Convention. (n.d.). USP General Chapter <711>: Dissolution.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Pfizer	TOVIAZ	fesoterodine fumarate	TABLET, EXTENDED RELEASE;ORAL	022030-001	Oct 31, 2008	AB	RX	Yes	No	⤷ Start Trial	⤷ Start Trial			Y		⤷ Start Trial
Pfizer	TOVIAZ	fesoterodine fumarate	TABLET, EXTENDED RELEASE;ORAL	022030-002	Oct 31, 2008	AB	RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial			Y		⤷ 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

Details for Patent: 8,501,723

Which drugs does patent 8,501,723 protect, and when does it expire?

Summary for Patent: 8,501,723