United States Patent 6,455,557: Tizanidine Food-Effect Claims, Scope, Expiration, and Patent Landscape

U.S. Patent No. 6,455,557 protects methods for administering immediate-release multiparticulate tizanidine with food to alter pharmacokinetics and reduce somnolence or peak plasma concentration. The patent covers food-timed administration, tizanidine dose ranges, bead-based multiparticulate dosage forms, rapid dissolution, and specified time-to-peak-plasma-concentration results. Its patent term expired in 2019, eliminating it as a current U.S. barrier to generic tizanidine products. The claims remain relevant to historical Orange Book listings, past Paragraph IV litigation, formulation design, and freedom-to-operate analysis.

What does U.S. Patent 6,455,557 protect?

The patent protects a method of using tizanidine, not tizanidine as a chemical entity. Every asserted claim requires administration of tizanidine in an immediate-release multiparticulate pharmaceutical composition, generally together with food.

The central claim concept combines four limitations:

A patient receives tizanidine for a therapeutic effect.
The dosage form is immediate-release and multiparticulate.
The dosage form is administered with food.
Food administration produces a defined pharmacokinetic or clinical result.

The principal claimed results are:

Reduced somnolence during tizanidine therapy.
Reduced peak plasma tizanidine concentration.
A peak plasma concentration earlier than approximately four hours.
For claim 19, a peak plasma concentration earlier than approximately two hours when administered without food.
Release of substantially all tizanidine within 60 minutes.
Release of at least 75% of tizanidine within 60 minutes.

The patent therefore targets the food-effect problem associated with conventional oral tizanidine products. It does not broadly cover every tizanidine tablet, capsule, solution, or method of treating spasticity.

What are the independent claims in U.S. Patent 6,455,557?

Claim	Core subject matter	Principal limitation
1	Reducing somnolence	Immediate-release multiparticulate tizanidine administered with food; peak concentration earlier than about four hours
10	Reducing peak plasma concentration	Same immediate-release multiparticulate and food-administration framework
19	Reducing peak plasma concentration	Peak concentration earlier than about two hours when administered without food
20	Reducing peak plasma concentration	Substantially all tizanidine released within 60 minutes
21	Reducing peak plasma concentration	At least 75% of tizanidine released within 60 minutes

Claims 1 and 10 establish the broadest practical claim groups. Claims 2 through 9 narrow claim 1 by dose, food timing, bead structure, unit dosage form, and capsule or unit-dose strength. Claims 11 through 18 provide parallel limitations for claim 10.

How are the claims organized?

Claims 1 through 9: reduced somnolence

Claim 1 is directed to reducing somnolence in a patient receiving tizanidine therapy. The composition must be immediate-release and multiparticulate, and the administration must occur with food. The pharmacokinetic result is a peak plasma concentration earlier than about four hours.

Dependent claims narrow the scope as follows:

Claims 2 and 3 specify doses of 0.5 to 12 mg and 2 to 8 mg.
Claims 4 through 6 define administration relative to food consumption.
Claim 7 requires tizanidine on beads.
Claim 8 requires a unit dosage form.
Claim 9 specifies 2 to 6 mg per unit dosage.

The claim set covers administration before, during, or shortly after a meal. Claim 4 covers administration from 30 minutes before to two hours after consuming food. Claim 5 focuses on administration substantially at the time of food consumption. Claim 6 covers administration immediately after food through one hour after consumption.

Claims 10 through 18: reduced peak plasma concentration

Claim 10 repeats the core dosage-form and food-administration limitations but changes the intended result from reducing somnolence to reducing peak plasma concentration.

Claims 11 through 18 mirror claims 2 through 9. This parallel structure gives the patent two principal therapeutic theories:

A clinical outcome, reduced somnolence.
A pharmacokinetic outcome, reduced peak plasma concentration.

A product or method could implicate claim 10 even if the sponsor does not characterize its labeling or clinical objective as reducing somnolence.

Claim 19: early peak concentration without food

Claim 19 requires administration of the multiparticulate composition with food but recites that the composition produces a peak plasma concentration earlier than about two hours when administered without food.

This claim is structurally more difficult to interpret than claims 1 and 10. The method requires administration with food, while the pharmacokinetic result is expressed by reference to administration without food. The claim may be read as requiring a composition that has an early peak under the no-food condition, while the claimed method itself uses the product with food. Its enforceability would depend heavily on claim construction, the specification, and the evidence establishing the relevant pharmacokinetic comparison.

Claims 20 and 21: rapid release

Claims 20 and 21 focus on dissolution or release rather than a specific peak-time result.

Claim 20 requires release of substantially all tizanidine within 60 minutes.
Claim 21 requires release of at least 75% within 60 minutes.

These claims potentially reach immediate-release multiparticulate products that meet the release threshold even if the sponsor does not use the same food-effect language in its labeling.

What formulation features are protected?

The claims require an immediate-release multiparticulate composition. Claim 7 expressly identifies tizanidine on beads. The patent therefore has greater relevance to bead-filled capsules, sachets, sprinkle products, and other dosage forms containing discrete drug-loaded particles than to a conventional monolithic tablet.

The formulation limitations can be grouped into four technical categories:

Technical element	Claim treatment	Commercial significance
Active ingredient	Tizanidine, generally administered at therapeutic doses	Limits claims to tizanidine products
Release profile	Immediate release; 75% or substantially all released within 60 minutes in claims 20 and 21	Captures rapid-release products
Multiparticulate structure	Multiparticulate form, including tizanidine on beads	Narrows claims against conventional single-unit dosage forms
Administration condition	With food, within specified timing windows	Creates a use and labeling limitation

The patent does not require a particular bead core, coating polymer, excipient, capsule shell, manufacturing process, particle-size distribution, or dissolution apparatus in the issued claims provided. Those details could matter for infringement analysis only if they are incorporated through claim construction or disclosed as necessary to satisfy the immediate-release and pharmacokinetic limitations.

How broad are the dosage and food-timing limitations?

The dose coverage is broad within ordinary tizanidine therapeutic use. Claims 2 and 11 cover 0.5 to 12 mg. Claims 3 and 12 narrow the range to 2 to 8 mg. Claims 9 and 18 narrow the unit dose to 2 to 6 mg.

The food-timing provisions cover most practical meal-related dosing scenarios:

Claim	Timing window
4 and 13	30 minutes before food through two hours after food
5 and 14	Substantially at the same time as food
6 and 15	Immediately after food through one hour after food

A product labeled for administration without regard to food could still raise historical infringement questions if patients routinely used it with food and the remaining claim limitations were satisfied. For induced-infringement analysis, the product label, promotional materials, prescribing information, and evidence of intended use would be material.

What is the patent’s pharmacokinetic scope?

The pharmacokinetic limitations are outcome-based. They do not merely require a composition that dissolves rapidly in vitro. They require a plasma concentration profile or release result.

For claims 1 and 10, the relevant endpoint is a peak plasma concentration earlier than approximately four hours after administration with food. The phrase “earlier than about 4 hours” introduces a numerical boundary with potential claim-construction issues. The specification and prosecution history would be important in determining how much variation “about” permits.

Claim 19 uses an approximately two-hour threshold under the no-food comparison. Claims 20 and 21 use release testing rather than plasma sampling:

“Substantially all” is a qualitative limitation in claim 20.
“At least 75%” is a quantitative limitation in claim 21.

Claims 20 and 21 may be easier to evaluate through standardized dissolution testing than claims 1, 10, and 19, which require pharmacokinetic evidence. A challenger or patent owner would likely need comparative data addressing food status, sampling time points, dose, patient population, and bioanalytical methods.

When did U.S. Patent 6,455,557 expire?

U.S. Patent 6,455,557 was issued on September 24, 2002. Its effective nonprovisional filing date was in 1999, producing a 20-year patent term that ended in 2019 under the applicable U.S. patent-term rules.[1]

Event	Date
U.S. patent application filing	1999
Patent issuance	September 24, 2002
Expected 20-year term endpoint	2019
Current enforceability	Expired

The patent is therefore not a current U.S. exclusion right. A historical patent listing or past litigation record does not restore enforceability after expiration. Any patent-term adjustment, terminal disclaimer, or term-restoration issue should be checked against the USPTO Patent Center record and the Orange Book patent listing history.[2]

What was the Orange Book status of the patent?

The patent was associated with the tizanidine product franchise, including Zanaflex products marketed in the United States. The relevant FDA regulatory framework included tizanidine tablets and capsules approved under NDA 020397 and later generic ANDAs.[3]

The patent’s practical Orange Book significance was greatest during the period when generic applicants were required to address listed patents through Paragraph IV certifications or other certification pathways. Because the patent expired in 2019, it no longer creates a current generic-entry block.

An Orange Book listing does not establish that every generic product infringes every claim. It identifies patents submitted by an NDA holder or listed pursuant to FDA procedures. Infringement depends on the approved product, labeling, dosage form, instructions for use, and claim limitations.[4]

Were there Paragraph IV challenges or patent litigation?

Tizanidine faced generic competition through the ANDA pathway, and the 6,455,557 patent was relevant to the patent-certification and litigation environment surrounding Zanaflex products. Public FDA records and Orange Book materials should be used to distinguish:

Paragraph IV certifications directed to the patent.
Declaratory-judgment actions.
Hatch-Waxman infringement suits under 35 U.S.C. § 271(e)(2).
Commercial settlements.
Later generic approvals after patent expiry.

The patent’s expiration means that any historical Paragraph IV dispute is now primarily relevant to launch chronology, damages analysis, settlement economics, and market-entry strategy. It does not support a current injunction against an otherwise approvable generic tizanidine product.

What is the current generic-entry risk?

The current U.S. risk is commercial rather than patent-based. Tizanidine hydrochloride is a long-established small-molecule product with generic tablets and capsules. There is no biosimilar pathway issue because tizanidine is not a biologic. The principal barriers are regulatory execution, product quality, manufacturing economics, market concentration, and substitution dynamics.

Risk category	Current assessment
Expired formulation/use patent	No current blocking effect from U.S. Patent 6,455,557
Paragraph IV exposure	Historical relevance only for this patent
Biosimilar risk	Not applicable
Generic substitution	Established market pathway
Formulation differentiation	Possible through capsules, tablets, multiparticulates, or modified administration instructions
Manufacturing barrier	Bead manufacture and content uniformity may create operational complexity
Regulatory barrier	ANDA requirements, bioequivalence, dissolution, and labeling compliance remain applicable

A new product using the same core tizanidine formulation could still face other unexpired patents, trademarks, trade dress rights, or regulatory exclusivities. Those rights must be evaluated separately from Patent 6,455,557.

How strong was the patent estate?

The patent had meaningful historical scope but a narrow technical center. Its strength came from combining:

A clinically recognized side effect.
Food-effect pharmacokinetics.
Immediate-release multiparticulate delivery.
Specific dose and timing ranges.
Objective release and plasma-concentration limitations.

Its weaknesses included the need to prove multiple limitations in combination. A potentially infringing product would need to satisfy the multiparticulate requirement, the food-administration condition, and the claimed pharmacokinetic or release result. A conventional immediate-release tablet without a multiparticulate structure would present a stronger noninfringement position against claims requiring multiparticulates or beads.

The patent also relied heavily on functional and result-oriented language. That could create disputes over:

The meaning of “reducing somnolence.”
The meaning of “reducing the peak plasma concentration.”
The scope of “about” four hours or two hours.
The required comparator for food versus no-food administration.
The meaning of “substantially all.”
The testing method for 75% release within 60 minutes.

Those issues would have affected claim construction and proof at trial. They no longer affect prospective enforcement because the patent has expired.

How does this patent compare with other tizanidine protections?

Protection type	Coverage	Current relevance
U.S. Patent 6,455,557	Food administration, somnolence reduction, peak concentration, multiparticulate immediate-release forms	Expired
Tizanidine compound protection	Active pharmaceutical ingredient	Long expired
Product patents	Specific commercial dosage forms or compositions	Requires separate patent-by-patent review
Method-of-use patents	Treatment of spasticity or administration regimens	Requires separate review
FDA exclusivity	NDA-based regulatory exclusivity	Expired for the legacy product
Trademark rights	Zanaflex branding	Separate from patent protection
Manufacturing know-how	Beads, coatings, granulation, content uniformity	May remain confidential but is not equivalent to patent exclusivity

What licensing and commercial issues were associated with the patent?

The patent was part of the intellectual-property environment supporting commercial tizanidine products marketed by the Zanaflex franchise. Licensing and commercialization arrangements involving the product, formulation, or U.S. rights would have affected ownership and enforcement during the patent term.

Patent ownership and product commercialization should be separated. The entity marketing Zanaflex was not necessarily the original inventor or original patent assignee. Assignment records, continuation filings, and recorded ownership should be checked through USPTO assignment records before attributing enforcement rights or licensing revenue to a particular company.[5]

Because the patent expired, it no longer supports royalty demands for future U.S. sales unless a separate contract contains independent payment obligations unrelated to patent enforceability.

What revenue exposure did the patent create?

The patent protected a product-level commercial advantage rather than a broad tizanidine market monopoly. Its revenue exposure depended on the extent to which the branded product’s sales relied on:

The multiparticulate dosage form.
Food-effect differentiation.
Reduced somnolence positioning.
Delayed generic entry.
Settlement terms with ANDA applicants.

Once generic tizanidine products entered the market, the patent’s economic value declined with generic substitution and price erosion. After expiration, the patent’s residual value is limited to historical damages, contract interpretation, and transactional due diligence.

Key Takeaways

U.S. Patent 6,455,557 covers methods of administering immediate-release multiparticulate tizanidine with food.
The patent’s main objectives are reducing somnolence and reducing peak plasma tizanidine concentration.
Claims 1 through 18 emphasize food timing, dose, beads, and unit-dose strength.
Claims 19 through 21 address early peak concentration and rapid release.
The claims are narrower than a general patent on tizanidine tablets or capsules because they require multiparticulate and pharmacokinetic or release limitations.
The patent expired in 2019 and is not a current U.S. barrier to generic tizanidine entry.
No biosimilar analysis applies because tizanidine is a small-molecule drug.
Historical Orange Book listings, Paragraph IV certifications, litigation, and settlements remain relevant to market-entry history but not current patent enforcement.
Current competition is governed primarily by FDA approval, bioequivalence, manufacturing capability, pricing, and commercial substitution.

FAQs

Does Patent 6,455,557 cover all tizanidine capsules?

No. The claims require an immediate-release multiparticulate composition and additional food-effect, pharmacokinetic, or release limitations. A conventional capsule may fall outside the claims if it lacks the required multiparticulate structure or does not satisfy the claimed results.

Can a generic tizanidine manufacturer rely on patent expiration?

Yes, with respect to U.S. Patent 6,455,557. The patent expired in 2019. The manufacturer must still address any other unexpired patents, FDA requirements, labeling obligations, and applicable regulatory exclusivity.

Does taking tizanidine with food infringe the patent?

Not by itself. Infringement would require the claimed combination, including the specific multiparticulate dosage form and the relevant pharmacokinetic or release limitation.

Are tizanidine bead formulations still patentable?

A new bead formulation could be patentable if it satisfies novelty, nonobviousness, written-description, enablement, and other statutory requirements. Patent 6,455,557 does not prevent later patenting of genuinely different formulation technology.

Is reduced somnolence a separate FDA-approved indication for tizanidine?

The patent claim uses reduced somnolence as a claimed therapeutic result. FDA labeling and approved indications are separate questions governed by the relevant NDA and labeling history. Patent claim language does not itself establish an FDA-approved indication.

References

U.S. Patent No. 6,455,557. (2002). Methods for reducing side effects of tizanidine therapy. United States Patent and Trademark Office.
United States Patent and Trademark Office. (n.d.). Patent Center. https://patentcenter.uspto.gov/
U.S. Food and Drug Administration. (n.d.). Drugs@FDA: FDA-approved drugs. https://www.accessdata.fda.gov/scripts/cder/daf/
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations, Orange Book. https://www.fda.gov/drugsatfda
United States Patent and Trademark Office. (n.d.). Assignment search. https://assignment.uspto.gov/

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
World Intellectual Property Organization (WIPO)	2005023252	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,455,557

Summary for Patent: 6,455,557