United States Patent 6,761,910: Scope, Claims, Expiration, and Fentanyl Patent Landscape

U.S. Patent No. 6,761,910 protects a water-free, sublingual drug-delivery platform based on micronized active-ingredient particles attached to larger, water-soluble carrier particles containing bioadhesive material. The claims specifically cover fentanyl compositions and sublingual treatment of acute or breakthrough pain.

The patent was important to the Abstral fentanyl citrate sublingual product but is no longer an enforceable exclusionary right. Its listed patent term ended in July 2019. The patent remains relevant for historical Orange Book analysis, invalidity analysis, freedom-to-operate reviews, and assessment of continuation or related formulation patents.

What technology does U.S. Patent 6,761,910 protect?

The core invention is a particulate sublingual formulation designed to deliver an active pharmaceutical ingredient rapidly through the oral mucosa.

Claim 1 requires all of the following:

A pharmaceutical composition for treating an acute disorder.
Sublingual administration.
An essentially water-free formulation.
Microparticles of at least one active pharmaceutical ingredient.
Microparticles adhered to the surfaces of larger carrier particles.
Water-soluble carrier particles.
A bioadhesion- or mucoadhesion-promoting agent mainly adhered to the carrier-particle surfaces.

The claim is a composition claim rather than a claim limited to a particular tablet shape, manufacturing process, excipient ratio, or active ingredient. Fentanyl appears only in dependent claims 16, 18, and 20.

The invention therefore has two layers of protection:

A broad formulation platform covering multiple active ingredients and excipient systems.
A narrower fentanyl-specific sublingual formulation and treatment regime.

What are the key claim limitations?

Claim 1: broad platform composition

Claim 1 is the principal composition claim. Its most important limitations are structural rather than purely chemical.

The accused product would need to contain a defined particulate architecture in which active-agent microparticles are adhered to larger carrier particles. A simple blend of fentanyl and excipients may not satisfy this limitation if the active particles are not adhered to the carrier surfaces.

The carrier particles must be substantially larger than the active microparticles and essentially water-soluble. The claim does not require a particular carrier material, but the dependent claims identify carbohydrates and inorganic salts as preferred materials.

The bioadhesive or mucoadhesive agent must be mainly adhered to the carrier particles. This limitation is significant because it may distinguish the claimed formulation from a tablet in which the polymer is uniformly dispersed throughout the entire matrix.

Claim 2: active-particle size

Claim 2 limits the active-agent microparticles to a weight-based mean diameter of less than 10 micrometers.

This limitation supports rapid dissolution and dispersion across the sublingual mucosa. It also creates an analytical issue: infringement may depend on particle-size testing, sampling methodology, agglomeration, and whether the product contains primary particles or aggregates.

Claim 3: carrier-particle size

Claim 3 requires a mean sieve diameter for the carrier particles between 100 and 600 micrometers.

This is a measurable limitation. A product outside that range may avoid claim 3 but could still fall within claim 1 if the carrier particles satisfy the broader relative-size requirement.

Claim 4: brittle carrier material

Claim 4 covers carrier particles made from a brittle material that fragments easily when compressed.

The limitation is directed to tableting behavior. It supports rapid exposure and dispersion of the active microparticles after compression or placement under the tongue.

Claims 5 through 7: mucoadhesive agents

Claim 5 requires the bioadhesive or mucoadhesive agent to constitute 0.1% to 25% by weight of the carrier particles.

Claim 6 narrows the polymers to specified classes, including:

Acrylic polymers.
Cellulose derivatives.
Natural polymers.
Mixtures of those materials.

Claim 7 lists specific polymers and polymer classes, including hydroxypropyl methylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, sodium carboxymethyl cellulose, carbomer, polyethylene oxide, chitosan, gelatin, sodium alginate, pectin, xanthan gum, guar gum, and related materials.

These claims provide fallback positions if a broader claim is challenged for prior art or lack of written description. They also create potential design-around opportunities through different polymers, different polymer locations, or different adhesion mechanisms.

Claims 8 through 10: surfactant system

Claim 8 adds a pharmaceutically acceptable surfactant in finely dispersed form and intimately mixed with the active agent.

Claim 9 limits the surfactant concentration to 0.5% to 5% by weight. Claim 10 identifies sodium lauryl sulfate, polysorbates, bile-acid salts, and mixtures.

This group of claims targets dissolution and dispersion of the micronized active ingredient. It is narrower than claim 1 and depends on a specific physical relationship between the surfactant and active agent.

Claims 11 and 12: water-soluble carriers

Claim 11 requires a water-soluble carbohydrate or inorganic salt as the carrier. Claim 12 identifies mannitol, lactose, calcium phosphate, and sugar.

The inclusion of calcium phosphate is notable because the claim set treats it as part of a carrier group even though its dissolution behavior differs from highly soluble sugars. Product-specific formulation evidence would be important in determining whether a particular grade and quantity satisfy the claim.

Claims 13 through 15: disintegrants

These claims cover formulations containing a pharmaceutical disintegrant that promotes dispersion of the active microparticles over the sublingual mucosa.

Claim 15 requires 1% to 10% disintegrant by weight. The listed materials include crospovidone, carboxymethyl starch, natural starch, microcrystalline cellulose, and cellulose gum.

Claims 16 through 18: fentanyl and breakthrough pain

Claim 16 limits the active ingredient to fentanyl or a pharmaceutically acceptable salt. Claim 18 further limits the use to acute or breakthrough pain.

These claims are directly relevant to sublingual fentanyl citrate products, including Abstral. They do not cover every fentanyl dosage form. A product must also satisfy the claim 1 formulation architecture and, for a method claim, the specified sublingual treatment use.

Claims 19 through 21: method of treatment

Claim 19 covers administering at least one dose unit sublingually to treat an acute disorder. The administered composition must contain:

An effective amount of active ingredient.
Active-agent microparticles adhered to larger carrier particles.
Essentially water-soluble carriers.
A bioadhesion or mucoadhesion-promoting agent.

Claim 20 limits the method to fentanyl. Claim 21 specifies a fentanyl dose of 0.05 mg to 20 mg.

The range in claim 21 is broad relative to commercial sublingual fentanyl doses. A product outside that range could avoid claim 21 but would not necessarily avoid claim 20 or the broader composition claims.

How many independent claims does U.S. Patent 6,761,910 have?

The patent has two principal independent claim categories:

Claim	Type	Core subject matter
1	Composition	Water-free sublingual particulate formulation
19	Method	Sublingual administration of the particulate formulation

Claim 17 is drafted as a composition claim that repeats the acute-disorder and sublingual-use concept. It does not materially expand the technical formulation requirements of claim 1. Claims 16 and 18 provide the principal fentanyl-specific composition limitations, while claims 20 and 21 narrow the treatment method to fentanyl and a specified dosage range.

When did U.S. Patent 6,761,910 expire?

U.S. Patent 6,761,910 issued on July 13, 2004. Its patent term ended in July 2019, based on the patent record and the term information historically associated with the patent.[1]

Event	Date or status
U.S. patent issued	July 13, 2004
Patent term basis	Twenty-year term measured from the relevant nonprovisional filing date, subject to adjustment
Listed expiration period	July 2019
Current enforceability	Expired
Current Orange Book blocking effect	None from this patent alone

An expired patent cannot support a new infringement action for post-expiration conduct. Historical infringement claims remain legally distinct from current market-exclusion rights, and expiration does not eliminate the patent’s evidentiary value in litigation involving earlier conduct.

What was the Orange Book status of the patent?

U.S. Patent 6,761,910 was associated with the Abstral fentanyl citrate sublingual product in historical FDA patent listings. Abstral was approved by FDA as a sublingual fentanyl product for breakthrough pain in opioid-tolerant patients.[2]

The Orange Book listing did not mean that every fentanyl product infringed every claim. The listing reflected the sponsor’s position that the patent covered the approved drug or an approved method of use. In a Paragraph IV certification, an ANDA applicant could challenge the patent’s validity, enforceability, or relevance to the proposed product.

Because the patent expired in 2019, it no longer provides a current regulatory barrier to ANDA approval. Later-issued patents, continuation patents, formulation patents, or method-of-use patents may still affect generic entry.

What Paragraph IV risks applied to fentanyl sublingual products?

A Paragraph IV challenger targeting a product associated with this patent would typically evaluate four issues:

Whether the proposed product contains the claimed ordered mixture.
Whether active microparticles are adhered to larger water-soluble carriers.
Whether the mucoadhesive agent is mainly adhered to the carrier surfaces.
Whether the patent was valid and enforceable when the ANDA was filed.

The strongest design-around position would involve a formulation that uses a conventional homogeneous matrix, a nonadhered active ingredient, a carrier outside the claimed size relationship, or a different delivery mechanism.

The strongest infringement position would focus on formulation and manufacturing records, including:

Particle-size distributions.
Carrier composition.
Polymer localization.
Granulation or adhesion steps.
Microscopic images.
Dissolution and dispersion data.
Batch records.
Blend uniformity results.

A product label alone may not disclose the physical arrangement needed to assess claim 1. Discovery of manufacturing information would often be material.

How strong is the patent estate for sublingual fentanyl?

The patent estate associated with sublingual fentanyl products generally has several layers:

Layer	Typical protection	Relevance
Platform formulation	Microparticles adhered to larger carriers	Broadest technical concept
Fentanyl composition	Fentanyl or fentanyl salt in the platform	Product-specific
Dose and treatment	Sublingual fentanyl for breakthrough pain	Method-of-use protection
Formulation improvements	Excipients, particle size, compression, dissolution	Later-entry barriers
Manufacturing	Ordered mixing, adhesion, granulation, tableting	Process and evidence issues
Regulatory exclusivity	FDA exclusivity associated with approval	Separate from patent term

U.S. Patent 6,761,910 was the foundational platform layer, but its expiration materially reduced the estate’s strength. The remaining risk depends on related patents and their expiration dates, claim scope, listing status, and litigation history.

What formulations are most likely to fall within the patent?

A formulation is most exposed when it has all of the following characteristics:

Fentanyl citrate or another fentanyl salt.
Micronized active ingredient below 10 micrometers.
Mannitol, lactose, sugar, or another water-soluble carrier.
Carrier particles in the 100-to-600-micrometer range.
Carbomer, cellulose derivative, or another listed mucoadhesive.
Adhesion of the active ingredient and polymer to carrier surfaces.
Sublingual administration for breakthrough pain.
A compressed, rapidly disintegrating tablet.

A formulation is less exposed to the narrower claims if it:

Uses a nonparticulate film or spray.
Uses a homogeneous polymer matrix.
Uses a non-water-soluble carrier.
Does not adhere the active particles to carrier surfaces.
Uses an active-particle size above the claim 2 threshold.
Uses a carrier outside the claim 3 range.
Delivers fentanyl through buccal, transdermal, nasal, injectable, or pulmonary administration.

Avoiding claims 2 through 15 does not necessarily avoid claim 1. The broad claim must be analyzed independently.

What manufacturing and intellectual-property barriers remain?

The manufacturing barrier is the controlled preparation of an ordered mixture. The key technical challenge is distributing very small active particles onto substantially larger carrier particles while maintaining blend uniformity, dose accuracy, adhesion, rapid disintegration, and acceptable mucosal residence.

Manufacturing evidence can also create infringement exposure. Even where the final tablet appears conventional, process documents may show that the active ingredient was adhered to carrier surfaces and that the mucoadhesive was localized on those particles.

The patent’s broad terminology creates both value and litigation risk. Terms such as “essentially water-free,” “ordered mixture,” “mainly adhered,” “substantially larger,” and “bioadhesion” require construction based on the specification, prosecution history, technical evidence, and relevant prior art.

What validity issues could affect the claims?

The principal validity issues would likely involve:

Anticipation and obviousness

The field already included sublingual, mucoadhesive, micronized, rapidly dissolving, and ordered-mixture technologies. A challenger would combine prior art on:

Micronized active ingredients.
Water-soluble carriers.
Mucoadhesive polymers.
Sublingual dosage forms.
Rapid tablet disintegration.
Ordered powder mixtures.

The most defensible claim feature may be the specific combination of particle architecture and surface localization rather than any single ingredient.

Written description and enablement

Claim 1 covers a broad range of active agents and mucoadhesive systems. A challenger could argue that the specification does not adequately support or enable the full breadth of the genus.

Claim construction

The phrases “essentially water-free,” “mainly adhered,” and “ordered mixture” may control the outcome. If construed narrowly, they may limit infringement. If construed functionally, they may cover a wider range of commercial formulations.

Indefiniteness

The size and concentration limitations are relatively measurable. The more qualitative terms, particularly “mainly adhered” and “bioadhesion,” present greater interpretive risk.

Were there licensing deals or settlements tied to this patent?

The patent record alone does not establish the complete commercial licensing history for products using the formulation. Commercial rights, development arrangements, and marketing agreements may have involved separate contracts that do not appear in the patent file.

A settlement involving an ANDA applicant would be relevant only if it addressed this patent or a related patent family. Because U.S. Patent 6,761,910 is expired, any current settlement analysis should focus on later patents listed for the relevant fentanyl product, not on this patent as an active exclusionary right.

How does this patent compare with other fentanyl delivery patents?

Delivery type	Typical technical focus	Relationship to U.S. 6,761,910
Sublingual tablet	Microparticles, carriers, mucoadhesion, rapid disintegration	Directly relevant
Buccal tablet	Buccal residence and transmucosal absorption	Generally outside the sublingual limitation
Buccal film	Polymer film and fentanyl release	Different dosage-form architecture
Nasal spray	Droplet size, nasal deposition, absorption	Different administration route
Transdermal patch	Reservoir or matrix release through skin	Unrelated formulation platform
Injectable fentanyl	Sterile solution or suspension	Outside the claimed composition architecture

The main competitive concern is substitution among rapid-onset fentanyl products, not direct infringement by every fentanyl product.

What generic launch risks exist now?

This patent creates no current generic launch block because it has expired. Current launch risk depends on:

Later patents listed for the reference product.
Patent term extensions or later-issued continuation rights.
FDA exclusivity.
Controlled-substance regulatory requirements.
REMS obligations.
Manufacturing equivalence and bioequivalence requirements.
The ability to demonstrate comparable sublingual performance.

There is no biosimilar pathway issue because fentanyl is a small-molecule active ingredient. The relevant pathway is generally an ANDA under section 505(j), not a biosimilar application under section 351(k).

Key Takeaways

U.S. Patent 6,761,910 covers an ordered, essentially water-free sublingual particulate formulation.
The core architecture is micronized active particles adhered to larger, water-soluble carrier particles containing a mucoadhesive agent.
Claims 16, 18, 20, and 21 make the patent specifically relevant to fentanyl and breakthrough pain.
The patent’s most important technical limitations are particle adhesion, carrier size, active-particle size, water solubility, and mucoadhesive localization.
The patent expired in July 2019 and is no longer a current market-exclusion right.
Historical Orange Book relevance does not create present-day patent blocking power.
A generic design-around could use a different physical architecture, delivery route, carrier system, or particle-size profile.
Current entry risk must be assessed against later patents and regulatory requirements associated with the specific fentanyl reference product.
No biosimilar risk applies to fentanyl.
Manufacturing records may be more important than the product label in assessing infringement of the ordered-mixture claims.

FAQs

Does U.S. Patent 6,761,910 cover all sublingual fentanyl products?

No. It covers products with the claimed particulate architecture. A sublingual fentanyl spray, film, solution, or different tablet matrix may not satisfy the claims.

Can an expired patent still affect a fentanyl generic launch?

It cannot block present-day launch through an infringement action for future conduct. It can remain relevant to historical damages, patent-family analysis, prosecution strategy, and assessment of related patents.

Is fentanyl citrate specifically required by the claims?

No. The claims refer to fentanyl or a pharmaceutically acceptable salt. Fentanyl citrate is one relevant salt, but the composition must also satisfy the other claim limitations.

Does claim 21 cover every fentanyl dose between 0.05 mg and 20 mg?

Only if the product and administration method satisfy the preceding limitations of claims 19 and 20. The dose range alone is not sufficient.

Are mucoadhesive polymers required to be chemically bonded to the carrier?

The claims require the agent to be mainly adhered to the carrier-particle surfaces. They do not expressly require covalent chemical bonding. Physical adhesion, coating, or another supported form of surface association may be relevant depending on claim construction and evidence.

References

United States Patent and Trademark Office. (2004). U.S. Patent No. 6,761,910, Pharmaceutical composition for sublingual administration.
U.S. Food and Drug Administration. (2011). Abstral (fentanyl citrate) sublingual tablets: Prescribing information.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs database.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Sweden	9803240	Sep 24, 1998

PCT Information
PCT Filed	September 24, 1999	PCT Application Number:	PCT/SE99/01687
PCT Publication Date:	March 30, 2000	PCT Publication Number:	WO00/16750

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	2236132	⤷ Start Trial	C300714	Netherlands	⤷ Start Trial
European Patent Office	2236132	⤷ Start Trial	CA 2015 00004	Denmark	⤷ Start Trial
European Patent Office	2236132	⤷ Start Trial	92636	Luxembourg	⤷ Start Trial
European Patent Office	2236132	⤷ Start Trial	122015000006	Germany	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 6,761,910