US Patent 6,264,980: Claim Scope, Buprenorphine Coverage, Expiration, and Patent Landscape

US Patent 6,264,980 covers transdermal and dermal drug compositions that use levulinic acid as an absorption enhancer. Claims 1 and 3 require levulinic acid in a subcooled melt. Claims 2 and 4 target compositions containing levulinic acid and buprenorphine base. The patent’s practical US exclusivity has ended. Its nominal patent term expired in November 2016, subject to the recorded patent-term calculation. The patent is therefore relevant to historical formulation ownership and Orange Book analysis, but it is not a current US barrier to generic or competing transdermal products.

What does US Patent 6,264,980 protect?

The patent protects a formulation concept rather than a particular patch design, adhesive, backing layer, drug loading, or release rate. Its central technical element is levulinic acid used to increase skin absorption.

The claims divide into two groups:

Claim	Drug scope	Levulinic acid requirement	Route or dosage-form scope
1	Any medicinal agent	Levulinic acid in a subcooled melt	Release to the skin
2	Buprenorphine base	Levulinic acid	Release to the skin
3	Any medicinal agent	Levulinic acid in a subcooled melt	Transdermal release
4	Buprenorphine base	Levulinic acid	Transdermal release

The patent uses the term “levulic acid” in the supplied claims. The relevant chemical is generally known as levulinic acid, or 4-oxopentanoic acid. Claim interpretation should follow the issued patent, prosecution history, specification, and any correction certificate rather than relying only on the claim text reproduced in a secondary source.

What is the core inventive concept?

The technical concept is the use of levulinic acid as a skin-permeation enhancer in a drug composition. In claims 1 and 3, the enhancer must be present “in a subcooled melt.” That limitation narrows the claims to a particular physical state or formulation condition.

A subcooled melt is generally a liquid system maintained below the material’s equilibrium melting point without crystallizing. In a transdermal formulation, that condition can affect solubility, drug partitioning, enhancer availability, and manufacturing behavior. The patent’s specification would control the precise meaning, including whether the subcooled melt relates to levulinic acid alone, a levulinic-acid-containing mixture, or the complete formulation.

Claims 2 and 4 omit the subcooled-melt limitation. They therefore reach more broadly, at least on their face, to compositions containing levulinic acid and buprenorphine base.

How broad are the four issued claims?

Claims 1 and 3: broad drug class plus a physical-state limitation

Claims 1 and 3 cover a drug composition containing:

A medicinal agent;
At least one absorption-enhancing auxiliary agent; and
Levulinic acid in a subcooled melt.

Claim 1 concerns release to the skin. Claim 3 expressly refers to transdermal release. The distinction may have limited practical value because a composition designed to deliver drug through intact skin will ordinarily be characterized as transdermal. Claim 3 may nevertheless provide a separate infringement theory where a product is expressly intended for systemic transdermal delivery.

The principal limitation is the subcooled-melt requirement. A product containing levulinic acid in an ordinary solution, suspension, adhesive matrix, or crystalline state may fall outside claims 1 and 3 unless the evidence establishes that the claimed subcooled-melt condition exists.

The phrase “comprises” makes the claims open-ended. Additional permeation enhancers, polymers, solvents, stabilizers, backing layers, liners, adhesives, and release-control agents can be present without avoiding the claims.

Claims 2 and 4: buprenorphine-specific claims without the subcooled-melt limitation

Claims 2 and 4 require buprenorphine base and levulinic acid. They do not expressly require levulinic acid to be in a subcooled melt.

These are the commercially significant claims because they are directed to buprenorphine transdermal compositions. A product containing buprenorphine base and levulinic acid could potentially meet the literal composition elements even if it uses a different adhesive system, patch construction, polymer, backing, or release-control technology.

The claims do not state:

A specific buprenorphine concentration;
A particular patch area;
A defined delivery rate;
A specified treatment duration;
A particular adhesive;
A particular polymer;
A required ratio of buprenorphine to levulinic acid;
A required amount or concentration of levulinic acid; or
A requirement that levulinic acid be in a subcooled melt.

Those omissions give claims 2 and 4 materially broader apparent formulation coverage than claims 1 and 3.

Does the patent cover Butrans or other buprenorphine patches?

The claims are directed to the same general formulation category as buprenorphine transdermal systems. Butrans is a buprenorphine transdermal system marketed by Purdue Pharma and approved by the FDA for chronic pain treatment in appropriate patients. Its labeling identifies buprenorphine as the active ingredient and lists formulation components, including levulinic acid in the system’s inactive ingredients [2].

That product-level fact does not, by itself, establish infringement. Infringement requires comparison of the approved formulation and manufacturing process with the properly construed patent claims. The relevant questions include whether the product contains buprenorphine base rather than a different chemical form, whether levulinic acid is present as claimed, and whether the composition satisfies the claim’s “drug composition” and transdermal-release limitations.

The presence of levulinic acid in a product label is strong evidence for evaluating claims 2 and 4. It does not independently establish that claims 1 and 3 are met because those claims include the additional subcooled-melt limitation.

When did US Patent 6,264,980 expire?

The patent was granted on July 24, 2001. Its priority chain traces to a German filing dated November 13, 1995, while the US application was filed on November 13, 1996, according to the patent record [1].

Event	Date
Earliest listed priority	November 13, 1995
US filing	November 13, 1996
US grant	July 24, 2001
Nominal US patent-term endpoint	November 13, 2016

For a US utility patent filed after June 8, 1995, the basic term is generally 20 years from the earliest effective nonprovisional US filing date, subject to patent-term adjustment, patent-term extension, terminal disclaimers, and other statutory rules under 35 U.S.C. §§ 154 and 156 [3].

The patent is listed in public patent databases as expired. No remaining enforceable US patent term should be assumed from the patent number alone. The official USPTO patent term data and any certificates of correction, terminal disclaimer, or patent-term adjustment control the final legal calculation.

What is the Orange Book status of US Patent 6,264,980?

US Patent 6,264,980 has been associated with the US regulatory patent landscape for buprenorphine transdermal products, including Butrans-related approval records. FDA Orange Book listings identify patents submitted by approved-product sponsors and provide patent-use and expiration information for listed drugs [4].

The patent’s commercial importance was greatest while it was listed against an approved buprenorphine transdermal product and remained unexpired. Because its nominal term ended in 2016, it no longer provides an active Orange Book patent barrier based on remaining patent life.

Orange Book analysis requires separating three issues:

Whether the patent was listed for a particular reference-listed drug;
Whether the listing remained active at a specific historical date; and
Whether the patent was expired when an ANDA applicant filed or received approval.

An expired Orange Book patent can remain relevant to historical Paragraph IV certifications, litigation records, and launch timing. It cannot support a new injunction based solely on an expired patent.

How would a Paragraph IV challenge apply?

A generic applicant seeking approval for a buprenorphine transdermal system could have addressed the patent through an ANDA patent certification if the patent was listed for the reference product at the time of filing.

A Paragraph IV certification would assert that the patent was invalid, unenforceable, or would not be infringed by the proposed product. Potential design-around and invalidity positions would include:

The proposed product does not contain levulinic acid;
The product uses a different buprenorphine chemical form;
The product does not qualify as the claimed drug composition;
Claims 1 and 3 are not met because there is no subcooled melt;
The composition does not release drug to or through the skin as claimed;
The claims lack written description or enablement across their full scope;
The claims are obvious over prior transdermal absorption-enhancer and buprenorphine disclosures; or
The claims are indefinite because “subcooled melt” lacks an objective boundary.

For claims 2 and 4, the subcooled-melt defense is unavailable because those claims do not contain that limitation. A generic product using buprenorphine base and levulinic acid would face a more direct literal-infringement analysis.

A Paragraph IV notice would have triggered the statutory 30-month stay only if the patent was listed and the NDA holder or patent owner filed an infringement action within the applicable statutory period under the Hatch-Waxman framework [5]. Because the patent has expired, any current generic applicant would not face a prospective 30-month stay based on this patent.

What formulation patents compete with US Patent 6,264,980?

The relevant competitive patent landscape includes four categories.

Buprenorphine transdermal composition patents

These patents claim buprenorphine-containing matrices, reservoirs, adhesives, permeation enhancers, or drug-release profiles. They may overlap with claims 2 and 4 but often add narrower limitations, such as polymer identity, enhancer ratios, drug loading, or release performance.

Patch-construction patents

Patch patents may cover backing layers, adhesive layers, drug-in-adhesive arrangements, liners, edge seals, or methods of preventing drug crystallization. A product can avoid the claims of US 6,264,980 while still requiring clearance of separate patch-construction patents.

Method-of-use patents

Method-of-use claims may cover treatment of chronic pain, opioid-experienced patients, dosing intervals, titration, or use in defined patient populations. US Patent 6,264,980 is principally a composition patent. It does not, based on the supplied claims, claim a patient population, disease, dose, or treatment method.

Manufacturing and process patents

Process patents may cover preparation of a subcooled melt, incorporation of levulinic acid into an adhesive, solvent removal, coating, drying, lamination, or control of buprenorphine crystallization. Claims 1 and 3 create particular process relevance because proving the subcooled-melt limitation may depend on manufacturing records, thermal analysis, formulation history, or product characterization.

How strong is the patent estate?

Strengths

Claims 2 and 4 have meaningful apparent breadth because they combine only two central formulation identifiers: buprenorphine base and levulinic acid. They do not require a specific patch architecture or delivery rate. The open “comprises” language permits additional ingredients.

The patent also has commercial relevance because buprenorphine transdermal products may use levulinic acid as a formulation component. A product matching those elements could have faced direct infringement exposure during the patent term.

Weaknesses

Claims 1 and 3 depend on the technically specific “subcooled melt” limitation. That limitation may create proof and claim-construction disputes.

Claims 2 and 4 may face prior-art and obviousness challenges if earlier references disclosed buprenorphine transdermal delivery together with levulinic acid or structurally similar absorption enhancers. Their breadth also increases exposure to written-description and enablement arguments if the specification does not adequately support the full range of possible buprenorphine and levulinic-acid compositions.

The most important weakness today is temporal. The patent has expired. Its claim strength no longer determines current US market entry.

Which companies challenged or licensed the patent?

The patent record identifies the patent owner or assignee and establishes ownership history, but patent ownership records do not disclose commercial licensing terms. The FDA approval record identifies the sponsor of the relevant marketed product, but it does not prove the existence, scope, or economic terms of any license involving US Patent 6,264,980 [1, 2].

A reliable licensing conclusion requires executed agreements, SEC disclosures, settlement documents, or court filings. The patent and FDA records alone do not establish a license arrangement.

The same limitation applies to litigation. A patent number and claim set do not establish whether a particular generic applicant received a Paragraph IV notice, whether the patent owner filed suit, or whether the parties settled. Those conclusions require docket-level review of ANDA litigation records and settlement filings.

What generic launch risks exist?

The patent creates no current standalone US launch risk because its patent term has ended. Historical launch risk differed by product design:

Proposed product characteristic	Historical risk under US 6,264,980
Buprenorphine base plus levulinic acid	High relevance under claims 2 and 4
Levulinic acid in a subcooled melt with any drug	High relevance under claims 1 and 3
Buprenorphine without levulinic acid	Lower risk under the supplied claims
Levulinic acid with a non-buprenorphine drug in ordinary liquid form	Potentially outside claims 1 and 3 if no subcooled melt
Buprenorphine salt rather than buprenorphine base	Requires chemical-form analysis
Different permeation enhancer and no levulinic acid	Generally outside the supplied claims
Product launched after patent expiration	No infringement risk based on this patent

A current product still requires clearance of later patents, regulatory exclusivity, trademarks, manufacturing patents, and method-of-use claims. Those rights are separate from US Patent 6,264,980.

Does biosimilar risk apply?

No. Buprenorphine is a small-molecule active pharmaceutical ingredient, not a biologic. The relevant regulatory pathway is an ANDA or, depending on the product and reference, an NDA pathway under the Federal Food, Drug, and Cosmetic Act. Biosimilar approval under the Public Health Service Act does not apply.

What geographic coverage does the patent provide?

US Patent 6,264,980 provides US rights only. It does not create patent protection in Europe, Canada, Japan, or other jurisdictions. Corresponding foreign applications may exist in the same priority family, but each jurisdiction has separate claims, prosecution history, term rules, validity standards, and expiration dates.

A global freedom-to-operate review must evaluate the relevant foreign family members independently. The US expiration date cannot be transferred to foreign jurisdictions.

Key Takeaways

US Patent 6,264,980 covers levulinic acid as a transdermal absorption enhancer.
Claims 1 and 3 require levulinic acid in a subcooled melt and cover medicinal agents broadly.
Claims 2 and 4 cover buprenorphine base with levulinic acid and omit the subcooled-melt limitation.
The claims are composition claims, not claims to a specific patch design, dose, treatment population, or delivery rate.
The patent was granted July 24, 2001, and its nominal US term ended November 13, 2016.
The patent is no longer a current US exclusivity barrier.
Butrans is commercially relevant because its labeling identifies buprenorphine and levulinic acid in the transdermal system.
Small-molecule generic risk is analyzed under the ANDA and Paragraph IV framework, not biosimilar law.
Later formulation, patch-construction, manufacturing, and method-of-use patents must be reviewed separately.
Patent ownership and FDA records do not, by themselves, establish licensing, settlement, or litigation outcomes.

FAQs

Can a transdermal product avoid US Patent 6,264,980 by using another permeation enhancer?

Yes, if the product does not contain levulinic acid and does not otherwise meet the claim limitations. A separate patent analysis would still be required for other enhancers and formulation technologies.

Does claim 2 require a transdermal patch?

The supplied language requires a drug composition for release of buprenorphine base to the skin. It does not expressly require a named patch architecture. A cream, gel, matrix, reservoir, or other delivery system could require analysis if it satisfies the claim limitations.

Does levulinic acid alone prove infringement?

No. Ingredient identification is not enough. The product must satisfy every limitation of at least one claim, including the required drug identity, route, and formulation characteristics.

Is a subcooled melt required for buprenorphine claims 2 and 4?

No. Claims 2 and 4, as supplied, require levulinic acid and buprenorphine base but do not expressly require a subcooled melt.

Can an expired patent block FDA approval?

An expired patent cannot provide a current patent-based injunction. It may have affected a historical ANDA certification or litigation strategy, but it does not create present patent exclusivity.

References

United States Patent No. 6,264,980. (2001). Drug composition for transdermal administration containing levulinic acid. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2023). Butrans (buprenorphine) transdermal system prescribing information. Purdue Pharma L.P.
35 U.S.C. §§ 154, 156. (2024). Patent term and patent-term extension provisions. United States Code.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book. Center for Drug Evaluation and Research.
21 U.S.C. § 355(j). (2024). Abbreviated new drug applications and patent certifications. United States Code.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Germany	44 46 600	Dec 24, 1994

PCT Information
PCT Filed	December 18, 1995	PCT Application Number:	PCT/EP95/05006
PCT Publication Date:	July 04, 1996	PCT Publication Number:	WO96/19975

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	172640	⤷ Start Trial
Australia	4387196	⤷ Start Trial
Germany	4446600	⤷ Start Trial
Germany	59504097	⤷ Start Trial
Denmark	0792145	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,264,980

Summary for Patent: 6,264,980