US Patent 4,994,267: Claim Scope, Expiration, and Transdermal Adhesive Patent Landscape

US Patent 4,994,267 covers drug-in-adhesive dermal compositions that combine an ethylene-vinyl acetate polymer, an acrylic polymer, natural or synthetic rubber, and a tackifying agent. The claims focus on adhesive composition architecture and component ratios, not on a single drug or delivery device. The patent was granted on February 19, 1991, and its ordinary 17-year patent term expired on February 19, 2008, assuming no unusual terminal disclaimer or term adjustment. The claims therefore do not create a current US exclusionary right. [1]

What does US Patent 4,994,267 protect?

The patent protects a pressure-sensitive adhesive matrix capable of incorporating a percutaneously absorbable drug. The claimed composition has four principal structural elements:

A drug.
A multipolymer containing:
- an ethylene-vinyl acetate polymer; and
- an acrylic polymer.
Natural or synthetic rubber.
A tackifying agent.

The central claim concept is a blended adhesive matrix in which the vinyl acetate/ethylene component contributes film-forming and mechanical properties, the acrylic polymer modifies adhesion and drug compatibility, the rubber contributes cohesive and elastomeric properties, and the tackifier adjusts tack and peel performance.

The claims are composition claims. They do not expressly require:

a backing layer;
a release liner;
a particular patch shape;
a specified drug-release rate;
a specified flux through human skin;
a particular manufacturing process;
a reservoir;
a particular dosage regimen; or
a particular therapeutic indication.

A finished transdermal patch could fall within the composition claims if its adhesive layer satisfies the recited chemical and quantitative limitations.

How do the individual claims differ?

Claim 1: Broad combination claim

Claim 1 requires an adhesive dermal composition containing the drug, multipolymer, rubber and tackifier. It establishes two ratio limitations:

Limitation	Claimed range
Multipolymer to rubber	About 1:10 to about 30:1
Vinyl acetate/ethylene polymer to acrylic polymer	About 20:1 to about 1:20

The claim is broad because it does not limit the drug to a particular therapeutic class. The drug can be solid or liquid under claim 4, provided that it is percutaneously absorbable and dissolved or dispersed in the composition.

The use of “about” creates a potential boundary dispute. Courts generally interpret “about” in light of the specification, examples, measurement methods and technical context. It does not eliminate the requirement that the accused composition fall within a reasonably supported range.

Claim 2: Narrower multipolymer-to-rubber range

Claim 2 narrows claim 1 by changing the multipolymer-to-rubber ratio to about 1:20 to about 20:1. This is not a simple narrowing in every direction. Compared with claim 1, it:

expands the lower end from 1:10 to 1:20; and
narrows the upper end from 30:1 to 20:1.

Claim 2 is therefore a separately defined ratio window, not a uniformly narrower version of claim 1.

Claim 3: Specific rubber and multipolymer combination

Claim 3 requires the rubber to be polyisobutylene and identifies the multipolymer as an acrylic polymer combined with a vinyl acetate/ethylene copolymer.

Polyisobutylene is commercially important in transdermal adhesives because it supplies tack, flexibility and cohesive strength. This limitation materially reduces the range of potentially covered adhesive systems compared with claim 1, which allows natural or synthetic rubber generally.

Claims 4 and 5: Drug characteristics and loading

Claim 4 requires the drug to be:

percutaneously absorbable;
solid or liquid at room temperature; and
dissolved or dispersed in the adhesive composition.

Claim 5 limits the drug concentration to about 0.1% to 50% by weight of the dermal composition.

The drug-loading limitation is unusually broad. At its lower end, it covers compositions containing only a small quantity of active ingredient. At its upper end, a formulation could contain a very high drug loading, subject to the practical requirement that the resulting material remain a usable dermal adhesive.

Claim 6: Steroid-focused independent claim

Claim 6 is a separate composition claim directed to a steroid. It requires:

a steroid;
an acrylic polymer/vinyl acetate-ethylene copolymer multipolymer;
natural or synthetic rubber; and
a tackifying agent.

The multipolymer-to-rubber ratio is about 1:1 to about 20:1.

Because claim 6 is independently drafted, an accused steroid composition could infringe claim 6 even if it does not satisfy every limitation of claim 1. The claim does not require estradiol unless one of the dependent claims is asserted.

Claims 7 and 8: Acrylic polymer and estradiol limitations

Claim 7 limits the acrylic polymer to polymethacrylic acid or polyacrylic acid.

Claim 8 limits the steroid to 17-beta-estradiol. This creates a focused claim directed to an estradiol-containing adhesive matrix rather than to steroid compositions generally.

Claims 9 to 12: Copolymer and ratio limitations

Claim 9 defines the copolymer as a terpolymer of ethylene, vinyl acetate and acrylic acid.

Claim 10 provides approximate monomer percentages:

Monomer unit	Approximate range
Ethylene	15% to 90%
Vinyl acetate	4% to 8%
Acrylic acid	0% to 5%

Claim 11 specifies approximately 60% ethylene and 40% vinyl acetate, with no acrylic acid. As drafted, claim 11 appears to describe an ethylene-vinyl acetate copolymer rather than a terpolymer containing acrylic acid. The claim language should be read against the patent specification and prosecution history to determine whether “terpolymer” was used broadly, whether the zero-acrylic-acid endpoint was intentional, or whether the claim contains an internal drafting inconsistency.

Claim 12 specifies a multipolymer-to-rubber ratio of approximately 1:3. A composition meeting this ratio must still satisfy the parent claim limitations.

Claims 13 and 14: Ingredient-percentage formulation claims

Claim 13 recites percentage ranges for the main components:

Component	Approximate percentage by weight
Ethylene/vinyl acetate copolymer	2% to 10%
Natural or synthetic rubber	2% to 20%
Polyacrylate	20% to 60%
Tackifying agent	5% to 30%
Drug	1% to 50%

Claim 14 narrows the drug to nitroglycerin or estradiol.

The ranges in claim 13 are broad and overlap in ways that do not necessarily produce a 100% composition. The claim should be interpreted as requiring a formulation whose recited ingredients fall within the stated ranges, with the balance potentially supplied by other ingredients or by the claimed components at selected levels. The specification and prosecution history would control whether the ranges are closed or open to additional materials.

What are the key claim-construction issues?

Does the “multipolymer” have to be a single chemical molecule?

The claim language distinguishes between a multipolymer containing an ethylene-vinyl acetate polymer and an acrylic polymer, and the dependent claims refer to mixtures or combinations involving these materials. A key issue is whether “multipolymer” means:

a single terpolymer molecule containing all relevant monomer units; or
a polymer blend containing an ethylene-vinyl acetate polymer and an acrylic polymer.

Claims 3, 9, 10 and 11 point in both directions. Claim 3 uses a combination of an acrylic polymer and a vinyl acetate/ethylene copolymer. Claims 9 and 10 refer to a terpolymer. A court would likely examine the specification’s definitions, examples and prosecution statements before deciding whether the claims cover both polymer blends and chemically integrated terpolymers.

Are the ratios calculated on a dry-weight basis?

The claims state ratios “by weight” but do not, in the supplied text, specify whether the calculation excludes solvents, residual monomers, plasticizers or other processing aids. For a commercial adhesive, the relevant calculation would normally focus on the nonvolatile formulation ingredients unless the patent specifies another basis.

What does “natural or synthetic rubber” cover?

The phrase is broad enough to encompass multiple elastomer classes, potentially including polyisobutylene, polyisoprene, butyl rubber and related synthetic rubbers. Claim 3 specifically identifies polyisobutylene, but the broader claims do not require that species.

Does a product need all listed components?

Yes. The independent claims require the stated adhesive components. A formulation lacking the tackifying agent, rubber or required polymer component would not literally satisfy the claim. An infringement theory based on equivalents would require a separate analysis and would be constrained by prosecution history, claim amendments and any disclosed prior art.

What drugs and dosage forms are implicated?

The claims are not restricted to one active ingredient. They expressly identify estradiol and nitroglycerin, while claim 4 covers any percutaneously absorbable drug meeting the composition requirements.

Estradiol

Estradiol is the most commercially important drug specifically associated with the claims. The patent claims contemplate estradiol dissolved or dispersed in a pressure-sensitive adhesive matrix. This is consistent with estrogen transdermal systems designed to deliver systemic hormone replacement therapy.

Potentially relevant formulation variables include:

estradiol concentration;
drug solubility in the adhesive;
polymer acid functionality;
tackifier selection;
rubber content;
adhesive layer thickness; and
skin flux.

Nitroglycerin

Nitroglycerin is expressly identified in claim 14. Nitroglycerin transdermal products historically used several adhesive and reservoir designs. A product would need to satisfy the claimed polymer, rubber, tackifier and ratio requirements to implicate the patent.

Other percutaneous drugs

Claim 4 could reach other drug classes, including analgesics, contraceptive hormones, corticosteroids and cardiovascular agents, if the active ingredient is percutaneously absorbable and the formulation satisfies the structural limitations. The patent does not claim a general transdermal delivery method independently of the adhesive composition.

What patents protect competing transdermal systems?

The relevant patent landscape includes several overlapping categories rather than one single patent family.

Patent category	Typical protected subject matter	Relevance to US 4,994,267
Drug-in-adhesive matrix patents	Drug dispersed or dissolved directly in pressure-sensitive adhesive	Directly overlapping technical area
EVA adhesive patents	Ethylene-vinyl acetate-based adhesive systems	Relevant to the claimed polymer component
Acrylic adhesive patents	Acrylic pressure-sensitive adhesives and functionalized acrylics	Relevant to the acrylic polymer limitation
Rubber-based adhesive patents	Polyisobutylene and related elastomer matrices	Relevant to claims 1, 3, 6 and 13
Estradiol patch patents	Estradiol dosage forms, delivery rates and patch structures	Relevant to claims 8 and 14
Nitroglycerin patch patents	Nitroglycerin reservoirs, matrices and dosing systems	Relevant to claims 4 and 14
Backing and release-layer patents	Patch construction and occlusive or semipermeable layers	Usually outside the composition claims
Manufacturing patents	Mixing, coating, drying and lamination processes	Potentially separate barriers
Method-of-use patents	Treatment of menopause, angina or other conditions	Separate from the adhesive composition claims

Examples of earlier transdermal patent activity include systems associated with nitroglycerin delivery, estradiol delivery and pressure-sensitive adhesive matrices. Patent overlap must be assessed claim by claim. A competing product may avoid US 4,994,267 by using a silicone adhesive, a different acrylic system, a reservoir design, or a rubber-free matrix while still implicating other expired or active patents.

When did US Patent 4,994,267 lose exclusivity?

The patent’s grant date was February 19, 1991. For a US patent subject to the pre-Uruguay Round patent term rule, the ordinary term was 17 years from grant. That produces an expected expiration date of February 19, 2008. [1]

Event	Date or status
Patent granted	February 19, 1991
Ordinary patent term	17 years from grant
Expected expiration	February 19, 2008
Current enforceability	Expired
Current Paragraph IV threat from this patent	None
Current royalty leverage from this patent	None, absent a separate right or contract

The patent’s expiration eliminates current infringement liability based solely on these claims. It does not eliminate the patent’s historical importance as prior art or its possible relevance to claim construction in later patent families.

What is the Orange Book status of US Patent 4,994,267?

US Patent 4,994,267 is a composition patent, not a drug-specific regulatory exclusivity right. Orange Book listing depends on whether the patent claims an approved drug substance, drug product or approved method of use and whether the patent holder properly submitted it for listing. [2]

The claims identify nitroglycerin and estradiol as possible drugs but do not appear limited to a specific approved product, strength, dosage form or labeling indication. A patent of this type would not automatically qualify for Orange Book listing merely because it covers a composition that could be used in a transdermal product.

The patent’s expiration also means it cannot presently block an abbreviated new drug application through a Paragraph IV certification. Any historical Orange Book listing would no longer provide a live patent barrier.

Were Paragraph IV challenges or litigation likely to matter?

A Paragraph IV challenge would have been relevant only while the patent remained unexpired and listed against an approved drug. The supplied claims do not identify a particular reference listed drug, NDA or approved product. The patent therefore should be treated as a formulation patent with potential historical litigation relevance, not as a currently operative Orange Book patent.

For a historical litigation review, the principal issues would have included:

whether the accused adhesive contained both required polymer classes;
whether the polymer-to-rubber ratio fell within the claimed range;
whether the accused product used polyisobutylene;
whether the active ingredient was dissolved or dispersed in the adhesive;
whether the drug loading fell within the recited range;
whether “multipolymer” covered a physical blend or only a terpolymer;
whether “about” encompassed measured values near the ratio boundaries; and
whether later prosecution statements narrowed the claims.

No current commercial launch can infringe an expired patent. Settlement agreements, licenses or covenant-not-to-sue arrangements could affect historical exposure, but they cannot extend the public-law patent term against third parties.

Does the patent create biosimilar risk?

No meaningful biosimilar risk arises from this patent. Estradiol and nitroglycerin are small-molecule active ingredients, not biologic products subject to the Biologics Price Competition and Innovation Act pathway. [3]

The relevant competitive pathways are:

an abbreviated new drug application for a generic small-molecule product;
a 505(b)(2) application for a modified delivery system or formulation; and
a full NDA where the product differs materially from approved products.

The patent could historically have affected formulation freedom to operate, but it is not a biosimilar patent and does not create current biologic exclusivity.

How strong is the patent estate?

Historical strength

The patent had meaningful historical breadth because claim 1 covered a wide range of drugs and a broad combination of polymer and rubber ratios. Claims 6, 13 and 14 added commercially relevant steroid, estradiol and nitroglycerin embodiments.

Its principal vulnerabilities were structural:

ambiguity concerning “multipolymer”;
overlap between blend and terpolymer terminology;
broad “about” ranges;
large drug-loading range;
possible written-description and enablement questions across many drugs; and
substantial prior-art exposure in transdermal adhesive technology.

Current strength

The patent has no current exclusionary strength because it expired in 2008. Its remaining value is historical and informational:

identifying an early adhesive platform;
mapping cited and citing patent families;
understanding formulation design choices;
assessing ownership or licensing history; and
serving as prior art against later patent claims.

What manufacturing and formulation barriers remain?

Although this patent no longer blocks manufacture, a modern transdermal product may face other IP and regulatory barriers involving:

adhesive polymer selection;
drug crystallization control;
skin permeation enhancers;
backing-layer composition;
release-liner treatment;
multilayer patch construction;
coating and drying conditions;
residual solvent limits;
adhesive stability;
dose uniformity;
drug-in-adhesive thickness;
extraction and leachables; and
manufacturing-process patents.

A design-around based only on changing the adhesive polymer may still encounter separate patents covering the active ingredient’s formulation, patch construction, manufacturing process or therapeutic use. Freedom-to-operate analysis therefore must review the complete product architecture, not only US 4,994,267.

How does US 4,994,267 compare with modern transdermal patents?

US 4,994,267 is composition-centered. It claims the adhesive matrix through ingredient identity and quantitative relationships.

Modern transdermal patent estates more often divide protection among several claim types:

Protection type	US 4,994,267	Modern transdermal portfolios
Adhesive composition	Core focus	Often one layer of protection
Active ingredient	Broad, with estradiol and nitroglycerin examples	Frequently drug-specific
Drug-release profile	Not expressly required	Common in some portfolios
Patch construction	Not expressly required	Often separately claimed
Manufacturing process	Not expressly required	Frequently claimed
Therapeutic method	Not the principal focus	Common in lifecycle patents
Device or wearable integration	Not covered	Increasingly common

The patent’s commercial value historically came from claiming the matrix itself. Current patent estates typically seek multiple independent barriers around the drug, formulation, device and manufacturing process.

Key Takeaways

US Patent 4,994,267 covers dermal adhesive compositions containing an ethylene-vinyl acetate polymer, acrylic polymer, rubber and tackifier.
The claims use broad polymer-to-rubber and polymer-to-polymer ratio ranges.
Claim 6 separately targets steroid compositions, while claims 8 and 14 identify estradiol and nitroglycerin.
Claim 13 provides broad component-percentage ranges for a formulation containing EVA, rubber, polyacrylate, tackifier and drug.
The “multipolymer” terminology creates a central claim-construction issue concerning polymer blends versus chemically integrated terpolymers.
The patent was granted on February 19, 1991, and its ordinary term expired on February 19, 2008.
The patent creates no current Paragraph IV, generic-entry or biosimilar barrier.
Any present freedom-to-operate risk must come from later patents covering specific drugs, patch structures, formulations, manufacturing processes or methods of use.
The patent remains relevant as historical prior art and as a technical reference for drug-in-adhesive transdermal systems.

FAQs

Can a company manufacture an estradiol patch covered by US 4,994,267 today?

Yes, expiration removes infringement liability based solely on this patent. The product must still clear any later-expiring patents covering estradiol formulations, patch construction, manufacturing or approved use.

Does claim 14 cover every estradiol or nitroglycerin transdermal patch?

No. The product must also satisfy the polymer, rubber, tackifier and concentration limitations incorporated from claim 13.

Can a silicone adhesive avoid the principal claims?

Generally, a silicone adhesive would not contain the claimed EVA/acrylic polymer combination. It could therefore avoid literal infringement of the supplied claims, subject to the patent’s full claim language and any separate patent rights.

Is an expired formulation patent relevant to a 505(b)(2) application?

It can remain relevant as prior art and as a historical formulation reference, but it cannot independently block approval through patent enforcement after expiration. Later patents may still affect the application.

Does the patent cover the patch backing and release liner?

The supplied claims do not expressly require or claim a backing layer or release liner. Those components may be covered by separate patents or may affect whether the complete product contains a claimed adhesive composition.

References

United States Patent and Trademark Office. (1991). Adhesive dermal composition, U.S. Patent No. 4,994,267.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations (Orange Book).
United States Congress. (2010). Patient Protection and Affordable Care Act, Pub. L. No. 111-148, § 7002, 124 Stat. 119, 804-821.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	002355	⤷ Start Trial
Austria	122240	⤷ Start Trial
Austria	144704	⤷ Start Trial
Austria	148633	⤷ Start Trial
Austria	223185	⤷ Start Trial
Austria	235898	⤷ Start Trial
Austria	99175	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 4,994,267