United States Drug Patent 4,849,224: Claim Scope, Patent Expiration, and Transdermal Patch Landscape

US Patent 4,849,224 covers a reservoir-type transdermal or transmucosal delivery device with a specific peelable-seal construction. The patent requires more than a drug reservoir, membrane, adhesive, and backing. Independent claim 1 requires a nested package architecture in which a removable impermeable layer protects the adhesive and is removed together with a peelable heat seal when the final release liner is removed.

The patent issued on July 18, 1989. Assuming no term adjustment, extension, disclaimer, or revival altered the statutory term, its U.S. patent term ended on July 18, 2006. The claims therefore do not present a current U.S. blocking right. The patent remains relevant as prior art and as a technical reference for transdermal patch design, but it cannot support a new U.S. infringement action based solely on the expired claims.[1][2]

What does US Patent 4,849,224 protect?

The patent protects a laminated patch having a reservoir between a backing layer and an active-agent-permeable membrane, together with a removable protective structure that prevents contact between the formulation and an adhesive before application.

The core architecture has these required elements:

Claim element	Required structure or relationship
Backing layer	Supports the device and forms one side of the reservoir
Permeable membrane	Allows the active agent to pass toward the skin or mucosa
Reservoir	Contains the active-agent formulation
Reduced reservoir periphery	Reservoir is smaller than the backing and membrane, leaving an outward border
First peelable impermeable layer	Covers the reservoir-side region and part of the outward border
Adhesive layer	Covers the first peelable layer and the outward border
Second peelable impermeable layer	Covers the adhesive layer and is removed before use
Permanent heat seal	Seals the reservoir perimeter between backing and membrane
Peelable heat seal	Sits outside the permanent seal between the backing and first peelable layer
Relative peel strengths	Adhesive bonds must resist separation more strongly than the peelable heat seal

The claim is therefore an integrated packaging and delivery-system claim. A product that has only a reservoir patch, or only a removable adhesive liner, does not necessarily fall within claim 1.

How should independent claim 1 be construed?

Claim 1 is narrow because it requires a particular sequence of layers and a specific release mechanism.

Reservoir and membrane

The backing and membrane define a reservoir. The membrane must be permeable to the active agent, which distinguishes the claimed device from an impermeable pouch that releases drug through a separate outlet or skin-contacting opening.

The reservoir must have a smaller periphery than the backing and membrane. This creates a border extending outside the reservoir. That border is important because the claim places the peelable seal and adhesive structure in that region.

Dual-seal construction

The claim requires two different heat seals:

A permanent heat seal around the reservoir.
A peelable heat seal outside the permanent seal.

The permanent seal maintains containment of the formulation. The peelable seal connects the backing to the first peelable impermeable layer and is designed to break during product preparation.

A patch with a single perimeter seal would not satisfy this limitation. A product using an adhesive bond rather than a peelable heat seal may also avoid literal infringement, depending on its construction and the applicable claim interpretation.

Two removable impermeable layers

The first peelable layer is positioned under the reservoir and part of the outward border. The adhesive is under that first layer. The second peelable layer covers the adhesive.

When the second layer is removed, the peelable heat seal breaks. The first layer and the portion of adhesive beneath it are removed with the second layer. This exposes fresh adhesive while preventing the formulation from contacting that adhesive during storage.

The removal sequence is a central limitation. A patch with one conventional silicone-coated release liner may not meet the claim because claim 1 requires the first peelable layer, adhesive, and second peelable layer to operate as a coupled release system.

What are the dependent claims and their additional limitations?

Claims 2 through 7 narrow claim 1 by adding compatibility, material, active-agent, solvent, or membrane limitations.

Claim	Added limitation	Scope effect
2	Adhesive is incompatible with one or more formulation components that permeate through the membrane	Requires the protective first peelable layer to address an adhesive-formulation compatibility problem
3	Backing is a laminate with an impermeable layer and inner heat-sealable layer	Narrows the backing construction
4	Acrylic adhesive; pindolol hydrochloride; isopropyl alcohol and methyl laurate	Covers a specified beta-blocker formulation and adhesive system
5	Microporous polyethylene membrane	Further narrows claim 4
6	Acrylic adhesive; nicardipine hydrochloride; isopropyl alcohol and methyl laurate	Covers a specified calcium-channel blocker formulation
7	Acrylic adhesive; calcitriol; ethanol, methyl laurate, and water	Covers a specified calcitriol formulation

Claim 4 contains the phrase “the device of claim” rather than “the device of claim 1.” In normal claim interpretation, this appears to be a drafting error and would ordinarily be read in context as depending from claim 1. The issued patent and prosecution history would control if the dependency were disputed.

What formulations are protected by US Patent 4,849,224?

The patent does not broadly claim every formulation containing pindolol, nicardipine, or calcitriol. Claims 4 through 7 require the claimed device architecture in combination with specified formulation ingredients.

Pindolol hydrochloride

Claim 4 requires:

Pindolol hydrochloride
Isopropyl alcohol
Methyl laurate
Acrylic adhesive
The claim 1 reservoir, membrane, seal, and release-liner arrangement

Claim 5 adds a microporous polyethylene membrane.

A pindolol formulation delivered by a different device, such as a drug-in-adhesive patch without the claimed dual peelable-layer architecture, would not literally meet claims 4 or 5.

Nicardipine hydrochloride

Claim 6 requires nicardipine hydrochloride with isopropyl alcohol and methyl laurate in the claimed device. The claim does not require the microporous polyethylene membrane specified in claim 5.

Calcitriol

Claim 7 requires calcitriol with ethanol, methyl laurate, and water. Because claim 7 depends on claim 1, the specific formulation must be used in the claimed reservoir and peelable-seal structure.

How strong is the patent estate for the claimed transdermal technology?

The '224 patent is technically specific but legally expired. Its historical strength depended on the combination of:

Reservoir delivery
A permeable membrane
A permanent heat seal
A separate peelable heat seal
Two peelable impermeable layers
Adhesive protection from formulation components
A controlled removal sequence

The strongest infringement theory during the patent term would have involved a product reproducing the complete packaging stack and peel-strength relationship. The weakest theories would have involved conventional matrix patches, drug-in-adhesive patches, or single-liner systems.

Risk factor	Assessment
Claim breadth	Narrow to moderate
Claim 1 coverage	Combination claim with multiple structural limitations
Formulation coverage	Narrow in claims 4-7
Design-around potential	High
Current enforceability	None in the United States after expiration
Prior-art value	Material for reservoir patches and peelable-seal systems
Biosimilar relevance	None
Generic-drug relevance	Limited and product-specific

The patent does not create a current barrier to developing a transdermal product. A new product may still encounter later patents covering the active ingredient, formulation, membrane material, adhesive chemistry, manufacturing process, dosing regimen, or commercial patch design.

When did US Patent 4,849,224 lose exclusivity?

The patent issued July 18, 1989. For a U.S. patent governed by the pre-Uruguay Round patent term, the ordinary term was 17 years from issue. On that basis, the patent expired July 18, 2006.[1][3]

Milestone	Date or status
U.S. patent grant	July 18, 1989
Ordinary statutory term	17 years from grant
Expected expiration	July 18, 2006
Current status	Expired
Current U.S. exclusivity	None
Post-expiration use	Permitted, subject to other unexpired rights

The expiration analysis should be distinguished from patent invalidity. An expired patent may have had enforceable claims during its term. Expiration ends the right to exclude going forward; it does not establish that the claims were invalid.

What is the Orange Book status of the patent?

US Patent 4,849,224 is not a current Orange Book barrier for pindolol, nicardipine, or calcitriol. The Orange Book identifies patents and exclusivities associated with approved drug products, but a historical transdermal device patent does not automatically qualify for listing.[4]

The claims concern a delivery device and formulations proposed for transdermal administration. They do not, by themselves, establish that the FDA approved a commercial transdermal product containing any of the three active agents.

Regulatory issue	Assessment
Current Orange Book blocking patent	None identified for the expired '224 patent
FDA exclusivity remaining	None based on this patent
Paragraph IV exposure	No current commercial impact from an expired patent
Approved transdermal product status	Not established by the patent
Device-drug combination relevance	Potentially relevant to an NDA or combination-product review, but not proof of approval

A Paragraph IV certification against the '224 patent would have had little practical value after 2006 because the patent was no longer enforceable. Paragraph IV remains relevant only to later, unexpired listed patents covering a specific approved product.

Which companies are challenging the patent?

The expired status makes current Paragraph IV challenges and patent litigation involving the '224 patent commercially immaterial. A patent challenge could have occurred during the patent term, but the claim set supplied does not identify an ANDA, NDA, litigation docket, settlement, or license.

No current biosimilar risk exists because the patent does not claim a biologic and does not create exclusivity for a biologic reference product. Generic risk is also not meaningfully constrained by this patent because the U.S. claims expired in 2006.

What patent litigation and settlement issues affect the patent?

The principal legal issue is expiration, not ongoing enforcement. Any present freedom-to-operate analysis should exclude the expired '224 patent as an enforceable U.S. right, while retaining it in the prior-art and prosecution-history review.

A settlement agreement involving the patent would not revive the expired claims. A historical license could remain relevant to royalties, confidentiality, know-how, or covenant obligations, but the patent itself cannot impose a new exclusionary period after expiration.

The highest litigation relevance now lies in later patents that may have claimed:

Specific transdermal formulations
Acrylic adhesive systems
Microporous polyethylene membranes
Calcitriol delivery
Pindolol or nicardipine dosage regimens
Manufacturing methods for heat-sealed reservoirs
Packaging methods that prevent adhesive contamination
Commercial patch dimensions, dose rates, or application schedules

How does this patent compare with competing transdermal patch designs?

Design type	Relationship to the '224 claims	Typical design-around path
Reservoir patch with dual peelable layers	Closest to the claimed architecture	Alter seal geometry, release sequence, or peel strengths
Drug-in-adhesive patch	Usually outside the reservoir limitation	Eliminate separate reservoir and permeable membrane
Matrix patch	Usually outside claim 1	Embed drug in polymer matrix rather than a liquid or gel reservoir
Single release-liner patch	Usually outside the two-layer requirement	Use one liner and a compatible adhesive
Pouch or sachet patch	May avoid the claimed seal arrangement	Use an external pouch with a separately manufactured patch
Microneedle or iontophoretic system	Technically distinct	Replace passive membrane diffusion with another delivery mechanism

The patent’s design-around value is high because claim 1 requires several interdependent components. A competitor could potentially avoid the claim by changing the reservoir geometry, eliminating the first peelable layer, using a single release liner, substituting a non-heat-sealed bond, or moving the drug into the adhesive.

What manufacturing and intellectual-property barriers remain?

The '224 patent no longer creates a U.S. manufacturing barrier. Manufacturing risk may still arise from later patents, trade secrets, process know-how, and regulatory requirements.

Relevant manufacturing controls include:

Heat-seal temperature and pressure
Seal-width uniformity
Peel-force control
Membrane permeability
Reservoir fill volume
Adhesive compatibility
Drug crystallization
Solvent retention
Package integrity
Dose-rate consistency
Stability under storage conditions

The claimed relative peel-strength requirement is particularly important from a process-control perspective. A commercial product would need the second liner to remove the first liner and adhesive portion without rupturing the permanent reservoir seal or leaving contaminated adhesive on the backing.

Geographically, the U.S. patent has no remaining exclusionary term. Foreign counterparts, continuation applications, or unrelated later patents must be reviewed separately. U.S. expiration does not establish freedom to operate in Europe, Japan, China, Canada, or other markets.

What generic launch risks exist for products related to the patent?

For a generic or follow-on transdermal product, the '224 patent presents no current U.S. launch delay. The relevant risks are likely to come from later patents and FDA requirements rather than this patent.

A launch assessment should distinguish four product categories:

A generic oral pindolol, nicardipine, or calcitriol product: generally unrelated to the device claims.
A transdermal product using a different architecture: potentially outside the expired claims but subject to later patents.
A follow-on product copying the historical patch configuration: legally permissible in the United States based on the expired patent alone.
A new combination product: subject to FDA review, device quality requirements, formulation stability testing, and any later patent claims.

Revenue exposure attributable solely to the '224 patent is zero after expiration. Historical revenue exposure cannot be calculated from the patent record alone because the patent does not establish commercial approval, launch, sales, or licensing income for a covered product.

Key Takeaways

US Patent 4,849,224 covers a specific reservoir transdermal patch architecture.
Claim 1 requires a permanent reservoir seal and an outer peelable heat seal.
The device must have two peelable impermeable layers surrounding the adhesive.
Claims 4-7 narrow the protection to pindolol hydrochloride, nicardipine hydrochloride, or calcitriol formulations.
The patent issued July 18, 1989 and ordinarily expired July 18, 2006.
The patent has no current U.S. blocking or Paragraph IV significance.
Biosimilar risk is not relevant because the patent does not claim a biologic.
Later formulation, adhesive, membrane, manufacturing, method-of-use, and packaging patents remain the principal freedom-to-operate risks.
The patent has high design-around potential because its independent claim requires a detailed combination of structural and functional limitations.

FAQs About US Patent 4,849,224

Does US Patent 4,849,224 still prevent manufacture of a transdermal patch?

No. The patent’s ordinary U.S. term ended in 2006. Manufacture is subject to other unexpired patents, regulatory requirements, and contractual obligations.

Does the patent cover every pindolol transdermal formulation?

No. Claim 4 requires the claimed device structure, acrylic adhesive, pindolol hydrochloride, isopropyl alcohol, and methyl laurate. Claim 5 adds a microporous polyethylene membrane.

Can a competitor avoid the patent by using a drug-in-adhesive patch?

A drug-in-adhesive design would generally avoid the reservoir limitation in claim 1, although later patents may cover the alternative design.

Is calcitriol a biosimilar issue under this patent?

No. Calcitriol is a small-molecule active agent, and the patent does not claim a biologic reference product or biosimilar pathway.

Does expiration eliminate the value of the patent?

Expiration eliminates its U.S. exclusionary power but does not eliminate its value as prior art, a technical reference, or a guide to identifying later patents that improved on reservoir patches and peelable adhesive protection.

References

United States Patent and Trademark Office. (1989). United States Patent No. 4,849,224.
United States Patent and Trademark Office. (n.d.). Patent Center. https://patentcenter.uspto.gov/
United States Code. (2024). 35 U.S.C. § 154: Contents and term of patents.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.accessdata.fda.gov/scripts/cder/ob/

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	154751	⤷ Start Trial
Austria	81023	⤷ Start Trial
Australia	2467788	⤷ Start Trial
Australia	5341690	⤷ Start Trial
Australia	603531	⤷ Start Trial
Australia	631417	⤷ Start Trial
Canada	1302824	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,849,224

Summary for Patent: 4,849,224