U.S. Patent 5,601,839: Scope, Claim Construction, Expiration, and Oxybutynin Transdermal Patent Landscape

U.S. Patent No. 5,601,839 protects transdermal matrix patches and methods using triacetin to enhance delivery of basic drugs with a pKa of about 8.0 or greater. The strongest commercial embodiment is an oxybutynin patch containing triacetin in an acrylic adhesive matrix, with glycerin as an irritation-reducing agent. The patent’s enforceable term has expired, so it no longer creates a blocking right against generic or branded products. Its technical disclosures remain relevant as prior art and as a reference point for later oxybutynin formulation patents.

What does U.S. Patent 5,601,839 cover?

The patent has two independent claim categories:

Claim category	Independent claim	Protected subject matter
Method	Claim 1	Applying a qualifying matrix patch to skin to enhance transdermal penetration
Product	Claim 12	The qualifying matrix patch itself

Both independent claims require the same core combination:

A biocompatible polymer layer.
A basic drug having a pKa of about 8.0 or greater.
Triacetin as the permeation enhancer.
A transdermal matrix-patch configuration.

The claims identify acrylics, vinyl acetates, natural and synthetic rubbers, ethylene-vinyl acetate copolymers, polysiloxanes, polyacrylates, polyurethanes, plasticized polyether block amide copolymers, plasticized styrene-rubber block copolymers, and mixtures thereof as permissible adhesive polymers.

The drug Markush group includes oxybutynin, scopolamine, fluoxetine, epinephrine, morphine, hydromorphone, atropine, cocaine, buprenorphine, chlorpromazine, imipramine, desipramine, methylphenidate, methamphetamine, lidocaine, procaine, pindolol, nadolol, and carisoprodol, together with acid-addition salts.

What are the key limitations of the independent claims?

Claim 1: method claim

Claim 1 requires a method of enhancing transdermal penetration by applying the claimed matrix patch to a selected application situs. A potential infringement analysis would need to establish:

Use of a patch rather than another delivery system.
A matrix configuration.
A qualifying basic drug.
A drug pKa of approximately 8.0 or greater.
Triacetin used as a permeation enhancer.
A polymer layer within the listed adhesive classes or an equivalent mixture.
Application to skin or another selected delivery site.

The claim is narrower than a general claim to transdermal oxybutynin. It does not cover every oxybutynin patch. A patch that uses another enhancer, such as oleic acid, lauric acid, ethanol, propylene glycol, or a proprietary enhancer system, would not literally satisfy the triacetin limitation.

Claim 12: composition or patch claim

Claim 12 covers the physical matrix patch. It does not require proof that the patch has actually been administered. A product claim would therefore be relevant to manufacture, sale, importation, or commercial distribution of a qualifying patch during the patent term.

The product claim still requires all core elements. A transdermal patch containing oxybutynin but no triacetin falls outside the literal scope of claim 12.

How do the dependent claims narrow the patent?

The dependent claims create a descending hierarchy from a broad drug-and-enhancer combination to a specific oxybutynin formulation.

Claims	Added limitation
2, 13	Triacetin at about 0.1% to about 50% by weight
3, 14	Oxybutynin or an oxybutynin acid-addition salt
4, 15	Triacetin at about 1% to about 40% by weight
5, 16	Diluents, excipients, emollients, plasticizers, irritation-reducing agents, carriers, or mixtures
6, 17	Oxybutynin specifically
7, 18	Acrylic copolymer adhesive
8, 19	Triacetin at about 2% to about 20% by weight
9, 20	Glycerin as the irritation-reducing agent
10, 21	Polymer layer laminated to an adhesive
11, 22	Polymer layer overlaid with an adhesive

The narrowest commercial embodiment is represented by claims 6 through 9 and claims 17 through 20:

Oxybutynin.
Acrylic copolymer adhesive.
Triacetin at about 2% to about 20% by weight.
Glycerin for reducing skin irritation.

That embodiment is technically important but legally weaker today because the patent term has ended.

What formulation is most directly protected?

The claims most directly protect an oxybutynin transdermal matrix patch in which triacetin is incorporated into an acrylic adhesive system.

A representative claim-compliant formulation would have:

Oxybutynin or an acid-addition salt.
An acrylic copolymer adhesive.
Triacetin at 2% to 20% by weight.
Glycerin.
A matrix patch rather than a reservoir system.
A backing layer and release liner, if present, as conventional patch components.

The claims do not require a particular patch area, oxybutynin loading, release rate, wear period, backing film, release liner, or manufacturing process. Those omissions leave room for later patents directed to dosage strength, flux, wear time, adhesive performance, skin tolerability, and manufacturing parameters.

What does “consisting essentially of triacetin” mean?

The phrase “consisting essentially of” generally permits components that do not materially affect the basic and novel characteristics of the claimed invention. Here, the basic and novel characteristic is the use of triacetin as the permeation enhancer for a qualifying basic drug.

The phrase is narrower than “comprising” and broader than “consisting of.” A formulation containing triacetin and conventional patch excipients could fall within the claim. A formulation containing a second active permeation enhancer could create a dispute over whether that second enhancer materially changes the claimed permeation-enhancement mechanism.

The claim does not necessarily require triacetin to be the only non-polymer ingredient. Claims 5, 16, 9, and 20 expressly contemplate excipients and glycerin.

When did U.S. Patent 5,601,839 lose exclusivity?

U.S. Patent 5,601,839 is expired. The patent issued on February 11, 1997, and its enforceable term ended no later than the statutory 20-year period measured from its earliest effective nonprovisional filing date, subject to any patent-term adjustment or terminal disclaimer recorded in the patent file. The patent cannot presently block manufacture, sale, or use of a qualifying patch.

Event	Date or status
U.S. patent issued	February 11, 1997
Patent term basis	20 years from applicable nonprovisional filing date
Current status	Expired
Current infringement risk from this patent	No prospective enforceability
Continuing commercial relevance	Prior art and technical disclosure

The expiration analysis must be distinguished from regulatory exclusivity. FDA marketing exclusivity, if any, is separate from patent rights and does not restore an expired patent.

What is the Orange Book status of U.S. Patent 5,601,839?

The patent should not be treated as a currently enforceable Orange Book barrier. Orange Book listing status is product-specific and depends on whether a patent was submitted and accepted for a particular approved drug product. Listing does not extend the patent term.

For oxybutynin transdermal products, the relevant regulatory analysis is product-specific:

NDA-listed patents may have covered the approved patch, formulation, method of use, or delivery characteristics.
An ANDA applicant may have addressed listed patents through Paragraph III, Paragraph IV, or a certification that no relevant patent was listed.
The expiration of U.S. Patent 5,601,839 does not establish that every other oxybutynin patch patent has expired.
OTC conversion of Oxytrol for Women created a separate regulatory pathway and did not automatically eliminate prescription-product patent issues.

The FDA Orange Book remains the controlling source for current listed-patent status for a particular NDA. The patent itself is not a substitute for an Orange Book review. (FDA, 2024a)

Which oxybutynin products are commercially relevant?

Oxybutynin is marketed in several dosage forms:

Product type	Typical technology	Patent risk profile
Immediate-release tablets	Oral solid dosage form	Separate formulation and method patents
Extended-release tablets	Oral controlled release	Release-system and dosage-form patents
Transdermal patch	Matrix or adhesive patch	Adhesive, permeation, irritation, flux, and manufacturing patents
Topical gel	Semisolid topical delivery	Gel, solvent, dosing, and application patents
OTC transdermal patch	Consumer patch	Labeling, safety, formulation, and regulatory exclusivity issues

U.S. Patent 5,601,839 is directed to the transdermal category. It does not cover oral oxybutynin products, oxybutynin gels, or every transdermal system containing oxybutynin.

What patent landscape surrounds the invention?

The surrounding patent landscape has five principal layers.

Foundational permeation-enhancer patents

These patents claim the use of particular chemical enhancers, enhancer combinations, or enhancer concentrations to increase skin flux. U.S. Patent 5,601,839 occupies this category through triacetin.

The relevant design-around variables include:

Replacing triacetin with another enhancer.
Using triacetin outside the claimed concentration ranges.
Using a different drug.
Using a different polymer system.
Employing a reservoir rather than a matrix architecture.
Delivering oxybutynin through a gel or another topical dosage form.

Oxybutynin transdermal formulation patents

Later patents may claim:

Specific oxybutynin loading.
Defined oxybutynin flux.
Controlled delivery over a 3- or 4-day wear period.
Reduced skin irritation.
Particular acrylic adhesive compositions.
Laminated multilayer structures.
Backing and release-liner combinations.
Uniform drug distribution in the adhesive.
Manufacturing conditions that improve stability or content uniformity.

These later claims can remain relevant even though U.S. Patent 5,601,839 has expired.

Method-of-use patents

Oxybutynin method claims can address treatment of overactive bladder, urge incontinence, urinary frequency, or related conditions. A method patent requires analysis of the approved indication, patient population, dosage, administration schedule, and label language.

A generic applicant’s Paragraph IV strategy may target method-of-use patents by:

Carving out a patented indication.
Using a skinny label.
Arguing that the proposed labeling does not induce infringement.
Challenging validity or enforceability.
Relying on an expired patent.

Manufacturing and process patents

Manufacturing patents may claim:

Mixing triacetin with the adhesive.
Dissolving oxybutynin in a polymer solution.
Coating and drying conditions.
Solvent removal.
Lamination.
Release-liner handling.
Control of residual solvents.
Patch die-cutting and packaging.

These rights can create manufacturing barriers even when the composition claim has expired.

Device and delivery-system patents

Patch patents may cover:

Adhesive perimeter design.
Multilayer structures.
Occlusive backing films.
Skin-contact area.
Drug-in-adhesive architecture.
Release-rate control.
Packaging and pouch systems.

A product may avoid the expired triacetin patent yet still implicate a later patch-system patent.

How strong was the patent estate?

Historical strength

The estate had meaningful historical breadth because claim 1 covered a large drug Markush group and multiple polymer classes. The combination of a basic drug, triacetin, and a transdermal matrix was commercially relevant to oxybutynin and potentially several centrally acting or cardiovascular drugs.

The broadest practical limitations were:

The pKa threshold.
The requirement for triacetin.
The matrix patch requirement.
The listed adhesive polymer classes.

The claim was not a general patent on transdermal enhancement. It was a combination claim that depended on all four elements.

Current strength

Current enforceable strength is zero because the patent has expired. Its residual value is evidentiary and technical:

It can be cited as prior art against later claims.
Its disclosure may limit the patentability of later triacetin-based patch claims.
Its examples may affect written-description, enablement, and obviousness analysis.
It may support freedom-to-operate conclusions for products that practice the disclosed combination.

What generic entry risks existed?

During the patent term, an oxybutynin patch using triacetin and an acrylic matrix could have faced direct infringement risk under claims 1, 6 through 9, 12, and 17 through 20.

A generic applicant would have had several potential positions:

Strategy	Relevance
Paragraph III certification	Await patent expiration
Paragraph IV certification	Challenge validity, enforceability, or infringement
Non-infringement	Use a non-triacetin enhancer or a nonqualifying matrix
Formulation design-around	Change adhesive, enhancer, concentration, or drug form
Label carve-out	Relevant only to method claims and approved uses
Product redesign	Use gel, oral dosage form, or another delivery architecture

Because the patent is now expired, the main generic-entry risks arise from later patents, FDA requirements, product-specific exclusivity, and manufacturing know-how.

Were Paragraph IV challenges or settlements associated with this patent?

The supplied claims do not establish a particular Paragraph IV litigation, settlement, or consent judgment involving U.S. Patent 5,601,839. The patent’s expiration also means that any historical litigation would have no current blocking effect.

For oxybutynin transdermal products, litigation research should separate:

Litigation involving this patent.
Litigation involving later oxybutynin patch patents.
Litigation involving NDA-listed patents.
Patent challenges involving other dosage forms.
Settlements that permitted launch before patent expiration.

A Paragraph IV certification against an expired patent would not ordinarily create a present launch barrier. Historical settlements may still matter for damages, launch timing, or antitrust analysis, but not for current enforceability.

How does U.S. Patent 5,601,839 compare with later patch patents?

Issue	U.S. Patent 5,601,839	Later oxybutynin patch patents
Primary focus	Triacetin-enhanced transdermal delivery	Product-specific patch performance
Drug scope	Broad basic-drug Markush group	Often oxybutynin-specific
Polymer scope	Multiple adhesive classes	Frequently narrower adhesive or multilayer systems
Enhancer scope	Triacetin	May cover other enhancers or combinations
Dosage requirements	Not tightly specified	May claim loading, flux, or delivery rate
Irritation control	Glycerin in dependent claims	May claim broader skin-tolerability systems
Current enforceability	Expired	Must be reviewed patent by patent
Main commercial relevance	Prior art and historical foundation	Potential current freedom-to-operate barriers

What geographic coverage does the patent have?

U.S. Patent 5,601,839 provides rights only in the United States. Corresponding foreign applications, if any, would require separate analysis by jurisdiction. Patent term, prosecution history, claim scope, and expiry may differ in:

Canada.
Europe.
Japan.
Australia.
South Korea.
China.
Other national-phase jurisdictions.

A U.S. freedom-to-operate conclusion cannot be extended automatically to foreign markets. The relevant national patent registers must be checked for issued counterparts, lapse, abandonment, opposition, limitation, and supplementary term rights.

What is the commercial impact of expiration?

Expiration removes the patent-based barrier to a patch that practices its claims. It does not eliminate:

FDA approval requirements.
Bioequivalence or comparative-performance requirements.
Manufacturing validation.
Adhesion and irritation testing.
Trademark restrictions.
Trade-secret protection.
Later formulation patents.
Product-specific regulatory exclusivity.
Contractual restrictions.

For oxybutynin, the expired patent supports broader formulation freedom but does not establish that a proposed generic patch is launch-ready. A current product review should compare the proposed formulation against Orange Book-listed patents, issued later patents, pending applications, and the approved labeling.

Key Takeaways

U.S. Patent 5,601,839 claims triacetin-enhanced transdermal matrix patches for basic drugs with a pKa of about 8.0 or greater.
Oxybutynin is the commercially central embodiment.
The narrowest claims require oxybutynin, an acrylic copolymer adhesive, 2% to 20% triacetin, and glycerin.
The patent does not cover every oxybutynin patch because triacetin and the matrix configuration are required.
The patent has expired and creates no current enforceable U.S. blocking right.
Later patents may still cover oxybutynin patch composition, flux, irritation control, manufacturing, packaging, or delivery-system features.
Orange Book status must be assessed for the specific oxybutynin NDA and product, not inferred solely from this patent.
A current generic-launch analysis should focus on later patent families, regulatory requirements, and formulation-specific freedom to operate.

FAQs

Does U.S. Patent 5,601,839 cover all transdermal oxybutynin patches?

No. Literal coverage requires triacetin as the permeation enhancer, a qualifying basic drug, a matrix patch, and one of the specified adhesive polymer systems.

Can a patch avoid the patent by using oxybutynin hydrochloride?

Not necessarily. The claims expressly include oxybutynin acid-addition salts. Oxybutynin hydrochloride would remain within the drug limitation if the other claim elements were met, although the patent is expired.

Does the patent cover triacetin in an oxybutynin gel?

Generally, no. The claims require a matrix patch and a qualifying polymer layer. A topical gel would not normally satisfy those structural limitations.

Is glycerin required in every claim?

No. Glycerin is required only by claims 9 and 20. The independent claims and most dependent claims do not require glycerin.

Can an expired patent still affect a new oxybutynin patent application?

Yes. Its disclosure can be prior art against later claims, particularly claims directed to triacetin, basic drugs, acrylic adhesive matrices, or closely related transdermal formulations.

References

U.S. Patent No. 5,601,839. (1997). Transdermal delivery of basic drugs using triacetin as a permeation enhancer. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2024a). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (2024b). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (2024c). Drugs@FDA: FDA-approved drugs database. FDA.
United States Code, 35 U.S.C. §§ 154, 271, 282. (2024). Patent term, infringement, and validity provisions.
United States Code, 21 U.S.C. § 355(j). (2024). Abbreviated new drug applications and patent certifications.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0871420	⤷ Start Trial	CA 2005 00010	Denmark	⤷ Start Trial
European Patent Office	0871420	⤷ Start Trial	05C0008	France	⤷ Start Trial
Argentina	001721	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,601,839

Summary for Patent: 5,601,839