US Patent 6,181,963: Claim Scope, Expiration, Orange Book Status, and Electrotransport Patent Landscape

US Patent 6,181,963 protects an electrotransport drug-delivery system that uses cetylpyridinium salt as an antimicrobial preservative in the cathodic reservoir. Its strongest commercial embodiment is an iontophoretic fentanyl device with a drug-containing anodic reservoir and a substantially drug-free cathodic hydrogel containing cetylpyridinium chloride. The claims are narrow because they require a specific reservoir architecture, preservative chemistry, polymer compatibility, and, for the process claims, non-delivery of cetylpyridinium ions.

The patent is a device and process patent, not a composition-of-matter patent for fentanyl or cetylpyridinium chloride. Its statutory term has expired under the 20-year patent-term rule applicable to post-June 8, 1995 applications. It therefore does not create current blocking exclusivity in the United States, although it remains relevant as prior art and as a technical reference for electrotransport systems.[1][2]

What does US Patent 6,181,963 protect?

The patent protects three related claim groups:

Claim group	Claims	Protected subject matter
Device claims	1-14	An electrotransport device with a cathodic reservoir containing an aqueous medium and cetylpyridinium salt
Drug-delivery process claims	15-22	Transdermal electrotransport in which the drug is delivered from the anode while cetylpyridinium ions are not delivered from the cathode
Manufacturing claims	23-26	Preparing the preserved aqueous medium and placing it in a compatible polymeric cathodic reservoir

The central technical problem is microbial growth in an aqueous hydrogel or reservoir. The claimed solution combines cetylpyridinium salt with a polymeric reservoir material that is compatible with the preservative. The claims do not cover every antimicrobial-preserved transdermal device. They require cetylpyridinium specifically, or a qualifying cetylpyridinium halide in the dependent claims.

How broad is independent claim 1?

Claim 1 is a combination claim with several mandatory elements:

A transdermal electrotransport device.
An anode and a cathode.
A power source electrically connected to both electrodes.
A cathodic electrode and cathodic reservoir.
A cathodic reservoir housing made from polymeric material.
An aqueous medium in contact with the housing.
A drug, electrolyte salt, or combination in the aqueous medium.
Cetylpyridinium salt in an amount sufficient to inhibit microbial growth.
A polymeric material compatible with the cetylpyridinium salt.

A competing product would need to satisfy every limitation to infringe literally. The claim does not require fentanyl, a hydrogel, a particular pH, a particular concentration, an anion exchange membrane, or a drug-containing cathode. Those features appear in dependent claims or in the process claims.

The phrase "compatible with the cetylpyridinium salt" is a material-performance limitation. It narrows the claim to polymers that do not cause unacceptable interaction with the preservative, such as absorption, degradation, loss of antimicrobial activity, or other incompatibility identified by the patent specification. The claim is therefore broader than a claim limited to one named polymer, but narrower than a claim covering any polymeric housing.

What do dependent claims 2 through 14 add?

The dependent claims create several technical fallbacks:

Claims	Limitation	Commercial or technical effect
2-3	pH from about 3 to 7.5, or 3.5 to 6.5	Narrows the aqueous environment and preservative operating range
4	Buffer	Covers pH-controlled cathodic media
5	Polyethylene terephthalate, modified PET, polypropylene, or mixtures	Identifies preferred reservoir materials
6	Cathodic medium contains electrolyte and is substantially drug-free	Separates the cathode from the drug reservoir
7-8	Drug in anodic reservoir, including fentanyl	Targets asymmetric iontophoretic delivery
9-10	Cetylpyridinium halide, including cetylpyridinium chloride	Narrows the antimicrobial to common commercial salts
11-13	At least 0.005%; 0.005%-2%; or 0.01%-1% by weight	Establishes concentration-based claim positions
14	Anion exchange membrane between cathodic electrode and reservoir	Adds an ion-selective transport barrier

The fentanyl limitations are commercially significant but do not convert the patent into a fentanyl composition patent. They cover fentanyl used in the claimed electrotransport configuration.

What does claim 15 require for a process infringement case?

Claim 15 is directed to the operation of the device rather than the device structure alone. It requires:

an anode containing a drug;
a cathode containing an electrolyte and cetylpyridinium salt;
a compatible polymeric cathodic reservoir;
application of electric current;
transdermal delivery of the drug from the anodic reservoir; and
no transdermal delivery of cetylpyridinium ions from the cathodic reservoir.

The final limitation is important. A system that releases cetylpyridinium ions through the skin could fall outside the literal scope of claim 15, even if its cathodic reservoir otherwise resembles the claimed system. The claim is directed to antimicrobial preservation of the reservoir without delivering the preservative to the patient.

Claims 16 and 22 specify fentanyl. Claims 17-19 specify a hydrogel and concentration ranges. Claim 21 requires that substantially no drug be delivered from the cathode.

What does claim 23 protect in the manufacturing process?

Claim 23 covers preparation of the device by:

preparing an aqueous medium containing a drug, electrolyte salt, or both;
adding cetylpyridinium salt in an amount sufficient to inhibit microbial growth;
placing the medium in a cathodic reservoir;
using a polymeric housing in contact with the medium; and
selecting the polymer for compatibility with the cetylpyridinium salt.

Claim 24 identifies PET, modified PET, polypropylene, and mixtures. Claim 25 covers a substantially drug-free medium. Claim 26 covers a cetylpyridinium halide.

These claims could have been relevant to contract manufacturers filling reservoirs or assembling iontophoretic patches. They do not broadly cover manufacturing any transdermal patch containing an antimicrobial agent.

Which claim limitations create the main design-around opportunities?

The most effective design-around strategies are directed at the cumulative limitations rather than one isolated feature.

Design-around approach	Potential claim issue
Use a preservative other than cetylpyridinium salt	Removes a central limitation of claims 1, 15, and 23
Use a nonaqueous cathodic medium	Avoids the aqueous-medium limitation
Use a cathodic reservoir without a polymeric housing	Avoids the reservoir-housing limitation
Use a polymer that materially interacts with cetylpyridinium	Raises the compatibility limitation
Place the antimicrobial in a separate layer or external package	May avoid the requirement that it be in the cathodic aqueous medium
Use a drug-containing cathode rather than a substantially drug-free cathode	Avoids claims 6, 15, 21, and 25, but not necessarily claim 1
Deliver the drug from the cathode	Avoids the anodic-delivery limitations of claims 15 and 16
Use a preservative that is delivered through the skin	May avoid the non-delivery limitation in claim 15
Use a non-electrotransport transdermal system	Removes the electrotransport-device requirement

Because the patent has expired, these design-arounds matter principally for freedom-to-operate history, prior-art analysis, and technology benchmarking.

When did US Patent 6,181,963 lose exclusivity?

US Patent 6,181,963 issued on January 30, 2001.[1] Under 35 U.S.C. § 154, a utility patent filed after June 8, 1995 generally expires 20 years after the earliest effective nonprovisional filing date, subject to patent-term adjustment, terminal disclaimers, and certain statutory extensions.[2]

The patent’s enforceable term has ended. The patent cannot support a new US infringement action based on conduct occurring after expiration. Patent expiration does not erase the claims from the prior-art record, and it does not invalidate contractual obligations or regulatory history associated with products that previously relied on the patent.

What is the Orange Book status of US Patent 6,181,963?

The patent is associated with the technology used in ALZA/Janssen iontophoretic fentanyl products, including IONSYS. A historical Orange Book listing, if submitted for the relevant NDA, would have provided regulatory patent-notice significance during the patent’s term. It does not provide current listed-patent exclusivity after expiration.[3]

The patent does not protect fentanyl itself. A generic or follow-on applicant would therefore analyze:

the NDA’s historical patent listings;
whether the listed patent claims covered the reference product;
any Paragraph IV certification made during the patent term;
whether the product used the claimed cathodic preservative system; and
whether other device, formulation, method-of-use, or manufacturing patents remained in force.

An Orange Book listing would not automatically establish infringement. FDA listing and patent enforceability are separate issues. FDA determines regulatory listing; courts determine infringement and validity.[3][4]

What Paragraph IV and generic-entry risks affected the patent?

A Paragraph IV certification could have challenged the patent if an ANDA applicant sought approval for a product that referenced a listed fentanyl iontophoretic system. The principal arguments would have included:

the accused product uses a different antimicrobial;
its cathodic reservoir is not polymeric or is not compatible in the claimed sense;
the aqueous medium lacks cetylpyridinium salt;
the product delivers the drug through a different electrode arrangement;
cetylpyridinium ions are delivered, defeating claim 15;
the claims are anticipated or obvious over earlier iontophoresis and preservative references; or
the listed claims do not cover the proposed generic product.

The practical generic-entry risk is now zero with respect to this expired patent. During the original term, risk would have been highest for an exact IONSYS-type product using cetylpyridinium chloride in a PET or polypropylene cathodic hydrogel.

What products and technologies are most closely related?

The closest commercial technology is the fentanyl iontophoretic transdermal system marketed as IONSYS. IONSYS used controlled electrical current to deliver fentanyl through the skin from a drug reservoir. The patent’s claims map most directly to the preservative system and cathodic reservoir rather than to the complete commercial product architecture.

Adjacent technologies include:

Technology	Relationship to US 6,181,963
Fentanyl iontophoresis	Expressly covered in claims 8, 16, and 22
Nonfentanyl iontophoresis	Potentially covered by claims 1 and 15 if all other limitations are met
Passive fentanyl patches	Generally outside the electrotransport limitations
Microneedle delivery	Usually outside the claimed electrode and current architecture
Electroporation	May avoid literal electrotransport limitations depending on device structure
Preserved hydrogel reservoirs	Technically adjacent, but cetylpyridinium and compatibility remain required
Implantable or oral fentanyl systems	Outside the transdermal electrotransport scope

No biosimilar issue applies. Fentanyl is a small-molecule drug, and a competing product would face generic-drug and device-combination requirements rather than the biosimilar pathway under the Public Health Service Act.[5]

How strong was the patent estate?

The patent had moderate claim strength within a narrow technical segment and weak breadth outside it.

Factor	Assessment
Claim specificity	High
Coverage of cetylpyridinium-preserved cathodes	Strong
Coverage of all antimicrobial preservatives	None
Coverage of passive transdermal products	None
Coverage of fentanyl generally	None
Design-around difficulty	Moderate to low
Manufacturing relevance	Moderate
Current enforceability	None because the patent has expired
Prior-art value	High for preserved electrotransport reservoirs

The strongest claims were the dependent claims tying together fentanyl, a drug-containing anode, a substantially drug-free cathode, cetylpyridinium chloride, and defined concentration ranges. The broadest claim, claim 1, still requires the distinctive cetylpyridinium-compatible cathodic reservoir.

What patent litigation and settlement issues are relevant?

The patent could have been asserted against a manufacturer or supplier producing an electrotransport system with the claimed cathodic reservoir. Potential defendants would include device manufacturers, fentanyl-product sponsors, reservoir-material suppliers, and contract assemblers.

A settlement involving this patent could have included:

a delayed generic or follow-on launch;
a license to use the reservoir-preservative technology;
restrictions on product architecture;
payment terms tied to commercial launch;
a covenant not to sue; or
a manufacturing transition.

No current litigation threat can arise from the expired patent itself. Any historical settlement would require review of the underlying court docket and agreement because FDA records do not disclose all private patent-license terms.

What is the commercial and revenue exposure?

The patent’s commercial exposure was concentrated in iontophoretic fentanyl systems rather than the broader transdermal market. Revenue attributable to the patent cannot be isolated from product sales because the patent covered one technical subsystem and process, not the complete fentanyl market.

The relevant economic questions were:

whether the product required the specific preserved cathodic reservoir;
whether competing systems could replace cetylpyridinium chloride;
whether the same product was protected by additional device or formulation patents;
whether hospital-use demand supported an iontophoretic fentanyl product; and
whether FDA manufacturing and human-factors requirements limited substitution.

Today, the patent has no remaining exclusionary revenue value. Its commercial relevance is historical and technical.

Key Takeaways

US Patent 6,181,963 covers cetylpyridinium-preserved cathodic reservoirs in transdermal electrotransport devices.
The claims require an aqueous medium, a polymeric reservoir housing, cetylpyridinium salt, and polymer compatibility.
Claims 15-22 add a process requirement that fentanyl or another drug be delivered from the anode while cetylpyridinium ions are not delivered from the cathode.
Claims 23-26 cover preparation and filling of the preserved cathodic reservoir.
The patent is closely associated with iontophoretic fentanyl technology, including IONSYS-type systems.
It is not a fentanyl composition patent and does not cover passive fentanyl patches.
The patent’s statutory term has expired, eliminating current US infringement risk.
The former patent estate had moderate strength in a narrow device architecture but offered several practical design-around routes.
No biosimilar pathway applies because fentanyl is a small molecule.
Any current product assessment must focus on later patents, regulatory requirements, product-specific device claims, and manufacturing know-how rather than US 6,181,963.

FAQs About US Patent 6,181,963

Does US Patent 6,181,963 cover cetylpyridinium chloride by itself?

No. The claims require cetylpyridinium salt in an electrotransport device reservoir or in a specified preparation and delivery process. They do not claim cetylpyridinium chloride as a standalone chemical compound.

Does the patent cover a fentanyl patch without electrical current?

No. The independent claims require a transdermal electrotransport device or an electrotransport delivery process. A passive fentanyl patch generally falls outside those limitations.

Can a company use cetylpyridinium chloride in a modern iontophoretic device?

The patent itself is expired, so it does not create current infringement liability. Other patents, regulatory requirements, and product-specific rights may still affect commercialization.

Is an anion exchange membrane mandatory in every claim?

No. It is required only by claim 14. Claims 1 and 15 do not require an anion exchange membrane unless the product also relies on claim 14.

What is the key difference between claims 1 and 15?

Claim 1 protects the device structure. Claim 15 protects operation of the device and requires that cetylpyridinium ions not be transdermally delivered from the cathodic reservoir.

References

United States Patent No. 6,181,963, Electrotransport delivery device with antimicrobial agent (issued Jan. 30, 2001), United States Patent and Trademark Office.
35 U.S.C. § 154. Patent term; contents and conditions of patent grants.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
35 U.S.C. §§ 271, 282. Infringement and presumptions of validity.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application process and generic drugs. FDA.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	1332100	⤷ Start Trial
Australia	766913	⤷ Start Trial
Canada	2349715	⤷ Start Trial
China	1170604	⤷ Start Trial
China	1324259	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,181,963

Summary for Patent: 6,181,963