US Patent 5,607,690: Diclofenac Plaster Claims, Expiration, and Patent Landscape

US Patent 5,607,690 covers diclofenac external plaster preparations that use diclofenac as a salt with hydroxyethylpyrrolidine or hydroxyethylpiperidine and maintain the plaster composition at pH 7.3 to 9.0. The core commercial relevance is diclofenac epolamine, the active salt used in products such as Flector.

The patent’s practical blocking value has ended. US Patent 5,607,690 issued on March 4, 1997 and, based on the pre-June 8, 1995 filing regime applicable to the patent family, its 17-year patent term expired on March 4, 2014, absent a term adjustment, extension, or terminal disclaimer. No current US exclusivity should be attributed to this patent.

What does US Patent 5,607,690 protect?

The patent protects a narrow combination of:

A diclofenac salt.
A cyclic organic base that is hydroxyethylpyrrolidine or hydroxyethylpiperidine.
A plaster or external adhesive preparation.
A pH between 7.3 and 9.0.
In claim 2, a narrower pH between 7.5 and 8.5.

The patent also claims a manufacturing process that maintains the pH within the specified range while incorporating, dissolving, dispersing, or kneading the ingredients before spreading the composition over a support.

Core protected subject matter

Claim	Claim type	Principal limitations	Scope
1	Composition	Diclofenac salt, hydroxyethylpyrrolidine or hydroxyethylpiperidine, pH adjuster, pH 7.3-9.0, optional excipients	Broadest composition claim
2	Composition	Claim 1 limitations, with pH 7.5-8.5	Narrower pH subrange
3	Process	Preparing the composition while maintaining pH 7.3-9.0, then spreading it on a support	Manufacturing-process protection
4	Combination product	Plaster preparation plus support; requires thickener, humectant, filler, preservative, and cross-linking agent	More formulation-specific product claim

The claims do not cover every diclofenac topical product. They are directed to a specific salt and plaster technology rather than diclofenac as a topical active in the abstract.

How does the patent define the diclofenac salt?

Diclofenac is chemically 2-[(2,6-dichlorophenyl)amino]benzeneacetic acid. The relevant salt is formed between diclofenac and one of the specified cyclic organic bases.

Hydroxyethylpyrrolidine is particularly important because diclofenac epolamine is generally identified as the salt of diclofenac and 2-(2-hydroxyethyl)pyrrolidine. A product using diclofenac sodium, diclofenac potassium, or another diclofenac salt would not literally satisfy the specified cyclic-base limitation.

Literal salt limitation

A product is most likely within the literal scope of claim 1 if it contains:

Diclofenac epolamine or an equivalent hydroxyethylpyrrolidine salt;
A hydroxyethylpyrrolidine or hydroxyethylpiperidine salt form;
A plaster or adhesive topical delivery system; and
A measured formulation pH from 7.3 through 9.0.

A formulation that contains diclofenac sodium plus hydroxyethylpyrrolidine as a separate excipient presents a different claim-construction question. The claim language characterizes the cyclic organic base as part of the active salt system. Mere coexistence of diclofenac sodium and an unrelated cyclic base would not necessarily satisfy that limitation.

What formulations are protected by US Patent 5,607,690?

Claim 1 permits a relatively broad excipient platform. The listed excipients include:

Thickening agents;
Humectants;
Fillers;
Preservatives;
Cross-linking agents; and
pH adjusters.

Because these components are optional in claim 1, a formulation can potentially fall within that claim without containing every listed excipient. Claim 4 is narrower because it requires a preparation comprising a thickener, humectant, filler, preservative, and cross-linking agent.

Formulation variables that matter

The following variables are central to infringement analysis:

Variable	Relevance
Active salt	Must involve hydroxyethylpyrrolidine or hydroxyethylpiperidine under the literal claim language
Dosage form	Must be an external plaster preparation or a preparation spread over a support
pH	Must be 7.3-9.0 for claims 1, 3, and 4; 7.5-8.5 for claim 2
Support	Required expressly in claim 4 and in the process endpoint of claim 3
Excipients	Optional under claim 1; required in combination under claim 4
Manufacturing sequence	Relevant primarily to claim 3
Finished-product measurement	Critical because pH may change during drying, storage, or packaging

The patent does not appear, from the supplied claims, to limit the invention to a particular patch size, diclofenac loading, adhesive chemistry, backing layer, release liner, application frequency, or treatment indication.

How should the pH limitation be construed?

The pH range is a material limitation, not a stated objective alone. A product that uses the claimed salt but has a finished plaster preparation below pH 7.3 or above pH 9.0 would fall outside the literal scope of claims 1, 3, and 4.

Claim 2 narrows the range to 7.5-8.5. It does not create an independent right to practice the invention outside claim 1. If claim 1 is not infringed because the pH is 7.4, claim 2 cannot restore infringement.

The patent claims do not specify:

The pH measurement temperature;
Whether pH is measured before or after application to the support;
Whether the plaster is extracted into water before measurement;
The permitted analytical tolerance; or
Whether pH must remain within range throughout shelf life.

Those issues could matter in litigation. Pharmaceutical pH is ordinarily measured under an established analytical method, but the patent language would be evaluated together with its specification, prosecution history, and technical evidence.

What does claim 3 add?

Claim 3 is a process claim. It requires more than producing a final plaster with the correct pH. The process must include preparation steps in which the composition is incorporated, dissolved or dispersed, and kneaded while pH is adjusted and maintained within 7.3-9.0.

This creates two distinct infringement theories:

Direct process infringement based on the accused manufacturing steps.
Product infringement under claims 1, 2, or 4 based on the final plaster composition.

A manufacturer could avoid claim 3 by using a process that does not maintain pH within the specified range during preparation, while still potentially infringing a product claim if the final formulation satisfies the composition limitations.

The process claim may also be difficult to enforce against a finished imported product unless the product itself provides evidence of the claimed manufacturing sequence or the statutory rules for process-product importation apply.

What is the patent expiration date?

Event	Date
US Patent 5,607,690 issued	March 4, 1997
Standard pre-1995 US term	17 years from grant
Expected expiration	March 4, 2014
Current status	Expired

The expected expiration date is March 4, 2014, subject to any patent-term adjustment, patent-term extension, or terminal disclaimer reflected in the official USPTO record. The patent is therefore not a current US barrier to generic or branded diclofenac plaster development.

The patent may still have historical importance because products launched while it was in force could have required a license or a noninfringement position. Expiration does not eliminate any accrued damages claims for conduct occurring before expiration.

What is the Orange Book status of US Patent 5,607,690?

US Patent 5,607,690 is not, by itself, evidence of an Orange Book-listed patent. The Orange Book lists patents submitted by sponsors for approved drug products and accepted by FDA for publication in the relevant product listing. A patent can be technically relevant to a product without appearing in the Orange Book.

For diclofenac products, Orange Book analysis must be conducted at the product level. Relevant products may include:

Diclofenac epolamine topical systems;
Diclofenac sodium topical gels;
Diclofenac sodium topical solutions; and
Other prescription diclofenac formulations.

A patent directed to a plaster composition may also be absent from the Orange Book if the sponsor did not submit it, if FDA did not publish it, or if the patent did not claim the approved product or an approved method of use.

Which competing diclofenac products are potentially relevant?

Flector and diclofenac epolamine patches

Flector is the closest commercial comparator because it uses diclofenac epolamine in a topical patch system. FDA approved Flector for the topical treatment of acute pain due to minor strains, sprains, and contusions. Its labeling identifies diclofenac epolamine as the active ingredient and describes a topical system applied to the affected area (FDA, 2023).

A Flector-type product could be technically aligned with the patent’s active-salt limitation if its formulation uses the claimed hydroxyethylpyrrolidine salt and falls within the claimed pH range. That does not establish infringement by itself. The product must also satisfy the plaster, support, and formulation limitations in the relevant claim.

Diclofenac sodium gel

Voltaren Arthritis Pain and generic diclofenac sodium topical gels use diclofenac sodium rather than diclofenac epolamine. They generally do not satisfy the claimed cyclic organic base limitation and are not plaster preparations. They are therefore outside the most direct literal scope of claims 1-4.

Pennsaid and diclofenac topical solutions

Pennsaid products use diclofenac sodium in a topical solution. A liquid solution without a plaster support ordinarily would not satisfy the dosage-form limitations in claims 1, 3, or 4.

Other diclofenac patches

A competing diclofenac patch could create a closer issue if it uses:

Diclofenac epolamine;
A hydroxyethylpyrrolidine or hydroxyethylpiperidine salt;
A hydrogel or adhesive plaster;
A formulation pH between 7.3 and 9.0; and
A support on which the preparation is spread.

Those products may have relied on later patents directed to patch architecture, adhesive systems, drug loading, release control, manufacturing conditions, or specific clinical uses.

Which companies challenged the patent?

The supplied claims do not identify any Paragraph IV certification, litigation, settlement, license, or named challenger involving US Patent 5,607,690. Because the patent expired in 2014, any current Paragraph IV challenge to this patent would be legally unnecessary.

For later diclofenac epolamine or diclofenac topical products, Paragraph IV disputes would ordinarily target patents listed for the relevant FDA-approved product, not an expired 1997 patent. A generic applicant could also file a Section viii statement if it sought approval for indications not covered by listed method-of-use patents.

What patent landscape replaced this patent?

The post-expiration landscape is likely defined by later patent families in five categories:

Patent category	Typical protection
Patch architecture	Backing layer, adhesive matrix, release liner, moisture control
Formulation chemistry	Hydrogel composition, polymer network, penetration enhancers
Salt and active form	Diclofenac epolamine composition or defined salt ratios
Manufacturing	Mixing, coating, drying, pH control, and scale-up methods
Method of use	Treatment of acute pain, osteoarthritis, or specific musculoskeletal conditions

The expiration of US Patent 5,607,690 removes the original pH-and-salt combination as a live US exclusion right. It does not establish freedom to operate against later patents covering a commercial product’s adhesive matrix, patch construction, manufacturing process, or approved use.

How strong is the patent estate?

Historical strength

The patent had meaningful historical scope because it combined:

A commercially relevant diclofenac salt;
A topical plaster dosage form;
A defined pH window; and
A process claim covering pH control during manufacture.

The combination limited design-around options for products using the same salt and patch format.

Current strength

Its current enforcement strength is zero because the patent has expired. Its remaining value is analytical:

It identifies the technical concept associated with diclofenac epolamine plaster systems.
It may help trace priority and licensing history.
It can inform invalidity, prosecution, and freedom-to-operate analyses for later patents.
It may remain relevant to prior-art searches for pH-controlled hydrogel patches.

What generic launch risks exist?

A generic diclofenac patch faces limited risk from US Patent 5,607,690 itself. The principal current risks are more likely to arise from:

Later formulation patents.
Patch-construction patents.
Manufacturing patents.
Orange Book-listed patents tied to the reference product.
Non-patent regulatory exclusivity or product-specific FDA requirements.
Trade-secret manufacturing processes not disclosed in patents.

A generic using diclofenac sodium gel or solution has a different risk profile because it is likely outside the expired patent’s salt and plaster limitations. A generic diclofenac epolamine patch has greater technical overlap but can no longer be blocked by this patent.

Key Takeaways

US Patent 5,607,690 claims diclofenac plaster preparations using hydroxyethylpyrrolidine or hydroxyethylpiperidine salts.
Diclofenac epolamine is the principal commercial salt relevant to the claims.
The central composition limitation is a pH of 7.3-9.0; claim 2 narrows the range to 7.5-8.5.
Claim 3 covers manufacture while maintaining the pH range during preparation.
Claim 4 requires a support and a fuller excipient combination.
The patent’s expected expiration date was March 4, 2014.
The patent has no current blocking effect on US generic or branded development.
Flector is the closest commercial comparator, while diclofenac sodium gels and solutions are generally outside the literal claim structure.
Current freedom-to-operate analysis must focus on later patch, formulation, manufacturing, and method-of-use patents.

FAQs

Does US Patent 5,607,690 cover diclofenac sodium gel?

No. Diclofenac sodium gel generally lacks both the claimed cyclic organic base salt and the plaster-support limitation.

Is diclofenac epolamine the same as hydroxyethylpyrrolidine diclofenac?

Diclofenac epolamine is generally identified as the salt of diclofenac with 2-(2-hydroxyethyl)pyrrolidine, making it the principal commercial salt relevant to the patent claims.

Can a diclofenac patch avoid the patent by changing the pH?

Changing the finished preparation outside pH 7.3-9.0 could avoid the literal pH limitation in claims 1, 3, and 4. The product would still require separate analysis under other patents.

Does the patent cover the backing layer of a diclofenac patch?

Claim 4 requires a support, but the supplied claims do not define the support material or grant a broad, standalone monopoly over patch backing layers.

Can a company launch a generic diclofenac epolamine patch based solely on this patent’s expiration?

The expired patent no longer blocks launch. A complete launch assessment must still address later patents, FDA requirements, Orange Book listings, regulatory exclusivity, and product-specific litigation risk.

References

Food and Drug Administration. (2023). Flector (diclofenac epolamine) topical system prescribing information. U.S. Department of Health and Human Services.

U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations: Orange Book. U.S. Department of Health and Human Services.

U.S. Patent No. 5,607,690. (1997). External anti-inflammatory and analgesic plaster preparation. United States Patent and Trademark Office.

United States Code, 35 U.S.C. §§ 154, 271, 282. (2024). Patent term and infringement provisions. Government Publishing Office.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Japan	5-119246	Apr 23, 1993

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	194828	⤷ Start Trial
Canada	2121065	⤷ Start Trial
Germany	69425292	⤷ Start Trial
European Patent Office	0621263	⤷ Start Trial
Spain	2149225	⤷ Start Trial
Greece	3034616	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,607,690

Summary for Patent: 5,607,690