United States Patent 3,904,682: Naproxen Scope, Claims, Expiration, and Patent Landscape

U.S. Patent No. 3,904,682 covers the chemical compound now known as naproxen, chemically 2-(6-methoxy-2-naphthyl)propionic acid, and specifically claims its D enantiomer. The patent issued on September 9, 1975, and, under the pre-URAA patent term applicable to it, expired no later than September 9, 1992. It no longer blocks manufacture, sale, formulation, or use of naproxen in the United States.

The patent has a narrow claim set but broad subject-matter significance. Claim 1 covers the naproxen molecular structure. Claim 2 depends on claim 1 and narrows the compound to the D optical isomer, corresponding to the commercially used active enantiomer generally identified as S-(+)-naproxen. The patent does not claim a formulation, dosage regimen, manufacturing process, salt, prodrug, or method of treating a disease.

What drug does U.S. Patent 3,904,682 protect?

U.S. Patent 3,904,682 protects naproxen, a nonsteroidal anti-inflammatory drug, or NSAID, used to treat pain, inflammation, dysmenorrhea, osteoarthritis, rheumatoid arthritis, and related conditions.

The compound in the patent is:

Attribute	Description
Generic name	Naproxen
Chemical name	2-(6-methoxy-2-naphthyl)propionic acid
Molecular formula	C14H14O3
Molecular weight	230.26 g/mol
Drug class	NSAID
Pharmacologic action	Cyclooxygenase inhibition
Commercial active form	S-(+)-naproxen
Common salt	Naproxen sodium
Original innovator	Syntex Corporation
U.S. patent	US 3,904,682
Patent issue date	September 9, 1975
Patent status	Expired

Naproxen is a chiral propionic-acid derivative. Its two enantiomers have the same constitutional formula but different three-dimensional arrangements. Claim 2 is directed to the D optical form rather than merely to the unsubstituted molecular formula.

What are the claims of U.S. Patent 3,904,682?

The supplied claim text contains typographical artifacts, including “metoxy,” repeated quotation marks, and “D 2-.” The claims can be read substantively as follows:

Claim	Scope	Legal characterization
1	2-(6-methoxy-2-naphthyl)propionic acid	Independent compound claim
2	D-2-(6-methoxy-2-naphthyl)propionic acid	Dependent claim directed to a specific optical isomer

Claim 1: the naproxen molecular structure

Claim 1 is a compound claim covering 2-(6-methoxy-2-naphthyl)propionic acid. It identifies the molecule by its chemical structure rather than by a therapeutic use or dosage form.

The claim reaches the core naproxen molecule. It does not require:

a particular tablet or capsule;
a particular dose;
a particular pharmaceutical excipient;
a particular manufacturing route;
a particular salt;
a particular polymorph;
a particular indication; or
a particular method of administration.

Because claim 1 is a composition-of-matter claim, infringement would have turned on making, using, selling, offering to sell, or importing the claimed compound during the enforceable patent term.

Claim 2: the D optical isomer

Claim 2 narrows claim 1 to D-2-(6-methoxy-2-naphthyl)propionic acid. In modern stereochemical terminology, the marketed therapeutic enantiomer is generally described as S-(+)-naproxen. Older pharmaceutical patents often use D/L or optical-rotation nomenclature rather than the R/S system.

The significance of claim 2 is that it isolates the enantiomer associated with naproxen’s commercial activity. A claim directed to the single active enantiomer can be narrower structurally than a claim covering the entire compound category, but it can have greater commercial relevance if the enantiomer is the form used in the approved product.

How broad is the scope of Patent 3,904,682?

The patent’s scope is broad in chemical terms and narrow in claim count.

What the patent covers

During its enforceable term, the patent covered:

The naproxen molecule identified in claim 1.
The claimed D optical isomer identified in claim 2.
Products containing the claimed compound, to the extent the product implicated an infringing making, using, selling, offering for sale, or importation activity.
Generic products containing the claimed active compound if marketed before patent expiration and otherwise within the patent’s legal scope.

What the patent does not cover

The patent does not, based on the two supplied claims, independently cover:

naproxen sodium as a separately claimed salt;
extended-release naproxen;
enteric-coated naproxen;
liquid suspensions;
topical formulations;
fixed-dose combinations;
a manufacturing process;
a treatment method;
a dosing schedule;
a patient population;
a pharmaceutical composition claim;
a crystalline form;
a hydrate or solvate; or
a specific impurity profile.

A salt product could still have implicated the patent if the salt dissociated to or contained the claimed naproxen compound under the relevant infringement analysis. But the patent does not appear to contain a separate salt claim based on the claim text provided.

When did U.S. Patent 3,904,682 expire?

U.S. Patent 3,904,682 issued on September 9, 1975. Because it was granted before the 1995 change to a term measured from the earliest effective nonprovisional filing date, its ordinary term was 17 years from issuance. The resulting expiration date was September 9, 1992, absent an earlier terminal disclaimer or other unusual adjustment.

Event	Date
Patent issued	September 9, 1975
Ordinary pre-URAA term	17 years from issue
Expected expiration	September 9, 1992
Current status	Expired
Current enforceability	None

The Hatch-Waxman patent-term-extension regime under 35 U.S.C. § 156 was enacted after this patent issued. Any regulatory exclusivity associated with naproxen would not revive an expired composition-of-matter patent.

What is the Orange Book status of naproxen?

The original naproxen patent is not a current Orange Book barrier. FDA’s Orange Book lists approved drug products and, where applicable, patents and exclusivity information associated with approved new drug applications. An expired 1970s composition patent does not provide current listed-patent protection against ANDA applicants.

Naproxen has been marketed in multiple regulatory categories:

Product type	Regulatory route or status
Prescription naproxen tablets and suspension	Approved prescription products
Naproxen sodium prescription products	Approved prescription products
Over-the-counter naproxen sodium	OTC monograph-based marketing
Combination products	Product-specific approval or OTC status
Generic naproxen	Widely approved and marketed

The key distinction is between naproxen itself and later product-specific patents. A manufacturer could have obtained later patents on a formulation, release profile, delivery system, or combination product. Those patents would not extend the term of US 3,904,682.

Did Patent 3,904,682 create generic-entry risk?

Yes. Once the patent expired in 1992, the core compound became available for generic manufacture and sale, subject to FDA approval, applicable regulatory requirements, and any separate unexpired patents.

The principal generic-entry consequences were:

no continuing composition-of-matter exclusivity;
no current Paragraph IV challenge directed to this patent;
no patent-based bar to ANDA approval arising from US 3,904,682;
availability of both naproxen and naproxen sodium products from multiple manufacturers; and
loss of practical leverage for the original patent owner in licensing or litigation.

A Paragraph IV certification is relevant only when an ANDA applicant addresses a listed patent that remains an obstacle to approval. Because US 3,904,682 expired decades ago, an applicant today would not need to challenge it as a live patent right.

Were there Paragraph IV challenges or litigation involving this patent?

The patent’s age means that any Hatch-Waxman litigation associated with it would have occurred after enactment of the Drug Price Competition and Patent Term Restoration Act of 1984 but before expiration in 1992. The patent could have been relevant to early generic filings if it was listed for an approved naproxen product and remained unexpired at the time of certification.

The present legal position is clear:

Issue	Current position
Patent infringement suit based solely on US 3,904,682	Not viable because the patent is expired
New Paragraph IV certification to this patent	Commercially irrelevant
Injunction based on this patent	Unavailable
Damages for post-expiration conduct	Unavailable
Declaratory judgment of invalidity	Generally unnecessary for an expired patent
Generic launch barrier	None from this patent

Expired patents can remain relevant in historical validity or ownership analysis, but they no longer support prospective market exclusion.

What later patents could have protected naproxen products?

The core patent should be separated from later patent categories.

Formulation patents

Later patents could cover:

sustained-release naproxen;
controlled-release tablets;
enteric-coated dosage forms;
liquid formulations;
taste-masked suspensions;
rapidly disintegrating tablets;
topical delivery systems;
combination products;
modified particle-size distributions; or
specific excipient systems.

Such claims protect a product architecture rather than the naproxen molecule itself. A generic manufacturer could avoid an unexpired formulation claim by using a different release mechanism, excipient profile, coating, or manufacturing process.

Method-of-use patents

A later patent could cover a particular therapeutic method, such as:

treating a defined inflammatory condition;
reducing gastrointestinal toxicity;
treating a specified patient subgroup;
using a particular dosage schedule; or
combining naproxen with another active ingredient.

A method patent would not recreate the expired composition patent. Its enforceability would depend on claim wording, FDA labeling, induced-infringement evidence, and the availability of a non-infringing label.

Manufacturing and process patents

A process patent could address:

resolution of naproxen enantiomers;
stereoselective synthesis;
chiral intermediates;
crystallization;
impurity control;
particle engineering; or
production of naproxen sodium.

Process protection can create supply-chain risk even when the drug molecule is off patent. It is usually easier to design around than a composition claim, but process claims may still affect API sourcing and importation.

How strong is the patent estate for naproxen?

The original estate was strong during its term because it included a composition claim to the commercial molecule. Its present strength is zero as an exclusionary right because the patent has expired.

Patent characteristic	Assessment
Claim type	Composition of matter
Number of supplied claims	Two
Core molecule covered	Yes
Enantiomer separately covered	Yes
Formulation protection	No claim shown
Method-of-use protection	No claim shown
Process protection	No claim shown
Current enforceability	None
Design-around difficulty during term	High
Current generic barrier	None

The strongest historical feature was claim 1’s direct coverage of the molecule. A generic manufacturer could not avoid that claim by changing excipients or dosage form if the same claimed compound was made or sold. The main historical routes around the patent would have involved timing, validity, non-infringement theories, or use of a different compound rather than ordinary formulation redesign.

How does naproxen compare with competing NSAIDs?

Naproxen competed with ibuprofen, diclofenac, indomethacin, ketoprofen, and other NSAIDs. Its patent position is now similar to that of other mature small-molecule NSAIDs: the original compound patents have expired, and competition is driven by manufacturing cost, regulatory approvals, dosage convenience, tolerability, brand recognition, and formulation differentiation.

Drug	Core patent position today	Main commercial issue
Naproxen	Core compound patent expired	Generic price competition
Ibuprofen	Core compound patent expired	High-volume OTC competition
Diclofenac	Core compound patent expired	Formulation and topical products
Celecoxib	Later patent history and product-specific claims	Formulation and indication competition
Meloxicam	Core exclusivity expired in major markets	Prescription generic competition

Naproxen sodium remains commercially relevant because of faster dissolution relative to naproxen acid in certain products, but the salt does not restore exclusivity to the expired patent.

What licensing and ownership issues matter?

The historical patent owner was Syntex Corporation. Roche acquired Syntex in 1994, after US 3,904,682 had expired. Any historical assignment or license affecting the patent does not create current exclusivity.

There is no commercially meaningful present-day license needed to practice the expired compound patent in the United States. Companies may still enter private agreements covering:

API supply;
trademarks;
formulation technology;
co-promotion;
geographic rights;
quality specifications; or
regulatory dossiers.

Those agreements are commercial arrangements, not extensions of US 3,904,682.

What geographic coverage did the patent provide?

US 3,904,682 provided rights only under United States patent law. It did not automatically protect naproxen in Canada, Europe, Japan, or other jurisdictions. Foreign equivalents would have required separate national filings and enforceable rights in each jurisdiction.

The United States patent’s expiration did not necessarily establish the expiration date of every foreign counterpart. Foreign patent terms, filing dates, prosecution history, maintenance requirements, and patent-term rules could differ. The practical global position is nevertheless that naproxen is a mature, widely genericized compound.

What generic launch scenarios existed and remain relevant?

During the patent term, generic entry could have taken several forms:

A Paragraph IV ANDA challenge alleging invalidity or non-infringement.
A Paragraph III certification awaiting patent expiration.
A launch after September 9, 1992.
A formulation-specific launch that avoided later product claims.
An OTC product marketed under the applicable FDA monograph framework.

The current scenario is simpler. A company seeking to market a standard naproxen or naproxen sodium product must address FDA approval, bioequivalence where applicable, quality requirements, labeling, manufacturing controls, and any separate live patents listed for the target reference product. US 3,904,682 is not a current obstacle.

Key Takeaways

U.S. Patent 3,904,682 covers 2-(6-methoxy-2-naphthyl)propionic acid, the compound known as naproxen.
Claim 1 is a compound claim to the naproxen molecular structure.
Claim 2 narrows the protection to the D optical isomer, corresponding to the commercial S-(+)-naproxen form under modern stereochemical nomenclature.
The supplied claims do not cover formulations, salts as separate subject matter, manufacturing processes, or treatment methods.
The patent issued on September 9, 1975, and expired on September 9, 1992.
It creates no current Orange Book, Paragraph IV, injunction, damages, or generic-entry barrier.
Later formulation, method-of-use, process, or combination patents would need separate analysis.
The historical patent estate was strong because it directly covered the commercial molecule. Its present exclusionary value is zero.

FAQs About U.S. Patent 3,904,682 and Naproxen

Is U.S. Patent 3,904,682 still enforceable?

No. The patent expired in 1992 and cannot support a current infringement injunction or post-expiration damages claim.

Does Patent 3,904,682 cover naproxen sodium?

It claims the naproxen compound, not a separately defined naproxen sodium salt. Later salt or formulation claims would require separate patent language.

Is naproxen protected by FDA exclusivity today?

The original compound patent does not provide current exclusivity. Any remaining protection would have to arise from a separate product-specific patent, regulatory exclusivity period, trademark, or formulation right.

Can a generic manufacturer make naproxen in the United States?

Yes, subject to FDA approval, applicable manufacturing requirements, labeling rules, and any separate unexpired patents covering the particular product or process.

Does the D enantiomer in claim 2 mean R-naproxen?

No. Commercial naproxen is generally identified as S-(+)-naproxen. Older D/L terminology and modern R/S nomenclature are not interchangeable without reference to the compound’s optical rotation and nomenclature convention.

References

United States Patent and Trademark Office. (1975). U.S. Patent No. 3,904,682: 2-(6-Methoxy-2-naphthyl)propionic acid. U.S. Department of Commerce.
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (2024). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA.
United States Code, 35 U.S.C. §§ 154, 156, and 271.
U.S. Food and Drug Administration. (2024). Naproxen and naproxen sodium prescribing information. FDA.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	1006270	⤷ Start Trial
Belgium	734275	⤷ Start Trial
Belgium	747812	⤷ Start Trial
Belgium	751445	⤷ Start Trial
Belgium	752627	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 3,904,682

Summary for Patent: 3,904,682