United States Patent 4,009,197: Naproxen Claim Scope, Expiration, and Patent Landscape

U.S. Patent No. 4,009,197 covers naproxen, naproxen salts, selected stereoisomers, an isoamyl ester, and 6-difluoromethoxy analogs. The patent issued on February 22, 1977, and, under the pre-URAA patent-term regime, its ordinary 17-year term expired on February 22, 1994. The patent has no current blocking value against generic naproxen or naproxen sodium products. It is historically important because it claimed the active dextrorotatory naproxen isomer and sodium salt, but it is no longer an enforceable U.S. patent right. (U.S. Patent No. 4,009,197, 1977)

What drug does U.S. Patent 4,009,197 protect?

The central compound is naproxen, chemically identified as 2-(6-methoxy-2-naphthyl)propionic acid. The claimed dextrorotatory form corresponds to the pharmacologically active S-(+)-naproxen configuration used in commercial naproxen products.

Patent element	Chemical or commercial identity
2-(6'-methoxy-2'-naphthyl)propionic acid	Racemic naproxen acid
d 2-(6'-methoxy-2'-naphthyl)propionic acid	Dextrorotatory, active naproxen enantiomer
Sodium salt of d naproxen	Naproxen sodium
Pharmaceutically acceptable salts	Salts of naproxen acid or its active enantiomer
6'-difluoromethoxy analog	A distinct naproxen-related analog
Isoamyl ester	Ester prodrug or derivative claim, not the standard marketed naproxen form

The patent claims compounds rather than a finished dosage form. It does not, on the face of the listed claims, claim tablets, capsules, suspensions, enteric coatings, sustained-release systems, dosing regimens, or a therapeutic method.

How many patents cover naproxen and naproxen sodium?

The principal early U.S. patent estate included U.S. Patent Nos. 3,904,682 and 4,009,197. The earlier patent is associated with the core 6-methoxy-alpha-methyl-2-naphthaleneacetic acid technology, while U.S. Patent 4,009,197 contains claims directed to naproxen, naproxen salts, the active enantiomer, and related derivatives.

U.S. patent	Subject matter	Historical term position
3,904,682	Core naproxen-related compound technology	Expired under pre-URAA term
4,009,197	Naproxen, naproxen salts, active enantiomer, sodium salt, isoamyl esters, difluoromethoxy analogs	Expired February 22, 1994

Later patents may have covered particular formulations, manufacturing processes, combinations, or delivery systems. Those later rights would have to be analyzed separately from the compound claims in U.S. Patent 4,009,197. A later formulation patent could not extend the expired compound claims, although it could have created a narrower barrier for a specific dosage form during its own enforceable term.

What is the scope of each claim in U.S. Patent 4,009,197?

Claims 1 and 11: isoamyl ester derivatives

Claim 1 covers the isoamyl ester of d-2-(6'-methoxy-2'-naphthyl)propionic acid. Claim 11 covers 1-isoamyl 2-(6'-methoxy-2'-naphthyl)propionate without the express d-enantiomer limitation.

These claims are directed to esterified derivatives rather than free naproxen acid or naproxen sodium. The claims would potentially reach a product containing the specified ester, but not an ordinary naproxen or naproxen sodium product that contains no isoamyl ester.

Claim 11 appears broader than claim 1 because it does not expressly limit the compound to the d form. Its practical scope would depend on how the chemical name was construed and whether the claim was interpreted to include racemic material, individual enantiomers, or both.

Claims 2 and 8: racemic naproxen acid and sodium salt

Claim 2 covers 2-(6'-methoxy-2'-naphthyl)propionic acid and pharmaceutically acceptable salts. Claim 8 specifically covers the sodium salt of that acid.

These are compound claims. Claim 2 is not limited to a particular dosage form, therapeutic use, purity level, particle size, or manufacturing process. Claim 8 is narrower because it is limited to the sodium salt.

The racemic acid contains both optical isomers. It is chemically distinct from the substantially single-enantiomer product claimed in claims 3 and 7, although commercial and regulatory treatment depends on the identity and stereochemical composition of the product.

Claims 3, 7, and 10: active naproxen and salts

Claim 3 covers the d form of 2-(6'-methoxy-2'-naphthyl)propionic acid and its pharmaceutically acceptable salts. Claim 7 specifically covers the sodium salt of the d form. Claim 10 separately covers pharmaceutically acceptable salts of the d form.

These claims are the most commercially significant provisions in the patent because they reach the active naproxen enantiomer and naproxen sodium. A product containing naproxen sodium would historically have implicated claim 7 if the claimed stereochemical and chemical limitations were met.

The distinction between claims 3 and 10 is structural. Claim 3 covers the d acid and its salts as a selected group. Claim 10 isolates the salt category. Claim 7 isolates the sodium salt.

Claims 4 through 6: difluoromethoxy analogs

Claim 4 covers 2-(6'-difluoromethoxy-2'-naphthyl)propionic acid and pharmaceutically acceptable salts. Claim 5 covers the dl, d, and l forms. Claim 6 specifically covers the d form.

These claims do not literally cover naproxen because naproxen has a 6-methoxy substituent, not a 6-difluoromethoxy substituent. The analog claims therefore represent separate chemical matter within the same general structural field.

The claims illustrate an effort to protect both the commercial methoxy compound and close fluorinated analogs. They would have been relevant to research compounds or products using the difluoromethoxy substitution, but they did not create a continuing monopoly over all naphthyl propionic acids.

How broad are the compound claims?

The broadest practical claim is claim 2, which covers the racemic naproxen acid and its pharmaceutically acceptable salts. Claim 3 is narrower in chemical identity but commercially important because it focuses on the active d enantiomer. Claims 7 and 8 narrow the salt coverage to sodium.

The claim architecture can be summarized as follows:

Claim	Covered subject	Relative breadth
1	d naproxen isoamyl ester	Narrow derivative claim
2	Racemic naproxen acid and salts	Broad compound claim
3	d naproxen acid and salts	Broad active-enantiomer claim
4	Difluoromethoxy analog and salts	Separate analog claim
5	dl, d, and l forms of analog	Stereochemical limitation
6	d difluoromethoxy analog	Narrow analog claim
7	Sodium salt of d naproxen	Product-specific salt claim
8	Sodium salt of racemic naproxen	Product-specific salt claim
9	Salts of racemic naproxen	Salt-only claim
10	Salts of d naproxen	Active-enantiomer salt claim
11	Isoamyl naproxen propionate	Ester derivative claim

The patent does not claim every NSAID, every naphthalene propionic acid, or every salt of every related compound. Its central coverage is molecule-specific.

When did U.S. Patent 4,009,197 lose exclusivity?

U.S. Patent 4,009,197 issued on February 22, 1977. Patents subject to the pre-June 8, 1995 regime generally received 17 years from issuance. On that basis, the patent expired on February 22, 1994. The term was not calculated under the modern 20-year-from-effective-filing-date rule because the patent predates the Uruguay Round Agreements Act transition date. (35 U.S.C. § 154; U.S. Patent and Trademark Office, n.d.)

Milestone	Date
Patent issued	February 22, 1977
Ordinary pre-URAA term	17 years from issue
Expected expiration	February 22, 1994
Current enforceability	Expired
Current compound blocking right	None

Patent expiration eliminates the ability to bring a new infringement action based on unlicensed commercial use of the claimed compounds. It also eliminates the practical value of a Paragraph IV challenge directed solely to this patent.

What was the Orange Book status of naproxen and naproxen sodium?

Naproxen and naproxen sodium are small-molecule drugs approved through the abbreviated new drug application and new drug application systems. They are not biologics and therefore do not have biosimilar exclusivity issues.

Historically, branded naproxen products, including Naprosyn, were associated with the original Syntex patent estate. FDA Orange Book listings for a drug can include patents covering the active ingredient, drug product, or method of use. The relevant compound patents from the 1970s are now expired and cannot delay approval or commercial launch of a conforming generic product. (FDA, 2024)

Current regulatory barriers for a generic naproxen product are therefore more likely to involve:

bioequivalence;
drug substance and impurity controls;
stereochemical composition;
salt form;
dissolution and stability;
labeling;
manufacturing compliance; and
any unexpired product-specific formulation patent.

An applicant would not face a live Orange Book patent obstacle from U.S. Patent 4,009,197.

Which companies challenged the naproxen patent estate?

The original patent estate generated the commercial conditions for generic competition after expiration. Publicly available patent records establish the Syntex ownership history and the expiration of the early compound patents, but U.S. Patent 4,009,197 itself does not identify every later ANDA filer, Paragraph IV notice, settlement, or district-court proceeding involving naproxen products.

A Paragraph IV certification would have had commercial significance only while a listed patent remained unexpired. After February 22, 1994, a Paragraph IV strategy directed to U.S. Patent 4,009,197 could no longer create the 30-month stay mechanism associated with an otherwise valid Orange Book patent listing.

The patent cannot support current litigation against manufacturers of naproxen or naproxen sodium solely because they practice the expired claims.

What formulation patents protect naproxen products?

U.S. Patent 4,009,197 is not a formulation patent. It does not expressly claim:

an immediate-release tablet;
an enteric-coated tablet;
a controlled-release dosage form;
a liquid suspension;
a particular excipient system;
a specific particle-size distribution;
a transdermal product; or
a combination product with another active ingredient.

Formulation patents can have a separate lifecycle from compound patents. For example, an enteric coating, sustained-release matrix, or improved suspension could be patentable if it satisfied novelty, nonobviousness, written-description, and enablement requirements. Such a patent would cover only the claimed formulation or process and would not revive the expired compound patent.

How does naproxen compare with naproxen sodium?

Issue	Naproxen	Naproxen sodium
Chemical form	Free acid	Sodium salt
Relevant claim categories	Claims 2, 3, 9, and 10	Claims 7 and 8
Solubility profile	Lower aqueous solubility	Improved salt-form properties
Regulatory category	Small molecule NSAID	Small molecule NSAID
Biosimilar pathway	Not applicable	Not applicable
U.S. Patent 4,009,197 status	Expired	Expired
Current compound patent risk from this patent	None	None

Naproxen sodium can have different pharmaceutical performance and formulation characteristics from naproxen. That distinction does not change the expiration of the claims in U.S. Patent 4,009,197.

How strong is the patent estate for naproxen today?

The patent estate is commercially weak as an exclusionary estate because the central compound patents expired decades ago. Its historical strength was greater: claims 2, 3, 7, 8, 9, and 10 were directed to the active ingredient and important salt forms rather than a narrow manufacturing step.

Strength factor	Assessment
Chemical specificity	High
Historical coverage of naproxen	Broad
Coverage of naproxen sodium	Direct
Formulation coverage in this patent	None apparent
Current enforceability	None
Current generic entry risk from this patent	None
Biosimilar exposure	Not applicable
Manufacturing barrier	Limited to any separate unexpired process rights
Licensing leverage	None from the expired patent alone

The remaining commercial barriers are regulatory and operational rather than patent-based. A generic manufacturer still must establish pharmaceutical equivalence, bioequivalence, quality, and compliant manufacturing.

What licensing deals affect U.S. Patent 4,009,197?

The patent identifies Syntex Corporation as the original patent owner or assignee in the historical patent record. Later corporate ownership and commercialization arrangements involving Syntex, Roche, branded-product companies, or generic manufacturers do not extend the patent term.

A license could authorize conduct during the patent term, but a license to an expired U.S. patent has no continuing exclusionary effect. Commercial agreements concerning trademarks, supply, formulation technology, or regulatory rights must be distinguished from a license to the expired compound claims.

What generic launch scenarios exist for naproxen?

For ordinary naproxen and naproxen sodium, the principal launch scenarios are:

An ANDA applicant demonstrates bioequivalence to the relevant reference product.
The applicant uses the same active ingredient or salt form without infringing an unexpired patent.
The product launches after satisfying FDA approval and labeling requirements.
Any remaining risk comes from later formulation, method-of-use, process, or contractual rights, not U.S. Patent 4,009,197.

The expired patent does not prevent generic launch, authorized generic supply, private-label products, or competing OTC products.

Key Takeaways

U.S. Patent 4,009,197 is a foundational naproxen patent.
Claims 2, 3, 7, 8, 9, and 10 cover naproxen, the active d enantiomer, and important salt forms.
Claims 1 and 11 cover isoamyl ester derivatives.
Claims 4 through 6 cover difluoromethoxy analogs rather than ordinary naproxen.
The patent issued on February 22, 1977, and expired under the pre-URAA 17-year term on February 22, 1994.
It has no current Orange Book blocking effect and cannot support a new infringement action.
Naproxen and naproxen sodium are small-molecule drugs, so biosimilar analysis does not apply.
Current market-entry risk depends on FDA requirements and any later unexpired formulation, manufacturing, or method-of-use patents.

FAQs About U.S. Patent 4,009,197 and Naproxen

Is U.S. Patent 4,009,197 still enforceable?

No. Its ordinary pre-URAA patent term expired on February 22, 1994.

Does U.S. Patent 4,009,197 cover ibuprofen?

No. It covers naproxen-related compounds containing the specified substituted naphthyl propionic acid structure.

Does the patent cover naproxen sodium tablets?

Historically, claim 7 directly covered the sodium salt of the d naproxen enantiomer. The patent no longer blocks those products because it has expired.

Can a company patent a new naproxen formulation?

Potentially, if the formulation satisfies patentability requirements. A new formulation patent would be narrower than the expired compound claims and would not restore exclusivity over naproxen itself.

Are biosimilars relevant to naproxen?

No. Naproxen is a chemically synthesized small-molecule drug. Competition proceeds through generic-drug pathways, principally ANDAs, rather than biosimilar applications.

References

Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.

United States Code. (2023). 35 U.S.C. § 154: Contents and term of patent; provisional rights.

U.S. Patent No. 3,904,682. (1975). 6-Methoxy-alpha-methyl-2-naphthaleneacetic acid. U.S. Patent and Trademark Office.

U.S. Patent No. 4,009,197. (1977). 2-(6'-Methoxy-2'-naphthyl) propionic acid and salts thereof. U.S. Patent and Trademark Office.

U.S. Patent and Trademark Office. (n.d.). Patent term adjustment and patent term calculation guidance. U.S. Department of Commerce.

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
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,009,197

Summary for Patent: 4,009,197