United States Patent 3,674,836: Claim Scope, Gemfibrozil Coverage, Expiration, and Patent Landscape

US Patent 3,674,836 covers substituted phenoxyalkanoic acids, including gemfibrozil, the active ingredient in Lopid. Claims 2-7 narrow the genus in claim 1 by limiting the terminal substituent or identifying specific compounds. The patent issued in 1972 and its ordinary 17-year term expired in 1989. It no longer creates a barrier to generic gemfibrozil manufacture, sale, or FDA approval.

What drug does US Patent 3,674,836 protect?

US 3,674,836 covers a chemical class of substituted phenoxyalkanoic acids. The commercially important compound within the patent is gemfibrozil:

Generic name: gemfibrozil
Chemical name: 5-(2,5-dimethylphenoxy)-2,2-dimethylpentanoic acid
Brand: Lopid
Therapeutic category: fibric acid derivative; lipid-regulating agent
Primary use: reduction of triglycerides and selected cholesterol abnormalities

Claim 6 expressly identifies 2,2-dimethyl-5-(2,5-xylyloxy)valeric acid. That compound is gemfibrozil. In chemical nomenclature, "2,5-xylyloxy" denotes a phenoxy group bearing methyl substituents at the 2- and 5-positions.

The patent therefore has historical composition-of-matter significance for gemfibrozil. It is not a current exclusivity right because the patent term has ended.

What are the claims of US Patent 3,674,836?

The supplied claims are dependent claims. Each depends on claim 1 and inherits all limitations contained in that claim.

Claim	Limitation	Scope
2	R is hydrogen	Covers the claim 1 compound with an unsubstituted terminal carboxylic-acid-related group, depending on the definition of R in claim 1
3	R is lower alkyl	Covers claim 1 compounds in which R is a lower-alkyl substituent
4	2,2-Dimethyl-5-phenoxyvaleric acid	Specific compound claim with an unsubstituted phenoxy ring
5	2,2-Dimethyl-6-phenoxyhexanoic acid	Specific homolog containing one additional methylene unit
6	2,2-Dimethyl-5-(2,5-xylyloxy)valeric acid	Gemfibrozil compound claim
7	2,2-Dimethyl-5-(3,5-xylyloxy)valeric acid	Positional isomer of the gemfibrozil structure

The scope of claims 4-7 is materially narrower than the genus in claim 1. A compound must satisfy the complete structure recited in claim 1 and the additional structural limitation in the dependent claim.

What does claim 6 cover?

Claim 6 covers gemfibrozil as a chemical compound, assuming the compound satisfies every limitation of claim 1. It is a product claim, not merely a treatment or manufacturing claim.

A product claim generally reaches:

The claimed active pharmaceutical ingredient itself
The compound regardless of whether it is made by a different synthetic route
Pharmaceutical compositions containing the compound, to the extent the independent claim and applicable claim construction support that result
Commercial products containing the claimed compound, subject to the patent's term and any jurisdiction-specific issues

Claim 6 does not automatically cover every formulation, salt, polymorph, dosage regimen, or manufacturing process involving gemfibrozil. Those categories require separate claim language.

For gemfibrozil, the free-acid structure identified in claim 6 is central. A materially different salt, ester, crystal form, or derivative would require a separate infringement analysis. A generic manufacturer could not avoid an expired composition claim by using a different manufacturing process, but it also would not need to avoid the claim after expiration.

How do claims 2 and 3 differ from claims 4 through 7?

Claims 2 and 3 are substituent-selection claims. They define alternatives for R within the broader structure of claim 1:

Claim 2 selects hydrogen.
Claim 3 selects lower alkyl.

Claims 4 through 7 identify specific compounds. These claims are narrower because they specify the phenoxy substitution pattern and carbon-chain length.

The claim hierarchy appears to have two functions:

Protect a broad chemical genus through claim 1 and the R-based dependent claims.
Preserve narrower fallback positions for individual compounds and positional isomers.

Claims 4 and 5 cover unsubstituted phenoxy compounds with different chain lengths. Claims 6 and 7 cover methyl-substituted phenoxy compounds. The distinction between claims 6 and 7 is the position of the two methyl groups on the aromatic ring:

Claim 6: 2,5-disubstitution
Claim 7: 3,5-disubstitution

That positional distinction can affect biological activity, pharmacokinetics, potency, and claim interpretation. Claim 7 does not cover gemfibrozil merely because it has the same molecular formula or a similar phenoxyalkanoic-acid skeleton.

What is the patent expiration date for US 3,674,836?

US Patent 3,674,836 issued on July 4, 1972. For a US utility patent filed before June 8, 1995, the ordinary term was 17 years from the grant date. On that basis, the patent expired on July 4, 1989.[1]

Event	Date or status
Patent grant	July 4, 1972
Ordinary patent term	17 years from grant
Expected expiration	July 4, 1989
Current status	Expired
Current blocking effect	None

A patent-term adjustment or extension would need to appear in the official prosecution and patent records to change that calculation. No modern exclusivity right associated with US 3,674,836 remains.

What is the Orange Book status of gemfibrozil?

Gemfibrozil is an FDA-approved small-molecule drug. It is not a biologic and does not use the biosimilar pathway. FDA-approved generic products have been marketed in tablet and capsule forms.

The original Lopid product was approved under an NDA. Generic gemfibrozil products were approved through ANDAs after the relevant patent and regulatory exclusivity barriers ended. FDA's Orange Book identifies approved drug products and, when applicable, patent and exclusivity information. An expired 1972 patent does not prevent current ANDA approvals.[2]

The key regulatory consequences are:

US 3,674,836 cannot support a current Paragraph IV challenge because it is expired.
The patent cannot delay approval of a new ANDA.
A generic applicant does not need a 30-month stay strategy against this patent.
Any current Orange Book patent issue would have to arise from a later, unexpired listed patent, not from US 3,674,836.

Gemfibrozil has no biosimilar risk. Biosimilars apply to biological products. Gemfibrozil is a chemically synthesized small molecule subject to the generic drug pathway.

When did gemfibrozil lose exclusivity?

Gemfibrozil lost the principal composition-of-matter protection associated with US 3,674,836 in 1989. Commercial generic competition developed after the relevant FDA approval and marketing-exclusivity framework permitted ANDA approvals.

Patent expiry and FDA regulatory exclusivity are separate concepts:

Exclusivity type	Relevance to gemfibrozil
Composition-of-matter patent	Expired in 1989 based on ordinary patent term
New chemical entity exclusivity	Historical issue only; no current effect
Pediatric exclusivity	No current effect identified from the cited patent
Formulation exclusivity	No current exclusivity tied to US 3,674,836
Orphan-drug exclusivity	Not applicable to the standard gemfibrozil approval
Biosimilar reference-product exclusivity	Not applicable
Current patent barrier	None from US 3,674,836

The 1989 date is the principal patent-expiry milestone. The commercial launch date for a particular generic manufacturer depends on its FDA approval date and any other product-specific patents or exclusivities.

What formulations are protected by US 3,674,836?

US 3,674,836 is principally a chemical compound patent based on the claims supplied. The listed claims do not expressly recite:

Tablets
Capsules
Oral suspensions
Specific excipients
Particle-size distributions
Dissolution profiles
Modified-release systems
Enteric coatings
Soft-gel formulations
Specific dosing strengths

A generic tablet or capsule containing gemfibrozil would historically have raised issues under a compound claim such as claim 6 because the product contained the claimed active ingredient. That analysis is no longer commercially relevant because claim 6 expired.

The patent should not be characterized as a modern formulation patent. It does not, based on the supplied claims, establish exclusive rights over a particular dosage form or manufacturing presentation.

What method-of-use rights does the patent provide?

The supplied claims are compound claims. They do not expressly claim:

Treatment of hypertriglyceridemia
Treatment of dyslipidemia
Reduction of very-low-density lipoprotein
Administration before meals
A specific dose or dosing schedule
Combination therapy with a statin or other lipid-lowering agent

Any method-of-use protection would have to arise from separate claims in the patent or from later patents. Claims 2-7 cannot be treated as method-of-treatment claims merely because the compounds were developed for therapeutic use.

The expiration of the compound claims also removes any practical patent barrier based on those claims, even if a manufacturer markets gemfibrozil for the same indication.

Which companies challenged or competed with the Lopid patent estate?

The competitive market developed through generic gemfibrozil suppliers rather than through a continuing dispute over US 3,674,836. Generic manufacturers have included companies that market FDA-approved gemfibrozil tablets or capsules under ANDA approvals. Commercial suppliers and label holders can change over time, and the FDA's Drugs@FDA and Orange Book databases are the controlling sources for current product status.[2,3]

The relevant competitive structure is:

Market segment	Participants
Original branded product	Parke-Davis/Warner-Lambert's Lopid franchise
Generic tablets	Multiple ANDA holders and contract manufacturers
Generic capsules	Multiple ANDA holders and contract manufacturers
Competing fibrates	Fenofibrate and other lipid-regulating products
Non-fibrate alternatives	Statins, omega-3 products, niacin, and combination therapies

There is no current need for a Paragraph IV strategy against US 3,674,836. Any present litigation would more likely concern product liability, labeling, manufacturing quality, reimbursement, or a later patent, rather than the expired compound patent.

How strong is the patent estate for gemfibrozil?

The original patent estate was strong in one respect: claim 6 directly identified the commercially valuable active ingredient. A valid composition-of-matter claim normally gives broad control over the compound independent of the manufacturing route.

Its current strength is zero as an exclusionary right because the patent expired.

Factor	Assessment
Claim type	Composition of matter
Commercial relevance	High because claim 6 identifies gemfibrozil
Structural specificity	High for claim 6
Dependence on manufacturing route	Low
Current enforceability	None after expiration
Formulation coverage	Not established by supplied claims
Method-of-use coverage	Not established by supplied claims
Generic-entry barrier	None
Biosimilar relevance	None

The patent's historical strength should not be confused with present commercial value. An expired composition patent can remain important for freedom-to-operate analysis, patent-history research, and invalidity or priority analysis, but it cannot support an injunction against a current generic product.

What manufacturing and intellectual-property barriers remain?

No manufacturing barrier follows from the expiration of US 3,674,836. Gemfibrozil is a small-molecule active ingredient with an established synthetic and formulation history. A manufacturer still must meet:

FDA current good manufacturing practice requirements
Active-ingredient identity, purity, and impurity specifications
Stability requirements
Bioequivalence requirements for the applicable dosage form
ANDA chemistry, manufacturing, and controls requirements
Labeling and pharmacovigilance obligations

These are regulatory and operational barriers, not surviving patent rights.

A later patent could theoretically cover a new process, formulation, crystal form, combination, or use. Such a patent would need independent verification in the USPTO, FDA Orange Book, and relevant litigation records. US 3,674,836 itself does not provide that protection today.

What generic launch risks exist for gemfibrozil?

The patent-related generic launch risk is minimal. The principal risks are commercial and regulatory:

Price erosion from multiple suppliers
Limited market growth in an older lipid-lowering category
Prescriber migration to newer therapies
FDA manufacturing observations
Supply-chain interruptions
Reimbursement pressure
Product-specific bioequivalence or labeling issues

There is no current launch risk from the expired patent's claims 2-7. A generic applicant would not need to wait for expiration, obtain a license, or settle with the original patent owner on the basis of US 3,674,836.

How does gemfibrozil compare with competing fibrate products?

Gemfibrozil's patent position differs from newer fibrates because the relevant compound patent expired decades ago. The comparative patent position is:

Product	Active ingredient	Broad patent status
Lopid/generic	Gemfibrozil	Original compound patent expired
Tricor/generic	Fenofibrate	Historically supported by later formulation and product patents
Trilipix	Fenofibric acid	Later product and formulation estate
Statin products	Various statins	Product-specific estates, mostly expired or substantially eroded

Gemfibrozil therefore has a mature generic market and little patent-based pricing protection. Fenofibrate products historically generated more formulation-patent activity, particularly around micronization, dosage forms, and bioavailability. That distinction matters for licensing, launch timing, and litigation exposure.

What is the revenue exposure from US 3,674,836?

The patent no longer protects branded revenue. Any historical Lopid revenue attributable to patent exclusivity ended after the patent term expired and generic competition became available.

Current revenue exposure is instead determined by:

Generic volume
Wholesale acquisition price
Contracting and reimbursement
Market share against fenofibrate and statin products
FDA-approved dosage forms
Supply reliability

Because the patent is expired, an acquirer or licensee should assign no current exclusivity premium to US 3,674,836. Its value is historical and analytical, not an enforceable asset.

Key Takeaways

US 3,674,836 covers substituted phenoxyalkanoic acids.
Claim 6 specifically covers 2,2-dimethyl-5-(2,5-xylyloxy)valeric acid, the compound known as gemfibrozil.
Claims 2 and 3 define R-based subclasses under claim 1.
Claims 4-7 identify specific compounds and positional isomers.
The patent issued July 4, 1972 and ordinarily expired July 4, 1989.
The patent is not a current formulation or method-of-use patent based on the supplied claims.
It cannot support a current Paragraph IV challenge, 30-month stay, injunction, or generic launch delay.
Gemfibrozil is a small-molecule drug, so biosimilar analysis does not apply.
Current commercial risk is driven by generic competition, FDA compliance, supply, and reimbursement rather than patent exclusivity.

FAQs About US Patent 3,674,836 and Gemfibrozil

Is claim 6 the gemfibrozil patent claim?

Yes. Claim 6 identifies 2,2-dimethyl-5-(2,5-xylyloxy)valeric acid, which is gemfibrozil.

Can a company obtain a license to US 3,674,836?

A license could be documented historically, but it has no current patent-exclusion value after expiration. A present license is not needed to practice the expired claims.

Does US 3,674,836 cover fenofibrate?

No. Fenofibrate is a different chemical compound and is not covered by the gemfibrozil-specific claim 6.

Does the patent cover gemfibrozil calcium or another salt?

The supplied claims identify the acid compound and do not expressly recite a particular salt. Salt coverage would depend on the precise claim language, claim construction, and the chemical form used.

Is there a current FDA exclusivity period for gemfibrozil?

No current exclusivity period follows from US 3,674,836. Gemfibrozil is marketed through approved generic small-molecule products.

References

United States Patent and Trademark Office. (1972). US Patent No. 3,674,836, substituted phenoxyalkanoic acids.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs.
DailyMed. (2024). Gemfibrozil prescribing information. National Library of Medicine.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	291228	⤷ Start Trial
Brazil	6911856	⤷ Start Trial
Germany	1925423	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 3,674,836

Summary for Patent: 3,674,836