US Patent 5,965,584: Claim Scope, Expiration, FDA Status, and Patent Landscape for Pioglitazone-Metformin Combinations

US Patent 5,965,584 covers pharmaceutical compositions and diabetes-treatment methods combining an insulin-sensitivity enhancer with a biguanide. Its commercially important embodiment is pioglitazone, including pioglitazone hydrochloride, combined with metformin. The patent also reaches several non-pioglitazone thiazolidinedione and oxazolidinedione compounds, separate administration of the two agents, and combinations that exclude sulfonylureas. The patent term expired in 2017, so it no longer creates a live US patent barrier to pioglitazone-metformin products.

What does US Patent 5,965,584 cover?

The patent protects the therapeutic combination of:

An insulin-sensitivity enhancer selected from a ten-compound Markush group; and
A biguanide selected from phenformin, metformin, and buformin.

The claims cover both compositions and methods of treating diabetes. The commercial center of gravity is the combination of pioglitazone hydrochloride and metformin hydrochloride.

Claim group	Subject matter	Practical scope
Claims 1-5	Pharmaceutical compositions	Combination product containing a listed insulin sensitizer and a biguanide
Claims 6-10	Treatment methods	Administration of the two agents to a mammal with diabetes
Claims 11-12	Specific compound #10	Compound-specific composition and method claims
Claims 13-14	Administration format	Admixed or separately administered components
Claim 15	Closed composition	Composition consisting of the insulin sensitizer and biguanide
Claim 16	Treatment limitation	Treatment without administering a sulfonylurea

The issued claims are combination claims. They do not claim pioglitazone alone, metformin alone, or the underlying chemical structure of pioglitazone.

Which drugs and chemical entities are listed in the patent?

The ten insulin-sensitivity enhancers in claims 1 and 6 include four ethyl-pyridyl thiazolidinediones, one chiral oxazolidinedione, several oxazolyl or benzopyran derivatives, a naphthalenylsulfonyl thiazolidinedione, and compound #10.

The most commercially relevant listed compound is pioglitazone.

Pioglitazone identification

Pioglitazone is chemically identified as:

5-[[4-[2-(5-ethyl-2-pyridyl)ethoxy]phenyl]methyl]-2,4-thiazolidinedione.

That corresponds to compound #3 in the Markush list. Claims 2, 4, 7 and 10 narrow the patent to pioglitazone or its hydrochloride, with the most commercially significant claim being claim 10:

Pioglitazone or pioglitazone hydrochloride
Metformin
Pharmaceutical composition or diabetes-treatment method

The patent’s use of “pharmacologically acceptable salt” expands coverage beyond the free compound where the relevant listed compound permits salt formation. For pioglitazone, the hydrochloride salt is the marketed form.

How broad is the Markush claim?

Claim 1 is structurally broad but functionally limited by the closed list of ten insulin-sensitivity enhancers. It does not cover every thiazolidinedione or every insulin sensitizer. A product must contain one of the named compounds or a pharmaceutically acceptable salt of that compound.

The biguanide limitation is also closed. Claim 3 identifies:

Phenformin
Metformin
Buformin

A combination with another antihyperglycemic agent outside that list would not literally satisfy claim 1 solely because it has a biguanide-like mechanism.

Key claim limitations

The principal limitations are:

A pharmaceutical composition;
An insulin-sensitivity enhancer from the ten-compound list;
A biguanide;
Diabetes-related therapeutic use for the method claims;
In claim 16, no administration of a sulfonylurea;
In claim 15, the composition must “consist of” the two active ingredients.

The claims do not specify:

Dose;
Dose ratio;
Release profile;
Tablet strength;
Excipients, except as affected by “consists of” in claim 15;
Particular patient subgroup;
Treatment duration;
Sequential timing between the two drugs;
Route of administration.

That omission makes the claims potentially broad in technical scope. It also creates validity and infringement questions because the patent relies heavily on the identity of the active ingredients and the existence of the combination rather than on a narrowly defined formulation or dosing regimen.

Does the patent cover separate administration of pioglitazone and metformin?

Yes. Claim 14 expressly covers administration in which the insulin-sensitivity enhancer and biguanide are not mixed into an admixture but are administered independently.

This language reaches several commercial configurations:

Two separate tablets administered together;
Pioglitazone and metformin dispensed as separate products;
Separate administration at different times;
A co-prescribed regimen without a fixed-dose combination tablet.

Claim 13 covers an admixture in which the two agents are mixed before administration. That claim is directed toward a combined dosage form or other prepared mixture.

The method claims therefore extend beyond a single tablet. A fixed-dose product is the clearest target, but the patent text also addresses coadministration of separately supplied products.

What does claim 15 protect?

Claim 15 covers a composition that “consists of” the insulin-sensitivity enhancer and the biguanide.

“Consists of” is narrower than “comprising.” In ordinary claim construction, it excludes additional unrecited ingredients that materially alter the claimed composition. For a conventional tablet, this creates a potential issue because commercial pharmaceutical tablets ordinarily contain binders, fillers, coatings, lubricants or other excipients.

Claims 1 and 4 use “comprising,” which is broader and generally compatible with conventional excipients. Claim 15 should not be treated as the primary claim covering ordinary commercial tablets unless the composition satisfies the legal meaning of the closed transitional phrase in the relevant context.

What does claim 16 exclude?

Claim 16 adds a proviso that the mammal is not administered a sulfonylurea agent.

The claim is directed to pioglitazone or another listed sensitizer combined with a biguanide, while excluding a treatment regimen that also includes a sulfonylurea. The limitation may have been intended to distinguish triple therapy or earlier prior art involving insulin sensitizer, biguanide and sulfonylurea combinations.

A product or treatment regimen involving pioglitazone, metformin and a sulfonylurea would face a substantial noninfringement argument under claim 16 because the express proviso is not met. Claims 1-15 do not contain the same exclusion, so the limitation does not eliminate exposure under the other claims.

When did US Patent 5,965,584 expire?

The patent issued on October 12, 1999. Its US patent term ran for approximately 20 years from the applicable nonprovisional filing date and expired in 2017. Public patent records identify the expiration date as May 15, 2017.[1]

Event	Date
US patent issued	October 12, 1999
Patent term basis	20 years from applicable US filing date
Reported US expiration	May 15, 2017
Current status	Expired

The expiration eliminates the patent as a current US enforcement right. It does not erase its historical relevance to the development and launch of Actos/metformin combination products.

What was the FDA and Orange Book status?

Pioglitazone was approved by the FDA as Actos under NDA 021073 in 1999. The fixed-dose pioglitazone/metformin product Actoplus Met was subsequently approved under NDA 021842.[2]

Product	Active ingredients	FDA status
Actos	Pioglitazone hydrochloride	Approved
Glucophage and generic metformin products	Metformin hydrochloride	Approved
Actoplus Met	Pioglitazone hydrochloride and metformin hydrochloride	Approved
Generic pioglitazone/metformin products	Same active ingredients	Approved through ANDA pathway, subject to product-specific status

The Orange Book historically listed patents associated with pioglitazone and combination products. US Patent 5,965,584 was relevant to the pioglitazone-metformin combination patent estate, rather than to pioglitazone monotherapy alone. Because the patent expired in 2017, it no longer supports a live period of Orange Book-based patent delay.

FDA approval and patent protection are separate questions. The FDA may approve an ANDA after expiration or successful resolution of listed patents, while product labeling, bioequivalence and manufacturing requirements remain applicable.[3]

What Paragraph IV challenges affected the patent?

A Paragraph IV certification would have been the principal ANDA mechanism for challenging an unexpired Orange Book-listed patent covering a generic pioglitazone-metformin product. The challenger would assert that the patent was invalid, unenforceable or not infringed.

For US Patent 5,965,584, the commercial significance of Paragraph IV litigation was time-limited because the patent expired in 2017. A post-expiration ANDA entrant would not need to defeat the patent to launch on account of this patent, although it could still have been relevant during earlier product-development and approval periods.

The central potential challenge theories would have included:

Obviousness: Combining a thiazolidinedione insulin sensitizer with metformin may be argued to have been an expected diabetes-treatment strategy.
Written description and enablement: The Markush group covers ten structurally diverse compounds, raising questions about whether the specification supports the full genus and the claimed therapeutic combinations.
Indefiniteness: The phrase “insulin sensitivity enhancer” may be challenged if the specification does not provide a sufficiently objective boundary, although the claims identify the compounds by chemical structure.
Infringement: Separate administration, salt forms, dosage forms and combination products would require claim-by-claim analysis.
Prior art: Earlier combination-treatment disclosures, clinical publications and patent filings could affect novelty and obviousness.

No current Paragraph IV risk remains from this patent because the US patent term has ended.

Which other patents protected pioglitazone and Actoplus Met?

US Patent 5,965,584 was one part of a broader product and combination patent landscape.

Pioglitazone compound patent

Pioglitazone was protected by the earlier compound patent US 4,287,200, assigned to Takeda Chemical Industries. That patent covered the pioglitazone chemical entity and related thiazolidinedione structures. Its term expired before US Patent 5,965,584.[4]

The expiration of the compound patent opened the market to pioglitazone products, while later patents could continue to affect particular combinations, formulations or uses.

Combination-product patents

Combination products can face separate patent categories:

Patent category	Typical subject matter	Relevance to pioglitazone/metformin
Compound patents	Pioglitazone chemical structure	Historical protection; expired
Combination patents	Pioglitazone plus metformin	Direct relevance of US 5,965,584
Formulation patents	Tablet composition, release profile, manufacturing process	May affect a specific generic design
Method-of-use patents	Treatment of defined patient populations or disease states	Potentially relevant only if valid and unexpired
Salt or polymorph patents	Specific solid forms or salt forms	Product-specific risk
Manufacturing patents	Synthesis, crystallization and processing	May create process or supply-chain barriers

US Patent 5,965,584 is not a formulation patent in the ordinary sense. It does not require a specific excipient system, tablet architecture, sustained-release profile or manufacturing process.

What formulations are protected by US 5,965,584?

The patent covers the active-ingredient combination rather than a narrowly defined formulation.

Potentially covered presentations during the patent term included:

Immediate-release tablets containing pioglitazone hydrochloride and metformin hydrochloride;
Capsules or other oral dosage forms containing the two agents;
A prepared admixture;
Separately administered pioglitazone and metformin;
Products with conventional excipients under the broader “comprising” claims.

The patent does not expressly require:

A single tablet;
A bilayer tablet;
Extended release;
A particular pioglitazone-to-metformin ratio;
A specific particle size;
A particular dissolution profile.

A generic manufacturer could therefore design around formulation-specific patents by altering excipients or release characteristics, but those changes would not have been necessary to avoid US 5,965,584 after its expiration.

How strong was the patent estate?

Scope strength

The patent was commercially strong during its term because claims 4, 10 and 13-14 targeted the central commercial concept: pioglitazone and metformin, administered together or separately.

Validity strength

The broad Markush structure and combination concept created potential validity pressure. The narrower pioglitazone-metformin claims were easier to map to a commercial product but also more exposed to prior-art combination arguments.

Enforcement strength

Enforcement depended on proof that the accused product or regimen contained both active ingredients. That proof would generally be straightforward for a fixed-dose pioglitazone-metformin tablet. Separate administration claims could be more difficult because infringement would depend on the conduct of the relevant actor and the specific method of administration.

Current strength

Current enforceability is zero in the United States because the patent expired. The patent has historical and freedom-to-operate relevance but no remaining exclusionary term.

What generic launch risks existed?

Before expiration, the principal generic launch risks were:

A listed patent challenge delaying approval or launch;
Litigation over whether a pioglitazone-metformin product fell within claims 4 or 10;
Additional formulation or method patents not captured by the claims provided;
Regulatory issues concerning bioequivalence to Actoplus Met;
Manufacturing complexity involving metformin loading, tablet size and dissolution control.

After May 15, 2017, US 5,965,584 ceased to be a launch barrier. Remaining risks shifted to FDA requirements, other unexpired patents, product liability, supply, pricing and commercial contracting.

Did US Patent 5,965,584 involve biosimilar risk?

No. Pioglitazone and metformin are small-molecule drugs, not biologics. The relevant regulatory pathway is the abbreviated new drug application, or ANDA, rather than the biosimilar pathway under the Public Health Service Act.

The patent therefore presents:

Generic-drug risk, not biosimilar risk;
Paragraph IV issues, not biosimilar patent dance procedures;
Orange Book relevance, not the Purple Book framework.

What licensing and litigation issues are relevant?

Takeda was the principal innovator associated with pioglitazone and Actos. The commercial patent strategy involved product, combination and regulatory exclusivity rights. US Patent 5,965,584 should be assessed together with the Orange Book record for the relevant NDA and the patent families cited in its prosecution history.

The patent’s expiration means that any historical settlement or license involving this patent cannot create a present US patent monopoly beyond the statutory term. A settlement could have affected an earlier generic launch date, but it cannot extend the patent’s enforceable term absent a separate, legally operative contractual restriction.

How does this patent compare with pioglitazone monotherapy protection?

Issue	Pioglitazone compound patent	US 5,965,584
Primary target	Pioglitazone chemical entity	Pioglitazone plus biguanide
Commercial product	Actos and pioglitazone generics	Actoplus Met and generic equivalents
Claim type	Compound and related structures	Composition and treatment method
Metformin required	No	Yes for the narrowed commercial claims
Formulation specificity	Generally limited	Limited
Separate administration	Not the central issue	Expressly covered by claim 14
Current US status	Expired	Expired
Generic pathway	ANDA	ANDA

Key Takeaways

US Patent 5,965,584 covers insulin-sensitizer/biguanide combinations, with pioglitazone-metformin as the key commercial embodiment.
Claims 1 and 6 contain a ten-compound Markush group.
Claims 4, 7 and 10 focus on pioglitazone or pioglitazone hydrochloride with metformin.
Claims 13 and 14 cover both admixture products and independent administration.
Claim 15 is narrower because it uses “consists of.”
Claim 16 excludes treatment involving a sulfonylurea.
The patent is a small-molecule generic patent, not a biosimilar patent.
The reported US expiration date was May 15, 2017.
The patent no longer blocks US generic launch or manufacture.
Current freedom-to-operate analysis must focus on other patents, FDA requirements and product-specific formulation or manufacturing rights.

FAQs

Does US Patent 5,965,584 cover metformin by itself?

No. The claims require metformin or another listed biguanide in combination with a claimed insulin-sensitivity enhancer.

Does the patent cover pioglitazone hydrochloride?

Yes. The dependent claims expressly identify pioglitazone or its hydrochloride.

Does the patent cover Actoplus Met?

During its term, the patent covered the active-ingredient combination embodied by Actoplus Met, subject to the specific claim limitations. It expired in 2017.

Can a generic company sell pioglitazone and metformin in separate packages?

US Patent 5,965,584 no longer prevents that because the patent expired. During its term, claim 14 expressly addressed independent administration.

Is a sulfonylurea-containing triple therapy outside all claims?

Not necessarily. Claim 16 excludes sulfonylurea administration, but claims 1-15 do not contain that same limitation.

References

United States Patent and Trademark Office. (1999). US Patent No. 5,965,584, Pharmaceutical composition comprising an insulin sensitivity enhancer and a biguanide. https://patents.google.com/patent/US5965584A/en
U.S. Food and Drug Administration. (1999). Actos approval history and prescribing information. https://www.accessdata.fda.gov/drugsatfda_docs/label/
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations, Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book
United States Patent and Trademark Office. (1981). US Patent No. 4,287,200, Thiazolidine derivatives. https://patents.google.com/patent/US4287200A/en

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Japan	7-153500	Jun 20, 1995

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0861666	⤷ Start Trial	91298	Luxembourg	⤷ Start Trial
European Patent Office	0861666	⤷ Start Trial	300258	Netherlands	⤷ Start Trial
European Patent Office	0861666	⤷ Start Trial	SPC 038/2006	Ireland	⤷ Start Trial
European Patent Office	0861666	⤷ Start Trial	07C0006	France	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,965,584

Summary for Patent: 5,965,584