United States Drug Patent 6,890,957: Claim Scope, Expiration, Orange Book Status, and Generic Entry Risk

U.S. Patent No. 6,890,957 protects a specific liquid oral metformin formulation rather than metformin generally. The independent claim requires metformin or a pharmaceutically acceptable salt, a non-glycemic sweetener, a polyhydroxy alcohol, a mineral acid, a bicarbonate salt, a controlled pH, and a liquid pharmaceutical carrier. The patent does not cover metformin tablets, extended-release tablets, injectable products, or every liquid metformin formulation.

The patent was issued in 2005 and had a patent-term endpoint in December 2021 based on the underlying filing chronology. Its composition claims therefore no longer create a current U.S. patent barrier, subject to any patent-term adjustment or other term-specific record in the USPTO file. The principal commercial significance of the patent was its protection of a palatable, stabilized metformin oral solution such as the formulation historically associated with Riomet.

What does U.S. Patent 6,890,957 protect?

The core protection is a liquid oral composition containing five mandatory formulation components:

Required element	Claim requirement
Active ingredient	Metformin or a pharmaceutically acceptable salt
Sweetener	Sweetener that does not increase blood glucose after ingestion
Polyhydroxy alcohol	About 15% to about 55% by weight
Acid-base system	Mineral acid and bicarbonate salt
pH	About 4.0 to about 9.0
Carrier	Pharmaceutically acceptable liquid carrier

Claim 1 is an all-elements composition claim. A competing product must contain every required element, properly construed, to fall within its scope. Omitting the bicarbonate salt, using a non-mineral acid, replacing the polyhydroxy alcohol with a non-qualifying excipient, or formulating outside the claimed concentration range could create a non-infringement position.

The patent is formulation-specific. It does not claim:

Metformin as a chemical compound.
Metformin hydrochloride tablets.
Extended-release metformin tablets.
A method of treating diabetes using metformin independent of the claimed liquid composition.
Manufacturing metformin itself.
Every oral solution containing metformin.
Every liquid product using a sweetener.

How are the claims organized?

Claims 2 through 15 narrow claim 1 through carrier, concentration, excipient, acid, pH, and bicarbonate limitations.

Claim	Added limitation	Commercial significance
1	Broad liquid metformin composition with acid, bicarbonate, polyhydroxy alcohol, sweetener, and pH range	Principal composition claim
2	Carrier is water	Covers conventional aqueous oral solution
3	Sweetener is 50% to 70% by weight	Narrows sweetener concentration
4	Sweetener is 55% to 65% by weight	Further narrows claim 3
5	Alkyl hydroxyethylcellulose, or AHEC	Covers viscosity-modified formulations
6	AHEC is 0.08% to about 0.2% by weight	Concentration-specific viscosity limitation
7	Polyhydroxy alcohol is 15% to about 40% by weight	Narrower polyol range
8	Alkyl group in AHEC has 2 to 10 carbon atoms	Narrows the polymer excipient
9	Sweetener is a sugar alcohol or non-nutritive sweetener	Defines principal sweetener classes
10	Polyhydroxy alcohol has 2 to 6 carbons and 2 to 6 hydroxyl groups	Targets low-molecular-weight polyols
11	Polyhydroxy alcohol is a 200 to 2,000 dalton polymer with defined repeating units	Targets polymeric polyols
12	Mineral acid is hydrochloric, nitric, or sulfuric acid	Limits acid identity
13	Mineral acid is hydrochloric acid	Narrowest acid-specific claim
14	pH is about 4.2 to about 7.0	Narrows the pH range
15	Bicarbonate is potassium bicarbonate	Narrows the bicarbonate salt

Claims 3 and 4 are particularly important because the sweetener constitutes a substantial percentage of the formulation. Claims 5, 6, and 8 address rheology and physical stability through alkyl hydroxyethylcellulose. Claims 12, 13, and 15 define the acid-base system more narrowly and would be relevant to a formulation that tracks the disclosed commercial recipe.

What technical problem does the patent address?

The formulation architecture appears directed to three product-development problems:

Improving palatability for metformin, which is associated with a strong bitter taste.
Stabilizing a concentrated aqueous liquid formulation.
Providing a low-glycemic or non-glycemic sweetening system suitable for diabetic patients.

The claimed polyhydroxy alcohol may contribute to taste masking, mouthfeel, viscosity, and solubility. The acid-bicarbonate combination controls pH and may affect buffering, stability, and organoleptic characteristics. Alkyl hydroxyethylcellulose adds viscosity and may help suspend or stabilize formulation components.

The pH limitation is broad in claim 1. A formulation at pH 4.0, 6.0, or 9.0 could technically fall within the claim if the remaining elements are present. Claim 14 is more commercially focused because it limits the pH to approximately 4.2 to 7.0, a range more consistent with many oral liquid products.

How broad is claim 1?

Claim 1 is materially broader than the dependent claims but narrower than a general liquid-metformin claim.

A formulation potentially within claim 1 would need to include:

Metformin hydrochloride or another pharmaceutically acceptable metformin salt.
A qualifying sweetener, even if the specific sweetener is not identified in claim 1.
A polyhydroxy alcohol at approximately 15% to 55% by weight.
Both a mineral acid and bicarbonate salt.
A pH from approximately 4.0 to 9.0.
A pharmaceutically acceptable liquid carrier.

The phrase "sweetener that does not increase the blood glucose level" is functional. It may encompass sugar alcohols, non-nutritive sweeteners, or other sweetening agents depending on the specification and claim construction. Claim 9 confirms two principal categories but does not necessarily exclude other qualifying sweeteners from claim 1.

The phrase "polyhydroxy alcohol" is also significant. Claim 10 covers low-molecular-weight compounds with multiple hydroxyl groups, while claim 11 covers certain polymeric materials. The dependent claims suggest that the specification contemplated both small-molecule polyols and polymeric polyhydroxy materials.

What formulation design-arounds exist?

Potential design-around strategies would focus on removing or changing one required element of claim 1.

Design-around approach	Likely claim impact
Omit the bicarbonate salt	Removes a mandatory claim 1 element
Use a non-mineral acid	Avoids the acid limitation if claim construction excludes the selected acid
Use a polyol concentration below 15% or above 55%	Moves outside the express concentration range
Replace the polyhydroxy alcohol with a non-qualifying excipient	Challenges the polyol limitation
Use a non-sweetened formulation	Removes the sweetener limitation
Use a sweetener that raises blood glucose	Creates a factual dispute over the functional limitation
Use a non-liquid dosage form	Avoids the liquid-composition requirement
Formulate outside the claimed pH range	Avoids claim 1 if the measured pH is outside the range
Use a non-AHEC viscosity modifier	Avoids claims 5, 6, and 8, but not necessarily claim 1
Use a non-potassium bicarbonate salt	Avoids claim 15 but not necessarily claim 1

A design that avoids claim 5 does not automatically avoid claim 1. A liquid containing the core acid-bicarbonate-polyol-sweetener architecture could still implicate claim 1 even if it uses xanthan gum, hydroxypropyl cellulose, or another viscosity modifier instead of AHEC.

The word "about" introduces ordinary claim-construction flexibility. A formulation slightly outside a stated numerical range could raise an infringement issue under the doctrine of equivalents, although the strength of that argument would depend on prosecution history, specification disclosure, and the technical distance from the claimed range.

When did U.S. Patent 6,890,957 expire?

Patent event	Date or status
U.S. patent	6,890,957
Patent title	Liquid pharmaceutical composition containing metformin
Issue date	May 10, 2005
Relevant term basis	Twenty years from the applicable nonprovisional filing date
Approximate expiration	December 2021
Current status	Expired based on the ordinary patent-term calculation

The expiration analysis should use the USPTO patent file for the definitive patent-term-adjustment calculation. FDA Orange Book listing does not extend the patent term. A patent-term extension under 35 U.S.C. § 156 would be relevant only if granted and reflected in the official record. The available commercial patent chronology places the operative term endpoint in December 2021.

Because the patent is expired, its claims no longer provide an enforceable exclusionary right against current U.S. liquid-metformin products. The patent remains relevant as prior art and as a historical explanation for formulation development, but not as a current blocking patent.

What was the Orange Book status of the patent?

The patent was associated with the U.S. liquid metformin product market, including the Riomet oral solution franchise. Orange Book-listed patent protection for an approved drug product can affect ANDA certification while the patent is unexpired. Once the listed patent expires, the patent itself no longer blocks approval or commercial launch.

The Orange Book analysis must distinguish among:

The reference listed drug.
Any approved liquid metformin solution.
Patent listings for the original solution.
Regulatory exclusivity independent of patent protection.
Later products, such as extended-release oral solutions, if separately approved.

An expired formulation patent does not eliminate all regulatory requirements. A generic applicant still must satisfy the applicable ANDA or other FDA pathway, demonstrate pharmaceutical quality, and meet labeling and product-performance requirements. The expired patent does remove the principal intellectual-property barrier represented by Patent 6,890,957.

Are Paragraph IV challenges relevant?

Paragraph IV certification is relevant when an ANDA applicant seeks approval before expiration of an Orange Book-listed patent and asserts that the patent is invalid, unenforceable, or not infringed. For Patent 6,890,957, any Paragraph IV significance was time-limited by the December 2021 expiration date.

A Paragraph IV strategy for a liquid metformin product could have challenged:

Written description or enablement of the broad functional sweetener limitation.
Anticipation by prior liquid metformin formulations.
Obviousness based on combining known metformin solutions with sweeteners, polyols, buffers, and viscosity agents.
Indefiniteness of terms such as "does not increase the blood glucose level," "about," and "sufficient amounts."
Infringement based on whether the accused product contains both mineral acid and bicarbonate.

After expiration, an applicant would ordinarily have no commercial reason to litigate the patent merely to obtain approval, unless a dispute concerned past damages, historical launch timing, or another collateral issue.

What patent litigation or settlements affect this patent?

The supplied claims establish the technical scope but do not establish a current litigation or settlement position. The key legal point is that an expired composition patent cannot support prospective injunctive relief for post-expiration launch activity.

Any historical litigation analysis would require review of:

Federal district court dockets.
Federal Circuit decisions.
ANDA litigation filings.
FDA patent-listing history.
Assignment and merger records.
Settlement agreements involving the reference product or authorized generics.

No settlement term can be inferred from the claim language alone. A commercial settlement, if one existed, could have imposed launch restrictions that ended before patent expiration, but such restrictions would arise from contract rather than from the patent claims.

How strong was the patent estate?

The estate appears narrow in product category but reasonably specific in formulation architecture.

Strength factor	Assessment
Product coverage	Limited to oral liquid formulations
Active ingredient	Broad for metformin and its pharmaceutically acceptable salts
Excipient coverage	Broad in claim 1, more specific in dependent claims
Numerical limitations	Provide technical boundaries but create design-around opportunities
Functional limitation	Sweetener definition may create construction and proof issues
Method-of-use coverage	None apparent from the supplied claims
Manufacturing coverage	None apparent from the supplied claims
Tablet coverage	None
Biologic or biosimilar relevance	None
Current enforceability	None after expiration

The patent’s commercial value depended on the formulation being difficult to replicate without using the same combination of high sweetener loading, polyhydroxy alcohol, acid, bicarbonate, and pH control. Its lack of method-of-use, manufacturing, tablet, and extended-release claims limited the estate’s ability to protect adjacent metformin markets.

How does this patent compare with metformin patent protection generally?

Metformin patent risk is substantially different across product types.

Product category	Relevance of Patent 6,890,957
Immediate-release metformin tablets	None
Extended-release metformin tablets	None
Metformin capsules	None unless formulated as the claimed liquid
Metformin oral solution	Direct relevance historically
Pediatric liquid metformin	Potential relevance if all claim elements are present
Compounded metformin liquid	Potential technical overlap, subject to applicable law
Injectable metformin	None
Biosimilars	Not applicable
Combination diabetes products	Not covered unless they include the claimed liquid composition

The patent does not create a general metformin monopoly. It addresses one delivery format and one excipient strategy.

What generic entry risks remain?

The patent-specific risk is low because the patent term has ended. Current entry risks are more likely to involve:

FDA formulation and manufacturing requirements.
Demonstration of equivalent active-ingredient performance.
Taste, viscosity, stability, and preservative control.
Labeling and dosing-device requirements.
Other unexpired formulation patents, if any.
Trademark and trade-dress issues involving the branded product.
Exclusivity or regulatory protections unrelated to Patent 6,890,957.

A generic liquid metformin developer should still screen the complete patent family and later-filed continuation, divisional, and improvement patents. Patent 6,890,957 alone does not prove that the entire liquid metformin patent landscape is clear.

What is the commercial impact of the patent’s expiration?

Expiration removes the patent premium associated with the protected formulation. It permits competing developers to commercialize liquid metformin products without licensing this patent, provided they satisfy FDA requirements and avoid other enforceable rights.

The market remains narrower than the tablet market because metformin tablets and extended-release products dominate diabetes treatment. Liquid metformin can have value for patients with swallowing difficulties, pediatric use, dose titration, or other administration needs. The patent’s expiration increases formulation competition but does not itself establish market size, sales, or revenue exposure.

Key Takeaways

U.S. Patent 6,890,957 is a liquid oral metformin formulation patent.
Claim 1 requires metformin, a non-glycemic sweetener, 15% to 55% polyhydroxy alcohol, mineral acid, bicarbonate salt, controlled pH, and a liquid carrier.
Dependent claims narrow protection through water, sweetener concentration, AHEC, polyol identity, acid identity, pH, and potassium bicarbonate.
The patent does not cover metformin tablets, extended-release tablets, metformin itself, or general diabetes treatment methods.
The patent’s ordinary term ended in December 2021.
Historical Orange Book and Paragraph IV relevance does not create a current patent barrier after expiration.
No biosimilar issue exists because metformin is a small-molecule drug.
Current liquid-metformin entry risk is more likely to involve FDA requirements and other unexpired rights than Patent 6,890,957.

FAQs

Does Patent 6,890,957 cover metformin hydrochloride tablets?

No. The claims require a liquid pharmaceutical composition for oral administration. Conventional immediate-release and extended-release metformin tablets fall outside the claimed dosage form.

Does a liquid metformin product infringe if it contains only a buffer and no bicarbonate?

Claim 1 expressly requires both a mineral acid and a bicarbonate salt. A liquid product lacking bicarbonate would have a strong non-infringement position against claim 1, subject to claim construction and the doctrine of equivalents.

Does using potassium bicarbonate automatically create infringement?

No. Potassium bicarbonate is specifically addressed by claim 15, but infringement still requires the other limitations inherited from claim 1, including metformin, the qualifying sweetener, polyhydroxy alcohol concentration, mineral acid, pH, and liquid carrier.

Is a liquid metformin product subject to biosimilar competition?

No. Metformin is a synthetic small-molecule active ingredient. Competing products proceed through generic-drug pathways rather than biosimilar pathways.

Can an expired patent still affect a liquid metformin launch?

Yes, as historical prior art and as a technical reference for formulation design. It cannot ordinarily provide a current basis for blocking a post-expiration launch, but other unexpired patents, regulatory requirements, trademarks, and contractual restrictions may remain relevant.

References

U.S. Patent and Trademark Office. (2005). U.S. Patent No. 6,890,957, Liquid pharmaceutical composition containing metformin. Washington, DC: U.S. Department of Commerce.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. Silver Spring, MD: U.S. Department of Health and Human Services.
U.S. Food and Drug Administration. (n.d.). Orange Book: Approved drug products with therapeutic equivalence evaluations, patent and exclusivity information. Silver Spring, MD: U.S. Department of Health and Human Services.
35 U.S.C. § 154. Patent term.
35 U.S.C. § 156. Extension of patent term.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	7659801	⤷ Start Trial
Brazil	0113102	⤷ Start Trial
Canada	2416767	⤷ Start Trial
China	1635881	⤷ Start Trial
European Patent Office	1387675	⤷ Start Trial
Croatia	P20030161	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,890,957

Summary for Patent: 6,890,957