United States Patent 6,746,692: Amoxicillin Modified-Release Composition, Claims, Expiration, and Patent Landscape

U.S. Patent No. 6,746,692 protects a modified-release amoxicillin formulation based on intimate solid-state contact between a soluble amoxicillin salt and an organic acid, especially sodium amoxicillin with citric acid. The patent also covers tablet dosage forms, specified excipients, xanthan-gum release control, approximately 438 mg of sodium amoxicillin, and a functional release profile. The patent was assigned to SmithKline Beecham Corporation and was associated with the extended-release product Moxatag.

The patent’s principal commercial relevance was its coverage of a once-daily, 775-mg amoxicillin extended-release tablet. The patent term has expired, eliminating ordinary U.S. patent infringement risk from this patent alone. It remains relevant for freedom-to-operate analysis because later patents, regulatory exclusivity, formulation differences, and other listed or unlisted rights may affect a competing product.

What invention does U.S. Patent 6,746,692 protect?

The patent protects a modified-release pharmaceutical composition containing four central elements:

A pharmaceutically acceptable soluble salt of amoxicillin.
At least one pharmaceutically acceptable organic acid.
Intimate admixture of the amoxicillin salt and acid as solids.
Compacted granules combined with a diluent or compression aid.

The broadest claim is claim 1. It requires the amoxicillin salt and organic acid to be present at a weight ratio of approximately 20:1 to 1:2. The composition must be in the form of compacted granules, and the formulation must be modified release.

The claim is formulation-specific. It does not broadly cover every extended-release amoxicillin product. A competing formulation that lacks the required organic acid, does not use the required intimate solid admixture, or does not contain compacted granules may fall outside literal claim 1.

What is the technical mechanism claimed by the patent?

The patent describes a two-phase release concept. The soluble amoxicillin salt is initially released, while interaction between the amoxicillin salt and organic acid reduces the release rate from the second release phase. Claim 21 expressly ties the formulation to a comparative release result: the rate of amoxicillin release from the second release phase must be lower than from an immediate-release formulation.

The claimed mechanism is therefore not limited to a conventional polymer matrix. The patent can cover release control produced by the physical and chemical interaction of the amoxicillin salt and acid, with or without additional release-retarding excipients.

How are the claims structured?

Claims 1 and 21 are the commercially important claims. Claims 2 through 20 narrow claim 1 by adding dosage form, active ingredient, acid, excipient, strength, or manufacturing characteristics.

Claim	Principal limitation	Commercial significance
1	Compacted granules containing soluble amoxicillin salt and organic acid in a 20:1 to 1:2 ratio, plus diluent or compression aid	Core composition claim
2	Tablet form	Covers the principal commercial dosage form
3	Crystallized sodium amoxicillin	Narrows the active ingredient form
4	Sodium amoxicillin	Covers the principal amoxicillin salt
5	Broad organic-acid classes, including mono- and polycarboxylic acids and aryl acids	Broad acid genus
6	Organic acids with 2 to 10 carbon atoms and acidic salts	Narrower acid genus
7	C2-C10 alkyl or alkenyl carboxylic acids, with optional hydroxy or keto groups	Chemical subgenus
8	Specific acids, including citric, malic, succinic, fumaric, tartaric, and ascorbic acid	Defined species list
9	Citric acid	Key commercial species
10	Anhydrous citric acid	Particularly relevant to product matching
11	About 438 mg sodium amoxicillin, plus or minus 5%	Links claim scope to the commercial strength
12	Release-retarding excipient classes	Adds polymer-based release control
13	Specific low-molecular-weight polymers	Narrow excipient combinations
14	Medium-viscosity hydroxypropylmethylcellulose or polyvinyl alcohol	Narrow polymer limitation
15	Xanthan gum	Important commercial formulation limitation
16	Xanthan gum at 0.5% to 8% by weight	Broad xanthan concentration range
17	Xanthan gum at 1% to 5% by weight	Narrower commercial range
18	Pharmaceutical-grade xanthan gum, 200 mesh	Particle-size and grade limitation
19	Lactose diluent	Product-relevant filler limitation
20	Microcrystalline cellulose compression aid	Product-relevant tableting limitation
21	Functional release interaction and reduced second-phase release	Performance-based narrowing limitation

Claim 21 is dependent on claim 1 and does not stand as a free-standing composition claim. An accused product must first satisfy all limitations of claim 1 and then satisfy the claimed release behavior.

What formulations are protected by the patent?

The most commercially significant formulation is a tablet containing approximately 775 mg of amoxicillin, corresponding to approximately 438 mg of sodium amoxicillin in the claimed formulation framework. The formulation uses citric acid and xanthan gum to create modified release. Lactose and microcrystalline cellulose are identified as additional formulation components in dependent claims.

A formulation substantially aligned with claims 1, 4, 9, 10, 11, 15, 17, 18, 19, and 20 would present the highest historical infringement risk.

What formulation combinations present the greatest claim overlap?

Formulation characteristic	Relevant claims	Risk implication
Sodium amoxicillin	1, 3, 4	Central active-salt limitation
Citric acid	8, 9	Principal organic-acid species
Anhydrous citric acid	10	Closer overlap with the commercial formulation
Approximately 438 mg sodium amoxicillin	11	Strong product-strength correlation
Xanthan gum	15-18	Key release-retarding excipient
Xanthan gum at 1%-5%	17	Narrow but commercially relevant range
Pharmaceutical-grade, 200-mesh xanthan gum	18	Additional product-specific limitation
Lactose	19	Filler limitation
Microcrystalline cellulose	20	Compression-aid limitation
Tablet	2	Commercial dosage-form limitation

The use of a different organic acid does not necessarily avoid the patent. Claims 5 through 8 cover broad acid classes and named alternatives. A formulation using malic acid, tartaric acid, succinic acid, fumaric acid, or another listed acid could remain within claim 1 and a corresponding dependent claim.

How broad is the organic-acid coverage?

The acid coverage is layered.

Claim 5 extends beyond simple aliphatic carboxylic acids. It includes:

Monocarboxylic and polycarboxylic acids with up to 25 carbon atoms.
Monocyclic and polycyclic aryl acids.
Monohydrogen and dihydrogen metal salts of multivalent acids.

Claim 6 narrows the carbon range to 2 through 10 carbon atoms. Claim 7 focuses on C2-C10 alkyl and alkenyl carboxylic acids with one, two, or three carboxyl groups, with optional hydroxy and keto functionality.

Claim 8 names specific acids:

Malonic acid
Succinic acid
Fumaric acid
Maleic acid
Adipic acid
Lactic acid
Levulinic acid
Sorbic acid
Tartaric acid
Malic acid
Ascorbic acid
Citric acid

The presence of a broad genus and a defined species list strengthens literal coverage against formulation substitutions that preserve the claimed acid-based release mechanism.

What is the scope of the modified-release limitation?

The claims require a modified-release composition, but claim 1 does not impose a single dissolution profile or a fixed release-time specification. Claim 21 provides a functional limitation requiring reduced release from the second release phase compared with an immediate-release formulation.

This creates two different infringement questions:

Whether the product has the required structural features, including compacted granules and intimate solid contact.
Whether the product exhibits the claimed modified-release behavior.

A formulation may contain sodium amoxicillin and citric acid but avoid claim 21 if it does not demonstrate the specified second-phase release reduction. It may still infringe claim 1 if the remaining structural and modified-release limitations are met.

The phrase "comprising" broadens the claims by allowing additional ingredients. A product is not outside the claim merely because it contains polymers, coatings, lubricants, binders, or other excipients not expressly listed.

How strong is the patent estate for Moxatag?

The patent is strongest against a product that reproduces the commercial formulation architecture:

Sodium amoxicillin.
Citric acid, particularly anhydrous citric acid.
Compacted granules.
Xanthan gum.
Lactose.
Microcrystalline cellulose.
Approximately 438 mg sodium amoxicillin per dosage unit.
Tablet dosage form.
Delayed or extended release from multiple formulation phases.

The patent is weaker against:

A non-acidic extended-release formulation.
A formulation using a different release mechanism, such as a coated multiparticulate system.
A product using a non-soluble amoxicillin form.
A liquid, capsule, injectable, or other dosage form that lacks the tablet and granule limitations.
A formulation that does not use intimate solid-state contact between amoxicillin salt and organic acid.
A formulation with a different granulation architecture.

The claim set has substantial dependent-claim redundancy. Claims 3 through 10 establish overlapping active-salt and acid limitations, while claims 15 through 20 identify a commercially coherent excipient combination. That structure gives the patent multiple infringement theories but also creates design-around opportunities.

When did U.S. Patent 6,746,692 expire?

U.S. Patent 6,746,692 was filed in the United States on December 17, 1999, claiming priority to a Great Britain filing dated December 18, 1998. It issued on June 8, 2004. The ordinary patent term was therefore tied to the U.S. nonprovisional filing date, subject to any applicable patent-term adjustment or extension.[1]

Public patent records identify December 18, 2019, as the relevant patent expiration date for the patent family. The patent is no longer an enforceable U.S. patent right. Any patent-term adjustment should be confirmed against the USPTO patent record and the Orange Book entry applicable to the product and relevant regulatory period.[1][3]

Event	Date
Earliest priority filing	December 18, 1998
U.S. filing	December 17, 1999
U.S. publication	May 30, 2002
Patent grant	June 8, 2004
Reported U.S. expiration	December 18, 2019

The expired status means a current generic or alternative amoxicillin extended-release product does not face infringement liability based solely on U.S. Patent 6,746,692. Expired patent claims may still be relevant in historical litigation, ANDA certifications, validity analysis, and prosecution-history review.

What was the FDA and Orange Book status?

The product associated with the patent was Moxatag, an extended-release amoxicillin tablet. The FDA approved Moxatag under NDA 022042 in 2008 for the treatment of tonsillitis and/or pharyngitis caused by Streptococcus pyogenes in adults and pediatric patients 12 years and older.[2]

The product contained 775 mg of amoxicillin and was administered once daily. The FDA-approved labeling described the product as an extended-release tablet and required administration according to the approved dosing instructions.[2]

The Orange Book listed U.S. Patent 6,746,692 in connection with the Moxatag NDA. Orange Book listing establishes that the NDA sponsor submitted the patent information for the approved drug. It does not independently establish validity, enforceability, or infringement.[3]

Regulatory item	Status
Product	Moxatag
Active ingredient	Amoxicillin
Dosage form	Extended-release tablet
Strength	775 mg
FDA pathway	NDA
NDA	022042
Initial approval	2008
Listed patent	U.S. 6,746,692
Current patent enforceability	Expired

Were there Paragraph IV challenges to this patent?

A Paragraph IV certification would have been the relevant ANDA pathway for a generic applicant asserting that the patent was invalid, unenforceable, or not infringed. The Hatch-Waxman framework can trigger a 30-month stay if the NDA holder or patent owner files suit within the statutory period after receiving notice of a Paragraph IV certification.[4]

No verified, material U.S. Paragraph IV litigation record involving U.S. Patent 6,746,692 is identified here. The absence of a confirmed litigation event should not be treated as evidence that no certification was ever submitted. Paragraph IV certifications, confidential settlement terms, withdrawn ANDAs, and products that never reached final approval may not be fully visible through ordinary patent databases.

The expiration of the patent removes the need for a current applicant to overcome this patent through a Paragraph IV validity or noninfringement position. A present-day ANDA strategy would focus on any remaining listed patents, regulatory exclusivity, drug-product equivalence, dissolution requirements, and FDA approval status.

What generic entry risks existed before patent expiration?

Before expiration, a generic applicant would have faced several possible entry scenarios.

Scenario 1: Paragraph IV challenge

The applicant could have argued that one or more limitations were absent or invalid, including:

No intimate contact between the amoxicillin salt and acid.
No compacted granules.
An acid outside the claimed classes.
A release profile that did not meet claim 21.
Lack of novelty or obviousness over prior modified-release amoxicillin formulations.
Indefiniteness or written-description issues concerning "intimate contact," "modified release," or the second release phase.

Scenario 2: Paragraph III certification

The applicant could have filed a Paragraph III certification and delayed commercial launch until patent expiration. This would avoid immediate patent litigation but defer entry.

Scenario 3: Formulation design-around

A competing product could have used a different architecture, such as:

Coated pellets.
A polymer-coated tablet.
A multiparticulate capsule.
A non-acidic matrix.
A different amoxicillin salt or drug form.
A release-controlling coating that prevents the claimed intimate salt-acid interaction.

The design-around must be evaluated against all claims, including the broad acid genus in claims 5 through 7 and the functional release language in claim 21.

What manufacturing and intellectual-property barriers did the patent create?

The patent’s manufacturing barriers were more specific than a conventional active-ingredient patent. A potential competitor would need to assess:

Granulation method.
Order of ingredient addition.
Dry versus wet processing.
Particle-size distribution.
Solid-state contact between sodium amoxicillin and acid.
Compression conditions.
Xanthan-gum grade and concentration.
Dissolution behavior across the claimed release phases.
Stability of amoxicillin in the presence of acid and moisture.

Manufacturing records could become important in litigation because the final tablet may not reveal whether the salt and acid were admixed in the claimed manner. Process controls, batch records, granule microscopy, powder blending data, and dissolution testing could support or defeat an infringement theory.

The patent does not claim every manufacturing step as an independent process claim in the supplied claim set. Its process relevance arises from the structural requirement that the final product contain compacted granules with the specified intimate solid admixture.

How does this patent compare with a conventional immediate-release amoxicillin product?

Attribute	U.S. Patent 6,746,692 formulation	Immediate-release amoxicillin
Release profile	Modified or extended release	Immediate release
Dosing objective	Once-daily administration for approved product	Multiple daily administrations commonly used
Active form	Soluble amoxicillin salt, particularly sodium amoxicillin in the claimed formulation	Commonly amoxicillin trihydrate or other approved form
Organic acid	Required by claim 1	Not required
Compacted granules	Required by claim 1	Not required
Xanthan gum	Covered by claims 15-18	Not required
Tablet strength	Claim 11 identifies approximately 438 mg sodium amoxicillin; commercial product contained 775 mg amoxicillin	Product-specific
Patent risk	Expired for this patent	No current risk from this patent alone

An immediate-release amoxicillin product generally would not satisfy the modified-release, compacted-granule, and acid-interaction limitations. The active ingredient alone is not enough for infringement.

What licensing deals and ownership changes affected the patent?

The patent was originally associated with SmithKline Beecham Corporation. The commercial Moxatag product was developed and marketed through MiddleBrook Pharmaceuticals. The patent and product history should be separated:

Patent ownership concerns title to the patent and enforcement rights.
NDA sponsorship concerns the FDA-approved drug application.
Commercial marketing concerns the company selling or promoting the product.
Licensing concerns contractual rights that may not be fully reflected in USPTO assignment records.

No material public license agreement transferring the core patent rights is established in the cited records. Patent assignment records should be distinguished from commercial licensing agreements, which may remain private.

What is the current competitive landscape?

The relevant competitive set includes:

Immediate-release amoxicillin capsules, tablets, and oral suspension.
Extended-release amoxicillin products.
Other once-daily oral antibacterial therapies used for overlapping indications.
Generic amoxicillin products approved through ANDAs.
Alternative modified-release formulations using coatings, matrices, or multiparticulates.

Moxatag’s commercial differentiation depended on dosing convenience rather than a new antibacterial mechanism. Its patent protection was formulation-based, and its competitive position depended on manufacturing reproducibility, dissolution performance, regulatory approval, and the ability to maintain a once-daily product profile.

Because U.S. Patent 6,746,692 has expired, the current commercial barrier is no longer this patent. The principal remaining barriers are likely to be product development cost, FDA approval requirements, bioequivalence or comparative dissolution, manufacturing scale-up, market size, and any later patent rights.

What revenue exposure did the patent create?

The patent protected the formulation architecture of the Moxatag product during the period before expiration. Revenue exposure was therefore concentrated in:

Sales of the branded extended-release tablet.
Potential generic substitution after patent expiration.
Licensing or partnering value associated with once-daily amoxicillin.
Litigation risk for an ANDA applicant seeking an equivalent formulation.
Manufacturing know-how associated with the granulation and release profile.

The patent did not block ordinary immediate-release amoxicillin products. Its revenue protection was narrower than a compound patent and depended on the commercial relevance of the extended-release dosage form.

Key Takeaways

U.S. Patent 6,746,692 is a formulation patent covering modified-release amoxicillin compositions.
Claim 1 requires compacted granules containing a soluble amoxicillin salt and an organic acid in a 20:1 to 1:2 ratio.
The most commercially important embodiment uses sodium amoxicillin, citric acid, xanthan gum, lactose, and microcrystalline cellulose.
Claim 11 identifies approximately 438 mg of sodium amoxicillin, corresponding to the formulation framework for the 775-mg Moxatag tablet.
Claims 5 through 10 provide broad and species-level coverage for organic acids.
Claims 15 through 18 specifically target xanthan-gum controlled release.
Claim 21 adds a functional release limitation concerning reduced release from the second release phase.
The patent was associated with Moxatag, an FDA-approved extended-release amoxicillin tablet under NDA 022042.
The patent’s reported expiration date was December 18, 2019.
The patent is expired and does not create current infringement liability by itself.
A current competitor must evaluate later patents, FDA requirements, product-specific equivalence, manufacturing reproducibility, and any surviving regulatory or contractual barriers.

FAQs

Does U.S. Patent 6,746,692 cover all extended-release amoxicillin tablets?

No. It covers compositions with the claimed soluble amoxicillin salt, organic acid, compacted granules, intimate solid contact, and modified-release characteristics. A different release architecture may avoid the claims.

Does using citric acid automatically create infringement?

No. Citric acid is only one limitation. Infringement also requires the claimed amoxicillin salt, granule structure, ratio, release profile, and other applicable limitations.

Is Moxatag a biologic subject to biosimilar competition?

No. Moxatag is a small-molecule amoxicillin product. A competing product would generally proceed through the generic drug framework, including an ANDA, rather than the biosimilar pathway.

Can a generic use the same 775-mg amoxicillin strength after patent expiration?

Patent expiration removes the barrier created by U.S. Patent 6,746,692, but FDA approval still requires the applicable demonstration of pharmaceutical equivalence, bioequivalence, quality, manufacturing control, labeling, and regulatory compliance.

Does an expired patent still matter in a freedom-to-operate review?

Yes. It can affect historical litigation, prosecution strategy, prior-art analysis, product-development records, and interpretation of related patent families. It does not, by itself, support a current U.S. infringement claim after expiration.

References

United States Patent and Trademark Office. (2004). U.S. Patent No. 6,746,692, modified release pharmaceutical compositions. U.S. Department of Commerce. https://patents.google.com/patent/US6746692B1/en
U.S. Food and Drug Administration. (2008). Moxatag (amoxicillin extended-release tablets) prescribing information. https://www.accessdata.fda.gov/drugsatfda_docs/label/
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.accessdata.fda.gov/scripts/cder/ob/
U.S. Food and Drug Administration. (2017). Regulatory procedures for drug products that are the subject of abbreviated new drug applications containing patent certifications and/or exclusivity provisions. FDA. https://www.fda.gov/regulatory-information/search-fda-guidance-documents/abbreviated-new-drug-application-submissions-containing-patent-certifications-andor-exclusivity-provisions

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
African Regional IP Organization (ARIPO)	1806	⤷ Start Trial
Argentina	031068	⤷ Start Trial
Austria	242629	⤷ Start Trial
Austria	4327	⤷ Start Trial
Australia	5702000	⤷ Start Trial
Australia	5837500	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,746,692

Summary for Patent: 6,746,692