US Patent 6,316,023: Rivastigmine Formulation Claims, Patent Scope, Expiration, and Generic Risk

US Patent 6,316,023 protects antioxidant-stabilized pharmaceutical compositions and transdermal devices containing rivastigmine, the active ingredient in Exelon and generic rivastigmine products. The patent covers specific concentration ranges for rivastigmine and antioxidants, selected antioxidant compounds, polymer-based compositions, and patch architectures. Its 20-year patent term expired in November 2019, eliminating current US patent exclusivity under this patent.

What drug and technology does US Patent 6,316,023 cover?

The claimed active ingredient is rivastigmine, chemically identified in the claims as:

(S)-N-ethyl-3-[(1-dimethylamino)ethyl]-N-methylphenyl carbamate

Rivastigmine is an acetylcholinesterase and butyrylcholinesterase inhibitor approved for Alzheimer’s disease and Parkinson’s disease dementia. It is marketed in oral capsules, oral solution, and transdermal patches.

The patent focuses on stabilizing rivastigmine-containing formulations with low concentrations of antioxidants. The technical problem addressed is degradation of rivastigmine, particularly in compositions and transdermal systems exposed to oxygen, heat, light, or long storage periods.

US 6,316,023 is directed to formulation and delivery technology rather than the underlying chemical composition of matter for rivastigmine.

What are the independent claims in US 6,316,023?

The patent has three principal independent claim categories:

Claim	Claimed subject matter	Core limitations
1	Pharmaceutical composition	1-40 wt% rivastigmine, 0.01-0.5 wt% antioxidant, and diluent or carrier
6	Narrow pharmaceutical composition	7-40 wt% rivastigmine free base, 10-30 wt% polymethacrylate or acid addition salt, and 0.05-0.3 wt% alpha-tocopherol
7	Transdermal device	A transdermal device containing the claim 1 composition

Claims 2 through 5 narrow claim 1 by specifying antioxidant identity and concentration. Claims 8 and 9 narrow claim 7 by defining the patch structure.

How broad is claim 1?

Claim 1 is the broadest composition claim. A product must contain all of the following:

Rivastigmine in the free-base form or as an acid-addition salt.
Rivastigmine at 1-40 weight percent of the total pharmaceutical composition.
An antioxidant at 0.01-0.5 weight percent.
A diluent or carrier.

The use of “comprising” makes the claim open-ended. Additional excipients, adhesives, permeation enhancers, plasticizers, stabilizers, solvents, polymers, and release-control agents may be present without avoiding the claim, provided the listed limitations are met.

The weight percentages are measured against the total composition, not merely the active layer or dry solids unless the claim construction or product evidence establishes a different basis. This measurement issue would be material in any infringement dispute involving a multilayer patch.

Claim 1 does not require:

A transdermal route.
A particular dosage strength.
A particular release rate.
A specific adhesive.
A specific patch size.
A specific antioxidant.
A specific polymethacrylate.
A particular rivastigmine salt.

The claim therefore has broad formulation coverage, but it is limited by the numerical ranges and the requirement for an antioxidant.

What antioxidants are protected by claims 2 through 5?

Claim 2 defines a closed list of antioxidant categories:

Tocopherol.
Tocopherol esters.
Ascorbic acid.
Ascorbic acid esters.
Butylhydroxytoluene, commonly BHT.
Butylhydroxyanisole, commonly BHA.
Propyl gallate.
Combinations of those compounds.

Claim 3 narrows the scope to alpha-tocopherol or ascorbyl palmitate. Claim 4 requires an antioxidant concentration of 0.05-0.2 weight percent. Claim 5 further narrows the concentration to 0.1-0.15 weight percent.

Claim	Antioxidant requirement
1	Any antioxidant within 0.01-0.5 wt%
2	Listed antioxidant classes within claim 1
3	Alpha-tocopherol or ascorbyl palmitate
4	0.05-0.2 wt% antioxidant
5	0.1-0.15 wt% antioxidant

Claims 2 and 3 can be important in product analysis because a generic manufacturer may avoid a dependent claim by selecting a different antioxidant while remaining within claim 1.

What does claim 6 protect?

Claim 6 is a narrower composition claim with three quantitative limitations:

7-40 weight percent rivastigmine free base.
10-30 weight percent polymethacrylate or the specified acid-addition-salt component.
0.05-0.3 weight percent alpha-tocopherol.

The claim is materially narrower than claim 1 because it requires rivastigmine free base, alpha-tocopherol, and a substantial polymethacrylate or acid-addition-salt component.

The phrase “polymethacrylate or acid addition salt” requires careful construction. In the context of rivastigmine formulation patents, an acid addition salt ordinarily refers to a salt form of rivastigmine, while polymethacrylate identifies a polymeric excipient or matrix component. Product-specific analysis must determine whether the claim language is being read as an alternative between those components or as a drafting shorthand involving the rivastigmine salt and polymer system.

What transdermal devices are covered by claims 7 through 9?

Claim 7 extends the claim 1 formulation to a transdermal device. It requires a device containing:

1-40 weight percent rivastigmine.
Rivastigmine as free base or acid-addition salt.
0.01-0.5 weight percent antioxidant.
A diluent or carrier.

Claim 8 requires a more conventional patch assembly with:

A backing layer.
The pharmaceutical composition.
An adhesive for contacting and fixing the composition to the backing layer.
A release liner.

Claim 9 describes a more specific multilayer construction:

A backing layer.
A layer containing rivastigmine and antioxidant in a polymer matrix.
A release liner.
An adhesive layer between the drug-containing polymer-matrix layer and the release liner.
An adhesive configured to fix the device to the patient’s skin.

Claim 9 is narrower than claim 7 because it requires a polymer-matrix drug layer and a separate adhesive layer in a defined relationship. A patch using a drug-in-adhesive design may raise different infringement issues from a reservoir or matrix patch, depending on the actual layer structure.

What formulation features create infringement risk?

A rivastigmine product would present the highest historical risk under US 6,316,023 if it had the following profile:

Feature	High-risk configuration
Active ingredient	Rivastigmine free base or acid-addition salt
Active loading	1-40 wt% under claim 1 or 7-40 wt% under claim 6
Stabilizer	Alpha-tocopherol, ascorbyl palmitate, BHT, BHA, propyl gallate, or listed derivative
Antioxidant loading	0.01-0.5 wt%, with higher risk at 0.1-0.15 wt%
Delivery form	Transdermal patch
Matrix	Polymer matrix containing rivastigmine and antioxidant
Adhesive	Separate skin-contact adhesive layer
Excipient system	Polymethacrylate at 10-30 wt% under claim 6

A product outside the claimed antioxidant range would not literally meet claims 1, 6, or 7. A product using an antioxidant outside the closed list could still fall under claim 1 if the compound qualifies as an antioxidant, but it would not fall under claims 2 or 3.

When did US Patent 6,316,023 expire?

The relevant patent-term timeline is:

Event	Date
Earliest priority period	1998
US patent application filing period	1999
US patent grant	November 13, 2001
Standard 20-year term endpoint	November 2019
Current status	Expired

The patent term is measured principally from the earliest effective nonprovisional or international filing date, not from the grant date. The 2001 grant date therefore did not create a new 20-year period.

The patent is no longer an enforceable US barrier to generic or follow-on rivastigmine formulation commercialization. Historical litigation and ANDA certification issues remain relevant to market-entry analysis, but no new product launched after expiration would face a live exclusion right under this patent alone.

What was the Orange Book status of US 6,316,023?

US 6,316,023 was associated with the Exelon transdermal patch patent estate and was relevant to FDA-approved rivastigmine patch products. Orange Book-listed patents can delay approval of an ANDA through the Hatch-Waxman framework if the patent is timely listed and not expired.

The key commercial effect ended when the patent term expired in 2019. An expired Orange Book patent does not provide a continuing 30-month stay against an ANDA based solely on that patent. FDA approval and market entry remain subject to other applicable patents, regulatory exclusivity, labeling requirements, and product-specific litigation.

The Orange Book should be evaluated historically by product and dosage form because patents listed for Exelon capsules, oral solution, and transdermal systems are not necessarily identical.

Which other patents shaped the rivastigmine patent landscape?

The rivastigmine estate has included several distinct patent groups:

Patent group	Subject matter	Commercial relevance
Active-ingredient patents	Rivastigmine molecule and stereochemistry	Earlier compound protection; expired before the formulation patents
Therapeutic-use patents	Treatment of Alzheimer’s disease or dementia	Method-of-use coverage, often limited by approved labeling
Oral formulation patents	Capsules, solutions, salts, excipients, and stability	Relevant to oral generic products
Transdermal formulation patents	Rivastigmine patches, matrix systems, adhesives, and stabilizers	Relevant to Exelon Patch and generic patches
Manufacturing patents	Synthesis, purification, stereochemical control, and salt formation	Potential process barriers, usually separate from product claims
Pediatric or regulatory exclusivity	FDA exclusivity attached to specific approvals	Regulatory exclusivity rather than patent protection

US 6,316,023 is principally a formulation and transdermal-delivery patent. It does not by itself cover every rivastigmine product. An oral capsule lacking the claimed antioxidant concentration and transdermal architecture would require separate analysis under other patents.

Were there Paragraph IV challenges to rivastigmine patch patents?

Generic rivastigmine patch applicants could challenge listed patents through Paragraph IV certifications under the Hatch-Waxman Act. A Paragraph IV certification states that the listed patent is invalid, unenforceable, or would not be infringed by the proposed generic product.

The principal dispute issues for this patent family would include:

Whether the generic patch contains the required antioxidant.
Whether the antioxidant concentration falls within the claimed range.
Whether the claimed weight percentages are calculated on the correct compositional basis.
Whether the active layer qualifies as a polymer matrix.
Whether the patch has a separate adhesive layer.
Whether the claims are anticipated or obvious based on earlier antioxidant-stabilized formulations.
Whether the patent’s formulation claims provide an enabling disclosure across the full numerical ranges.

Because US 6,316,023 expired in 2019, Paragraph IV litigation under this patent no longer creates a forward-looking launch block. Any historical litigation must be separated from current freedom-to-operate analysis.

How strong was the patent estate?

The patent had meaningful historical value because it combined broad formulation coverage with claims directed specifically to transdermal devices. Its strongest features were:

Coverage of both free-base and acid-addition-salt rivastigmine.
Broad 1-40 weight percent active range.
Coverage of multiple conventional antioxidants.
Separate claims for transdermal devices.
Specific matrix and adhesive-layer architecture.
Narrower fallback claims directed to alpha-tocopherol and polymethacrylate systems.

Its principal vulnerabilities were:

The use of known pharmaceutical antioxidants.
Broad numerical ranges that may have invited prior-art and obviousness challenges.
Potential ambiguity in weight-percent calculations for multilayer products.
The ability of competitors to alter antioxidant identity, concentration, or patch architecture.
Expiration before the current wave of commercial generic competition.

The patent was commercially stronger as part of the broader Exelon patch estate than as a standalone right. A competitor designing around the antioxidant limitations could potentially avoid this patent while still needing to address other patch patents.

What generic launch scenarios existed?

After expiration, the main generic rivastigmine patch pathways were:

Non-infringing formulation design

A manufacturer could use a different antioxidant, omit an antioxidant, or select a concentration outside the claimed ranges, subject to product stability and FDA requirements.

Paragraph IV launch before expiration

A generic applicant could file an ANDA with a Paragraph IV certification and litigate validity or infringement. This path carried potential 30-month-stay exposure if the NDA holder filed suit within the statutory period.

Post-expiration launch

After November 2019, applicants could launch without waiting for this patent to expire, although other listed patents, regulatory exclusivity, manufacturing constraints, and commercial readiness still mattered.

505(b)(2) development

A reformulated rivastigmine patch or a product with materially different delivery characteristics could use a 505(b)(2) pathway rather than an ANDA, depending on the extent of reliance on the reference product and the proposed labeling.

What manufacturing and geographic barriers remained?

The patent’s US expiration removed the US composition and device exclusion right, but manufacturing and market-entry barriers remained in several areas:

Stable manufacture of rivastigmine-containing adhesive or matrix systems.
Control of oxidation during blending, coating, drying, and packaging.
Uniform drug loading across the patch web.
Adhesion performance during wear.
Control of rivastigmine release over the labeled wear period.
Protection of manufacturing know-how and process parameters.
Regulatory approval in each jurisdiction.
Separate patent terms in Europe, Japan, China, and other markets.

US expiration does not establish freedom to operate outside the United States. Foreign family members require jurisdiction-by-jurisdiction review, including national-phase status, supplementary protection certificates, patent-term adjustments, and local litigation.

What is the current commercial significance of US 6,316,023?

Current direct patent risk is low because the patent expired in 2019. The patent remains commercially relevant for:

Historical analysis of Exelon Patch exclusivity.
Review of prior Paragraph IV strategies.
Benchmarking formulation patent drafting.
Evaluating whether a generic patch copied the original antioxidant-stabilized architecture.
Understanding the distinction between active-ingredient, formulation, device, and manufacturing protection.

It is not a current blocking patent for US rivastigmine products.

Key Takeaways

US 6,316,023 covers antioxidant-stabilized rivastigmine compositions and transdermal devices.
Claim 1 requires 1-40 wt% rivastigmine, 0.01-0.5 wt% antioxidant, and a carrier or diluent.
Claims 2-5 narrow the antioxidant identity and concentration, with alpha-tocopherol and ascorbyl palmitate receiving specific treatment.
Claim 6 is a narrower free-base formulation with polymethacrylate or the specified acid-addition-salt component and alpha-tocopherol.
Claims 7-9 cover transdermal devices, including polymer-matrix and separate-adhesive configurations.
The patent expired in November 2019.
Its Orange Book and Hatch-Waxman significance is historical rather than currently blocking.
Current rivastigmine patch analysis must consider other patents, FDA requirements, foreign rights, manufacturing know-how, and product-specific formulation details.

FAQs

Does US 6,316,023 cover rivastigmine capsules?

Not necessarily. The patent’s broad composition claims can apply to a pharmaceutical composition in the claimed concentration ranges, but the transdermal claims do not cover capsules. A capsule would require separate analysis of the antioxidant content, carrier, active concentration, and other rivastigmine patents.

Does a rivastigmine patch infringe if it contains no antioxidant?

It would not literally meet the antioxidant limitation in claims 1 and 7. It also would not meet claims 2-6, which depend on antioxidant limitations or require alpha-tocopherol. Other patents could still be relevant.

Does the patent cover rivastigmine hydrogen tartrate?

Claim 1 expressly covers rivastigmine in free-base or acid-addition-salt form. Rivastigmine hydrogen tartrate would generally require analysis as an acid-addition salt, subject to the applicable claim construction and product composition evidence.

Can a generic use alpha-tocopherol after patent expiration?

Yes. Expiration of US 6,316,023 removes the patent-based restriction on using alpha-tocopherol in the claimed formulation ranges. FDA approval, product quality, stability, and any other unexpired patent rights remain separate issues.

Is US 6,316,023 still relevant to foreign rivastigmine markets?

Potentially. US expiration does not determine the status of corresponding patents or supplementary protection rights in other countries. Each national family member must be reviewed separately.

References

U.S. Patent No. 6,316,023. (2001). Pharmaceutical compositions containing rivastigmine and antioxidants. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
U.S. Food and Drug Administration. (2024). Exclusivity and patent information in the Orange Book. Center for Drug Evaluation and Research.
U.S. Food and Drug Administration. (2020). Exelon (rivastigmine transdermal system) prescribing information. Novartis Pharmaceuticals Corporation.
United States Code, 35 U.S.C. § 154. (2024). Contents and term of patent; provisional rights.
United States Code, 21 U.S.C. § 355. (2024). New drugs and abbreviated applications.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	9800526	Jan 12, 1998

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	223711	⤷ Start Trial
Australia	2278599	⤷ Start Trial
Australia	745661	⤷ Start Trial
Brazil	9906920	⤷ Start Trial
Canada	2315784	⤷ Start Trial
China	1129427	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,316,023

Summary for Patent: 6,316,023