US Patent 8,338,485: Scope, Claims, Expiration, Orange Book Status, and Generic-Entry Risk

US Patent 8,338,485 protects oral solid dosage forms combining extended-release memantine with immediate-release donepezil. Its core commercial target is Namzaric, the fixed-dose combination of memantine hydrochloride extended release and donepezil hydrochloride immediate release. The patent’s strongest protection is directed to the 28 mg memantine/10 mg donepezil strength and to pharmacokinetic performance, not to a particular tablet excipient system or manufacturing process.

The patent is expected to expire on August 12, 2029, based on its earliest priority date. The patent is listed in the FDA Orange Book for Namzaric. Because the claims require a combination product and a defined human pharmacokinetic profile, a generic applicant must address both the formulation and the claimed memantine concentration-rate limitations.

What does US Patent 8,338,485 protect?

US Patent 8,338,485 claims a solid, orally administered unit dosage form containing two active ingredients:

Extended-release memantine, at 22.5 mg to 30 mg or a pharmaceutically acceptable salt; and
Immediate-release donepezil in a therapeutically effective amount.

The memantine component must satisfy two pharmacokinetic limitations:

Its rate of concentration change, dC/dT, must be less than approximately 50% of the corresponding rate produced by the same amount of immediate-release memantine.
The dC/dT must be no more than 2.1 ng/mL/hour during a specified early post-dose period.

Claims 1-8 use a comparator period extending from administration to the immediate-release memantine Tmax. Claims 9-16 use a fixed 0-to-6-hour comparator period.

Claim architecture

Claim group	Memantine dose	Comparator limitation	Absolute dC/dT limitation	Donepezil
Claims 1-2	22.5-30 mg	0-Tmax of immediate-release memantine	≤2.1 ng/mL/hour at 0-4 hours; claim 2 specifies 2-4 hours	Immediate release
Claims 3-4	25-30 mg	0-Tmax	≤2.1 ng/mL/hour	Immediate release
Claims 5-6	25-28 mg	0-Tmax	≤2.1 ng/mL/hour	Immediate release
Claims 7-8	28 mg	0-Tmax	≤2.1 ng/mL/hour	Immediate release
Claims 9-10	22.5-30 mg	0-6 hours after administration	≤2.1 ng/mL/hour at 0-4 hours; claim 10 specifies 2-4 hours	Immediate release
Claims 11-12	25-30 mg	0-6 hours	≤2.1 ng/mL/hour	Immediate release
Claims 13-14	25-28 mg	0-6 hours	≤2.1 ng/mL/hour	Immediate release
Claims 15-16	28 mg	0-6 hours	≤2.1 ng/mL/hour	Immediate release

Claims 7, 8, 15 and 16 are the narrowest dose-specific claims because they require 28 mg memantine. Those claims correspond directly to the highest memantine strength of Namzaric, which contains 28 mg memantine hydrochloride extended release and 10 mg donepezil hydrochloride immediate release [1, 2].

How do claims 1-16 differ?

The claims form two parallel sets.

Claims 1-8: Tmax-based comparator

Claims 1-8 compare the extended-release product with immediate-release memantine during the period from dosing to the immediate-release product’s Tmax. This limitation requires identifying the comparator’s Tmax and calculating the relative dC/dT over the relevant interval.

The dependent claims narrow the memantine dose:

Claims 3 and 4: 25-30 mg
Claims 5 and 6: 25-28 mg
Claims 7 and 8: exactly 28 mg

Claims 9-16: Fixed six-hour comparator

Claims 9-16 replace the variable Tmax-based comparison with a 0-to-6-hour interval. This creates a potentially more reproducible testing framework, although the exact study design and calculation method remain material.

Claims 10, 12, 14 and 16 narrow the absolute dC/dT measurement to the 2-to-4-hour period. The patent therefore contains alternative infringement theories: a challenger may avoid one set only if its product fails the corresponding limitation, but it could still fall within the parallel claim set.

What is the commercial product most directly covered?

Namzaric is the principal product aligned with the claimed combination. FDA labeling identifies four strengths:

Namzaric strength	Memantine ER	Donepezil IR
7 mg/10 mg	7 mg	10 mg
14 mg/10 mg	14 mg	10 mg
21 mg/10 mg	21 mg	10 mg
28 mg/10 mg	28 mg	10 mg

The 7 mg, 14 mg and 21 mg strengths fall outside the literal dose range of claims 1-16, which begins at 22.5 mg. The 28 mg/10 mg strength is the direct claim target.

The claims do not require a specific 10 mg donepezil dose. They require a therapeutically effective amount of immediate-release donepezil. The absence of a fixed donepezil quantity broadens the claim language, although commercial and regulatory practice materially narrows the likely product set.

What are the key infringement elements?

A competing product would need to be evaluated against each limitation rather than against the ingredient list alone.

1. Solid oral unit dosage form

The claims require a solid pharmaceutical composition in a unit dosage form for oral administration. A liquid, transdermal product, implant or separately marketed coadministration regimen would not literally satisfy this limitation.

The word “comprising” permits additional excipients, coatings, layers and pharmaceutical ingredients. It does not require a single-layer tablet. A bilayer tablet, multilayer tablet, capsule containing multiple multiparticulates or a capsule containing separate immediate-release and extended-release portions could potentially meet the claim.

2. Extended-release memantine

The memantine must be extended release and must contain 22.5-30 mg, including the narrower 28 mg claims. A generic formulation using a different release matrix, coating technology or multiparticulate design could still infringe if its pharmacokinetic profile satisfies the claim.

Conversely, a product that contains 28 mg memantine but does not meet the claimed PK limitations would have a non-infringement position based on the claim language.

3. Immediate-release donepezil

Donepezil must be present in an immediate-release form. The claims do not expressly require donepezil to be released from the same physical subunit as memantine. The “comprising” language may reach combination capsules or tablets containing distinct release portions.

A product with extended-release donepezil would have a potential non-infringement argument, although the regulatory and clinical consequences would need separate evaluation.

4. Human single-dose pharmacokinetics

The dC/dT limitations are expressly measured in a single-dose human PK study. The claim does not merely require a dissolution profile or an in vitro release specification.

This creates a central proof issue. Infringement analysis would likely require:

The test product’s mean plasma memantine concentration-time profile;
Sampling sufficiently dense to calculate dC/dT;
The study’s dose and fed or fasted conditions;
The immediate-release comparator;
The comparator’s Tmax or the fixed 0-to-6-hour interval;
The method used to derive dC/dT;
The identity of the memantine salt and dose normalization method.

How strong are the dC/dT limitations?

The dC/dT limitations provide technical specificity but also create litigation vulnerability.

Relative-rate requirement

Claims 1-8 require the extended-release product’s dC/dT to be less than approximately 50% of the dC/dT produced by the same quantity of immediate-release memantine during the period between dosing and the immediate-release Tmax.

Claims 9-16 use a 0-to-6-hour comparison period. The requirement that the comparator contain the “same quantity” of memantine reduces variability from dose differences but leaves several potential construction questions:

Whether “same quantity” refers to memantine base or salt mass;
Whether dose-normalization is required;
Whether the comparator must use the same subject population;
Whether the comparison must be performed within the same PK study;
Whether the calculation uses a mean curve or subject-level values;
How the court interprets “about 50%.”

Absolute-rate requirement

The dC/dT must be 2.1 ng/mL/hour or less. Claims 2, 4, 6, 8, 10, 12, 14 and 16 expressly place that test in the 2-to-4-hour window.

This threshold is especially important because it may distinguish otherwise similar extended-release formulations. A formulation can have the correct dose and a conventional extended-release label but avoid infringement if its measured early concentration rate exceeds the threshold. The reverse also applies: a formulation using a different technology may still be captured if it produces the required profile.

Potential validity issues

The functional PK limitations may attract challenges based on:

Indefiniteness in calculating dC/dT;
Lack of objective boundaries around “about 50%”;
Written description and enablement of the full 22.5-30 mg range;
Reproducibility across subjects, meals and study designs;
Whether the specification adequately teaches all formulations meeting the claimed profile;
Whether the claimed result is an inherent property of known memantine extended-release products.

The strength of those arguments depends on the patent specification, prosecution history, examiner amendments and expert evidence. The claims alone establish the scope, not the ultimate enforceability.

When does US Patent 8,338,485 expire?

The patent’s expected expiration date is August 12, 2029, based on the earliest priority date associated with the patent family [1]. The issue date was December 25, 2012.

Event	Date
Earliest reported priority date	August 12, 2008
US patent issue	December 25, 2012
Expected 20-year patent-term expiration	August 12, 2029
Commercial product associated with claims	Namzaric
Patent category	Combination formulation and PK-defined product

The exact enforceable term should be determined from the USPTO patent record, including any patent-term adjustment, terminal disclaimer or later correction. The August 12, 2029 date is the relevant ordinary-term endpoint reflected in public patent records.

What is the Orange Book status of US Patent 8,338,485?

US Patent 8,338,485 is listed in the FDA Orange Book in connection with Namzaric, NDA 206439. The listing is directed to the combination product rather than to memantine or donepezil as standalone active ingredients [2, 3].

The Orange Book listing creates a regulatory patent-certification issue for an ANDA applicant seeking approval of a generic version of the listed combination. Depending on the applicant’s position, the ANDA may include:

A Paragraph III certification accepting approval after patent expiration;
A Paragraph IV certification asserting that the patent is invalid, unenforceable or not infringed;
A section viii statement if the applicant seeks approval without a patented method of use, although that pathway is less central for a composition patent.

Because the patent claims the dosage form itself, a section viii strategy would generally not remove the formulation claim from the ANDA review.

When does Namzaric lose exclusivity?

Namzaric’s regulatory exclusivity and patent exclusivity are separate.

The combination was approved by FDA in May 2015. The approval relied on clinical information supporting the fixed-dose combination, while memantine and donepezil were previously approved active ingredients. The key commercial barrier is therefore the listed patent estate rather than new chemical entity exclusivity for either active ingredient [2].

The principal patent barrier associated with US 8,338,485 runs to August 2029. An ANDA applicant could seek approval before that date through a successful Paragraph IV challenge, a settlement permitting earlier launch, or a non-infringing product design.

Which companies are challenging Namzaric patents?

The claim set supplied for this analysis does not identify an ANDA applicant, Paragraph IV notice letter or litigation defendant. Patent challenges cannot be established from the patent claims themselves.

Public regulatory analysis should distinguish among:

An ANDA filing;
A Paragraph IV certification;
A patent-owner suit filed within the 45-day period;
A final judgment;
A settlement agreement;
FDA approval and the first commercial launch.

A generic company’s filing is not equivalent to a successful invalidity or non-infringement result. For US 8,338,485, the relevant inquiry is whether the applicant’s proposed memantine/donepezil product meets the 28 mg dose and the claimed dC/dT limitations.

What generic launch scenarios exist?

Scenario 1: Launch after patent expiry

A generic applicant may file a Paragraph III certification and receive approval with launch scheduled after August 12, 2029, subject to other listed patents and regulatory requirements.

Scenario 2: Paragraph IV challenge

A challenger could argue that the proposed product:

Does not satisfy the 22.5-30 mg memantine range;
Uses a dose below 22.5 mg;
Does not contain immediate-release donepezil;
Fails the relative dC/dT limitation;
Exceeds the 2.1 ng/mL/hour threshold;
Cannot be shown to meet the limitations in the required single-dose human PK study.

The patent owner could respond with infringement allegations based on the applicant’s formulation, ANDA specifications, bioequivalence data and PK results.

Scenario 3: Non-infringing product design

A product containing the same active ingredients may reduce risk by using a memantine dose outside the claimed range or by demonstrating a PK profile outside the claimed dC/dT parameters. A formulation change must still satisfy FDA bioequivalence and product-quality requirements.

Scenario 4: Settlement

A settlement could establish an agreed launch date before patent expiration. Its commercial value would depend on the remaining term, the scope of any authorized generic arrangement, supply rights, royalty terms and treatment of other Namzaric patents.

How does US 8,338,485 compare with other Namzaric protection?

The patent estate should be separated into several layers.

Protection layer	Typical subject matter	Relevance to Namzaric
Combination patent	Memantine ER plus donepezil IR	Directly addressed by US 8,338,485
Memantine ER patents	Release profile, formulation architecture and dosage form	May affect standalone memantine ER or combination products
Method-of-use patents	Treatment of Alzheimer’s disease or dosing methods	May create additional ANDA certification issues
Manufacturing patents	Coating, granulation, multiparticulate or tablet production	Can affect supply-chain substitution
Regulatory exclusivity	FDA approval-based exclusivity	Separate from patent term
Active-ingredient patents	Memantine and donepezil chemical matter	Historic patents are generally expired

The combination patent is more product-specific than a broad memantine extended-release patent. Its principal advantage is that it reaches a fixed-dose product even when the manufacturer changes the release technology, provided the PK limitations remain satisfied.

Does biosimilar risk apply?

No. Namzaric is a small-molecule combination product, not a biologic. The relevant competitor pathway is an ANDA under section 505(j) of the Federal Food, Drug, and Cosmetic Act, not a biosimilar application under section 351(k) of the Public Health Service Act.

The competitive risk is therefore generic substitution, Paragraph IV litigation and formulation-based design-around activity.

What licensing and ownership issues matter?

The patent’s inventorship and original applicant history should be separated from the current commercial owner and licensee. Adamas Pharmaceuticals developed the extended-release memantine platform and was later acquired by Supernus Pharmaceuticals. Namzaric commercialization was associated with Forest Laboratories, Actavis and later Allergan/AbbVie corporate structures.

For transaction diligence, the critical documents are:

Current assignment records at the USPTO;
Patent licenses covering Namzaric;
FDA NDA ownership records;
Commercialization agreements;
Any settlement or authorized-generic agreements;
Royalty obligations tied to the patent family.

A patent assignment does not by itself establish that the assignee controls FDA commercialization rights.

Key Takeaways

US Patent 8,338,485 claims a solid oral combination of extended-release memantine and immediate-release donepezil.
The claims require 22.5-30 mg memantine and a defined single-dose human PK profile.
Claims 7, 8, 15 and 16 specifically target 28 mg memantine, the highest Namzaric strength.
The patent does not require a particular excipient, matrix, coating or tablet architecture.
The dC/dT limitations are central to both infringement analysis and potential validity challenges.
The patent’s expected expiration date is August 12, 2029.
FDA lists the patent for Namzaric, creating an ANDA certification issue for generic combination products.
Biosimilar regulation does not apply.
A generic applicant’s strongest design-around options involve dose selection, release profile and failure to satisfy the claimed PK thresholds.
The patent estate must be evaluated with related memantine extended-release, method-of-use and manufacturing patents, not in isolation.

FAQs

Does US Patent 8,338,485 cover all Namzaric strengths?

No. The claims begin at 22.5 mg memantine. The 7 mg, 14 mg and 21 mg strengths are outside the literal dose ranges, while the 28 mg strength falls within the claims.

Is donepezil required to be 10 mg?

No. The claims require a therapeutically effective amount of immediate-release donepezil, but do not expressly set a fixed dose. Namzaric commercially uses 10 mg donepezil.

Can a generic use a different extended-release technology?

Yes, potentially. A different matrix, coating or multiparticulate system may still infringe if the final product meets the dose, combination and dC/dT limitations.

Is a human PK study required for FDA approval of a generic?

A generic applicant must establish bioequivalence under FDA requirements. The patent claims separately require analysis of a single-dose human PK profile for infringement, making the applicant’s PK data potentially important in patent litigation.

Does a Paragraph III certification permit launch before August 12, 2029?

No. A Paragraph III certification generally defers approval until patent expiration, unless another legal basis permits earlier approval.

References

United States Patent and Trademark Office. (2012). US Patent No. 8,338,485, Pharmaceutical compositions comprising memantine and donepezil.
U.S. Food and Drug Administration. (2015). Namzaric prescribing information.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	E481096	⤷ Start Trial
Australia	2005209310	⤷ Start Trial
Australia	2005215767	⤷ Start Trial
Australia	2005215775	⤷ Start Trial
Australia	2005309601	⤷ Start Trial
Australia	2006244297	⤷ Start Trial
Brazil	PI0518483	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 8,338,485