US Patent 9,351,975: Oxcarbazepine Once-Daily Formulation Claims and Patent Landscape

US Patent 9,351,975 covers once-daily oxcarbazepine formulations built around a homogeneous matrix that combines oxcarbazepine, a solubility-enhancing agent and a pH-dependent release-promoting polymer. The claims extend to specific excipients, polymer concentrations, pharmacokinetic targets, 600 mg tablets and other oral dosage forms.

The estate is technically focused rather than molecule-wide. It does not claim oxcarbazepine itself, its active monohydroxy metabolite, or every extended-release formulation. Infringement risk is highest for a once-daily solid oral product using an enteric or pH-dependent polymer with a solubility enhancer and a matrix-forming polymer.

What does US Patent 9,351,975 claim?

The independent claim requires four core characteristics:

Oxcarbazepine as the active pharmaceutical ingredient.
A solubility-enhancing agent.
A pH-dependent polymer that promotes release.
A homogeneous matrix in a once-daily pharmaceutical formulation.

Claim 1 defines the central chemical and formulation combination:

Claim element	Scope
Active ingredient	Oxcarbazepine
Dosing frequency	Once daily
Physical structure	Homogeneous matrix
Solubility enhancer	Surface-active agent, complexing agent, cyclodextrin or pH-modifying agent
Release-promoting polymer	pH-dependent polymer
Polymer examples	Cellulose acetate phthalate, cellulose acetate succinate, methylcellulose phthalate, polyvinyl acetate phthalate, Eudragit L100-55 and related copolymers

The claim is structured as a Markush combination. A formulation can potentially fall within claim 1 through any listed member of each functional category, provided the formulation satisfies the homogeneous-matrix and once-daily limitations.

The claim does not require a particular manufacturing process, tablet hardness, dissolution profile, coating operation, particle size or excipient ratio unless those limitations appear in a dependent claim.

How broad is the independent claim?

Claim 1 is broad in excipient selection but narrow in formulation architecture.

Its breadth comes from four sources:

Multiple classes of solubility enhancers are covered.
Multiple pH-dependent polymers are listed.
The claim does not require one specific release mechanism or dissolution profile.
The dosage form is not limited to tablets.

Its limitations are equally important:

The product must be once daily.
The components must form a homogeneous matrix.
The release-promoting component must be a polymer with pH-dependent solubility.
Oxcarbazepine must be combined with a solubility enhancer, not merely a conventional filler or binder.
The formulation must operate as a pharmaceutical dosage form rather than as a standalone composition of matter.

A once-daily oxcarbazepine tablet using a neutral hydrophilic matrix alone would face a stronger non-infringement position if it does not contain a claimed pH-dependent release-promoting polymer. A formulation using an enteric polymer only as an external coating may also present a design-around argument, depending on whether the coating is part of the claimed homogeneous matrix.

What dependent claims add to the patent scope?

The dependent claims create several narrower infringement positions.

Polymer concentration and matrix architecture

Claim 2 requires the matrix-forming polymer to represent 1% to 50% by weight of the formulation.

Claim 5 adds a matrix-forming polymer selected from:

HPMC, HPC, HEC, methylcellulose and other cellulosic polymers;
Alginates;
Gums;
Cross-linked polyacrylic acid;
Carrageenan;
Polyvinylpyrrolidone;
Polyethylene oxides;
Polyvinyl alcohol.

Claims 6 through 8 narrow the pH-dependent polymer by dissolution behavior. The polymer remains intact below pH 4 and dissolves above pH 4, 5 or 6. These limitations connect the formulation to gastrointestinal pH-dependent release.

Claims 9 and 10 establish quantitative ranges:

Component	Claim 9	Claim 10
Release-promoting agent	10% to 90%	30% to 70%
Solubility-enhancing agent	1% to 80%	1% to 80%

These ranges can be valuable in litigation because they provide measurable composition limitations. They also create straightforward design-around routes if a competitor can maintain comparable performance outside the claimed ranges.

Surfactants and solubility enhancers

Claim 3 specifically covers:

Sodium docusate;
Sodium lauryl sulfate;
Sodium stearyl fumarate;
Polyethylene oxide-modified sorbitan monoesters;
Fatty-acid sorbitan esters;
Polyethylene oxide-polypropylene oxide block copolymers;
Combinations of those agents.

A product using one of these agents may face a direct claim 3 issue if the other claim 1 elements are present. A different solubilizer, such as a nonlisted complexing agent or a different pH modifier, could remain within claim 1 because claim 1 covers categories broader than the examples in claim 3.

Lubricants

Claims 11 through 13 cover conventional lubricants and waxes, including magnesium stearate, calcium stearate, zinc stearate, stearic acid, polyethylene glycol, leucine, glyceryl behenate, sodium stearyl fumarate, hydrogenated vegetable oils and waxes.

Claim 13 requires a lubricant concentration of 0.1% to 20% by weight. These claims are commercially relevant because many tablet formulations use magnesium stearate or sodium stearyl fumarate. Their practical value depends on whether the asserted product also satisfies the core formulation limitations.

Pharmacokinetic limitations

Claims 14 through 16 introduce metabolite-based performance requirements for the monohydroxy derivative of oxcarbazepine, commonly known as MHD.

The claimed targets are:

Pharmacokinetic feature	Claimed range
Steady-state MHD blood level	About 2 to 10 µg/mL
Cmax	About 6 to 10 µg/mL
Cmin	About 2 to 5 µg/mL
Objective	Minimize Cmin-to-Cmax fluctuation

These claims may create evidentiary complexity. Infringement analysis would likely require formulation testing, pharmacokinetic data or clinical data. A product can have the same composition but fall outside a claimed pharmacokinetic range in a particular patient population or dosing condition. Conversely, a product with different excipients could potentially meet the functional limitations if the claim construction treats the pharmacokinetic result as limiting.

What dosage forms and strengths are protected?

Claims 17 through 20 focus on 600 mg oxcarbazepine products.

Claim 17 covers a formulation containing 600 mg of oxcarbazepine. Claim 18 extends the formulation to pellets, tablets, granules and capsules. Claim 19 narrows the dosage form to tablets. Claim 20 requires each tablet to contain 600 mg.

The strongest product-level overlap is therefore a 600 mg once-daily tablet containing:

Oxcarbazepine;
A listed or categorically covered solubility enhancer;
A pH-dependent release-promoting polymer;
A matrix-forming polymer;
Optional lubricant and other conventional excipients.

The claims do not exclude other strengths. A 300 mg or 900 mg product could still implicate claim 1 or other dependent claims if it satisfies the relevant composition and performance limitations.

What are the principal design-around routes?

A generic or follow-on manufacturer could examine several routes.

Use a different release mechanism

A formulation based on a conventional hydrophilic matrix, osmotic system or multiparticulate system could reduce exposure to the homogeneous-matrix limitation. The risk would depend on whether the product nevertheless contains a claimed pH-dependent polymer as part of the dosage form.

Avoid the claimed pH-dependent polymer classes

A manufacturer could use a neutral or pH-independent polymer, provided the product still achieves the required release profile and does not meet the functional limitations of claims 6 through 8.

Separate the excipients physically

The word "homogeneous" creates a possible distinction between a uniform matrix and a layered, coated, reservoir or multiparticulate design. This is not an automatic safe harbor. Courts would examine the specification, prosecution history and technical meaning of "homogeneous matrix."

Use a different solubility strategy

A product could use particle-size reduction, amorphous dispersion, lipid-based solubilization or a nonclaimed excipient. Claim 1 remains broad because it includes categories such as complexing agents and pH-modifying agents, so the design-around analysis must test both the specific ingredient and the broader functional category.

Change concentration ranges

Claims 9 and 10 can potentially be avoided by using concentrations outside the stated ranges. This strategy would not avoid claim 1, which does not include those quantitative limitations.

How strong is the patent estate based on the claims?

The claims have moderate technical breadth and a mixed enforcement profile.

Strength factor	Assessment
Active ingredient limitation	Narrow; limited to oxcarbazepine
Dosage frequency	Narrow; once-daily requirement
Excipient selection	Broad because of Markush categories
Matrix limitation	Potentially important but construction-sensitive
Polymer limitation	Technically specific and comparatively easier to test
Pharmacokinetic claims	Potentially useful but evidence-intensive
600 mg tablet claims	Commercially focused
Manufacturing-process protection	Not present in the supplied claims
Broad method-of-use protection	Not present in the supplied claims
Composition-of-matter protection	Not present

The estate is more capable of blocking a particular extended-release formulation than of preventing all generic oxcarbazepine competition. Immediate-release oxcarbazepine products, different dosing schedules and formulations without the claimed pH-dependent matrix architecture occupy materially different positions.

How does the patent compare with oxcarbazepine product competition?

Trileptal and generic immediate-release oxcarbazepine

Trileptal is an immediate-release oxcarbazepine product associated with Novartis. Generic oxcarbazepine tablets and oral suspensions compete primarily on the active ingredient and immediate-release dosage form. Those products generally do not target the once-daily matrix architecture described in the supplied claims.

Oxtellar XR

Oxtellar XR is a once-daily extended-release oxcarbazepine product marketed by Supernus Pharmaceuticals. Its product profile is the closest commercial comparator because it uses extended-release technology to reduce dosing frequency and manage MHD exposure. The existence of commercial overlap does not establish infringement. A definitive comparison requires the approved product's quantitative composition, manufacturing structure, patent listings and claim construction.

Product category	Likely relevance to the '975 claims
Immediate-release oxcarbazepine tablet	Lower formulation overlap
Immediate-release oral suspension	Lower overlap
Once-daily extended-release tablet	Highest potential overlap
Multiparticulate or pellet product	Potential overlap under claim 18
Alternative controlled-release capsule	Potential overlap if homogeneous matrix limitations are met

What is the FDA and Orange Book relevance?

Oxcarbazepine is an FDA-approved antiepileptic drug. FDA approval of an extended-release product does not itself establish that every patent claim covering the product is valid or enforceable. Orange Book relevance depends on whether the patent is listed for the relevant approved product and whether the listed claims cover an approved method of use or drug product.

For a generic applicant, the principal regulatory pathway would ordinarily involve an abbreviated new drug application and a patent certification under the Hatch-Waxman framework. A Paragraph IV certification would assert that a listed patent is invalid, unenforceable or not infringed. The commercial effect would depend on the patent's listing status, the timing of certification, notice, litigation and any 30-month stay.

The supplied claim text does not establish:

Orange Book listing status;
The NDA to which the patent is linked;
Any Paragraph IV certification;
The date of a generic notice letter;
Litigation or settlement terms;
Patent-term adjustment or patent-term extension;
Current expiration date.

Those issues cannot be reliably inferred from the claims alone.

Are biosimilars relevant to US Patent 9,351,975?

No. Oxcarbazepine is a small-molecule active ingredient, not a biologic. The relevant competitive pathway is generic entry under the ANDA process, not biosimilar entry under the Biologics Price Competition and Innovation Act.

The principal regulatory questions are bioequivalence, dosage-form equivalence, labeling, patent certification and potential substitution. A follow-on product would not need to establish biosimilarity to MHD, but it would need to satisfy the applicable oxcarbazepine product requirements.

What litigation, licensing and settlement issues affect the patent?

The supplied claims contain no evidence of litigation, licensing or settlement activity. Those matters require review of court dockets, USPTO assignment records, FDA Orange Book data and publicly disclosed company agreements.

The commercially material issues would include:

Whether the patent is listed against a once-daily oxcarbazepine product;
Whether a Paragraph IV challenge has been filed;
Whether the patent owner brought an infringement action within the statutory period;
Whether a 30-month stay delayed approval;
Whether a settlement permits an authorized generic or licensee entry;
Whether the patent has been disclaimed, terminally disclaimed or held unenforceable;
Whether related continuation patents remain pending or enforceable.

Key Takeaways

US Patent 9,351,975 is directed to a once-daily oxcarbazepine formulation, not oxcarbazepine as a molecule.
Claim 1 requires a homogeneous matrix containing oxcarbazepine, a solubility enhancer and a pH-dependent release-promoting polymer.
Claims 5 through 10 add matrix polymers, pH dissolution thresholds and quantitative concentration ranges.
Claims 14 through 16 add MHD pharmacokinetic limitations that may require clinical or bioanalytical evidence.
Claims 17 through 20 focus on 600 mg dosage forms, especially tablets.
The highest infringement exposure is for a once-daily extended-release oxcarbazepine tablet using a pH-dependent polymer and solubility-enhancing excipient.
Immediate-release oxcarbazepine products and nonmatrix controlled-release designs present lower apparent overlap.
Biosimilar analysis is not relevant because oxcarbazepine is a small molecule.
The supplied claims do not establish the patent's expiration date, Orange Book status, Paragraph IV activity, litigation record, licensing arrangements or settlement terms.

FAQs

Does US Patent 9,351,975 cover all once-daily oxcarbazepine products?

No. The product must satisfy the claim limitations, including the homogeneous matrix, solubility-enhancing agent and pH-dependent release-promoting polymer.

Can a 600 mg oxcarbazepine tablet avoid the patent?

Yes, potentially. Strength alone is insufficient for infringement. The tablet would need to be assessed against the matrix structure, excipient categories, polymer identity, concentrations and any pharmacokinetic limitations.

Are Eudragit polymers covered by the patent?

Claim 1 expressly identifies Eudragit L100-55 and related methacrylic acid-ethyl acrylate or methyl acrylate-methacrylic acid copolymers. The formulation must still satisfy the remaining claim elements.

Do oxcarbazepine capsules fall within the claims?

Potentially. Claim 18 expressly includes capsules, although the capsule must satisfy the broader formulation limitations. Claim 19 and claim 20 are narrower because they focus on tablets and 600 mg tablets.

Does the patent claim a method of treating epilepsy?

The supplied claims do not. They are formulation claims. No treatment-method claim appears in the claim set provided.

References

United States Patent No. 9,351,975, claims 1-20. U.S. Patent and Trademark Office.
U.S. Food and Drug Administration. (n.d.). Orange Book: Approved drug products with therapeutic equivalence evaluations.
U.S. Food and Drug Administration. (n.d.). Oxtellar XR prescribing information. DailyMed.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Supernus Pharms	OXTELLAR XR	oxcarbazepine	TABLET, EXTENDED RELEASE;ORAL	202810-001	Oct 19, 2012	AB	RX	Yes	No	⤷ Start Trial	⤷ Start Trial	Y				⤷ Start Trial
Supernus Pharms	OXTELLAR XR	oxcarbazepine	TABLET, EXTENDED RELEASE;ORAL	202810-002	Oct 19, 2012	AB	RX	Yes	No	⤷ Start Trial	⤷ Start Trial	Y				⤷ Start Trial
Supernus Pharms	OXTELLAR XR	oxcarbazepine	TABLET, EXTENDED RELEASE;ORAL	202810-003	Oct 19, 2012	AB	RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial	Y				⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Patented / Exclusive Use	>Submissiondate

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	E496623	⤷ Start Trial
Australia	2007242984	⤷ Start Trial
Canada	2597740	⤷ Start Trial
China	101489560	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 9,351,975

Which drugs does patent 9,351,975 protect, and when does it expire?

Summary for Patent: 9,351,975