United States Drug Patent 5,912,013: Carbamazepine Pellet Claims, Patent Scope, and Generic Entry Analysis

U.S. Patent No. 5,912,013 covers carbamazepine pharmaceutical compositions built around high-drug-load, mechanically robust pellets. The core limitations are at least 70 wt.% carbamazepine and approximately 5 wt.% polyvinylpyrrolidone, or PVP, used as a binder. Separate claim branches address conventional, sustained-release, and enteric-release pellets.

The patent issued on June 15, 1999. Its ordinary U.S. patent term ended in 2016, subject to any applicable patent-term adjustment or extension. The patent therefore does not create a current U.S. blocking right against generic carbamazepine products. Its historical value is primarily as a formulation patent and as a reference point for later carbamazepine pellet, multiparticulate, controlled-release, and enteric-coating patents.

What does U.S. Patent 5,912,013 protect?

The patent protects a composition containing a robust carbamazepine pellet with a high active-drug concentration and PVP binder.

Claim element	Requirement
Dosage form	Pharmaceutical composition
Physical structure	Robust pellet
Active ingredient	Carbamazepine
Carbamazepine concentration	At least 70 wt.% of the pellet
Binder	Polyvinylpyrrolidone
Binder concentration	About 5 wt.%
Release profile	Unspecified in claim 1; sustained release in claim 2; enteric release in claim 3
Molecular-weight limitation	At least 100,000 number-average molecular weight in claims 4, 5 and 8
Coating limitation	About 1% to about 25% w/w in claims 6 and 9
Narrow coating range	About 10% to about 20% w/w in claims 7 and 10

The claims use the transitional term “comprising.” That generally permits additional excipients, coatings, release-control agents, pigments, lubricants, plasticizers and other formulation components, provided the claimed elements remain present.

How many independent claims does Patent 5,912,013 have?

Claims 1, 2 and 3 are the principal independent claims.

Claim 1: general carbamazepine pellet

Claim 1 requires a robust pellet containing:

At least 70 wt.% carbamazepine; and
Approximately 5 wt.% high-number-average-molecular-weight PVP binder.

The claim does not expressly require sustained release or enteric release. A product with an immediate or otherwise unspecified release profile could fall within claim 1 if the pellet, drug loading and PVP limitations are met.

Claim 2: sustained-release pellet

Claim 2 adds a sustained-release limitation to the claim 1 formulation architecture. A potentially infringing product would need to contain a carbamazepine pellet that is both mechanically robust and designed to release carbamazepine over an extended period.

The claim does not specify a particular release-control polymer, coating thickness, dissolution curve or release-time window. That broadens the possible formulation coverage but creates evidence issues concerning whether a product is legally “sustained release.”

Claim 3: enteric-release pellet

Claim 3 covers an enteric-release robust pellet with at least 70 wt.% carbamazepine and approximately 5 wt.% PVP. The claim requires an enteric function but does not specify a particular enteric polymer or pH threshold in the text provided.

Potential enteric coating materials could include methacrylic acid copolymers, cellulose acetate phthalate, hypromellose phthalate or related pH-dependent polymers. The specific specification and prosecution history would control how broadly “enteric release” and “robust pellet” are construed.

What formulation parameters are protected?

The patent’s strongest technical limitations are the combination of drug loading, binder concentration and pellet integrity.

High carbamazepine loading

The minimum 70 wt.% carbamazepine limitation excludes many lower-loading multiparticulate systems. It is commercially relevant because carbamazepine is a poorly water-soluble drug and pellet manufacturers may need to balance drug loading against:

Pellet strength;
Granulation behavior;
Spheronization performance;
Dissolution control;
Dose uniformity; and
Coating durability.

A product containing 69 wt.% carbamazepine would not literally satisfy the “at least 70 wt.%” limitation, although the doctrine of equivalents could have been relevant during the patent’s enforceable period.

PVP binder

PVP is not merely an incidental excipient under these claims. It is recited as the binder and is present at approximately 5 wt.%. The dependent claims narrow the molecular-weight requirement to at least 100,000 number-average molecular weight.

The specification would be important in determining whether “high number average molecular weight” has a defined technical meaning, whether a particular commercial PVP grade falls within the claim, and whether molecular weight is measured by a specified method.

Robustness

“Robust pellet” is a functional or qualitative limitation. Relevant evidence could include:

Friability;
Crushing strength;
Attrition during coating;
Resistance to mechanical handling;
Pellet fracture rates;
Sphericity and surface quality; and
Stability during packaging and transport.

The term may be enforceable if the specification provides a sufficiently clear meaning or test. It could also be a vulnerability if the patent does not establish objective boundaries for robustness.

What do the dependent claims add?

Claim	Added limitation
4	Claim 1 PVP has number-average molecular weight of at least 100,000
5	Claim 2 PVP has number-average molecular weight of at least 100,000
6	Claim 2 includes coating material at about 1% to about 25% w/w
7	Claim 6 coating narrowed to about 10% to about 20% w/w
8	Claim 2 PVP has number-average molecular weight of at least 100,000
9	Claim 3 includes coating material at about 1% to about 25% w/w
10	Claim 9 coating narrowed to about 10% to about 20% w/w

Claims 5 and 8 appear substantively duplicative based on the supplied claim text. That may reflect an issued-claim structure, a transcription issue or parallel dependent-claim drafting. The duplicate limitation does not materially expand the scope beyond the sustained-release branch.

Claims 6 and 9 are important because coating weight is measured against the relevant composition or pellet basis. The specification and prosecution history would determine whether “coating material” refers to dry coating solids, total applied coating dispersion or final pellet weight.

When did Patent 5,912,013 lose exclusivity?

The patent’s ordinary U.S. term ended in 2016. Patent term for a post-1995 U.S. utility patent generally runs 20 years from the earliest effective nonprovisional filing date, subject to patent-term adjustment, terminal disclaimers and any applicable extension under 35 U.S.C. § 156.

Event	Date or period
Patent issued	June 15, 1999
Ordinary patent-term endpoint	2016
Current enforceability	No ordinary patent exclusivity remains
Current generic blocking effect	None from Patent 5,912,013 alone
Possible historical use	Formulation patent listed or asserted during the pre-2016 period

The patent should not be treated as a live barrier to a 2026 U.S. generic launch. A current product may still face other active patents, regulatory exclusivity, manufacturing patents or contractual restrictions, but those rights would need to be analyzed separately.

What was the likely Orange Book significance?

The patent claims a small-molecule dosage-form composition rather than a new active ingredient. If it was listed in the Orange Book against a carbamazepine reference product, its relevance would have been limited to products matching the listed dosage form and formulation scope.

Orange Book patent listing does not itself establish infringement. It identifies patents submitted by the NDA holder or applicant as claiming the drug, formulation or approved method of use. The legal effect of an Orange Book listing historically included a potential 30-month stay after a Paragraph IV notice, subject to statutory requirements and litigation timing.[1]

For current regulatory analysis:

Patent 5,912,013 is expired.
A Paragraph IV challenge directed only to this patent would not delay approval on the basis of a live patent right.
The FDA may retain historical listing information even after patent expiration.
An ANDA applicant would still need to address any other unexpired Orange Book-listed patents.

The patent is not a biologic patent and does not create biosimilar exclusivity. Carbamazepine is a chemically synthesized small molecule regulated through the ANDA pathway under section 505(j) of the Federal Food, Drug, and Cosmetic Act.

What Paragraph IV challenges and litigation affected the patent?

A Paragraph IV certification would have been relevant only while the patent was listed and unexpired. A generic applicant could certify that:

The patent was not infringed;
The patent was invalid; or
The patent was unenforceable.

The supplied claims present several potential historical challenge theories:

Non-infringement

A generic manufacturer could design around the claims by using:

Less than 70 wt.% carbamazepine;
A binder other than PVP;
PVP at a materially different concentration;
Lower-molecular-weight PVP;
A non-pellet dosage form;
A non-robust granule or tablet;
A release profile outside the sustained-release or enteric-release limitation; or
A coating system outside the claimed coating ranges.

Invalidity

Potential validity issues would have included:

Anticipation by earlier carbamazepine pellet formulations;
Obviousness based on known carbamazepine, PVP and pelletization techniques;
Indefiniteness of “robust pellet,” “high number average molecular weight” or “about 5 wt.%”;
Lack of written description for the full breadth of sustained-release and enteric-release embodiments; and
Enablement across all formulations satisfying the broad composition language.

A complete litigation history requires the USPTO Patent Center, PACER, CourtListener and FDA Orange Book records. The patent number alone does not establish that a particular ANDA litigation or settlement involved this patent. No current litigation right remains based solely on the expired patent.

How strong is the patent estate?

The patent had moderate historical formulation coverage but limited present-day value.

Factor	Assessment
Core technical concept	High-drug-load carbamazepine pellets with PVP binder
Claim breadth	Moderate
Independent claim count	Three
Release profiles covered	General, sustained release and enteric release
Numerical limitations	Significant; 70 wt.% carbamazepine and about 5 wt.% PVP
Product-specific limitations	Limited in the supplied claims
Manufacturing coverage	Limited; claims are composition-focused
Coating coverage	Present in dependent claims
Current enforceability	None after ordinary expiration
Design-around potential	Meaningful
Biosimilar relevance	None

The patent does not expressly claim a manufacturing process, extrusion-spheronization sequence, specific coating polymer, dissolution profile, capsule configuration, tablet assembly or commercial brand. That limits its ability to block technically distinct products.

Its strongest historical position would have been against a product deliberately using the same architecture: high-load carbamazepine cores, approximately 5% high-molecular-weight PVP, and a sustained-release or enteric coating.

What manufacturing and intellectual-property barriers remain?

Patent 5,912,013 is no longer the principal barrier. Current barriers are more likely to arise from manufacturing performance and other rights.

Manufacturing barriers

Carbamazepine multiparticulates can present practical problems involving:

Poor aqueous solubility;
Polymorphism and crystallinity;
Dose uniformity at high drug loading;
Pellet fracture during coating;
Drug migration into coating layers;
Release-rate variability;
Scale-up from laboratory spheronization to commercial equipment; and
Stability under humidity and temperature stress.

These issues can support separate process, equipment or formulation patents even when the 5,912,013 claims have expired.

Potential surrounding patent categories

A current freedom-to-operate review should separate this expired patent from:

Modified-release carbamazepine formulations;
Controlled-release capsules containing multiple pellet populations;
Enteric-coated carbamazepine particles;
Taste-masked or orally disintegrating formulations;
Carbamazepine polymorph and particle-size patents;
Manufacturing methods for extrusion and spheronization;
Dissolution-control coatings;
Combination products containing carbamazepine; and
Patents covering specific reference products.

Those categories may have different owners, filing dates and expiration dates. They should not be treated as part of Patent 5,912,013 without claim-level evidence.

How does Patent 5,912,013 compare with a modern generic formulation?

Issue	Patent 5,912,013	Modern design-around strategy
Drug loading	At least 70 wt.%	Use lower loading or establish a different measured basis
Binder	PVP	Use hydroxypropyl cellulose, hypromellose or another binder
PVP level	About 5 wt.%	Move outside the construed “about” range
PVP molecular weight	At least 100,000 in dependent claims	Use lower molecular weight or a different polymer
Dosage form	Robust pellet	Use granules, matrix tablets or a different multiparticulate structure
Release	Sustained or enteric in separate claims	Use another release mechanism or profile
Coating	About 1% to 25% w/w in dependent claims	Use a different coating basis or amount
Current legal risk	Expired patent	Focus on other unexpired patents and regulatory requirements

Key Takeaways

U.S. Patent 5,912,013 covers carbamazepine pellets containing at least 70 wt.% carbamazepine and approximately 5 wt.% PVP binder.
Claims 1, 2 and 3 cover general, sustained-release and enteric-release pellet compositions.
Dependent claims add PVP molecular weight of at least 100,000 and specified coating-weight ranges.
The claims are composition claims, not broad manufacturing-process claims.
“Robust pellet,” “about 5 wt.%,” and “high number average molecular weight” would have been central claim-construction issues.
The patent’s ordinary U.S. term ended in 2016.
The patent does not create a current generic-entry block or biosimilar barrier.
Historical Paragraph IV risk would have focused on anticipation, obviousness, indefiniteness and non-infringement.
Current carbamazepine freedom-to-operate risk must be assessed against later formulation, manufacturing, release-control and product-specific patents.

FAQs

Is U.S. Patent 5,912,013 still enforceable?

No. Its ordinary U.S. patent term ended in 2016, subject to any recorded term adjustment or extension.

Does Patent 5,912,013 cover Tegretol XR?

The claims could be relevant to a sustained-release carbamazepine product if its pellets satisfy every claimed limitation. The patent number alone does not establish that it covers or was listed against Tegretol XR.

Can a generic use PVP in a carbamazepine pellet?

Yes. Because Patent 5,912,013 is expired, the patent no longer blocks PVP use. A current product must still be evaluated against later unexpired patents and regulatory requirements.

Does the patent cover carbamazepine tablets?

Not by the supplied claims alone. The claims require a pellet. A tablet containing no claimed pellet structure would generally fall outside the literal scope of these claims.

Is a carbamazepine product with 70% drug loading automatically covered?

No. It must also contain the required PVP binder at the claimed concentration and satisfy the relevant pellet, robustness and release-profile limitations.

References

U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA.
United States Patent and Trademark Office. (1999). U.S. Patent No. 5,912,013. U.S. Department of Commerce.
U.S. Food and Drug Administration. (n.d.). Abbreviated new drug application submissions: Patent certifications and 30-month stays. FDA.
United States Code, 35 U.S.C. § 154. Patent term.
United States Code, 35 U.S.C. § 156. Extension of patent term.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	185268	⤷ Start Trial
Canada	2114014	⤷ Start Trial
Germany	69230112	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,912,013

Summary for Patent: 5,912,013