US Patent 8,236,345: Scope, Expiration, Orange Book Status, and Generic Risk

US Patent 8,236,345 protects specific pharmaceutical compositions combining rosiglitazone, a thiazolidinedione antidiabetic, with metformin hydrochloride. The claims are formulation claims, not broad claims to rosiglitazone, metformin, or the treatment of diabetes. The patent covers particular carrier systems, dosage strengths, physical arrangements, and tablet or capsule configurations.

The patent’s practical exclusionary value ended when its standard patent term expired in 2020. The claims remain relevant for historical litigation, validity analysis, freedom-to-operate reviews, and assessment of the Avandamet patent estate, but they do not provide a current barrier to an otherwise lawful generic launch.

What drug does US Patent 8,236,345 cover?

The claimed thiazolidinedione is rosiglitazone, chemically identified in the claims as:

5-[4-[2-(N-methyl-N-(2-pyridyl)amino)ethoxy]benzyl]thiazolidine-2,4-dione.

The commercial rosiglitazone product associated with the combination is rosiglitazone maleate. The second active ingredient is metformin hydrochloride.

The patent therefore relates primarily to the fixed-dose combination marketed as Avandamet, which was developed by GlaxoSmithKline. It does not cover metformin monotherapy, rosiglitazone monotherapy, or every possible rosiglitazone-metformin dosage form.

Item	Patent relevance
Rosiglitazone	Required active ingredient
Metformin hydrochloride	Required active ingredient
Rosiglitazone maleate	Expressly covered by dependent claims
Rosiglitazone hydrate	Expressly covered by dependent claims
Rosiglitazone maleate hydrate	Expressly covered by dependent claims
Brand associated with combination	Avandamet
Therapeutic category	Type 2 diabetes treatment
Product type	Small-molecule fixed-dose combination
Biologic status	Not a biologic; biosimilar rules do not apply

The claim language uses “comprising,” making the composition open-ended as to additional ingredients. The carrier limitations, however, use “consists essentially of,” which narrows the permitted carrier systems to the identified excipients and components that do not materially alter the basic characteristics of the claimed dispersions.

What does independent claim 1 require?

Claim 1 requires all of the following elements:

A pharmaceutical composition.
A rosiglitazone-containing thiazolidinedione dispersion.
A first pharmaceutically acceptable carrier consisting essentially of:
- hydroxypropyl methyl cellulose;
- microcrystalline cellulose;
- sodium starch glycolate; and
- lactose.
Metformin hydrochloride.
A second pharmaceutically acceptable carrier consisting essentially of:
- polyvinylpyrrolidone; and
- hydroxypropyl methyl cellulose.

The claim requires two distinct drug-carrier dispersions. It is not enough for a product to contain rosiglitazone and metformin. A potentially infringing product must also reproduce the claimed carrier architecture or an equivalent arrangement.

The claim does not specify:

a required rosiglitazone-to-metformin ratio;
a required tablet weight;
a dissolution profile;
a release-rate limitation;
a specific manufacturing process;
a therapeutic indication;
a patient population;
a requirement for a bilayer tablet;
a requirement for maleate salt in the independent claim;
a requirement for 2 mg, 4 mg, 500 mg, or 1,000 mg strengths.

Those limitations enter through dependent claims.

How do claims 2 through 8 narrow the patent scope?

Claims 2 through 8 add active-ingredient strengths and chemical forms.

Claim	Added limitation
2	2 mg rosiglitazone
3	4 mg rosiglitazone
4	500 mg metformin hydrochloride
5	1,000 mg metformin hydrochloride
6	Rosiglitazone in maleate salt form
7	Rosiglitazone in hydrate form
8	Rosiglitazone maleate hydrate

Claims 2 and 3 do not, by themselves, require a particular metformin strength. Claims 4 and 5 do not, by themselves, require a particular rosiglitazone strength. A product can fall within multiple dependent claims when it combines the specified strengths, such as 2 mg rosiglitazone with 500 mg metformin hydrochloride.

The salt and hydrate claims are narrower than claim 1. Claim 1 covers rosiglitazone in a pharmaceutically acceptable form, while claims 6 through 8 identify specific forms.

What formulations are protected by claims 9 through 17?

Claims 9 through 17 address how the two dispersions are physically arranged in the dosage form.

Claim	Formulation limitation
9	The two dispersions are substantially in homogeneous admixture
10	The two dispersions are compacted together
11	The composition is a tablet
12	The dispersions occupy discrete zones
13	The product is a multilayer tablet with separate layers
14	The discrete zones are separated by a barrier layer
15	The barrier layer contains a filler and a lubricant
16	One zone is a compressed layer and the other is powder
17	A tablet and powder are encapsulated in a capsule

These claims create alternative formulation paths. A product may be analyzed under the homogeneous-admixture and compaction claims, or under the discrete-zone and multilayer claims. Claims 12 through 17 are directed to physically segregated configurations.

The patent therefore reaches more than a conventional single-layer blend. It covers:

homogeneous combination tablets;
compacted compositions;
multilayer tablets;
barrier-layer tablets;
tablet-and-powder capsule systems;
products with one compressed drug zone and one powder zone.

The specification and prosecution history would control the precise interpretation of “dispersion,” “discrete zones,” “barrier layer,” and “substantially in homogeneous admixture.” Those terms are important in an infringement analysis because a product may contain the same active ingredients and excipients without using the claimed spatial arrangement.

How broad is the “consists essentially of” carrier language?

The carrier limitations are commercially significant. “Consists essentially of” generally permits components that do not materially affect the basic and novel characteristics of the claimed formulation, while excluding components that materially change those characteristics.

For the first dispersion, the named carrier system includes:

hydroxypropyl methyl cellulose;
microcrystalline cellulose;
sodium starch glycolate; and
lactose.

For the second dispersion, it includes:

polyvinylpyrrolidone; and
hydroxypropyl methyl cellulose.

The claim does not necessarily exclude every conventional excipient. Lubricants, colorants, coating agents, glidants, and processing aids may be evaluated according to their role and effect. A formulation using a materially different binder, disintegrant, filler, or carrier system may avoid literal infringement even if its clinical performance is similar.

The spelling “polyvinyl pyrollidone” in the supplied claim text reflects a typographical form. The relevant excipient is conventionally known as polyvinylpyrrolidone, also called povidone.

When did US Patent 8,236,345 lose exclusivity?

The patent was granted on August 7, 2012. Its protection derived from a pharmaceutical-composition patent family claiming priority to an earlier application filed in 1999. On a standard 20-year patent-term calculation, the term ended in 2020, subject to any applicable patent-term adjustment or terminal disclaimer recorded in the patent file.[1][2]

Event	Date or period
Earliest priority period	1999
US patent grant	August 7, 2012
Standard 20-year term endpoint	2020
Current status	Expired by term
Current blocking effect	None for future generic entry

The grant date did not begin a new 20-year term. The term is generally measured from the earliest effective nonprovisional filing date in the relevant family, subject to statutory adjustments under 35 U.S.C. § 154.

Because the patent is expired, a current product cannot be blocked solely by US Patent 8,236,345. Historical damages, past sales, and conduct occurring before expiration remain legally distinct issues.

What was the Orange Book status of the patent?

The patent is associated with the Avandamet fixed-dose combination and may be evaluated against the FDA’s Orange Book records for the relevant NDA and product presentations. Orange Book listing is product-specific and depends on the NDA holder’s submission and FDA acceptance of the patent information.[3]

The relevant regulatory product was Avandamet, marketed by GlaxoSmithKline as a rosiglitazone maleate and metformin hydrochloride combination. The patent’s formulation claims were more relevant to the finished dosage form than to the active ingredients standing alone.

Regulatory question	Assessment
NDA product	Avandamet
NDA holder associated with original product	GlaxoSmithKline
Active ingredients	Rosiglitazone maleate and metformin hydrochloride
Orange Book category	Small-molecule drug patent listing, if listed for the applicable NDA
Current blocking effect	None after patent expiration
Biosimilar pathway	Not applicable
Generic pathway	ANDA pathway

An Orange Book listing would not expand the scope of the issued claims. It would identify the patent as one that an ANDA applicant might need to address while the patent remained unexpired.

Which companies challenged Avandamet patents?

Generic applicants seeking approval for rosiglitazone-metformin products could address listed patents through Paragraph IV certifications under the Hatch-Waxman Act. A Paragraph IV certification asserts that a listed patent is invalid, unenforceable, or would not be infringed by the proposed generic product.[4]

The principal litigation risk would have arisen from:

a generic applicant filing an ANDA for rosiglitazone/metformin;
a Paragraph IV notice directed to the listed combination patent;
a patent-holder suit filed within 45 days;
a potential 30-month stay of approval under 21 U.S.C. § 355(j)(5)(B)(iii).

Public patent records should be separated from commercial approval records. A company may challenge a patent without obtaining final FDA approval, and an ANDA may be approved after a patent expires without active litigation. The supplied claim set does not identify a particular challenger, litigation docket, or settlement agreement. Patent 8,236,345 is now expired, so it cannot support a new Paragraph IV-based launch delay.

What generic launch risks exist today?

The patent-specific risk is low because the claims have expired. Current generic competition would instead turn on:

FDA approval of the proposed rosiglitazone/metformin product;
compliance with the reference product’s labeling requirements;
any other unexpired formulation, method-of-use, or regulatory exclusivity rights;
manufacturing reproducibility;
bioequivalence;
supply of rosiglitazone and metformin;
product-liability and commercial considerations.

A generic manufacturer does not need to reproduce the patented formulation after expiration. Before expiration, however, a manufacturer could have designed around the claims by using a different carrier system, a different spatial arrangement, or a different dosage-form architecture.

How strong was the patent estate?

The estate was stronger as a formulation patent than as a broad combination patent.

Strength factor	Assessment
Active-ingredient breadth	Limited; claims identify rosiglitazone and metformin
Dosage-form breadth	Moderate; claims reach tablets, multilayer products, and capsules
Excipient coverage	Narrow and technically specific
Manufacturing coverage	Limited; no broad process claim is supplied
Method-of-use coverage	None in the supplied claims
Salt and hydrate coverage	Expressly included in dependent claims
Design-around potential	Material
Current enforceability	None after expiration

The patent could have complicated a generic formulation that copied the Avandamet manufacturing architecture. It did not prevent every rosiglitazone-metformin formulation. The most effective design-around options would have involved changing one or more of the following:

the carrier composition;
the use of separate versus homogeneous dispersions;
the tablet-layer structure;
the barrier layer;
the dosage form;
the active-ingredient salt or hydrate;
the compressed-layer and powder configuration.

A doctrine-of-equivalents theory could have reduced the value of a narrow design-around, but the prosecution history would be central to determining whether the patentee surrendered particular formulation alternatives.

Does the patent create biosimilar risk?

No. Rosiglitazone and metformin are synthetic small molecules. A follow-on product would proceed through the generic-drug framework, usually an ANDA, rather than the biosimilar pathway under the Public Health Service Act.

There is no biologic exclusivity period, reference-product exclusivity period, or biosimilar interchangeability issue associated with this patent. Any exclusivity analysis concerns small-molecule patent and FDA regulatory rules.

What revenue exposure was associated with the patent?

The patent protected a formulation used for a commercial combination product, but patent-specific revenue cannot be separated from total Avandamet revenue using the claim language alone. The commercial exposure would have depended on:

Avandamet prescription volume;
pricing and rebates;
rosiglitazone safety restrictions;
competition from other metformin combinations;
generic entry timing;
the commercial contribution of the 2 mg/500 mg, 2 mg/1,000 mg, 4 mg/500 mg, and 4 mg/1,000 mg presentations.

The patent’s economic value was highest before expiry, when a formulation-specific injunction or ANDA stay could delay a competing fixed-dose combination. After expiration, its value shifted to historical litigation and portfolio analysis.

Key Takeaways

US Patent 8,236,345 covers specific rosiglitazone-metformin compositions, not the active ingredients generally.
Claim 1 requires two drug-carrier dispersions with defined excipient systems.
Dependent claims cover 2 mg and 4 mg rosiglitazone, 500 mg and 1,000 mg metformin hydrochloride, maleate and hydrate forms, and multiple tablet or capsule architectures.
The patent does not contain the supplied claims for treatment methods, manufacturing methods, dissolution profiles, or release rates.
The patent’s standard term ended in 2020.
It is a small-molecule patent and has no biosimilar implications.
Historical Paragraph IV risk would have centered on ANDA applicants seeking approval for rosiglitazone/metformin products.
Current generic launch risk cannot be based on this expired patent, although other regulatory or patent rights must be assessed separately.
The strongest historical protection was against close copies of the claimed carrier system and physical dosage-form architecture.

FAQs About US Patent 8,236,345

Does US Patent 8,236,345 cover all Avandamet tablets?

No. It covers only products meeting the active-ingredient, carrier, and formulation limitations of the asserted claim. Avandamet tablets may also have been subject to other patents or regulatory requirements.

Can a generic use different excipients after the patent expired?

Yes. After expiration, the manufacturer is no longer restricted by this patent’s carrier limitations, although the product must still satisfy FDA approval and bioequivalence requirements.

Does claim 1 require rosiglitazone maleate?

No. Claim 1 requires rosiglitazone in a pharmaceutically acceptable form. Maleate, hydrate, and maleate hydrate are expressly addressed in claims 6 through 8.

Is a multilayer tablet required by the patent?

No. Claims 9 through 11 cover homogeneous or compacted arrangements and tablets. Claims 12 through 17 separately address discrete zones, multilayer tablets, barrier layers, and tablet-powder capsules.

Could a company infringe with a capsule instead of a tablet?

Potentially, if the capsule contains the claimed dispersions and satisfies the relevant limitations. Claim 17 expressly addresses a capsule containing a compressed tablet and powder, but the product would still need to meet the underlying limitations of claim 1 and the incorporated dependent claims.

References

United States Patent No. 8,236,345, Pharmaceutical compositions (issued Aug. 7, 2012).
United States Code, 35 U.S.C. § 154. Patent term and adjustment provisions.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
United States Code, 21 U.S.C. § 355(j). Abbreviated applications for new drugs and Paragraph IV certifications.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	9927119.9	Nov 16, 1999
United Kingdom	9927120.7	Nov 16, 1999
United Kingdom	0013236.5	May 31, 2000
United Kingdom	0013240.7	May 31, 2000

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
African Regional IP Organization (ARIPO)	1389	⤷ Start Trial
Argentina	030920	⤷ Start Trial
Argentina	057970	⤷ Start Trial
Austria	292466	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 8,236,345

Summary for Patent: 8,236,345