US Patent 5,626,874: Scope, Claims, Expiration, and Controlled-Release Tablet Patent Landscape

US Patent 5,626,874 covers a Geomatrix-type controlled-release tablet with a drug-containing central core, two polymeric barrier layers, and a defined exposed lateral core surface. The patent issued on May 6, 1997, and its ordinary US patent term expired in 2015. It does not create current market exclusivity, but its claim structure remains relevant to freedom-to-operate reviews involving multilayer modified-release tablets, hydrophilic matrices, erodible barriers, and enteric-coated dosage forms. [1]

What does US Patent 5,626,874 protect?

The patent protects a three-layer controlled-release tablet in which the active pharmaceutical ingredient is located in a central core. The core is sandwiched between upper and lower barrier layers. The barrier layers control drug release while leaving part of the core's lateral surface exposed.

The essential architecture under claim 1 is:

Element	Claim requirement
Dosage form	Controlled-release pharmaceutical tablet
Shape	Lenticular
Central layer	Core containing an active principle
Outer layers	Two superimposed barrier layers above and below the core
Barrier composition	Gellable and/or erodible polymeric material
Core exposure	Only the lateral surface remains exposed
Exposed surface	5% to 35% of total tablet surface
Release mechanism	Barriers limit release from the central core

The claim is directed to a physical dosage-form structure, not to a particular drug, therapeutic indication, release-time profile, or manufacturing process.

The central innovation is the combination of:

A drug-containing core;
Two polymeric barriers covering the top and bottom surfaces;
A partially exposed lateral core surface;
A lenticular tablet geometry; and
A specified exposed-surface percentage.

A tablet that merely contains a drug in a hydrophilic matrix would not fall within claim 1 unless it also has the claimed three-layer geometry and lateral exposure.

How broad is independent claim 1?

Claim 1 is broad in composition but narrow in structure.

Broad aspects

The claim does not limit:

The active ingredient;
The drug loading;
The specific polymer;
The exact release duration;
The tablet dimensions;
The identity of the manufacturer;
The therapeutic indication; or
The presence of additional excipients in the core.

The phrase "gellable and/or erodible polymeric material" covers multiple polymer classes. A competitor cannot necessarily avoid claim 1 merely by replacing one hydrophilic polymer with another if the replacement remains gellable or erodible and all structural limitations are met.

Narrow aspects

The claim requires all of the following:

A lenticular tablet;
Three over-imposed layers;
A central active-containing core;
Two barrier layers, one above and one below the core;
Lateral exposure of the core;
Exposure limited to 5% to 35% of total tablet surface.

The 5% to 35% limitation is particularly important. A fully coated core, a tablet with no exposed sidewall, or a configuration exposing more than 35% of the total tablet surface should fall outside the literal scope of claim 1, subject to any doctrine-of-equivalents analysis.

The phrase "only the lateral surface of the core" also excludes a configuration in which portions of the core are exposed through the top or bottom faces.

What do dependent claims 2 through 6 add?

Claims 2 through 6 progressively narrow the formulation and coating requirements.

What formulation is covered by claim 2?

Claim 2 adds a broad excipient Markush structure for the central core. The core may contain:

1% to 90% polymeric release-modulating substances;
Hydrophilic substances such as sorbitol, mannitol, lactose, or xylitol;
Surface-active or wetting agents; and
Hydrophobic substances such as glyceryl monostearate, hydrogenated castor oil, waxes, and substituted glycerides.

The polymer list includes hydroxypropylmethylcellulose, hydroxypropylcellulose, crosslinked polyvinylpyrrolidone, sodium carboxymethylcellulose, acrylic and methacrylic polymers, polyvinyl alcohols, glucan, scleroglucan, mannan, and related materials.

Claim 2 is formulation-oriented but remains subordinate to claim 1's tablet geometry.

What does claim 3 require?

Claim 3 narrows the core to:

10% to 45% polymeric substance by core weight;
Hydroxypropylmethylcellulose, crosslinked polyvinylpyrrolidone, sodium carboxymethylcellulose, or mixtures;
Mannitol as the hydrophilic substance; and
Hydrogenated castor oil as the hydrophobic substance.

A product must satisfy claim 1 and these additional core-composition limitations to infringe claim 3 literally.

What do claims 4 and 5 protect?

Claim 4 covers the composition of the upper and lower barrier layers. Each barrier must contain:

5% to 90% of a gellable or erodible polymer; and
One or more listed adjuvants.

The polymer list includes various grades of hydroxypropylmethylcellulose, hydroxypropylcellulose, carboxyvinyl polymers, polyvinyl alcohols, glucans, xanthans, alginic acid, polyanhydrides, polyamino acids, methyl vinyl ether/maleic anhydride copolymers, carboxymethylcellulose, ethylcellulose, and methylcellulose.

Claim 5 narrows claim 4 to barrier layers containing:

50% to 90% hydroxypropylmethylcellulose;
Apparent viscosity of 5 to 100,000 centipoise; and
An adjuvant selected from mixtures involving hydrogenated castor oil, polyvinylpyrrolidone, magnesium stearate, and colloidal silica.

The broad viscosity range makes claim 5 potentially applicable to many HPMC grades, but the product must still satisfy the core geometry and lateral-exposure requirements of claim 1.

What does claim 6 cover?

Claim 6 adds a gastroresistant, enterosoluble film that wholly coats the finished three-layer tablet.

The permitted film materials include:

Cellulose acetate phthalate;
Cellulose trimellitate;
Acrylic polymers; and
Methacrylic polymers and copolymers with pH-dependent solubility.

Claim 6 therefore covers an enteric-coated version of the claimed three-layer tablet. It is not a standalone enteric-coating claim. A product using the listed enteric film but lacking the underlying lenticular, partially exposed-core configuration would not satisfy claim 6.

When did US Patent 5,626,874 expire?

US Patent 5,626,874 issued on May 6, 1997. The US application was filed in 1995. The patent's ordinary 20-year term ran from the effective US nonprovisional filing date, resulting in expiration in 2015. Public patent records identify the patent as expired. [1]

Event	Date
US application filing	May 9, 1995
Patent issued	May 6, 1997
Expected ordinary expiration	May 9, 2015
Current enforceability	Expired

The patent therefore cannot support a new US infringement action based on acts occurring after expiration. Expiration does not eliminate its value as prior art. It may still be relevant to validity analyses for later patents and to historical technology landscaping.

What is the Orange Book status of US Patent 5,626,874?

US Patent 5,626,874 is not an active Orange Book patent in the ordinary sense because it is a platform patent that does not claim a specific approved drug product, active ingredient, dosage strength, or approved method of use.

The FDA Orange Book generally associates listed patents with an approved new drug application and its corresponding drug product. A formulation-platform patent can be relevant to an approved product only if the NDA holder submits it and the FDA accepts it for listing under the applicable regulatory categories. [2]

The patent itself does not establish:

FDA approval;
Regulatory exclusivity;
New chemical entity exclusivity;
Three-year clinical-investigation exclusivity;
Pediatric exclusivity; or
Product-specific generic-delay rights.

For a small-molecule product, the commercial impact of this patent would have depended on a separate NDA, an Orange Book listing, and the patent's unexpired term. Those conditions no longer produce current US exclusivity for this patent.

Does US Patent 5,626,874 create biosimilar risk?

No. Biosimilar litigation does not apply to this patent because it concerns a pharmaceutical tablet and not a biologic product. The relevant competitive pathway is abbreviated new drug approval under an ANDA, not a biosimilar application under the Public Health Service Act.

The patent could be relevant to a generic modified-release tablet if the reference product used the claimed geometry. A generic applicant would assess the patent under the ANDA certification framework, including whether the patent was listed, expired, or subject to a Paragraph IV certification. [3]

What Paragraph IV challenges and litigation affected the patent?

A Paragraph IV challenge is not commercially meaningful today because the patent expired in 2015. Any historical ANDA litigation would have been time-limited and product-specific.

The patent number alone does not identify:

A particular reference listed drug;
An ANDA applicant;
A notice-letter date;
A district-court case;
A settlement agreement;
A 180-day generic exclusivity event; or
A current litigation bar.

No current enforceable patent dispute can arise from US Patent 5,626,874 itself. Historical litigation, if associated with a particular product using the technology, would need to be analyzed through the relevant NDA, ANDA, complaint, docket, and settlement documents rather than through the patent record alone.

How strong was the patent estate?

The patent was strongest against products that copied the complete dosage-form architecture. Its practical strength can be ranked as follows:

Claim area	Relative scope	Main vulnerability
Claim 1: three-layer lenticular tablet	Moderate	Prior art, geometry measurement, obviousness
Claim 2: broad core excipients	Broad but dependent	Markush breadth and prior art
Claim 3: HPMC/PVP/CMC, mannitol, hydrogenated castor oil	Narrower	Easy formulation design-around
Claim 4: barrier polymers and adjuvants	Moderate	Ingredient substitutions and prior art
Claim 5: high-HPMC barrier layer	Narrow	HPMC concentration and viscosity limitations
Claim 6: enteric-coated tablet	Narrowest	Avoidance of full enteric coating or different system

The patent's principal enforcement value would have come from claim 1. Dependent claims added formulation specificity but also created more opportunities for design-around.

Potential validity challenges would focus on:

Prior art multilayer controlled-release tablets;
Known hydrophilic matrix systems;
Obvious use of HPMC or related polymers;
Predictability of release modulation through barrier thickness and exposed sidewall area;
Whether the 5% to 35% surface limitation produced an unexpected technical result;
Written-description support for the broad polymer lists; and
Definiteness of "lenticular form," "gellable," and "erodible."

The patent's expired status makes these validity questions historical rather than a current enforcement issue.

What design-arounds avoid the claims?

A product-development team could reduce literal infringement risk through several structural approaches:

Use a non-lenticular tablet shape.
Fully surround the drug core with an external barrier.
Expose no lateral core surface.
Expose less than 5% or more than 35% of the total tablet surface.
Use a single matrix tablet rather than a three-layer tablet.
Place the active ingredient in the barrier layer rather than a distinct central core.
Use a multiparticulate, coated-pellet, osmotic, capsule, or layered film system.
Use release-controlling membranes that do not qualify as gellable or erodible polymeric barriers.

A change in polymer alone may not be sufficient because claim 1 uses broad functional language. Geometry and layer arrangement are more reliable design-around levers than simple substitution of one hydrophilic polymer for another.

What licensing deals relate to the technology?

The patent is associated with the Geomatrix controlled-release technology developed by Italian pharmaceutical researchers and commercialized through entities associated with Jagotec and later SkyePharma. Geomatrix technology was licensed and incorporated into various modified-release products, but a patent-number-specific license agreement cannot be inferred from the patent record.

A commercial due-diligence review should distinguish:

Licenses to the Geomatrix platform;
Product-specific development and commercialization agreements;
Licenses to later continuation or improvement patents;
Rights to manufacturing know-how; and
Rights to trademarks, regulatory dossiers, and formulation data.

Because US Patent 5,626,874 expired, any surviving commercial value would generally lie in know-how, later patents, regulatory assets, or contractual rights rather than in this patent's exclusionary term.

What is the geographic coverage?

US Patent 5,626,874 provides rights only in the United States. Foreign counterparts, if granted, had separate terms, claim scopes, maintenance requirements, and expiration dates.

A global freedom-to-operate analysis should not treat the US expiration as dispositive for:

Europe;
Canada;
Japan;
Australia;
China;
India; or
Latin American jurisdictions.

The key questions in each country are whether a counterpart was granted, whether it remained in force, whether annuities were paid, and whether later patents claimed improvements to the same tablet architecture.

Key Takeaways

US Patent 5,626,874 claims a lenticular, three-layer controlled-release tablet.
Claim 1 requires a drug-containing central core, two polymeric barriers, and 5% to 35% lateral core exposure.
Claims 2 through 5 narrow the core and barrier compositions, with emphasis on HPMC, PVP, sodium carboxymethylcellulose, mannitol, and hydrogenated castor oil.
Claim 6 covers a fully enteric-coated version of the tablet.
The patent issued in 1997 and expired in 2015.
It does not independently provide current FDA exclusivity or biosimilar protection.
Any historical Paragraph IV or ANDA dispute would have been product-specific.
The most effective design-arounds target tablet geometry, core exposure, and layer architecture.
Current commercial value is more likely to reside in later patents, formulation know-how, regulatory assets, or licenses than in this expired patent.

FAQs

Can a generic manufacturer use the same HPMC polymer after US Patent 5,626,874 expired?

Yes. The patent's expiration removes its US patent-based exclusionary rights. Other active patents, trade secrets, regulatory restrictions, or product-specific claims could still affect commercialization.

Does a tablet need to be exactly oval to be "lenticular"?

Not necessarily. "Lenticular" generally describes a lens-shaped or biconvex configuration, but infringement would depend on the product's construction, the intrinsic patent evidence, prosecution history, and potentially expert testimony.

Does an enteric coating alone infringe claim 6?

No. Claim 6 depends on the tablet limitations in claim 1 and adds the enterosoluble coating requirement. An enteric-coated tablet without the claimed three-layer geometry should not literally satisfy claim 6.

Can a fully coated multilayer tablet infringe US Patent 5,626,874?

A fully coated tablet would face difficulty satisfying the express requirement that only the lateral surface of the core remain exposed. The risk would depend on whether the accused structure is legally equivalent to the claimed partial exposure.

Is US Patent 5,626,874 relevant to extended-release tablets approved today?

It may remain relevant as historical prior art and as evidence of the Geomatrix platform, but its expired claims do not block current US commercialization. Later patents and product-specific regulatory records require separate review.

References

United States Patent No. 5,626,874. (1997). Controlled release pharmaceutical tablets. U.S. Patent and Trademark Office.
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application submissions: Refuse-to-receive standards. FDA.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Italy	MI93A2519	Nov 30, 1993

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	207740	⤷ Start Trial
Canada	2137017	⤷ Start Trial
Germany	69428862	⤷ Start Trial
Denmark	0656204	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,626,874

Summary for Patent: 5,626,874