US Patent 5,110,605: Scope, Claims, Expiration, and Patent Landscape for Polycarbophil-Alginic Acid Complexes

U.S. Patent No. 5,110,605 covers controlled-release and topical compositions formed by interacting calcium polycarbophil with alginic acid or an alginate salt in the presence of a medicinal or cosmetic active agent. Its claim scope is composition-centered, with one treatment-method claim family directed to release through skin or mucous membrane.

The patent issued on May 5, 1992. Its 17-year pre-URAA patent term expired on May 5, 2009, absent an unusual term adjustment or enforceable terminal-disclaimer issue. The patent is therefore no longer an enforceable U.S. blocking right. Its technical disclosure remains relevant to freedom-to-operate analysis because later patents may claim specific actives, dosage forms, manufacturing processes, or delivery platforms using related polymers. [1]

What does U.S. Patent 5,110,605 cover?

The patent covers a reaction complex between two polymer systems:

Calcium polycarbophil, a water-swellable and water-insoluble cross-linked carboxy-functional polymer.
Alginic acid or an alginate salt.

The complex must be formed in the presence of an active agent and at a pH of approximately 3 to 10. The active agent may be medicinal or cosmetic.

The central technical concept is an ionically and physically associated polymeric matrix intended to control the release of an incorporated active ingredient. Calcium polycarbophil supplies a cross-linked carboxyl-functional polymer network. Alginic acid or alginate supplies a second carboxylate-containing polysaccharide phase capable of interacting with calcium and the polycarbophil matrix.

The claims are not limited to one drug, therapeutic area, route of administration, or commercial product. They use broad functional categories covering cardiovascular agents, agents for internal diseases, anti-inflammatory agents, antibacterial agents, and cosmetic agents.

What are the key limitations of independent claim 1?

Claim 1 requires the following elements:

Claim element	Requirement
Composition type	A polymeric complex composition
First polymer	About 0.1% to about 90% calcium polycarbophil
Polycarbophil properties	Water-swellable, water-insoluble, fibrous, cross-linked, carboxy-functional polymer
Carboxyl content	At least about 80% of repeating units contain at least one carboxyl functionality
Cross-linking	About 0.05% to about 1.5% cross-linking agent
Cross-linker exclusion	Substantially free from polyalkenyl polyether
Second polymer	About 0.1% to about 99% alginic acid or an alginate salt
Formation conditions	Interaction at pH about 3 to 10
Active ingredient	Medicinal or cosmetic agent present during interaction
Calcium form	Calcium polycarbophil originally present as the calcium salt
Polymer-to-active ratio	About 200,000:1 to about 1:100
Product structure	A reaction complex, not merely a physical blend

The claim uses composition and process-history limitations together. The requirement that calcium polycarbophil be “originally present” in the calcium-salt form may be important in distinguishing a product made from a neutralized calcium polycarbophil starting material from a product made by subsequently exposing another polymer form to calcium ions.

The phrase “reaction complex” is also central. A product containing polycarbophil and alginate would not necessarily fall within the claim merely because both ingredients are present. The claimant would need to establish that the ingredients interacted under the claimed pH and active-agent conditions and produced the claimed complex.

The supplied text contains apparent transcription defects. Claim 1 ends with “having a calcium,” while claim 12 specifies a calcium content of 5% to 25% based on polycarbophil weight. The original patent text and prosecution history should control claim construction. [1]

How do dependent claims 2 through 11 narrow the composition scope?

Claim 2: Comminuted particles and saturated active solute

Claim 2 requires particles capable of passing through a 100-mesh U.S. Standard Sieve and an active agent present as a saturated solute in a physiologically acceptable aqueous carrier.

This limitation points toward particulate or suspension formulations. A product supplied as a larger hydrogel, film, tablet, or coated implant would not meet claim 2 unless the claimed 100-mesh particle and saturated-solute requirements were also satisfied.

Claim 3: Coated medicinally inert matrix

Claim 3 covers a three-dimensional medicinally inert matrix having at least one surface portion, with the polymeric complex disposed on that surface.

Potential embodiments include coated devices, patches, films, inserts, or other solid structures. The claim is narrower than claim 1 because it requires a matrix-plus-surface arrangement rather than a free composition.

Claims 4 through 7: Therapeutic categories

These claims identify broad classes of active agents:

Cardiovascular agents.
Agents for internal diseases and disorders.
Anti-inflammatory agents.
Antibacterial agents.

They do not identify individual molecules. The categories therefore have limited narrowing value unless the specification supplies a restricted definition or the prosecution history limits their interpretation.

Claims 8 and 9: Higher carboxyl functionality

Claims 8 and 9 increase the minimum percentage of carboxyl-containing repeating units from about 80% to at least about 90% and at least about 95%, respectively.

These limitations may distinguish more highly functionalized acrylic-acid polymers from copolymers with substantial non-carboxylated comonomer content.

Claim 10: Narrower cross-linker range

Claim 10 limits the cross-linking agent to about 0.1% to about 1% by weight. This sits within the broader claim 1 range of about 0.05% to about 1.5%.

Claim 11: Acrylic-acid functionality

Claim 11 requires the carboxyl functionality to be provided by polymerized acrylic acid. This limitation is significant because it focuses the claim on cross-linked polyacrylic-acid-type materials rather than every possible carboxy-functional polymer.

What does claim 12 cover as a method of treatment?

Claim 12 covers a controlled-release treatment method with two principal steps:

Providing the claimed polycarbophil-alginate reaction complex containing an active agent.
Contacting skin or mucous membrane with the composition for a period sufficient to release a therapeutically effective amount.

The method claim is narrower in route than claim 1. It requires contact with skin or mucous membrane. A swallowed tablet, injectable product, or purely oral gastrointestinal delivery system would not satisfy the express contact limitation unless the relevant claim interpretation treated the gastrointestinal mucosa as the claimed mucous membrane and the remaining elements were met.

Claim 12 also expressly requires calcium polycarbophil having 5% to 25% calcium content based on polycarbophil weight. That limitation is absent from the supplied version of claim 1 but should be checked against the issued patent.

Claim 13 narrows claim 12 to an intimate mixture of the reaction complex and active agent. It may be relevant where the active is blended into the complex rather than being held in a separate layer, reservoir, or coating.

How broad is the patent’s practical claim scope?

The patent has broad chemical and therapeutic coverage but narrow structural requirements.

A potentially covered product would generally need to satisfy all of the following:

A qualifying calcium polycarbophil.
The specified carboxyl functionality and cross-linking range.
Alginic acid or an alginate salt.
Formation at pH 3 to 10.
Active agent present during formation.
A qualifying reaction complex rather than a simple admixture.
The claimed polymer-to-active ratio.
For claim 12, skin or mucosal contact and controlled therapeutic release.

The broad active-agent language creates theoretical coverage across many drug classes. The main practical enforcement issue would have been proof that a commercial product contained the claimed polymer complex and had been manufactured under the claimed conditions. Analytical evidence could include polymer composition, calcium content, alginate content, swelling behavior, spectroscopic or thermal characteristics, particle size, and manufacturing records.

The patent does not claim:

A specific named drug.
A specific dosage strength.
A specific commercial brand.
A specific disease indication beyond broad categories.
A particular tablet, capsule, patch, gel, or insert unless the dependent limitations are met.
A manufacturing apparatus.
A biologic or biosimilar.
A particular release profile expressed in hours or percentage released.

When did U.S. Patent 5,110,605 lose exclusivity?

The patent issued on May 5, 1992. For a pre-URAA U.S. application, the ordinary term was 17 years from grant. On that basis, the patent expired on May 5, 2009. [1]

Event	Date or status
Patent issuance	May 5, 1992
Ordinary statutory term	17 years from grant
Expected expiration	May 5, 2009
Current enforceability	Expired
Current Paragraph IV significance	None for this patent
Current biosimilar significance	None
Orange Book exclusivity	Not established by this composition patent

Patent expiration eliminates infringement liability for activities occurring after expiration. It does not eliminate possible liability under later patents that claim a narrower formulation, a particular active agent, a manufacturing process, or a delivery device.

What is the Orange Book status of U.S. Patent 5,110,605?

U.S. Patent 5,110,605 is a broad polymer-composition and treatment-method patent rather than a patent directed to an identified FDA-approved drug product. It should not be treated as an Orange Book-listed patent merely because it concerns drug delivery.

FDA Orange Book listing generally concerns patents submitted by an NDA holder that claim the approved drug substance, drug product, or an approved method of use. A generic applicant’s Paragraph IV certification is directed to patents listed for the reference listed drug, not to every expired or technically relevant pharmaceutical patent. [2]

The patent’s expiration also removes it as a practical barrier to an ANDA launch. A product-specific Orange Book analysis would still be required for any later-approved drug using a related polycarbophil or alginate delivery system.

Are Paragraph IV challenges relevant?

No direct Paragraph IV challenge is commercially relevant to this patent today because the patent expired in 2009.

Before expiration, an ANDA applicant could have considered:

Paragraph IV invalidity arguments.
Non-infringement based on lack of reaction-complex formation.
Non-infringement based on a different polymer, calcium level, cross-linking system, pH, or polymer-to-active ratio.
A section viii statement if the relevant patent claims covered only an unapproved method of use.
A challenge based on indefiniteness, written description, enablement, anticipation, or obviousness.

A Paragraph IV notice would not revive the expired patent or create a current launch bar. Any present generic-entry analysis should focus on later, unexpired patents.

What patent landscape surrounds polycarbophil-alginate controlled release?

The surrounding landscape has four principal layers.

Foundational polycarbophil patents

Earlier patents generally concern:

Cross-linked polyacrylic acid polymers.
Water-swellable bioadhesive polymers.
Polycarbophil compositions.
Calcium-containing or neutralized forms.
Mucoadhesive and gastrointestinal delivery systems.

Those patents establish the polymer platform but are largely historical because pre-URAA patents in this field generally expired years ago.

Alginate and polysaccharide delivery patents

A separate group concerns:

Alginate gels.
Calcium-induced alginate cross-linking.
Alginate beads and microspheres.
Oral, topical, buccal, vaginal, and mucosal delivery.
Drug encapsulation and diffusion control.

These patents may claim alginate systems without requiring polycarbophil. They can remain relevant where later filings were directed to particular process conditions, particle structures, or active ingredients.

Formulation and dosage-form patents

Later patent families may claim:

Mucoadhesive tablets.
Bioadhesive films.
Topical gels.
Vaginal or rectal inserts.
Controlled-release microparticles.
Drug-loaded polymer coatings.
Specific particle sizes or hydration characteristics.
Combination systems using polyacrylic acid and alginate.

These patents present the most plausible post-2009 blocking risk because they can be filed after the original platform patent and can obtain terms extending into the 2020s or later.

Active-agent and method-of-use patents

A product incorporating the disclosed polymer complex may also implicate patents directed to:

A specific active ingredient.
A particular indication.
A dosing schedule.
A mucosal or dermal route.
A release profile.
A combination therapy.

The original patent’s broad therapeutic categories do not displace later molecule-specific or indication-specific rights.

How strong was the patent estate?

The patent was technically broad but legally vulnerable in several areas.

Issue	Assessment
Chemical breadth	Broad, because the active agent is defined generically
Polymer definition	Moderately narrow due to carboxyl content and cross-linking limits
Product identification	Potentially difficult because “reaction complex” requires structural proof
Method coverage	Narrower because claim 12 requires skin or mucous-membrane contact
Therapeutic coverage	Broad categories, but limited molecule specificity
Enforceability today	None because the patent expired
Relevance to later products	Historical platform relevance; no current blocking effect by itself

Potential validity issues would have included the breadth of the “reaction complex” limitation, the support for the full polymer and active-agent ranges, enablement across the broad active-agent categories, and whether the claimed complex was distinguishable over known polycarbophil, alginate, and calcium-cross-linked delivery systems.

The cross-linker exclusion, calcium-form requirement, pH range, and active-agent ratio provide meaningful claim limitations. They also create non-infringement pathways for products that use a different polymer architecture or form the drug-polymer system under materially different conditions.

Which companies are likely to matter in a current competitive analysis?

The original polycarbophil platform was associated with specialty polymer and pharmaceutical-material suppliers, including B.F. Goodrich and successor organizations associated with Carbopol and polycarbophil materials. Current commercial risk is more likely to arise from:

Suppliers of cross-linked polyacrylic-acid excipients.
Manufacturers of alginate drug-delivery systems.
Developers of mucoadhesive films, gels, and inserts.
Generic-drug companies using formulation-specific patents.
Specialty companies commercializing vaginal, buccal, topical, or gastrointestinal delivery products.

Supplier identity alone does not establish infringement. The analysis must compare the supplied polymer’s composition, calcium content, cross-linking agent, alginate interaction, manufacturing pH, and final dosage form against the claims of later unexpired patents.

What manufacturing and geographic barriers remain?

The expired patent does not create a U.S. manufacturing barrier. A manufacturer may use the disclosed concept in the United States without infringing Patent 5,110,605.

Manufacturing barriers may still arise from:

Proprietary grades of polycarbophil.
Control of calcium neutralization.
Reproducible alginate-polymer interaction.
Particle-size control.
Drug loading and content uniformity.
Release-rate validation.
Adhesion and residence-time performance.
Scale-up of hydrated polymer systems.
Residual monomer and extractables specifications.
GMP validation and regulatory comparability.

Geographic rights must be analyzed separately. U.S. expiration does not establish expiration in Canada, Europe, Japan, China, or other jurisdictions. Foreign counterparts may have different filing dates, prosecution outcomes, disclaimers, maintenance histories, or national-phase status. A global launch requires a country-by-country family review rather than reliance on the U.S. expiration date.

What generic launch risks exist?

For a product relying only on the technology disclosed in U.S. Patent 5,110,605, the patent itself presents no current generic-launch risk.

The relevant launch risks are:

Later patents covering the active ingredient.
Later Orange Book-listed patents for a reference product.
Formulation patents claiming a specific dosage form.
Method-of-use patents covering mucosal or dermal treatment.
Process patents covering manufacture of the complex.
Device patents covering coated matrices or delivery inserts.
Foreign patents that remain in force.
Regulatory exclusivity unrelated to patent term.

A generic applicant should not rely on the expiration of this patent as evidence that a particular commercial product is free of patent constraints. The patent is a historical platform right, not a complete product clearance.

Key Takeaways

U.S. Patent 5,110,605 covers calcium polycarbophil-alginate reaction complexes containing medicinal or cosmetic active agents.
Claim 1 is the principal composition claim and requires defined polymer composition, cross-linking, pH, calcium-salt origin, active-agent presence, and polymer-to-active ratios.
Claims 2 and 3 narrow the invention to particulate and surface-coated matrix embodiments.
Claims 4 through 7 cover broad therapeutic classes.
Claims 8 through 11 narrow carboxyl functionality, cross-linking, and acrylic-acid composition.
Claims 12 and 13 cover controlled release through skin or mucous membrane, including intimate mixtures.
The patent issued May 5, 1992 and ordinarily expired May 5, 2009.
It has no current Paragraph IV blocking effect and should not be treated as a current Orange Book barrier.
Later formulation, active-agent, method-of-use, manufacturing, device, and foreign patents remain the principal freedom-to-operate risks.
The “reaction complex” limitation would have been an important infringement and validity issue because a simple polycarbophil-alginate blend may not satisfy the claim.

FAQs

Does U.S. Patent 5,110,605 cover polycarbophil by itself?

No. The independent claims require interaction with alginic acid or an alginate salt and the presence of a medicinal or cosmetic active agent. Polycarbophil alone falls outside the express combination requirement.

Does the patent cover every alginate controlled-release formulation?

No. The claims require a qualifying calcium polycarbophil and a claimed reaction complex. An alginate formulation without the required polycarbophil structure is outside the patent’s express scope.

Can a company make a product using the disclosed polymer complex today?

In the United States, the expired patent itself does not prohibit manufacture or sale. Later unexpired patents, regulatory requirements, and foreign rights may still affect commercialization.

Is a product using polycarbophil and alginate automatically infringing?

No. Infringement would require satisfaction of every applicable claim limitation, including polymer composition, cross-linking, calcium form, pH, active-agent presence, ratio, and reaction-complex requirements.

Does the patent create biosimilar risk?

No. The claimed subject matter is a small-molecule and polymeric drug-delivery composition, not a biologic product. Biosimilar approval under the Public Health Service Act is not the relevant regulatory pathway. [3]

References

U.S. Patent No. 5,110,605. (1992). Polymeric complex compositions. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.
U.S. Food and Drug Administration. (2024). 351(k) biosimilar biological product pathway. U.S. Department of Health and Human Services.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	137404	⤷ Start Trial
Australia	8444291	⤷ Start Trial
Germany	69119217	⤷ Start Trial
Denmark	0497956	⤷ Start Trial
European Patent Office	0497956	⤷ Start Trial
Spain	2088500	⤷ Start Trial
Greece	3020502	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,110,605

Summary for Patent: 5,110,605