United States Patent 4,798,725: Scope, Claims, Expiration, and Sustained-Release Patent Landscape

United States Patent 4,798,725 covers an oral sustained-release capsule using a particulate mixture of an active drug, polyvinylpyrrolidone, and a carboxyvinylpolymer, with the two polymers present substantially in separate particles. The central limitation is the combination of polymer identity, quantitative ranges, and particle-level separation. The patent issued January 17, 1989, and, under the pre-Uruguay Round patent-term regime, its ordinary 17-year term would have ended January 17, 2006, absent an unusual terminal disclaimer or term adjustment. The claims are therefore expired and do not presently block generic manufacture or commercialization in the United States.

What technology does U.S. Patent 4,798,725 protect?

The patent protects a multiparticulate sustained-release capsule rather than a specific drug product.

The claimed delivery system contains:

Element	Claimed requirement
Dosage form	Oral capsule
Capsule shell	Soluble in gastrointestinal juice
Active ingredient	Weak acid, neutral drug, or weak base
First polymer	Polyvinylpyrrolidone, commonly called PVP or povidone
Second polymer	Carboxyvinylpolymer, generally corresponding to cross-linked polyacrylic acid or carbomer
Physical arrangement	PVP and carboxyvinylpolymer occur substantially entirely in separate particles
Release mechanism	Sustained release, although no numerical dissolution profile is specified

The invention is built around the interaction of two polymer populations. PVP is a water-soluble polymer that can bind or hold drug particles. The carboxyvinylpolymer is a high-molecular-weight, cross-linked swelling polymer. On exposure to gastrointestinal fluid, the carboxyvinylpolymer can hydrate and form a viscous barrier, while the PVP-containing particles contribute to drug dispersion and matrix formation.

The claims do not require a particular active pharmaceutical ingredient, dosage strength, release duration, particle size, manufacturing equipment, or dissolution specification.

How broad is claim 1 of U.S. Patent 4,798,725?

Claim 1 is the principal composition claim and is relatively broad in drug selection but narrower in formulation architecture.

It requires all of the following:

A sustained-release pharmaceutical capsule.
Oral administration.
A capsule shell soluble in gastrointestinal juice.
A particulate mixture inside the shell.
Between about 0.01% and 90% active drug.
Between about 5% and 96% PVP.
Between about 4% and 40% carboxyvinylpolymer.
The PVP and carboxyvinylpolymer must occur substantially entirely in separate particles.

The use of "comprising" makes the claim open-ended. A product may contain additional excipients, lubricants, glidants, coating materials, stabilizers, or other formulation components and still fall within the claim if every required element is present.

The quantitative limitations appear to apply to the particulate mixture. The claim does not expressly define whether percentages are weight percentages, although pharmaceutical patent drafting convention strongly suggests weight percentages. A product developer would need to evaluate the specification and prosecution history for the intended calculation basis.

What does "substantially entirely in separate particles" require?

This is the most important structural limitation.

The claim does not merely require that PVP and carboxyvinylpolymer be chemically distinct. It requires that they be distributed in separate particles for substantially the entire formulation. A formulation in which both polymers are deliberately co-granulated into the same granules may fall outside the literal claim, depending on the degree of intermixing and the prosecution history.

Potentially relevant distinctions include:

Formulation architecture	Likely claim exposure
Separate PVP particles and separate carbomer particles blended into a capsule	High
Drug-PVP granules blended with separate carbomer particles	Potentially high
PVP and carbomer co-granulated into a single composite granule	Lower literal exposure
PVP and carbomer dissolved together and spray-dried	Lower literal exposure
Carbomer-coated drug particles with no PVP	Outside claim 1
PVP-only sustained-release capsule	Outside claim 1
Carbomer-only matrix capsule	Outside claim 1
Tablet dosage form rather than capsule	Outside claim 1
Enteric capsule shell that is not soluble in gastric or gastrointestinal juice as claimed	Potentially outside claim 1

The phrase "substantially entirely" creates potential construction disputes. A court would likely examine the specification, examples, prosecution record, and evidence concerning ordinary pharmaceutical formulation practice.

What do claims 2 through 10 add?

Claims 2 through 10 narrow the composition by specifying polymer concentrations, polymer characteristics, capsule shell type, and molecular weight.

Claim	Principal limitation
2	PVP from about 10% to 70%
3	PVP from about 15% to 60%
4	Claim 2 plus carboxyvinylpolymer from about 5% to 25%
5	Claim 3 plus drug from about 10% to 70% and carboxyvinylpolymer from about 5% to 15%
6	Claim 2 plus drug from about 10% to 70% and carboxyvinylpolymer from about 7% to 10%
7	Claim 4 plus carboxyvinylpolymer molecular weight of at least about 1,250,000 and hard gelatin shell soluble in gastric juice
8	Claim 5 plus approximately 3,000,000 molecular weight cross-linked polyacrylic acid
9	Claim 6 plus the same approximately 3,000,000 molecular weight cross-linked polyacrylic acid
10	Claim 8 plus PVP molecular weight from about 7,000 to 700,000

Claims 8 and 9 identify the carboxyvinylpolymer by a technical description: polyacrylic acid cross-linked with approximately 1% polyallyl sucrose having an average of approximately 5.8 allyl groups per sucrose molecule. That description is directed to a high-molecular-weight cross-linked carbomer-type material.

The dependent claims create narrower fallback positions but do not materially expand the patent. A formulation that does not satisfy claim 1 cannot infringe claims 2 through 10.

What do process claims 11 through 14 cover?

Claims 11 through 14 cover preparation of the same type of capsule.

Claim 11 requires:

Preparing the particulate mixture.
Including the active drug, PVP, and carboxyvinylpolymer in the specified ranges.
Maintaining the PVP and carboxyvinylpolymer substantially entirely in separate particles.
Filling the particulate mixture into a gastrointestinally soluble capsule shell.

The process claims do not require a particular granulation technique, blending time, filling machine, or sequence beyond preparation of the particulate mixture followed by capsule filling.

Claims 12 through 14 narrow the process by adding concentration and polymer specifications. Claim 14 contains the term "polyvinylpyrroline," while the composition claims use "polyvinylpyrrolidone." That appears to be a drafting or transcription error. Its legal effect would depend on the issued patent text, certificate of correction, prosecution history, and how a court construes the term.

Process claim exposure generally depends on the manufacturing steps used by the accused party. A finished product may be evidence of performance of the claimed process, but product claims and process claims require separate infringement analyses.

When did U.S. Patent 4,798,725 lose exclusivity?

The patent issued on January 17, 1989. Because it was issued before June 8, 1995, its ordinary term was generally 17 years from issue under the law then in effect. The resulting ordinary expiration date was January 17, 2006.[1]

Event	Date or status
Patent issued	January 17, 1989
Ordinary statutory term	17 years from issue
Ordinary expiration	January 17, 2006
Current status	Expired
Current blocking effect	None for U.S. patent enforcement based on the expired claims

Patent term adjustment under 35 U.S.C. § 154 applies to certain USPTO delays, but the patent record must be reviewed to determine whether any adjustment existed. A terminal disclaimer could also affect term. Neither possibility changes the commercial conclusion absent a recorded extension beyond January 17, 2006.[2]

Patent expiration does not erase the technical relevance of the disclosure. It means the claimed U.S. technology is in the public domain. A later patent could still protect a particular drug, formulation, manufacturing process, particle architecture, or release profile that falls within the general concept disclosed by Patent 4,798,725.

Does U.S. Patent 4,798,725 have Orange Book or FDA exclusivity relevance?

The patent is not, by itself, an FDA regulatory exclusivity record.

The Orange Book lists patents submitted by an NDA holder for an approved drug product, including patents directed to drug substance, drug product, or method of use under the applicable FDA framework.[3] Patent 4,798,725 is drafted as a platform formulation patent. Its claims do not identify a specific active ingredient, approved brand, dosage strength, or therapeutic indication.

The likely regulatory conclusions are:

Regulatory issue	Assessment
NDA-specific patent	Not apparent from the claim language
Drug-substance patent	No
Drug-product patent	Potentially, if listed for a specific approved capsule product
Method-of-use patent	No
Orange Book listing	Cannot be inferred from the patent claims
Current Orange Book blocking effect	None if the patent is expired
Hatch-Waxman Paragraph IV relevance	No current blocking effect from an expired patent

A Paragraph IV certification is commercially relevant when an ANDA applicant challenges a listed patent that has remaining enforceable term. An expired patent cannot support the usual 30-month stay mechanism under 21 U.S.C. § 355(j)(5)(B)(iii).[4]

What generic entry risks arise from the expired patent?

The patent itself presents no current U.S. generic entry risk. The more relevant issue is whether later, unexpired patents protect a commercial product using the same PVP-carbomer architecture.

A generic applicant could still face risk from:

A later patent covering a specific active ingredient in sustained-release form.
A formulation patent covering a defined dissolution profile.
A capsule-filling or multiparticulate manufacturing process.
A patent on a specific carbomer grade or particle-size distribution.
A method-of-use patent listed in the Orange Book.
A patent covering an abuse-deterrent, chronotherapeutic, or pH-dependent release system.
Trade-secret manufacturing controls that are difficult to reverse engineer, even though they are not patent barriers.

The expired patent may be useful as prior art against later claims that attempt to monopolize the same broad combination of PVP, cross-linked polyacrylic acid, separate particles, and a soluble capsule shell.

How strong is the patent estate for this technology?

The issued patent has strong breadth at the ingredient-category level but limited breadth at the formulation-structure level.

Strengths of the claims

The drug category is broad and covers weak acids, neutral drugs, and weak bases.
The active ingredient is not limited to one chemical entity.
The claims cover both composition and manufacturing process.
The "comprising" language permits additional excipients.
The separate-particle limitation identifies a concrete physical arrangement.
The dependent claims provide narrower positions around high-molecular-weight carbomer and hard gelatin capsules.

Vulnerabilities of the claims

The PVP and carbomer combination may face obviousness attacks based on known hydrophilic binders and swelling polymers.
Sustained-release capsules and multiparticulate dosage forms were established pharmaceutical technologies before the patent issued.
The claim does not define a minimum release duration or dissolution performance.
"Substantially entirely" may be challenged as indefinite or fact-intensive.
The drug category is broad, increasing exposure to prior art involving different active ingredients.
The claimed percentage ranges are wide and overlap many conventional formulations.
The process claims may be vulnerable if the physical separation is not consistently measurable.
The claim language does not expressly define particle size, granulation status, or the analytical method for determining separate particles.

Because the patent expired, these validity issues have no current enforcement consequence. They remain relevant to assessing the patent's contribution as prior art and the validity of later patents.

What formulation patents could still block a similar product?

A later formulation patent could be enforceable even if it uses the same general polymer pair. The key distinction is claim specificity.

Potential later claim categories include:

Drug-specific sustained-release claims

A later patent may claim a particular active ingredient with PVP and carbomer at defined ratios, particle sizes, or release rates. Such a claim could be narrower than Patent 4,798,725 but commercially important for one product.

Dissolution-profile claims

Claims may specify release at one or more time points under USP dissolution conditions. A product that uses the same excipients could avoid infringement if it does not meet the claimed profile, or could infringe if the profile is expressly claimed.

Multiparticulate and granulation claims

A later patent may distinguish between:

Drug-containing PVP granules and separate carbomer granules.
Drug particles coated with PVP.
Carbomer-containing pellets.
Layered beads.
Capsule-in-capsule systems.
Particles with different release rates.

These physical distinctions are important because Patent 4,798,725 already places emphasis on separate polymer particles.

Manufacturing and scale-up claims

A later patent may cover fluid-bed granulation, dry blending, roller compaction, controlled moisture exposure, or capsule-filling conditions. Such claims may create manufacturing barriers even when the final composition is old.

Are biosimilar risks relevant to Patent 4,798,725?

No. Biosimilar competition is not relevant to this patent because the claims cover a small-molecule oral pharmaceutical capsule, not a biologic drug or biological manufacturing process.

The relevant competitive pathway is an ANDA for a generic drug, or, where no suitable reference product exists, a different FDA approval pathway such as a 505(b)(2) application. The patent does not claim a biologic, biosimilar, protein sequence, cell line, or biologic formulation.

What licensing and litigation information is associated with the patent?

The patent claims do not establish any license, assignment, settlement, or litigation agreement. Patent ownership, historical assignments, and licensing arrangements must be distinguished from the issued claim scope.

Because the patent expired in 2006:

A new license would generally have little value for excluding competitors from the claimed U.S. technology.
Historical licensing could still matter for royalty disputes, audit rights, or foreign rights.
A settlement agreement could have affected market entry during the patent term but would not restore expired U.S. patent exclusivity.
Any current dispute would more likely involve a later patent, trade secret, contract, or regulatory issue.

The patent number alone does not establish that a branded product relied on the patent or that the patent was listed in the Orange Book.

How does this patent compare with modern sustained-release patent strategies?

Patent 4,798,725 uses a platform formulation strategy. Modern patent portfolios generally divide protection across several layers:

Protection layer	Patent 4,798,725	Modern portfolio approach
Active ingredient	Broad drug categories	Specific molecule or salt
Dosage form	Capsule	Capsule, tablet, pellet, bead, implant
Excipients	PVP and carboxyvinylpolymer	Defined grades, ratios, and functional properties
Particle arrangement	Separate polymer particles	Detailed granulation and coating architecture
Performance	Sustained release, unquantified	Defined dissolution profile
Manufacturing	Mixing and capsule filling	Process parameters and scale-up controls
Use	No therapeutic indication	Disease-specific or population-specific claims
Regulatory coverage	Not inherently Orange Book-listed	NDA-linked product and method claims

The older patent is broad in concept but less precise in performance-based claiming. A modern estate would usually seek overlapping composition, process, product-by-process, dissolution, and method-of-use claims.

Key Takeaways

U.S. Patent 4,798,725 covers a sustained-release oral capsule containing an active drug, PVP, and carboxyvinylpolymer.
The central structural limitation is that PVP and carboxyvinylpolymer occur substantially entirely in separate particles.
Claims 1 through 10 cover compositions; claims 11 through 14 cover preparation and capsule filling.
The patent issued January 17, 1989, and its ordinary U.S. term expired January 17, 2006.
The expired patent does not create a current U.S. generic or Paragraph IV barrier.
The patent is not a biosimilar patent and does not claim a biologic.
Current commercial risk would arise from later drug-specific, dissolution, manufacturing, or method-of-use patents.
The patent remains relevant as prior art against later attempts to claim the same broad PVP-carbomer sustained-release architecture.

FAQs About U.S. Patent 4,798,725

Can a generic manufacturer use PVP and carbomer in a sustained-release capsule today?

Yes, the expired U.S. patent does not prevent use of the claimed formulation concept. A generic manufacturer must still assess later patents, FDA requirements, product-specific Orange Book listings, and non-patent regulatory barriers.

Does Patent 4,798,725 cover Carbopol?

The claims use "carboxyvinylpolymer." Claims 8, 9, and 14 describe a high-molecular-weight cross-linked polyacrylic acid consistent with certain carbomer-type materials. Product-specific infringement would depend on the identity and properties of the material used.

Does the patent cover tablets containing the same polymers?

No. The asserted composition claims require a capsule, and the process claims require filling the particulate mixture into a capsule shell soluble in gastrointestinal juice.

Could a formulation avoid the patent by co-granulating PVP and carbomer?

Co-granulation may avoid the literal separate-particle limitation, but the outcome would depend on the actual microstructure, claim construction, equivalents doctrine, and the patent's prosecution history. Because the patent is expired, this is primarily a historical or prior-art issue in the United States.

Is the patent relevant to an FDA 505(b)(2) application?

It may be relevant as historical prior art or background technology, but the expired patent does not independently prevent approval. A 505(b)(2) applicant must evaluate current patents, exclusivity, reference-product requirements, and any product-specific regulatory obligations.

References

United States Patent and Trademark Office. (1989). United States Patent No. 4,798,725.
35 U.S.C. §§ 154, 156.
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations, 43rd ed.
21 U.S.C. § 355(j); 21 C.F.R. §§ 314.94, 314.107.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	398165	⤷ Start Trial
Austria	A151587	⤷ Start Trial
Australia	589866	⤷ Start Trial
Australia	7421287	⤷ Start Trial
Canada	1295247	⤷ Start Trial
Germany	3772269	⤷ Start Trial
Denmark	306587	⤷ Start Trial
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Details for Patent: 4,798,725

Summary for Patent: 4,798,725