U.S. Drug Patent 4,327,725: Claim Scope, Expiration, Patent Landscape, and Generic Risk

U.S. Patent No. 4,327,725 covers an osmotic drug-delivery device that combines a semipermeable wall, a drug compartment, an expandable hydrogel layer, and an outlet passageway. The patent issued in 1982 and its ordinary U.S. patent term expired in 1999. It therefore does not create current U.S. exclusionary rights, block generic entry, or support a present Paragraph IV infringement claim. Its commercial importance is historical: the claims describe an early platform architecture associated with controlled-release osmotic delivery systems.

What does U.S. Patent 4,327,725 protect?

The patent protects device architecture rather than a single drug product. Its central concept is a compartmentalized osmotic device in which water crosses a semipermeable membrane, hydrates or dissolves the drug, expands a hydrogel, and forces drug formulation through a delivery passageway.

The broadest technical limitations are:

Limitation	Claim requirement
Device type	Osmotic controlled-delivery device
External environment	Aqueous fluid or biological environment
Wall	Semipermeable to exterior fluid and substantially impermeable to drug or beneficial agent
Internal structure	Drug or beneficial-agent compartment plus an expandable hydrogel layer
Outlet	Passageway connecting the drug compartment to the exterior
Operating mechanism	Fluid imbibition, drug dissolution or suspension, hydrogel swelling, and controlled expulsion
Delivery setting	Gastrointestinal tract, vagina, ano-rectal canal, or another biological environment
Covered substances	Drugs, pesticides, herbicides, germicides, fungicides, insecticides, algicides, and listed drug species

Claims 1 and 7 provide the principal platform coverage. Claim 19 addresses a different formulation condition, namely a poorly soluble drug combined with an osmotically effective solute.

How broad is independent claim 1?

Claim 1 is directed to an osmotic device for delivering a beneficial agent to a fluid environment. It requires:

A semipermeable wall.
A compartment formed by that wall.
A layer of beneficial agent that is insoluble to very soluble in the aqueous fluid.
A layer of expandable hydrogel.
A passageway communicating with the agent layer and the exterior.

The claim is broad in four respects.

First, it is not limited to pharmaceutical drugs. Claim 4 expressly extends the agent category to agricultural and antimicrobial substances.

Second, it does not require a specific membrane thickness, membrane permeability coefficient, hydrogel chemistry, device geometry, osmotic-agent concentration, dosage strength, or release duration.

Third, the claim covers a layered internal configuration rather than a narrowly defined manufacturing process.

Fourth, the claim does not expressly require the hydrogel to be cross-linked. Cross-linking is added by dependent claim 5.

The principal narrowing feature is the required combination of a semipermeable wall, an agent layer, a separate expandable hydrogel layer, and an outlet passageway. A conventional osmotic tablet that uses only a drug core and a semipermeable coating, without the claimed hydrogel layer, would not satisfy the complete literal combination of claim 1.

What does claim 7 add for pharmaceutical products?

Claim 7 is a separate independent claim focused on a beneficial drug delivered into a biological environment. It requires:

A shaped semipermeable wall.
A drug that is soluble to very soluble in the biological fluid.
An osmotic pressure gradient across the wall.
An expandable hydrogel layer in contact with the drug formulation.
A passageway through which the drug formulation is delivered over a prolonged period.

Claim 7 is more pharmaceutical-specific than claim 1 because it requires a drug and a biological environment. It also expressly requires the drug to exhibit an osmotic pressure gradient across the wall. The claim is therefore directed to drugs that can contribute materially to osmotic pumping, rather than merely being transported by an independent osmotic excipient.

Claim 8 supplies the operating sequence: fluid enters through the membrane, drug solution forms, the hydrogel expands, and the combined action delivers the solution through the outlet.

What does independent claim 19 cover?

Claim 19 addresses a formulation for drugs that are insoluble to poorly soluble in the biological fluid. It requires:

A semipermeable wall.
A drug formulation containing a poorly soluble drug.
An osmotically effective solute soluble in the exterior fluid.
A hydrogel layer contacting the drug formulation.
A passageway for controlled delivery.

This claim is technically important because it addresses a problem not fully covered by claim 7. A highly soluble drug can generate osmotic pressure directly. A poorly soluble drug generally requires a separate osmotically effective solute, such as a salt or other soluble osmagent, to drive fluid influx and formulation delivery.

The distinction between claims 7 and 19 can be summarized as follows:

Issue	Claim 7	Claim 19
Drug solubility	Soluble to very soluble	Insoluble to poorly soluble
Osmotic driver	Drug itself exhibits osmotic pressure gradient	Separate osmotically effective solute
Formulation	Drug formulation	Drug plus osmotic solute
Hydrogel	Required	Required
Biological environment	Required	Required through the claim structure and dependent claims
Commercial relevance	Soluble-drug osmotic systems	Poorly soluble-drug osmotic suspensions or dispersions

What dependent claims narrow the patent?

The dependent claims add specific materials, environments, drugs, and operating properties.

Claims	Added subject matter
2, 6, 9	Osmagent in the drug layer or formulation
3	Cellulose acylate and acetate membrane materials
4	Pesticides, herbicides, germicides, fungicides, insecticides, and algicides
5, 13	Cross-linked hydrogel
8	Fluid imbibition, drug-solution formation, hydrogel expansion, and expulsion
10	Drug present as a layer
11	Gastrointestinal delivery
12	Vaginal delivery
15	Ano-rectal delivery
14, 26	Suspending agent
16	Specific drug classes and named drugs
17, 20	Human use
18	Broad therapeutic categories
21	Oral gastrointestinal device
22	Vaginal device adapted for retention
23	Ano-rectal device
24	Hydrogel volume increase of 2 to 50 fold
25, 27	Precipitate at the hydrogel-drug formulation interface
28-40	Specific active agents

Claims 28 through 40 are species claims dependent on claim 1. They identify phenoxybenzamine, progestins, metoprolol, diclofenac, indomethacin, oxprenolol, levodopa, and valproate, among others. Spelling variations in the supplied text, such as “metaprolol” and “valporate,” do not alter the likely intended drug references, but the issued patent text controls the legal interpretation.

Are claims 20 through 27 drafted consistently?

No. Claims 20 through 27 appear to contain dependency-reference errors. They state that the device is “according to claim 17,” although several limitations concern the drug formulation and hydrogel structure introduced in claim 19.

For example:

Claim 17 depends on claim 7 and addresses use in a human.
Claim 19 is an independent claim directed to poorly soluble drugs, osmotic solutes, and hydrogel expansion.
Claims 20 through 23 refer to claim 17 but add limitations that appear conceptually related to claim 19.
Claims 24 through 27 also refer to claim 17 while reciting the hydrogel and precipitate limitations associated with claim 19.

This creates potential issues under 35 U.S.C. § 112(d), which requires a dependent claim to refer to a preceding claim and further limit that claim. The error may be treated as a drafting or prosecution-record issue if the intended dependency is clear from the specification and prosecution history. It also creates a potential validity and construction issue if a party relies on the claims as written rather than on an apparent clerical correction.

The dependency defects do not revive the patent or create current enforcement rights, but they matter when assessing historical claim scope, prosecution history, and the value of the patent as prior art.

What formulations are protected by U.S. Patent 4,327,725?

The patent reaches several formulation classes:

Soluble-drug formulations

Claims 7-18 address drugs that dissolve readily in biological fluid. The drug may be mixed with:

An osmagent.
A suspending agent.
Other formulation components consistent with delivery through the passageway.

Poorly soluble-drug formulations

Claim 19 addresses poorly soluble drugs combined with an osmotically effective solute. The hydrogel absorbs incoming fluid and swells without dissolving, helping maintain pressure and move the formulation toward the outlet.

This architecture can cover suspensions, dispersions, and other formulations in which the active ingredient is not fully dissolved in the biological fluid.

Hydrogel structures

The hydrogel limitations include:

Expandability from a rested to an expanded state.
Fluid absorption.
Swelling without dissolution.
Cross-linking.
A 2- to 50-fold increase in volume.
Formation of a precipitate at the interface between hydrogel and drug formulation.

The hydrogel is not merely an excipient. It is a functional mechanical element that contributes to delivery by swelling and displacing the drug formulation.

What membrane materials are covered?

Claim 3 lists cellulose-based membrane materials:

Cellulose acylate.
Cellulose diacylate.
Cellulose triacylate.
Cellulose acetate.
Cellulose diacetate.
Cellulose triacetate.

The claim does not require one specific cellulose derivative. A device using a different semipermeable polymer could avoid claim 3 while still potentially falling within broader claim 1 or claim 7, provided all other limitations are present.

The broad claims also require the wall to be semipermeable to exterior aqueous fluid and substantially impermeable to the drug. A membrane that allows substantial drug passage could fall outside the literal claim language, although infringement would depend on the actual permeability characteristics and claim construction.

Which drugs are expressly identified?

The patent lists the following active ingredients:

Claim	Drug or drug group
16	Metoprolol, diclofenac, oxprenolol, hydralazine, aspirin, levodopa, valproate, theophylline
28	Phenoxybenzamine
29	Norgestrel
30	Norethindone
31	Norethynodrel
32	Norgesterone
33	Norethisterone
34	Progesterone
35	Metoprolol
36	Diclofenac
37	Indomethacin
38	Oxprenolol
39	L-dopa
40	Valproate

Claim 18 separately covers therapeutic categories including cardiovascular, anticonvulsant, antiparkinson, analgesic, anti-inflammatory, hormonal, contraceptive, hypoglycemic, ophthalmic, and central nervous system drugs.

The named-drug claims are narrower than the platform claims. They would require both the specified drug and the structural limitations inherited from claim 1.

When did U.S. Patent 4,327,725 lose exclusivity?

The patent issued in 1982. For a U.S. patent subject to the pre-1995 term rule, the ordinary term was 17 years from issuance. On that basis, U.S. Patent 4,327,725 expired in 1999, approximately 17 years after issuance. The patent cannot provide current U.S. patent exclusivity.

Event	Date or period
U.S. patent issuance	1982
Statutory term applicable to the period	17 years from issuance
Ordinary U.S. expiration	1999
Current enforceability	Expired
Current Paragraph IV threat	None from this patent
Current royalty leverage	None based solely on this patent

No modern patent-term adjustment or Hatch-Waxman patent-term extension should be assumed for this 1982 device patent. A drug-delivery platform patent of this type generally does not obtain the product-specific regulatory extension available to an eligible approved drug patent under 35 U.S.C. § 156.

What is the Orange Book status of U.S. Patent 4,327,725?

The Orange Book lists patents submitted for approved drug products, including qualifying drug substance, drug product, and method-of-use patents. U.S. Patent 4,327,725 is a broad delivery-device patent rather than a patent directed to one approved drug product.

Its claims do not identify a single FDA-approved product, dosage strength, sponsor, or labeling indication. The patent therefore should not be treated as an Orange Book barrier merely because it covers controlled-release architecture. Any Orange Book analysis must be performed at the individual product level, where later formulation, dosage-form, or method-of-use patents may be listed.

An expired platform patent also cannot independently support a current 30-month stay under the Hatch-Waxman framework. A Paragraph IV notice directed only to U.S. Patent 4,327,725 would not create present litigation exposure because the patent term has ended.

How does this patent compare with later osmotic-delivery patents?

U.S. Patent 4,327,725 is an early platform patent. Later osmotic-delivery estates generally divided into narrower technical and product categories:

Patent category	Typical protected subject matter	Relationship to 4,327,725
Core osmotic device	Semipermeable wall, osmotic pressure, outlet	Broad conceptual overlap
Push-pull osmotic system	Bilayer tablet with drug layer and push layer	More specific implementation
Membrane and laser drilling	Coating composition, pore formation, passageway manufacturing	Manufacturing-focused improvement
Drug-specific dosage form	Particular active ingredient and release profile	Product-focused
Abuse-deterrent or gastroretentive system	Retention, tamper resistance, or gastrointestinal behavior	Functional improvement
Manufacturing process	Compression, coating, drilling, assembly, testing	Process barriers
Method of use	Specific dosing schedule or indication	Regulatory and label-focused

A later product may practice the general osmotic concept described in the expired patent while relying on later patents for its commercially relevant protection. Freedom to operate therefore turns on current patents covering the specific active ingredient, dosage form, membrane, manufacturing process, and labeled use.

What manufacturing and intellectual-property barriers remain?

The expiration of U.S. Patent 4,327,725 removes one historical barrier but does not eliminate all barriers to commercial development.

Potential current barriers include:

Patents on a specific controlled-release formulation.
Patents on bilayer or multilayer tablet construction.
Patents on membrane composition or coating processes.
Patents on laser-drilled or mechanically formed passageways.
Patents on drug-specific release profiles.
Patents on manufacturing equipment and process controls.
Trade secrets involving coating uniformity, hydrogel compression, and device yield.
Regulatory requirements for in vitro and in vivo release matching.
Product-specific Orange Book patents.
Method-of-use patents covering the approved labeling.

For biologics, biosimilar risk is generally irrelevant to this patent because the claims concern non-biologic osmotic devices and small-molecule or non-biologic agents. Biosimilar applicants would instead analyze biologic composition, formulation, manufacturing, and method-of-treatment patents.

Which companies may have commercial exposure?

The patent’s technology is historically associated with osmotic controlled-release systems developed by Alza Corporation and later incorporated into the broader Johnson & Johnson pharmaceutical platform. Commercial products using osmotic delivery, including certain extended-release oral products, may have relied on later patents, licenses, manufacturing know-how, or product-specific rights.

The expired patent itself does not establish that any current product infringes or that any company owes royalties. A company’s exposure must be assessed against live patents in the jurisdiction where the product is made, sold, imported, or used.

No current licensing obligation, settlement agreement, or active litigation can be inferred from the claims. Historical licensing and litigation would require review of assignment records, prosecution files, court dockets, and related patent families. The expiration of the patent ends any claim for future infringement after expiration but does not erase historical rights for conduct occurring during the enforceable term.

What generic launch scenarios exist?

For a U.S. generic or follow-on product, the principal scenarios are:

An immediate launch analysis based on the expiration of this patent. U.S. Patent 4,327,725 is not a current blocking patent.
A Paragraph IV challenge to later, live patents listed for the reference drug.
A design-around using a conventional matrix, reservoir, or non-hydrogel osmotic system.
A platform implementation that uses the expired architecture but avoids later patents covering specific membrane, formulation, passageway, or manufacturing details.
A delayed launch caused by regulatory exclusivity or live product-specific patents unrelated to this patent.

The key distinction is between freedom to practice the old platform and freedom to market a particular approved drug product. The former may be available while the latter remains restricted by later intellectual property.

How strong is the patent estate today?

The current U.S. strength of U.S. Patent 4,327,725 is zero as an enforceable exclusionary right because the patent expired in 1999. Its historical claim strength was moderate to broad at the platform level, subject to several vulnerabilities:

Functional language concerning permeability and expansion.
Potential enablement questions across broad agent and drug classes.
Ambiguity in the hydrogel and precipitate limitations.
Dependency errors in claims 20-27.
Possible prior-art challenges involving earlier osmotic pumps and controlled-release devices.
Limited commercial value of claims tied to drugs that are no longer commercially important.

Its continuing value is primarily technical and historical. It may remain relevant as prior art against later patent applications, as evidence of industry knowledge, or as a reference point for claim construction in disputes involving later osmotic systems.

Key Takeaways

U.S. Patent 4,327,725 covers a semipermeable-wall osmotic device with a drug compartment, expandable hydrogel layer, and delivery passageway.
Claims 1, 7, and 19 are the principal independent claims.
Claim 7 focuses on soluble drugs whose formulation contributes to the osmotic pressure gradient.
Claim 19 focuses on poorly soluble drugs combined with a separate osmotically effective solute.
Dependent claims cover cellulose acetate membranes, cross-linked hydrogels, suspending agents, gastrointestinal, vaginal and ano-rectal delivery, and named drugs.
Claims 20-27 contain apparent dependency-reference errors.
The patent issued in 1982 and ordinarily expired in 1999.
It has no current U.S. exclusionary force and cannot independently block a generic launch.
Current commercial risk lies in later patents covering particular drugs, formulations, dosage forms, membranes, manufacturing processes, and methods of use.
Biosimilar risk is not material because the patent concerns non-biologic osmotic delivery technology.
The patent is historically significant as a foundational osmotic-delivery platform but has no present U.S. royalty or litigation leverage by itself.

FAQs About U.S. Patent 4,327,725

Does U.S. Patent 4,327,725 cover every osmotic-release tablet?

No. It requires a specific combination of a semipermeable wall, drug or agent compartment, expandable hydrogel layer, and passageway. Osmotic systems lacking the claimed hydrogel or using a materially different architecture may fall outside the claims.

Can a company use the hydrogel osmotic design described in the patent today?

In the United States, the expired patent does not prevent use of the disclosed design. The company must still review later patents covering the specific drug, formulation, membrane, manufacturing process, or therapeutic use.

Does the patent cover OROS products sold by Alza or Johnson & Johnson?

The claims describe technology associated with osmotic delivery platforms, but the patent alone does not establish infringement by a particular product. Product coverage depends on claim construction and the product’s actual structure. Commercial products may have been protected by later patents.

Is claim 19 broader than claim 7?

No. The claims address different formulation categories. Claim 7 covers soluble to very soluble drugs that exhibit an osmotic pressure gradient. Claim 19 covers poorly soluble drugs combined with a separate osmotically effective solute. Their comparative breadth depends on the accused device and the applicable construction.

Can an expired patent still be cited against a later patent application?

Yes. An expired patent remains prior art if it qualifies under the applicable statutory prior-art provisions. Expiration removes enforceability; it does not remove the publication or disclosure from the prior-art record.

References

Alza Corporation. (1982). Osmotic device with expandable hydrogel (U.S. Patent No. 4,327,725). U.S. Patent and Trademark Office.

Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations (Orange Book). U.S. Department of Health and Human Services.

U.S. Patent and Trademark Office. (n.d.). Patent term adjustment and patent term expiration provisions. U.S. Department of Commerce.

U.S. Code. (2023). 21 U.S.C. §§ 355 and 505.

U.S. Code. (2023). 35 U.S.C. §§ 102, 112, 154, and 156.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	15606	⤷ Start Trial
Germany	3172338	⤷ Start Trial
European Patent Office	0052917	⤷ Start Trial
Japan	S5793065	⤷ Start Trial
Japan	S6043045	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,327,725

Summary for Patent: 4,327,725