United States Patent 4,576,604: Scope, Claim Construction, Expiration, and Osmotic-Drug Patent Landscape

U.S. Patent No. 4,576,604 covers an osmotic drug-delivery device that combines prolonged delivery from an internal compartment with rapid or pulsed delivery of a drug incorporated into the device wall. The patent issued to Alza Corporation on March 18, 1986, and its original 17-year patent term expired on March 18, 2003. It has no current blocking value against generic, branded, or device competitors.

The patent remains relevant as prior art for osmotic pumps, pulsatile delivery systems, multilayer pharmaceutical coatings, and dosage forms that provide an initial loading dose followed by controlled release.

What does U.S. Patent 4,576,604 protect?

The patent protects a dosage device with two separate release mechanisms:

A drug-containing internal compartment delivers drug through an osmotic passageway over an extended period.
Drug incorporated into one or more external wall layers is released rapidly, in a pulse, or before or during compartment delivery.

The central inventive concept is therefore a combined delivery profile. The device can produce an immediate or delayed pulse from the wall and a sustained release phase from the osmotic compartment.

The patent does not claim cimetidine, ranitidine, phenylpropanolamine, or another active ingredient as a composition of matter. Those drugs appear in dependent claims as possible payloads within the device.

What are the independent claims of Patent 4,576,604?

Claim 1: Broad osmotic device with drug in the wall

Claim 1 requires:

Limitation	Scope
Osmotic device	A device delivering a beneficial agent to an external environment
Wall	A substantially inert wall surrounding a compartment
Wall permeability	Permeable to environmental fluid but substantially impermeable to the compartment agent
Internal compartment	Contains a beneficial-agent formulation
Drug-containing wall	The wall itself contains a beneficial agent released during operation
Osmotic passageway	Connects the compartment to the exterior
Osmotic operation	Environmental fluid enters through the wall, creates an osmotic pressure gradient, and drives compartment contents through the passageway

Claim 1 is broad because it does not require a particular drug, dosage form, animal, anatomical site, polymer, multilayer construction, or release timing. It does require drug in the wall. A conventional osmotic tablet with drug only in the core would not meet the claim as written.

Claim 12: Drug-delivery device for biological use

Claim 12 is a second independent claim directed to a drug-delivery device for a biological environment. It adds or emphasizes:

A shaped semipermeable wall.
A drug formulation in the compartment.
A dosage amount of drug.
An osmotic pressure gradient across the wall.
A passageway that releases the formulation to the environment.

The supplied text contains a duplicated paragraph designation in claim 12. The duplication appears to be a transcription or drafting issue and does not materially alter the technical concept.

Claim 12 is narrower than claim 1 in practical scope because it focuses on a drug device for biological use and requires a dosage amount. It remains structurally broad because it does not require a specific wall architecture or specific release interval.

How do the dependent claims narrow the patent scope?

The dependent claims divide the invention into material, payload, timing, and anatomical-use limitations.

Drug-release timing

Claims 2 through 11 and 21, 25, and 26 address release sequencing:

Pulsed release from the wall.
Short-period wall release followed by prolonged compartment delivery.
Concomitant wall and compartment release.
Wall release followed by compartment delivery.
Initial release from an outer water-soluble layer, followed by release from a microporous middle layer.
Sustained delivery from the compartment over a prolonged period.

These limitations are important because the commercial value of the invention lies in its release profile, not merely in the presence of an osmotic pump.

Wall and laminate construction

The patent describes several wall configurations:

Claim	Wall structure
2	Semipermeable wall containing drug
3	Inner semipermeable lamina and outer microporous lamina containing drug
4	Inner semipermeable lamina and outer water-soluble drug-containing lamina
5	Drug in both semipermeable and water-soluble laminas
7	Inner semipermeable, middle microporous, and outer water-soluble laminas
8	Three-layer wall with drug in the middle and outer layers
27	Semipermeable and microporous laminas
32	Drug carried by a water-soluble lamina
33	Drug carried by a coating applied to the shaped wall
34	Drug carried by the microporous lamina

The claims distinguish between the semipermeable layer controlling fluid influx, a microporous layer that can provide a later pulse, and a water-soluble layer that can provide rapid initial release.

Active ingredients and payload identity

Claims 15 through 17 identify:

Cimetidine.
Ranitidine.
Phenylpropanolamine.

Claims 22 and 29 require the wall drug and compartment drug to be the same. Claims 23 and 30 permit different agents in the wall and compartment.

This permits several therapeutic designs. For example, the wall could provide an immediate dose of the same drug used in the sustained-release core, or it could provide a different agent intended to produce a separate pharmacologic effect.

Environment and route of administration

Claims 18 through 20 identify:

The gastrointestinal tract.
A human.
Oral use in a warm-blooded animal.

Claim 20 describes the operating mechanism in functional terms. The device imbibes fluid, approaches osmotic equilibrium, forms a drug solution, and releases that solution continuously through the passageway.

What is the likely claim construction of the key terms?

“Drug carried by the wall”

This limitation requires more than a drug deposited on an unrelated package or label. The drug must be incorporated into, contained by, or carried on a wall layer that releases it when the device operates.

Claim 33 expressly covers a drug-containing lamina coated onto the shaped wall. That language supports a broad interpretation encompassing multilayer coatings, provided the coating forms part of the claimed wall structure.

“Substantially inert material”

The term describes the wall material’s functional role in the device. The material must not rapidly dissolve or allow uncontrolled passage of the internal drug. It must remain sufficiently intact to regulate environmental-fluid entry and compartment-drug exit.

The term does not require chemical inactivity under every condition. The claims separately permit water-soluble and microporous external layers.

“Osmotic passageway”

The passageway is the outlet connecting the internal compartment to the environment. The claims do not require a particular hole diameter, laser-drilled opening, membrane, or geometry. A competing device could avoid literal infringement only if its outlet structure or operating mechanism falls outside the claim limitations.

“Pulsed amount” and “short period of time”

These terms describe the release pattern but are not defined numerically in the supplied claims. In an infringement analysis, the specification, prosecution history, experimental examples, and expert evidence would likely determine whether a release qualifies as a pulse or short-period release.

The absence of a numerical time limit creates both breadth and validity risk. A court would likely assess the terms in the context of the specification and the claimed therapeutic function.

What materials and formulations are protected?

Claim 14 identifies the semipermeable material as one selected from:

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

The patent also claims microporous and water-soluble laminas. The claims are therefore directed to a functional multilayer system rather than a single polymer species.

Potentially relevant formulation components include:

An osmagent in the compartment.
Drug formulation capable of generating an osmotic pressure gradient.
Semipermeable cellulose-based membranes.
Microporous external layers.
Water-soluble drug-containing coatings.
Different drugs in the external layer and internal compartment.

Claim 13 expressly requires an osmagent in the compartment. Claims 31 and 12 require or describe the osmotic pressure gradient.

When did Patent 4,576,604 lose exclusivity?

Event	Date or status
Patent issued	March 18, 1986
Applicable term	17 years from issuance under the pre-URAA term regime
Original expiration	March 18, 2003
Current enforceability	Expired
Current Orange Book exclusivity	None
Current Paragraph IV significance	None as an enforceable patent barrier

The patent predates the change to a filing-date-based patent term. Under the applicable pre-URAA rule, the patent term ran for 17 years from issuance. The patent therefore expired in 2003 under 35 U.S.C. § 154 as then applicable [2].

Any continuation, divisional, or related patent would require separate analysis. The expiration of Patent 4,576,604 does not automatically establish the expiration of every related Alza osmotic-delivery patent.

What is the Orange Book status of Patent 4,576,604?

Patent 4,576,604 is not a conventional active-ingredient, formulation, or method-of-use patent associated with a currently protected FDA-approved drug product. It claims a drug-delivery device and was issued decades before the current commercial Orange Book landscape for many extended-release products.

The patent should not be treated as a current Orange Book barrier to an ANDA. The FDA Orange Book generally lists patents submitted by an NDA holder for an approved drug product, including qualifying drug substance, drug product, and method-of-use patents. A historical device patent may be relevant to freedom-to-operate analysis but does not create current regulatory exclusivity merely because it once covered an osmotic dosage form [3].

Are there Paragraph IV challenges or generic-entry risks?

There is no current Paragraph IV risk tied to Patent 4,576,604 because the patent expired in 2003. A generic applicant does not need to certify against an expired patent as a live barrier to approval.

The historical risk profile would have been different. During the patent term, a generic or competing extended-release product using all required elements could have faced:

A patent-infringement action under 35 U.S.C. § 271(e)(2).
A Paragraph IV certification if the patent was listed for the relevant approved product.
A potential 30-month stay if statutory listing and certification requirements were satisfied.
Litigation over the meaning of “pulsed amount,” “drug carried by the wall,” and “osmotic passageway.”

Those consequences are no longer available for this patent itself.

Which companies and products are commercially relevant?

Alza Corporation is the central historical assignee associated with the patent and with osmotic drug-delivery technology. Alza later became part of Johnson & Johnson.

The patent’s architecture is related to the broader OROS family of oral osmotic systems. Commercial osmotic products have included dosage forms using semipermeable membranes, laser-drilled orifice technology, push-pull layers, and controlled-release drug compartments. Products such as Concerta and certain extended-release cardiovascular and gastrointestinal medicines rely on later patents and product-specific regulatory protection, not on the continued enforceability of Patent 4,576,604.

The claims could historically have affected a product that combined:

An oral osmotic core.
A cellulose-based semipermeable wall.
An immediate-release drug-containing coating.
A microporous or water-soluble intermediate layer.
Sustained delivery through a wall passageway.

A product using only an osmotic core without drug in the wall would present a materially different infringement position.

How strong was the patent estate?

Strengths

The patent had several strengths during its term:

Two independent claims.
Broad functional coverage of drug in the wall plus osmotic delivery from the compartment.
Coverage of single-layer and multilayer wall systems.
Same-drug and different-drug configurations.
Oral, gastrointestinal, human, and veterinary-use language.
Claims to rapid, pulsed, concomitant, and prolonged delivery patterns.

Weaknesses

The patent also had limitations:

It expired in 2003.
The claims use potentially fact-intensive terms such as “substantially inert,” “pulsed amount,” and “short period of time.”
The claims require drug in the wall, which excludes many conventional osmotic tablets.
The listed active ingredients are old and largely generic.
The patent does not claim a new chemical entity or a pharmaceutical composition independent of the device.
Later osmotic systems may differ through push-pull architecture, multilayer cores, delivery orifices, or coating chemistry.

The patent was strategically important as an early platform patent but has no remaining exclusionary force.

What manufacturing and intellectual-property barriers remain?

The expired patent does not eliminate all barriers to developing an osmotic product. Current barriers may include later patents covering:

Specific semipermeable membranes.
Laser-drilled orifice formation.
Push-pull osmotic cores.
Drug-layer and expandable-layer structures.
Tablet coating processes.
Multiparticulate osmotic systems.
Specific drugs in extended-release dosage forms.
Manufacturing controls needed to achieve reproducible release profiles.
FDA requirements for in vitro and in vivo release equivalence.

The principal current risk is therefore a later-patent freedom-to-operate issue, not infringement of Patent 4,576,604.

How does Patent 4,576,604 compare with conventional extended-release patents?

Issue	Patent 4,576,604	Conventional matrix extended-release patent
Release mechanism	Osmotic pressure through a passageway	Diffusion, erosion, or matrix swelling
Wall role	Controls fluid entry and may contain drug	Usually coating or matrix barrier
Immediate dose	Drug in wall provides pulse	Often separate immediate-release layer
Sustained dose	Internal osmotic compartment	Drug dispersed through matrix
Key structural element	Semipermeable wall plus passageway	Polymer matrix or coating
Product design	Multilayer osmotic dosage form	Matrix tablet, pellet, or coated particle
Current patent status	Expired	Depends on individual patent

Key Takeaways

U.S. Patent 4,576,604 covers an osmotic device with drug in the wall and drug formulation in an internal compartment.
Its core concept is an immediate or pulsed wall dose combined with prolonged osmotic delivery.
Claims 1 and 12 are the principal independent claims.
Dependent claims cover cellulose-based membranes, microporous and water-soluble laminas, specific drugs, oral use, and same-drug or different-drug payloads.
The patent issued on March 18, 1986, and expired on March 18, 2003.
It is not a current Orange Book or Paragraph IV barrier.
No current biosimilar issue applies because the patent claims a drug-delivery device, not a biologic.
Current commercial risk must be assessed against later osmotic-delivery, formulation, manufacturing, and product-specific patents.

Frequently Asked Questions

Does Patent 4,576,604 cover Concerta?

No. The patent expired in 2003, and Concerta relies on later product-specific technology and regulatory protection. The claims of Patent 4,576,604 are not the basis for current Concerta exclusivity.

Does the patent claim cimetidine or ranitidine itself?

No. Claims 15 and 16 identify cimetidine and ranitidine as drugs that may be used in the claimed osmotic device. They do not claim either drug as a chemical compound.

Can an osmotic tablet avoid the patent by omitting drug from the wall?

During the patent term, omission of wall-carried drug could have avoided a literal limitation of the principal claims. That issue is no longer commercially material because the patent expired.

Is Patent 4,576,604 relevant to biosimilar development?

No. Biosimilars involve biological products and biologic patent estates. This patent concerns an oral osmotic delivery device for small-molecule drugs.

What patent should be reviewed next for an osmotic drug product?

The relevant review should cover later patents directed to the specific drug, dosage form, osmotic architecture, semipermeable membrane, delivery orifice, coating process, manufacturing method, and FDA-approved product.

References

U.S. Patent No. 4,576,604. (1986). Osmotic device with pulsed delivery. United States Patent and Trademark Office. https://patents.google.com/patent/US4576604
United States Code, Title 35, § 154. (2024). Contents and term of patent; provisional rights. https://uscode.house.gov/view.xhtml?req=granuleid:USC-prelim-title35-section154
U.S. Food and Drug Administration. (2025). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	396056	⤷ Start Trial
Austria	397179	⤷ Start Trial
Austria	A150889	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,576,604

Summary for Patent: 4,576,604