United States Drug Patent 4,765,989: Claim Scope, Expiration, Orange Book Status, and Patent Landscape

U.S. Patent No. 4,765,989 covers a dual-compartment osmotic oral delivery system for nifedipine, prazosin, and doxazosin. The claimed architecture uses a semipermeable wall, a drug-containing composition, a separate osmotic composition, and one or more passageways. The patent issued on August 23, 1988, and its base U.S. patent term expired on August 23, 2005, assuming no term adjustment, terminal disclaimer, or patent-term extension altered the calculation. The patent therefore has no current blocking effect on generic or follow-on products.

The principal commercial relevance is historical. The claims are directed to the type of osmotic controlled-release platform associated with products such as nifedipine extended-release tablets and doxazosin extended-release tablets. The patent should be analyzed as an expired platform patent, not as a current exclusivity barrier.

What does U.S. Patent 4,765,989 cover?

The patent covers an oral osmotic delivery device with two internal compositions that operate together to deliver a drug over time.

Claim element	Required technical feature
Semipermeable wall	Permits external fluid to enter while substantially preventing drug passage
Compartment	Encloses both internal compositions
First composition	Contains the active drug and an osmopolymer
Second composition	Contains an osmopolymer and functions as an expanding or osmotic driving composition
Passageway	Connects the drug-containing composition to the exterior
Delivery mechanism	External fluid enters through the wall, generating pressure and dispensing the drug through the passageway
Covered drugs	Nifedipine, prazosin, and doxazosin
Administration	Oral administration to an environment of use or warm-blooded animal

The central inventive concept is a bilayer or dual-composition osmotic system. The drug layer is separated from a second osmotic layer. Fluid entering through the semipermeable wall hydrates the osmotic materials. The expanding second composition urges the drug-containing composition toward the delivery passageway.

The claims do not cover every extended-release tablet containing nifedipine, prazosin, or doxazosin. They require the claimed osmotic structure and operating mechanism.

How are the 19 claims divided by drug and claim type?

Claims 1 through 5 concern nifedipine. Claims 6 through 11 concern prazosin. Claims 12 through 19 concern doxazosin.

Claims	Drug	Primary subject matter	Key narrowing features
1-2	Nifedipine	Osmotic device	Second composition; claim 2 adds an osmotically effective solute
3-5	Nifedipine	Administration and treatment methods	Plasma-level management and cardiovascular treatment
6-8	Prazosin	Osmotic device	Claim 7 covers pharmaceutically acceptable salts; claim 8 adds an osmotic solute
9-11	Prazosin	Administration and treatment methods	Plasma-level management and cardiovascular treatment
12-14	Doxazosin	Osmotic device	Claims 13-14 specify pore-based passageways and leached pores
15-19	Doxazosin	Administration and treatment methods	Cardiovascular treatment; claims 18-19 specify antihypertensive and alpha-adrenoceptor effects

The claim set contains six principal device or method groupings:

Nifedipine device claims.
Nifedipine administration and treatment claims.
Prazosin device claims.
Prazosin administration and treatment claims.
Doxazosin device claims.
Doxazosin administration and treatment claims.

The patent uses both apparatus claims and method claims. That structure broadens the historical enforcement theory because a product could potentially implicate the device claims while use of the product could implicate method claims.

What is the scope of independent claim 1 for nifedipine?

Claim 1 requires all of the following:

An oral osmotic device.
A semipermeable wall.
A compartment enclosed by that wall.
A first composition containing nifedipine and an osmopolymer.
A second composition containing an osmopolymer.
At least one passageway communicating with the first composition.
Controlled delivery of nifedipine through the passageway.

The claim is compositionally broad in that it does not specify a particular osmopolymer, wall polymer, tablet geometry, pore diameter, nifedipine dose, release duration, or manufacturing method. It is structurally limited because the device must have two compositions and the passageway must communicate with the nifedipine-containing composition.

A single-compartment nifedipine osmotic tablet lacking a separately identifiable second osmotic composition would present a weaker literal infringement case. A conventional matrix tablet, coated sustained-release tablet, reservoir system without the claimed osmotic composition, or diffusion-controlled system would generally fall outside the literal scope of claim 1.

What do claims 2 through 5 add to the nifedipine coverage?

Claim 2 narrows claim 1 by requiring the second composition to contain an osmotically effective solute. This adds a material limitation to the push or expansion layer.

Claim 3 covers a method of orally administering nifedipine to an animal. It requires:

A shaped semipermeable wall.
A nifedipine-containing first composition.
A second expanding composition.
A passageway connected to the first composition.
Fluid imbibition through the wall.
Delivery caused by the combined actions of the two compositions.

Claim 4 focuses on managing plasma levels in a patient. It requires a therapeutically effective amount of nifedipine delivered from the claimed osmotic structure.

Claim 5 covers treatment of a cardiovascular condition using the nifedipine osmotic device. The cardiovascular-treatment language is broad, but the device limitations remain central.

The method claims do not cover all oral nifedipine treatment. They require administration from an osmotic device having the specified two-composition structure.

What is the scope of the prazosin claims?

Claims 6 through 11 apply the same dual-composition osmotic architecture to prazosin.

Claim 6 requires:

A fluid-permeable and drug-impermeable wall.
A compartment.
A first composition containing prazosin and an osmopolymer.
A second composition containing an osmopolymer.
A passageway connecting the first composition with the exterior.

Claim 7 specifies that prazosin may be present as a pharmaceutically acceptable salt. Prazosin hydrochloride is the principal pharmaceutical salt associated with marketed prazosin products.

Claim 8 adds an osmotically effective compound to the second composition.

Claims 9 through 11 cover oral administration, plasma-level management, and treatment of a cardiovascular condition. As with the nifedipine method claims, the treatment claims are tethered to the claimed osmotic device. They are not standalone claims to administering ordinary immediate-release prazosin.

What is the scope of the doxazosin claims?

Claims 12 through 19 cover doxazosin in the same general osmotic platform.

Claim 12 requires:

A fluid-permeable wall.
A compartment.
A first composition containing doxazosin and an osmopolymer.
A second composition containing an osmopolymer.
A passageway connecting the exterior with the device interior.

Claim 13 narrows the passageway to at least one pore. Claim 14 further narrows the pore to one formed by leaching a material from the wall.

Claims 15 through 17 cover administration, plasma-level management, and cardiovascular treatment. Claim 18 specifies an antihypertensive effect. Claim 19 specifies an alpha-adrenoceptor antagonist effect that lowers blood pressure by reducing peripheral resistance.

The doxazosin claims are technically significant because they expressly address pore-based osmotic delivery. A device using a drilled or laser-formed orifice may satisfy claim 13 if the other limitations are met. Claim 14 is narrower because it requires a leached pore.

Which claim limitations are most important for infringement analysis?

The following limitations are likely to control a literal infringement analysis:

Two distinct internal compositions

The claims require a first drug-containing composition and a second composition containing an osmopolymer. The second composition must be more than an incidental excipient mixture if it is to satisfy the claim as construed. Its role is to generate osmotic pressure or expansion.

Semipermeable wall

The wall must admit external fluid while being substantially impermeable to the drug. A conventional enteric coating or diffusion membrane may not satisfy this limitation if it does not operate as the claimed osmotic wall.

Passageway connected to the drug composition

The passageway must communicate with the first composition or the compartment, depending on the claim. The connection requirement is important for distinguishing a bilayer osmotic pump from a system that releases drug solely by diffusion through the wall.

Osmopolymer in both compositions

The independent claims generally require an osmopolymer in the first and second compositions. A formulation with an osmotic solute but no claimed osmopolymer in the drug layer could avoid literal infringement of several claims, subject to construction and equivalents analysis.

Oral, controlled delivery

The device claims expressly concern oral administration or an environment of use. Injectable, transdermal, topical, and implantable products would not ordinarily satisfy the oral-administration limitations.

When did U.S. Patent 4,765,989 lose exclusivity?

U.S. Patent No. 4,765,989 issued August 23, 1988. For a pre-June 8, 1995 U.S. patent, the ordinary term was 17 years from grant under the transitional patent-term rules. The base expiration date was therefore August 23, 2005.[1]

Event	Date or status
U.S. patent grant	August 23, 1988
Base patent term	17 years from grant
Base expiration	August 23, 2005
Current enforceability	Expired
Current Paragraph IV blocking risk	None from this patent
Current Orange Book exclusivity value	None from this patent

Patent-term adjustment generally did not apply to patents issued under the older grant-based term in the same manner as it applies to later application-based patents. No current patent-term extension can be assumed from the supplied record. The patent is over 20 years past its base expiration date in 2025.

What is the Orange Book status of U.S. Patent 4,765,989?

The patent should not be treated as a current Orange Book barrier.

The Orange Book identifies patents submitted by sponsors for approved drug products and lists relevant patent expiration information. A patent that has expired cannot prevent FDA approval or commercial launch based on remaining patent rights. The patent number may appear in historical product-patent records or secondary databases, but any listing would have no live exclusivity effect after expiration.[2]

For an ANDA applicant today:

A Paragraph IV certification directed to this patent would have no practical blocking value.
A Paragraph III certification would be unnecessary if the patent is no longer listed as an unexpired patent.
FDA approval would not need to await the patent’s expiration because the patent already expired.
Litigation based solely on this patent would face expiration-based mootness and lack of enforceable patent rights.

FDA regulatory exclusivity and patent exclusivity are separate. The expiration of this patent does not determine whether an individual product has other regulatory exclusivities, but it removes this patent from the current patent barrier analysis.

What generic entry risks exist for nifedipine, prazosin, and doxazosin?

The direct risk from Patent 4,765,989 is zero as a current enforceability matter. Commercial risk depends on other patents, product-specific listings, formulation differences, and regulatory requirements.

Product category	Historical relevance of Patent 4,765,989	Current risk from this patent
Nifedipine osmotic extended-release	Potentially high if the product used the claimed bilayer architecture	None due to expiration
Immediate-release nifedipine	Outside the principal device scope	None
Prazosin immediate-release	Generally outside the osmotic-device claims	None
Doxazosin extended-release osmotic product	Potentially high if the device used the claimed structure	None
Non-osmotic extended-release product	Depends on structure; may avoid literal scope	None
Non-oral delivery system	Generally outside the oral claims	None

A current generic applicant would instead focus on:

Any unexpired formulation patents.
Manufacturing patents covering coating, laser drilling, membrane formation, or bilayer compression.
Product-specific Orange Book listings.
Drug-device combination requirements.
Bioequivalence and food-effect requirements for modified-release products.
Any later patents covering release profiles or commercial formulations.

How does this patent compare with formulation and method-of-use patents?

Patent 4,765,989 is primarily a drug-device and delivery-platform patent. It is not limited to a single excipient recipe, release-rate profile, or clinical indication.

Patent category	Typical protected subject matter	Relationship to Patent 4,765,989
Platform/device patent	Osmotic wall, compartments, osmopolymer layers, passageway	Direct subject of Patent 4,765,989
Formulation patent	Specific polymers, excipients, ratios, coating thickness, dose	More composition-specific
Manufacturing patent	Bilayer compression, membrane coating, pore creation, drilling	May be separate and later-expiring
Method-of-use patent	Hypertension, angina, plasma-level control, dosing schedule	Patent 4,765,989 includes broad treatment methods
Product-by-process patent	Defined manufacturing process or structural result	Potentially narrower than this patent
Regulatory exclusivity	FDA exclusivity period	Separate from patent rights

The broadest commercial value historically would have come from the device claims, particularly claims 1, 6, and 12. The method claims could have supported enforcement against commercial use, but only where the marketed device contained the required structural elements.

What formulations and delivery systems are implicated?

The claims are directed to a push-pull or bilayer osmotic design with the following functional sequence:

Gastrointestinal fluid contacts the semipermeable wall.
Fluid enters the device.
The first and second compositions hydrate.
Osmotic pressure develops across the wall.
The second composition expands or otherwise generates force.
The nifedipine, prazosin, or doxazosin composition is pushed through the passageway.
Drug release continues over a controlled period.

The claims do not require a particular polymer. Potential osmopolymer classes in historical osmotic systems include swellable hydrophilic polymers such as cellulose derivatives, polyalkylene oxides, and related water-absorbing polymers. The specific polymer selection, viscosity grade, molecular weight, membrane composition, and pore-forming agent would usually be assessed against the patent specification and prosecution history.

Claim 14’s leached-pore limitation is narrower than claims requiring only a passageway. A laser-drilled or mechanically drilled passageway may not satisfy claim 14 literally, although it could fall within claim 13 or another broader passageway claim.

Which companies were commercially associated with these technologies?

Alza Corporation was a leading developer of osmotic drug-delivery systems and commercialized the OROS platform through its own products and collaborations. Products associated with osmotic controlled-release technology included:

Nifedipine extended-release products marketed under brands such as Procardia XL and Adalat OROS.
Doxazosin extended-release products such as Cardura XL.
Other OROS products involving unrelated active ingredients.

The existence of a commercial OROS product does not, by itself, establish that Patent 4,765,989 was the sole protecting patent or that the product was covered by every claim. Commercial products commonly rely on layered patent estates, including platform, formulation, manufacturing, and product-specific patents.

Historical licensing and commercialization arrangements involving Alza and branded-drug companies may have supported product launches, but a reliable determination of whether Patent 4,765,989 itself was licensed requires the assignment records, license agreements, and litigation files. Patent ownership and product commercialization should not be inferred from branding alone.

What patent litigation and Paragraph IV challenges affect this patent?

No current Paragraph IV challenge can create a meaningful entry delay based solely on Patent 4,765,989 because the patent expired in 2005.

Historically, an ANDA applicant challenging a listed patent could have filed a Paragraph IV certification under the Hatch-Waxman framework. A timely Paragraph IV notice could trigger patent litigation and, in some circumstances, a 30-month FDA approval stay under 21 U.S.C. § 355(j)(5)(B)(iii).[3] Those mechanisms have no present blocking effect for an expired patent.

A complete historical litigation assessment would require matching the patent against:

Nifedipine extended-release ANDA litigation.
Doxazosin extended-release ANDA litigation.
Any prazosin controlled-release development program.
Declaratory-judgment actions.
Settlement agreements and launch licenses.
Federal Circuit decisions construing the claims.

The supplied claims alone do not establish that a particular generic manufacturer infringed, challenged, settled, or licensed this patent.

How strong was the patent estate, and how strong is it now?

Historical strength

The patent had meaningful historical coverage because it combined:

Specific cardiovascular drugs.
A commercially important osmotic delivery architecture.
Device claims.
Administration claims.
Plasma-level management claims.
Cardiovascular-treatment claims.
Pore-specific limitations for doxazosin.

Its principal vulnerability would have been claim construction and proof that a commercial product contained two separately functioning compositions, each with the required osmotic characteristics. Prior-art and obviousness analysis would also have been material because osmotic pumps, semipermeable membranes, osmotic solutes, and drug-delivery passageways were established technologies before the patent issued.

Current strength

The current enforceable strength is zero because the patent expired. Any remaining commercial significance is limited to:

Historical freedom-to-operate analysis.
Prior-art review.
Technology provenance.
Validity and inventorship research.
Assessment of later patents that may have built on the same platform.

What geographic coverage did the patent provide?

Patent 4,765,989 provided rights only in the United States. It did not create automatic protection in Europe, Canada, Japan, or other markets.

International protection would require separate national patents or regional filings. The U.S. patent number alone does not establish the existence, status, or expiration of foreign counterparts. Foreign patent terms and enforceability could differ because of filing dates, priority claims, prosecution delays, national-stage procedures, and maintenance requirements.

For global freedom-to-operate work, the relevant search must distinguish:

U.S. patent 4,765,989.
Continuations and divisionals.
Foreign priority applications.
PCT publications.
National-phase patents.
Later Alza or successor-owned osmotic delivery patents.

What manufacturing and intellectual-property barriers remain?

Patent 4,765,989 no longer creates a manufacturing barrier. A current manufacturer may still face technical and regulatory barriers unrelated to this patent:

Reproducible bilayer compression.
Uniform semipermeable membrane coating.
Controlled formation of the delivery orifice.
Stable drug-layer and push-layer interfaces.
Release-rate consistency across gastrointestinal pH conditions.
Food-effect control.
Dose dumping evaluation.
Bioequivalence for modified-release dosage forms.
Device performance and extractables testing.
Unexpired process or formulation patents owned by other parties.

These barriers can affect development cost and launch timing even when the principal platform patent has expired.

What is the commercial exposure from Patent 4,765,989?

There is no current revenue exposure attributable to this patent as an enforceable right. The patent cannot support a current injunction, royalty demand, Paragraph IV stay, or patent-based launch delay.

Historical exposure was potentially concentrated in:

Nifedipine extended-release osmotic products.
Doxazosin extended-release osmotic products.
Any prazosin osmotic product developed before expiration.

The patent did not independently protect the active ingredients themselves. Nifedipine, prazosin, and doxazosin were known drugs, and the patent’s economic value depended on the delivery system and commercial product implementation.

Key Takeaways

U.S. Patent 4,765,989 covers dual-composition oral osmotic devices for nifedipine, prazosin, and doxazosin.
The core structure is a semipermeable wall, drug-containing osmotic composition, separate osmotic composition, and delivery passageway.
Claims 1, 6, and 12 are the principal device claims.
Claims 3-5, 9-11, and 15-19 cover administration, plasma-level management, and cardiovascular treatment.
Claims 13 and 14 narrow doxazosin devices to pore-based and leached-pore passageways.
The patent issued August 23, 1988, and its base term expired August 23, 2005.
It presents no current Orange Book, Paragraph IV, generic-entry, litigation, or licensing barrier.
Current freedom-to-operate analysis should focus on later formulation, manufacturing, product, and modified-release patents.
U.S. rights cannot be extrapolated to foreign jurisdictions without reviewing the patent family.

FAQs

Does Patent 4,765,989 cover Procardia XL?

It may have been technically relevant to nifedipine osmotic controlled-release products, but the patent number alone does not establish that Procardia XL was covered by every claim or that it was the only relevant patent. Procardia XL product coverage could have included separate formulation, manufacturing, or product patents.

Can a generic manufacturer launch an osmotic nifedipine product without licensing this patent?

Yes, this patent expired in 2005. A generic manufacturer does not need a license to practice the expired U.S. patent, although other unexpired patents and FDA requirements may remain relevant.

Does the patent cover immediate-release prazosin hydrochloride?

No. The claims require an osmotic device with the specified semipermeable wall, two compositions, osmopolymer components, and passageway. Ordinary immediate-release prazosin hydrochloride tablets do not ordinarily meet those limitations.

Are claims 4, 5, 9, 11, 16, and 17 independent method-of-use claims?

They are method claims directed to administering the relevant drug from the specified osmotic device. Their treatment or plasma-level language does not eliminate the required device limitations.

Could a later patent still block a doxazosin osmotic product?

Yes. Patent 4,765,989 is expired, but a later patent could cover a specific doxazosin formulation, membrane, pore-forming process, manufacturing method, release profile, or commercial product configuration.

References

United States Patent and Trademark Office. (n.d.). Patent term calculator and patent term provisions. U.S. Department of Commerce.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
21 U.S.C. § 355(j)(5)(B)(iii) (2024).
United States Patent and Trademark Office. (1988). U.S. Patent No. 4,765,989.
U.S. Food and Drug Administration. (n.d.). Orange Book: Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	394944	⤷ Start Trial
Austria	397180	⤷ Start Trial
Austria	A150789	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,765,989

Summary for Patent: 4,765,989