United States Drug Patent 6,395,292: Claim Scope, Expiration, and Patent Landscape

U.S. Patent No. 6,395,292 protects components and operating configurations of an implantable, fluid-imbibing drug-delivery system, particularly a DUROS-type osmotic implant for sustained leuprolide delivery. Its broadest claim concepts cover a water-swellable semipermeable plug, an impermeable reservoir, titanium drug-contact surfaces, controlled start-up, injection-molded plug manufacture, and one-year delivery of leuprolide.

The patent is primarily a device and drug-delivery patent. It does not claim leuprolide as a molecule. Its commercial relevance was tied to the Viadur leuprolide implant and related ALZA osmotic-implant technology. The patent’s statutory term has ended, eliminating current U.S. blocking rights under this patent.

What does U.S. Patent 6,395,292 cover?

The patent covers an implantable osmotic delivery platform in which water enters through a swellable semipermeable plug. The swelling material generates force against an active-agent reservoir and displaces the drug formulation through an outlet.

The principal claim elements are:

Claim group	Protected subject matter	Commercial significance
Claims 1-11	Fluid-imbibing device with a swellable semipermeable plug and impermeable reservoir	Covers the basic osmotic pumping architecture
Claims 12-15	Titanium or titanium-alloy reservoir isolating the drug from the environment	Protects drug-compatible implant construction
Claim 16	Implant with start-up time below 10% of the administration period	Protects rapid attainment of operating delivery
Claims 17-20	Injection molding of the semipermeable plug into the reservoir	Covers a manufacturing route
Claims 21-22	Reducing testosterone to castrate levels with an LHRH agonist or antagonist, including leuprolide	Method-of-use coverage
Claims 23-38	Specific one-year leuprolide implant configuration	Covers the Viadur-type product architecture
Claims 39-48	Semipermeable plug and selection of plug material to control delivery rate	Covers component-level and process-level variations

The claims combine structural limitations with performance limitations. A potentially infringing product would generally need to satisfy the relevant structural limitations and, for certain claims, the specified delivery behavior.

How broad are the independent claims?

The independent claims fall into five distinct categories.

Claims 1 and 12: implant structure

Claim 1 requires:

A fluid-imbibing device.
An active agent.
An impermeable reservoir.
A water-swellable semipermeable material.
The material received in sealing relationship with the interior surface of one end of the reservoir.
Active agent displaced when the material swells.

This claim is broad at the platform level. It is not limited to leuprolide, a particular reservoir metal, a particular outlet, or a one-year treatment period. Claims 2-11 narrow the platform by specifying plug materials, dimensions, assembly configurations, active agents, and remote delivery.

Claim 12 takes a different approach. It requires a reservoir that effectively seals and isolates the active-agent chamber, with at least part of the reservoir formed from metal and the drug-contacting metal being titanium or a titanium alloy. Claim 13 narrows the alloy to at least 60% titanium.

The distinction is important. A delivery system might fall within claim 1 without using titanium. Conversely, a titanium reservoir alone would not necessarily satisfy claim 12 without the required sealing and drug-isolation characteristics.

Claim 16: start-up performance

Claim 16 requires an implantable active-agent delivery system in which time to start-up is less than 10% of the predetermined administration period.

For a 12-month implant, the limitation would require start-up in less than approximately 36.5 days. For a three-month implant, the threshold would be less than approximately 9.1 days.

This claim is performance-dependent. Infringement analysis would require reliable testing of the accused product under relevant conditions, including fluid environment, temperature, formulation, plug material, and outlet configuration.

Claim 17: injection-molded plug

Claim 17 protects a method of preparing the system by injection molding a semipermeable plug into the end of an impermeable reservoir so that the reservoir protects the plug.

Claims 18-20 narrow the plug material to polyurethane, polyamide, or cellulosic material. The claim is directed to manufacturing integration rather than only the final implant structure. A competing product made with a preformed plug could avoid this particular claim while potentially implicating claims 1, 12, 16, or 23.

Claims 21 and 23: leuprolide treatment and product configuration

Claim 21 covers reducing testosterone to castrate levels by administering the fluid-imbibing device with an LHRH agonist or antagonist. Claim 22 narrows the active agent to leuprolide.

Claim 23 is more technically specific. It requires:

An impermeable reservoir.
A piston dividing the reservoir into first and second chambers.
A water-swellable agent formulation in the first chamber.
An LHRH agonist or antagonist in the second chamber.
A semipermeable plug in the first chamber.
A back-diffusion-regulating outlet in the second chamber.
Effective sealing and isolation of the active agent.

Claims 24-38 add the product-specific limitations associated with a long-acting leuprolide implant, including titanium, a styrene-ethylene-butylene copolymer piston, sodium chloride, PEG 400, a leuprolide/DMSO formulation, a 65-mg drug load, a polyurethane plug, a helical polyethylene outlet, approximately 0.35 microliters per day, approximately 150 micrograms of leuprolide per day, and about one year of continuous delivery.

What formulations and delivery systems are protected?

The most specific formulation limitations are in claims 27-38.

Feature	Claim limitation
Osmotic formulation	At least about 64 mg sodium chloride
Osmopolymer system	Sodium chloride, a gelling osmopolymer, granulation aids, and processing aids
Additive	PEG 400
Drug formulation	Leuprolide acetate dissolved in DMSO
Drug assay	37% leuprolide
Drug load	65 mg leuprolide
Semipermeable plug	Polyurethane with 20% water uptake
Outlet	Polyethylene with a helical flow path
Outlet diameter	0.003 to 0.020 inch
Outlet length	2 to 7 centimeters
Delivery volume	About 0.35 microliter per day
Delivery period	About one year
Steady state	At least about 70% by day 14
Leuprolide delivery	About 150 micrograms per day

These limitations create a layered claim strategy. Claims 1 and 21 address broad platform and therapeutic concepts. Claims 23-38 focus on a narrower commercial embodiment. A product could avoid the narrower claims by changing the reservoir, drug load, solvent, plug material, outlet geometry, or dosing period, but it might still require analysis under the broader claims.

What semipermeable plug technology is protected?

Claims 39-48 separately protect the plug as a component and the selection of plug material as a method of controlling delivery rate.

The claimed materials include:

Plasticized cellulosic materials.
Enhanced polymethylmethacrylate.
Hydroxyethylmethacrylate.
Elastomeric materials.
Polyurethanes.
Polyamides.
Polyether-polyamide copolymers.
Thermoplastic copolymers.

The claims require the plug to be water-swellable, to expand linearly in the delivery system, and to initiate pumping after insertion into the fluid environment. Claims 42-45 define delivery periods of one, two, three, or 12 months.

These claims have potentially broad technical coverage, but their enforceability depends on construction of terms such as "expanding linearly," "commence pumping," and "selection of the material ... determines the rate of delivery." Those terms would likely require specification-based interpretation and experimental evidence.

When did U.S. Patent 6,395,292 expire?

U.S. Patent 6,395,292 was issued on May 28, 2002. Its enforceable term has ended under the applicable U.S. patent-term framework. The patent therefore does not presently create a live U.S. patent barrier to manufacturing or marketing a competing implant.

Patent expiration does not eliminate other possible rights. A commercial entrant would still need to evaluate:

Continuation and divisional patents.
Related ALZA or DUROS patents.
Formulation patents.
Manufacturing patents.
Device-component patents.
Trademark rights.
FDA approval requirements.
Trade-secret protection for manufacturing processes.

The expiration of this patent also does not establish freedom to operate for every implantable leuprolide product. It removes only the rights arising from U.S. Patent 6,395,292.

What was the FDA and Orange Book status?

The patent’s commercial context is the Viadur leuprolide acetate implant, an osmotic implant approved by the FDA for treatment of advanced prostate cancer. Viadur used a DUROS osmotic delivery system and delivered leuprolide continuously over approximately one year. FDA product information describes the implant, its drug formulation, and the delivery system components. [2]

The Orange Book is relevant for drug-product patent listings, but it does not convert every device patent into an automatically enforceable barrier. Listing depends on the product, patent claims, FDA listing practice, and whether the patent claims the drug, formulation, approved method of use, or a qualifying delivery system. [3]

Viadur was later discontinued in the United States for commercial and manufacturing reasons. The discontinuation did not represent an FDA determination that the product was unsafe or ineffective. A discontinued product may have limited practical Orange Book value even when historical patent listings or regulatory records remain accessible.

Were Paragraph IV challenges or settlements associated with this patent?

The patent’s term has ended, so a current Paragraph IV challenge to this patent would have no practical blocking effect. Paragraph IV litigation historically could have involved an ANDA applicant asserting that the patent was invalid, unenforceable, or not infringed. The relevant statutory framework is the Hatch-Waxman Act. [4]

The supplied claim set does not establish that a Paragraph IV notice, district-court action, or settlement agreement specifically involved U.S. Patent 6,395,292. Patent-level litigation conclusions should not be inferred from the patent text alone.

For present commercial planning, the key point is that any historical Paragraph IV dispute would be subordinate to the patent’s expired status. Current generic or follow-on competition would be governed primarily by FDA pathway, product discontinuation status, formulation equivalence, device performance, and other unexpired patents.

Is there biosimilar risk for this patent?

There is no conventional biosimilar issue for U.S. Patent 6,395,292.

Leuprolide is a synthetic peptide drug, not a monoclonal antibody or other biologic typically pursued through the biosimilar pathway. A competing leuprolide product would more likely use an abbreviated new drug application, a 505(b)(2) application, or a full NDA depending on formulation, delivery system, route, and reference-product availability.

The main regulatory risk is product complexity. A long-acting implant would need to establish performance characteristics such as:

Drug release rate.
Start-up period.
Dose uniformity.
Implant integrity.
Biocompatibility.
Sterility.
Reservoir and outlet performance.
Removal or retrieval characteristics.
Long-term stability.

How strong is the patent estate?

The patent was technically significant when active because it claimed multiple layers of an osmotic implant:

The swelling plug.
The reservoir.
The drug-contacting metal.
The piston and dual-chamber system.
The formulation.
The outlet.
The delivery-rate profile.
The manufacturing method.
The leuprolide treatment method.

Its historical strength came from claim redundancy. A competitor might avoid one narrow product claim yet remain exposed under a broader device claim or a plug claim. The estate is weaker today as a blocking asset because the focal patent has expired and the commercial product has been discontinued.

The most defensible technical claims are the concrete structural claims, particularly those requiring a dual-chamber reservoir, titanium drug-contacting surfaces, a defined plug, and a specific outlet. The more functional claims, such as start-up and linear expansion, are more dependent on testing and claim construction.

What generic launch scenarios exist?

A competing product could pursue several routes:

Scenario	Likely pathway	Main technical issue
Same active ingredient, different implant	505(b)(2) or NDA	Establishing release and clinical bridging
Conventional depot leuprolide	ANDA if a suitable reference exists	Formulation and dosing equivalence
One-year osmotic implant	505(b)(2) or NDA	Device-drug combination requirements
Reformulated implant	505(b)(2)	New excipients, outlet, plug, or reservoir
Foreign-market implant	Local regulatory pathway	Country-specific patent and device rules

The patent itself does not prevent launch. A competing product could still encounter manufacturing barriers because implantable osmotic systems require precision molding, controlled plug permeability, low-volume outlet formation, sterile assembly, and long-term stability data.

What geographic coverage remains?

U.S. Patent 6,395,292 provides U.S. rights only. Foreign counterparts, if any, must be evaluated separately by jurisdiction. Patent term, maintenance fees, prosecution history, claim amendments, and litigation outcomes may differ in Europe, Canada, Japan, Australia, and other markets.

Expiration of the U.S. patent does not establish expiration of any foreign counterpart or related patent family member.

Key Takeaways

U.S. Patent 6,395,292 covers a DUROS-type osmotic implant and associated manufacturing, formulation, and treatment methods.
The broadest technical concept is a water-swellable semipermeable plug sealing an impermeable drug reservoir.
Claims 23-38 target a highly specific one-year leuprolide implant configuration.
Claims 39-48 protect plug materials and use of material selection to control delivery rate.
The patent’s U.S. term has ended and it is not a current blocking patent.
The patent is not a leuprolide composition-of-matter patent.
Leuprolide competition would generally involve an ANDA, 505(b)(2), or NDA pathway rather than a biosimilar pathway.
Historical Orange Book or Paragraph IV relevance does not restore exclusivity after patent expiration.
Current freedom-to-operate analysis must include related ALZA, DUROS, formulation, manufacturing, and device patents.

FAQs

Does U.S. Patent 6,395,292 claim Viadur by name?

No. The claims do not depend on the trademark Viadur. They claim structural, formulation, manufacturing, performance, and leuprolide-treatment features associated with the product.

Is leuprolide itself protected by this patent?

No. The patent claims delivery systems and methods using leuprolide. It does not claim the underlying leuprolide molecule.

Can a competitor use a polyurethane osmotic plug?

Yes, expiration of the patent removes its current U.S. exclusionary effect. A competitor must still assess other unexpired patents and regulatory requirements.

Does patent expiration permit immediate sale of a competing implant?

No. Patent expiration removes one legal barrier but does not satisfy FDA approval, sterility, combination-product, clinical, manufacturing, or quality requirements.

Does a different outlet design avoid every claim?

No. A different outlet may avoid the specific limitations in claims 34-38, but broader device, plug, manufacturing, or treatment claims must be analyzed separately.

References

United States Patent and Trademark Office. (2002). U.S. Patent No. 6,395,292, fluid-imbibing implantable active agent delivery system. https://patents.google.com/patent/US6395292
U.S. Food and Drug Administration. (2000). Viadur leuprolide acetate implant prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book
Drug Price Competition and Patent Term Restoration Act of 1984, 21 U.S.C. § 355(j).

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	006079	⤷ Start Trial
Argentina	010595	⤷ Start Trial
Austria	235224	⤷ Start Trial
Austria	245042	⤷ Start Trial
Austria	277595	⤷ Start Trial
Austria	281153	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,395,292

Summary for Patent: 6,395,292