United States Patent 5,242,391: Scope, Claim Construction, Expiration and Urethral Drug-Delivery Patent Landscape

U.S. Patent No. 5,242,391 covers a preassembled urethral dosage form combining a drug-bearing shaft, a retention plug and a protective container. Its claims are directed to the delivery architecture, not to a particular active ingredient or disease indication. The patent issued on September 7, 1993, and its ordinary 17-year term expired on September 7, 2010, absent a patent-term extension. No current U.S. exclusivity remains under this patent.[1][2]

The claims are broad in therapeutic-agent coverage but narrow in structural combination. A competing product would need to assess the shaft, plug, container, dose location and dose-displacement limitations together. Because the patent has expired, the claims have no current blocking effect on U.S. generic, branded or device commercialization.

What does U.S. Patent 5,242,391 protect?

The patent protects a urethral drug-delivery dosage form in which an insert is packaged inside a container. The insert has a shaft that enters the urethra, a larger plug that prevents complete insertion, and a therapeutic dose carried by the shaft. The container protects the insert before use and forms a sliding seal around the plug.

The claimed system has two principal components:

Component	Required claim element	Functional purpose
Insert	Shaft sized for urethral insertion	Places the dose in the urethra
Insert	Plug larger than the urethral diameter	Prevents complete insertion
Insert	Therapeutic dose carried entirely by shaft	Delivers the drug from the shaft
Container	Closed at one end and open at the other	Stores and protects the insert
Container	Length sufficient to receive shaft and part of plug	Encloses the insert
Container	Open end forms a sliding seal with plug	Controls movement and protects the dose

The independent claim does not identify alprostadil, prostaglandin E1, erectile dysfunction, a particular formulation, a particular polymer or a specific delivery mechanism. “Therapeutic agent” is functionally defined and can encompass a broad range of active pharmaceutical ingredients, subject to the claim’s physical configuration.

How should claim 1 be construed?

Claim 1 is a combination claim. Every listed structural and functional limitation must be present for literal infringement.

“Dosage form”

The claim is directed to an integrated dosage form rather than merely a drug, applicator or package. The product must include the insert and container relationship described in the claim.

“Insert component received within a container component”

The insert must be located inside the container before administration. A loose urethral suppository sold without the claimed container relationship would not necessarily satisfy this limitation.

“Shaft portion sized to be received within the urethra”

The shaft must have a size and configuration suitable for urethral placement. The claim does not specify a precise shaft diameter, cross-sectional shape or material.

“Plug ... having a dimension greater than the diameter of the urethra”

The plug performs a retention function. It prevents the user from inserting the complete insert into the urethra. A product using a separate flange, collar or external stop could raise an equivalent-structure issue, but it would not necessarily meet the literal “plug” limitation.

“Dose being carried in its entirety by said shaft”

This limitation is important. The claimed dose cannot be partly located in the plug, container or another component if the entire dose must be carried by the shaft. Claims 3 through 5 provide a specific coating embodiment, while claims 6 through 9 provide a cavity-and-displacement embodiment.

“Sliding seal”

The container opening must be sized to seal against the plug while permitting sliding movement. A package that merely surrounds the insert without this plug-to-container sealing relationship would present a non-infringement position.

What additional limitations appear in claims 2 through 5?

Claims 2 through 5 narrow the basic container and coating design.

Claim	Added limitation	Commercial significance
2	Plug is fully inside the container; cap is too large to enter the container; container abuts cap	Defines an external handling and insertion-stop configuration
3	Dose is an agent-containing coating on at least part of the shaft exterior; container remains spaced from coating	Protects a coated-shaft product and prevents package contact with the drug layer
4	Dose does not exceed urethral dose-retaining capacity and contains agent dispersed in a dispersant	Adds a formulation-volume and dispersion limitation
5	Dose weighs less than 100 mg	Narrows claim 4 by dose mass

Claim 3 is directed to a surface-coated shaft. The container’s interior must remain spaced from the coating. This condition can matter in design-around analysis: a package that contacts, compresses or scrapes the drug layer may fall outside claim 3 while raising separate product-quality concerns.

Claims 4 and 5 do not claim a specific excipient, polymer or solvent. “Dispersant” is a functional formulation term. The claim also requires a dose amount that does not exceed the urethra’s dose-retaining capacity, creating a potentially fact-intensive limitation involving dose volume, formulation behavior and administration conditions.

What do claims 6 through 9 protect?

Claims 6 through 9 cover a second delivery architecture. Instead of requiring the dose to be an external coating, these claims require:

A cavity at the end of the shaft opposite the plug;
The dose located inside the cavity; and
A movable mechanism that displaces the dose into the urethra.

This is a mechanical expulsion embodiment. The dose begins in a first position within the cavity and moves to a second position after actuation.

Claim 7 adds a mechanism preventing unintended dose displacement. The claim does not specify whether the mechanism is a latch, friction fit, removable seal, breakable component or another retaining structure.

Claims 8 and 9 add the same dose-retention and dispersant limitations found in claims 4 and 5. The cavity embodiment therefore covers a unit-dose applicator with an internal payload and an actuation mechanism, rather than only a coated rod.

What do claims 10 through 13 cover?

Claims 10 through 13 return to the broader claim 1 or claim 2 configuration and impose formulation and dose limitations.

Claim	Added limitation
10	Dose does not exceed urethral retaining capacity and contains agent dispersed in a dispersant
11	Dose weighs less than about 50 mg
12	Shaft is about 2 to 5 cm long
13	Dose weighs less than 100 mg

Claim 11 is narrower than claim 13 because it uses a less-than-about-50-mg limitation. Claim 13 allows a dose below 100 mg but remains dependent on claim 10’s dispersant and urethral-retention requirements.

The 2-to-5-centimeter shaft limitation in claim 12 is a dimensional restriction. A product with a shaft outside that range could avoid claim 12 while remaining potentially relevant to claims 10, 11 or 13.

Is U.S. Patent 5,242,391 an alprostadil or MUSE patent?

The claim language does not limit the invention to alprostadil. It covers a delivery form for a “therapeutic agent.” The patent is associated with the urethral drug-delivery technology used in the MUSE product, an intraurethral alprostadil system approved by the FDA for erectile dysfunction.[1][3]

The distinction matters:

The patent claims the delivery form.
The FDA approval concerns the specific drug product, alprostadil.
The claims do not require erectile dysfunction treatment.
The claims do not require a particular alprostadil dose.
The claims do not independently claim the alprostadil molecule or its chemical synthesis.

A product could therefore implicate the historical claim language even if it used a different therapeutic agent, provided all structural limitations were met. Conversely, an alprostadil product using a different delivery architecture would not automatically infringe.

When did U.S. Patent 5,242,391 expire?

The patent issued on September 7, 1993. Because it issued under the pre-Uruguay Round patent-term regime, the ordinary term was 17 years from issuance. The resulting ordinary expiration date was September 7, 2010.[1][4]

Event	Date
Patent issued	September 7, 1993
Ordinary patent term	17 years from issue
Ordinary expiration	September 7, 2010
Current enforceability	Expired
Current blocking effect	None

The public patent record does not identify a current extension that would revive the patent. Patent-term adjustment rules introduced by later legislation do not extend a pre-1995 patent’s ordinary term in the manner applicable to later-issued patents.[4]

What was the Orange Book status of the patent?

U.S. Patent 5,242,391 was associated with the MUSE alprostadil product and its urethral delivery system. Orange Book listing provides notice of a patent asserted by the NDA holder or sponsor against a listed drug product. It does not convert every claim in the patent into a product-specific chemical monopoly.[2]

The practical status is now historical:

Orange Book issue	Assessment
Product association	MUSE alprostadil urethral system
Patent subject matter	Urethral dosage-form and delivery-device architecture
Active patent term	No
Current Paragraph IV exposure	No meaningful exposure to this expired patent
Current automatic stay risk under Hatch-Waxman	None based solely on this patent
Current injunction risk	None based solely on this expired patent

A Paragraph IV certification can challenge a listed patent while it remains in force. It has no commercial blocking significance after patent expiration. A generic applicant would focus on any other unexpired Orange Book patents, regulatory exclusivity, product-specific requirements and device compatibility issues.[2][5]

Does the patent contain formulation or method-of-use protection?

The patent has formulation-related limitations, but it is not a conventional composition-of-matter patent.

Formulation protection

Claims 4, 8 and 10 require a dose dispersed in a dispersant and limited to the urethra’s dose-retaining capacity. Claims 5, 9, 11 and 13 add dose-weight limits.

These claims could historically have been relevant to:

Low-mass intraurethral formulations;
Drug-coated shafts;
Dispersed drug systems;
Small-volume urethral delivery;
Unit-dose applicators.

They do not identify a specific excipient, particle size, release rate, dissolution profile or chemical form.

Method-of-use protection

The patent does not claim treatment of erectile dysfunction or another disease. It claims a dosage form. A method-of-use patent would typically recite administering a defined agent to treat a defined condition. Those limitations are absent from the supplied claims.

Manufacturing protection

The claims do not cover manufacturing steps. They do not require a particular coating process, molding process, filling process, sterilization method or assembly sequence. Manufacturing infringement would therefore require a separate patent with process claims.

How strong was the patent estate?

The patent had meaningful historical value because it combined drug placement, retention and packaging in a single claim. Its principal strengths were:

Broad therapeutic-agent language;
Coverage of both coated-shaft and cavity-displacement embodiments;
No requirement for a particular disease indication;
Coverage of the container-to-plug sliding seal;
Multiple dependent dose and dimension limitations.

Its principal limitations were:

Dependence on a specific physical architecture;
Requirement that the dose be carried by the shaft;
Requirement for a plug larger than the urethral diameter;
Requirement for a container with a sliding seal;
Lack of chemical-composition claims;
Lack of manufacturing claims;
Expiration in 2010.

The claim set would have been vulnerable to a design that used a conventional dissolving suppository, a catheter-delivered liquid, a dose deposited by a separate actuator, or a package without the claimed plug-seal relationship.

What generic entry risks exist today?

The patent creates no current U.S. generic-entry barrier. A generic or competing product can use a urethral insert, coated shaft, internal cavity or expulsion mechanism without facing infringement liability under an expired patent.

Current commercial risks would arise from other sources:

Unexpired patents covering later formulations or applicator improvements;
FDA requirements for a drug-device combination product;
Product-specific bioequivalence or local-delivery requirements;
Manufacturing validation and sterility controls;
Trademark and trade-dress restrictions;
Market access and supply constraints.

For alprostadil, biosimilar analysis is not applicable. Alprostadil is a chemically defined small-molecule drug, not a biologic subject to the biosimilar pathway under the Public Health Service Act. A competing product would generally pursue an abbreviated new drug application or another applicable drug approval route, not a biosimilar application.[3][5]

Which companies are challenging the patent?

No current Paragraph IV challenge can block entry based on U.S. Patent 5,242,391 because the patent expired in 2010. The patent’s historical litigation or settlement status does not create present exclusivity.

Any current challenge involving an intraurethral alprostadil product would need to target a different unexpired patent, regulatory exclusivity, or a product-specific approval issue. This patent alone cannot support a current infringement suit or a Hatch-Waxman stay.

What geographic coverage did the patent provide?

U.S. Patent 5,242,391 provided rights only in the United States. Its claims do not establish protection in Europe, Canada, Japan, China or other markets.

Foreign rights would depend on corresponding national patents, their claim scope, maintenance status and expiration dates. A foreign patent family could have materially different claims. The U.S. expiration date cannot be transferred automatically to every jurisdiction, although many related applications would have expired on comparable timelines.

Key Takeaways

U.S. Patent 5,242,391 covers a urethral insert inside a protective container.
Claim 1 requires a drug-bearing shaft, oversized retention plug and plug-sealing container.
Claims 3 through 5 cover external coatings and low-mass dispersed doses.
Claims 6 through 9 cover an internal dose cavity with a movable displacement mechanism.
Claims 10 through 13 add dispersant, urethral-retention, dose-weight and shaft-length limitations.
The claims are agent-neutral and are not limited to alprostadil or erectile dysfunction.
The patent is a delivery-system patent, not a composition-of-matter, method-of-use or manufacturing patent.
The ordinary patent term expired on September 7, 2010.
The patent has no current Orange Book blocking effect and cannot support a current Paragraph IV stay.
Biosimilar analysis does not apply to alprostadil because it is a small-molecule drug.
Current competitive risk must be assessed against later patents, FDA requirements and manufacturing barriers.

FAQs

Can a competing product use a urethral drug-coated shaft now?

Yes. U.S. Patent 5,242,391 is expired. A competitor must still evaluate later patents covering the specific coating, formulation, applicator or manufacturing process.

Does the patent cover a catheter that delivers a liquid drug?

Not on the supplied claims alone. A liquid catheter system generally would lack the claimed insert shaft, retention plug, container seal and shaft-carried dose combination.

Does claim 1 require the dose to dissolve inside the urethra?

No. The supplied claim language requires a therapeutic dose carried by the shaft but does not expressly require a dissolution mechanism, release rate or release profile.

Would a product with a separate external flange infringe the plug limitation?

It may avoid literal infringement if the flange is not a “plug,” but the analysis would depend on claim construction, prosecution history and the doctrine of equivalents. Because the patent is expired, this issue has no current U.S. enforcement consequence under this patent.

Is MUSE protected by this patent today?

No. MUSE was associated with the patent historically, but U.S. Patent 5,242,391 expired in 2010. Any present protection would have to arise from other patents, regulatory rights, trademarks or commercial agreements.

References

United States Patent and Trademark Office. (1993). U.S. Patent No. 5,242,391, urethral drug delivery system.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
U.S. Food and Drug Administration. (1997). MUSE (alprostadil) urethral suppository prescribing information.
United States Code. (2024). 35 U.S.C. §§ 154 and 156: Patent term and patent term extension.
U.S. Food and Drug Administration. (2024). Abbreviated new drug application and generic drug approval requirements.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	173603	⤷ Start Trial
Australia	655420	⤷ Start Trial
Australia	7856391	⤷ Start Trial
Canada	2040914	⤷ Start Trial
Canada	2352552	⤷ Start Trial
Germany	69130529	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,242,391

Summary for Patent: 5,242,391