United States Drug Patent 5,317,032: Claim Scope, Expiration, and Patent Landscape

U.S. Patent No. 5,317,032 protects a method of producing a cathartic effect by administering defined 15-keto-16-halogen prostaglandin analogs, their pharmaceutically acceptable 1-esters, or salts. The patent is a use patent rather than a composition-of-matter patent. Its broadest claim covers a large structural genus, but infringement requires proof of the claimed prostaglandin structure, administration to a patient requiring catharsis, and a cathartic-inducing effective amount.

The patent issued on May 31, 1994. Based on the pre-Uruguay Round patent-term rule applicable to patents of this vintage, its ordinary term was 17 years from issuance, producing an expected expiration date of May 31, 2011, absent a terminal disclaimer or an unusual adjustment. It is therefore no longer an enforceable U.S. patent barrier. [1, 2]

What does U.S. Patent 5,317,032 protect?

The patent protects a therapeutic process for inducing catharsis with selected 15-keto-16-halogen prostaglandins. Claim 1 requires all of the following:

Claim element	Scope
Therapeutic objective	Providing a cathartic effect
Recipient	A patient in need of the cathartic effect
Active ingredient	A 15-keto-16-halogen PGA, PGE, or PGF compound
Structural limitation	The prostaglandin skeleton must be saturated or contain only specified unsaturation
Permitted unsaturation	2,3-, 5,6-, or 17,18-double bond, or a 5,6-triple bond
Substitution	Optional substitution at C-3, C-6, C-17, C-19, or C-20
Permitted substituents	Halogen, alkyl, alkoxy, carbonyl, hydroxyl, phenyl, or phenoxy
Pharmaceutical form	Parent compound, pharmaceutically acceptable 1-ester, or pharmaceutically acceptable salt
Administration	A cathartic-inducing effective amount
Formulation	A pharmaceutically acceptable carrier

The claim does not require a particular route of administration, dosage strength, dosage interval, disease diagnosis, formulation type, or treatment duration. It also does not require a named prostaglandin analog.

The claim is therefore a broad genus claim directed to the use of compounds sharing a particular 15-keto-16-halogen prostaglandin architecture.

How should claim 1 be construed?

Claim 1 has two independent scope components: a chemical genus and a therapeutic-use limitation.

Chemical genus

The active compounds must be:

Prostaglandin A, E, or F derivatives;
15-keto compounds;
16-halogen compounds;
Saturated or limited to the enumerated unsaturation patterns; and
Unsubstituted or substituted at specified carbon positions.

The claim is not directed to all halogenated prostaglandins. The 15-keto and 16-halogen requirements are central structural limitations. A compound lacking the 15-keto group or the 16-halogen atom would fall outside the literal scope of claim 1, even if it retained cathartic activity.

The claim also excludes unsaturation patterns not expressly permitted. For example, a compound containing a double bond outside the listed 2,3-, 5,6-, or 17,18-positions could face a non-infringement position, subject to the exact chemical structure and claim construction.

Substitution pattern

Claim 1 permits substitution at C-3, C-6, C-17, C-19, and C-20. The permitted substituents include:

Halogen;
Alkyl;
Alkoxy;
Carbonyl;
Hydroxyl;
Phenyl; and
Phenoxy.

Claims 2 through 7 narrow these alternatives:

Dependent claim	Limitation
Claim 2	Halogen is fluorine, chlorine, or bromine
Claim 3	Alkyl is methyl, ethyl, isopropyl, or isopropenyl
Claim 4	Alkoxy is methoxy or ethoxy
Claim 5	The claim 3 alkyl group is at C-3, C-17, or C-19
Claim 6	Carbonyl group is at C-6
Claim 7	Alkyl or alkoxy group is at C-20

The dependent claims narrow the genus but remain structurally broad. None identifies a single commercial active ingredient.

What are the strongest and weakest limitations in claim 1?

The strongest limitations are the specific 15-keto-16-halogen architecture and the defined prostaglandin skeleton. These limitations distinguish the claim from ordinary prostaglandins, non-halogenated prostaglandins, and analogs lacking the 15-keto group.

The broadest and potentially vulnerable limitations are:

“PGA, PGE or PGF,” which covers three prostaglandin classes;
The broad list of permitted substituents;
The lack of a fixed dose or route;
The phrase “cathartic-inducing effective amount”; and
The inclusion of pharmaceutically acceptable esters and salts.

A challenger could examine whether the specification provides adequate written description and enablement across the full genus. The relevant question would be whether the patent teaches a skilled person to make and use the full claimed class without undue experimentation. The absence of a particular approved drug in the claim does not itself invalidate the genus, but broad chemical claims are typically tested against representative examples, synthetic guidance, and the scope of the disclosed structure.

What do claims 2 through 7 add?

Claims 2 through 7 create narrower fallback positions, but they do not materially change the patent’s commercial character.

Claim 2 limits the halogen to fluorine, chlorine, or bromine. It excludes other halogens if the term “halogen” in claim 1 is construed to include them.

Claim 3 limits alkyl substitution to methyl, ethyl, isopropyl, or isopropenyl. Claim 5 further restricts that alkyl substitution to C-3, C-17, or C-19.

Claim 4 limits alkoxy substitution to methoxy or ethoxy.

Claim 6 requires a carbonyl group at C-6.

Claim 7 covers alkyl or alkoxy substitution at C-20 without limiting the group to the narrower list in claim 3 or claim 4. Its interpretation would depend on the dependency language and the parent-claim limitations.

Because every dependent claim incorporates claim 1, each still requires the cathartic-use limitation and the 15-keto-16-halogen prostaglandin framework.

When did U.S. Patent 5,317,032 lose exclusivity?

U.S. Patent 5,317,032 lost enforceable patent exclusivity no later than its ordinary statutory expiration in 2011.

Event	Date or status
Patent issued	May 31, 1994
Governing term for a 1994-issued patent	Generally 17 years from issuance
Expected ordinary expiration	May 31, 2011
Current enforceability	Expired
Current ability to block U.S. generic entry	None based solely on this patent

The patent issued before the modern 20-year-from-earliest-effective-filing-date regime became the general rule for U.S. utility patents. The Uruguay Round Agreements Act preserved the 17-year-from-issuance framework for relevant pre-June 8, 1995 applications, subject to statutory exceptions. [2]

A patent expiration date does not eliminate historical infringement exposure for conduct occurring before expiration. It does, however, eliminate prospective enforcement against post-expiration manufacture, sale, or use.

What is the Orange Book status of U.S. Patent 5,317,032?

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

A patent can be listed in the FDA Orange Book only in connection with an approved drug application and a patent that meets the applicable listing categories, such as a drug substance, drug product, or method-of-use patent. [3] U.S. Patent 5,317,032 is a method-of-treatment patent directed to catharsis with a broad prostaglandin genus. The record supplied does not identify an approved New Drug Application, a commercial active ingredient, or an Orange Book-listed product tied to this patent.

Even if the patent had historically been listed, its expiration would prevent it from creating a current patent-based delay to ANDA approval. A generic applicant would not face a present Paragraph IV risk from an expired patent.

Are Paragraph IV challenges relevant to this patent?

Paragraph IV litigation is no longer commercially relevant to U.S. Patent 5,317,032 because the patent has expired.

During the patent term, an ANDA applicant seeking approval for a product covered by a listed method-of-use patent could have submitted a Paragraph IV certification asserting that the patent was invalid, unenforceable, or would not be infringed. The Hatch-Waxman framework permits a patent owner to sue after receiving a Paragraph IV notice, potentially triggering a 30-month stay of approval under the statutory conditions. [4]

For this patent:

A current ANDA applicant would not need to defeat the expired patent.
A Paragraph IV notice would not restore exclusivity.
Any historical litigation would have lost prospective blocking effect after expiration.
The main present regulatory issue would be whether another unexpired patent or regulatory exclusivity covers the relevant product.

What formulations are protected by the patent?

Claim 1 includes “a pharmaceutically acceptable carrier,” but it does not claim a specific formulation technology.

The claim can potentially reach administration of the active ingredient in a broad range of dosage forms, including:

Oral tablets;
Capsules;
Solutions;
Suspensions;
Emulsions;
Liquid concentrates;
Unit-dose preparations; and
Other pharmaceutical preparations containing a suitable carrier.

The carrier limitation does not create a formulation patent in the conventional sense. It is an element of the claimed therapeutic process. The patent does not, based on the supplied claims, require:

A sustained-release matrix;
An enteric coating;
A particular excipient;
A specific particle size;
A controlled-release profile;
A transdermal system; or
A defined pharmacokinetic target.

A later formulation patent could have provided separate protection if it claimed a particular dosage form or release technology. Nothing in the supplied claims establishes such a formulation estate.

Does the patent cover methods of use or compositions?

It covers methods of use.

The claim begins with “A process for providing a cathartic effect” and requires administration to a patient. It does not claim:

The prostaglandin compound per se;
A pharmaceutical composition per se;
A method of synthesizing the compound;
A dosage form per se; or
A manufacturing process.

This distinction matters. A compound manufacturer could potentially practice the claimed chemistry without infringing the patent if it did not make, sell, or use the compound for the claimed cathartic purpose during the patent term. Conversely, a company administering a covered analog for catharsis could have faced method-of-use exposure even if the compound itself was known or separately patented.

What manufacturing and intellectual-property barriers existed?

The patent itself did not create a manufacturing monopoly over the claimed prostaglandin analogs. It created a use restriction during its term.

Separate barriers could have arisen from:

Compound patents covering specific 15-keto-16-halogen analogs;
Process patents covering stereoselective synthesis;
Intermediate patents;
Formulation patents;
Salt, ester, or crystalline-form patents;
Regulatory exclusivity for an approved product;
Trade secrets involving synthesis or purification; and
Supplier control over specialized prostaglandin intermediates.

The supplied claims do not identify any of those separate rights. A freedom-to-operate analysis for a particular active ingredient must therefore distinguish this expired method patent from any compound or process patents directed to that ingredient.

How strong was the patent estate?

The estate appears broad in claim breadth but narrow in claim type.

Strength factor	Assessment
Chemical breadth	Broad genus covering PGA, PGE, and PGF analogs
Therapeutic breadth	Broad cathartic-use language
Formulation coverage	Limited to a carrier limitation
Composition-of-matter protection	Not present in supplied claims
Manufacturing protection	Not present in supplied claims
Commercial product linkage	Not established
Remaining U.S. term	None
Current blocking value	None

The claim could have been commercially useful if a specific cathartic product fell within the genus and no narrower compound patent or competing method patent limited the field. Its value would have been weaker if the specification disclosed only a small number of examples or if the relevant commercial compound fell outside the precise 15-keto-16-halogen structure.

Because the patent has expired, claim breadth now has historical rather than prospective significance. It may still matter in assessing prior licensing positions, historical launch timing, or past infringement exposure.

Which companies challenged the patent?

No company, Paragraph IV certification, or reported federal litigation can be identified from the claim text alone. The patent number does not establish that the patent was ever asserted against an ANDA applicant or licensed to a commercial drug manufacturer.

The absence of an identified challenge is consistent with several possibilities: the patent may not have been linked to an approved drug, may not have generated commercial litigation, or may have been one of several patents in a broader prostaglandin program. A definitive litigation history would require the patent’s prosecution and court records, together with FDA drug-listing records.

What is the competitive landscape?

The relevant competitive field was not conventional stimulant laxatives or osmotic laxatives alone. The patent targeted prostaglandin analogs as agents capable of inducing catharsis.

Potential competitors would have included:

Non-halogenated prostaglandin analogs;
Other prostaglandin-based gastrointestinal agents;
Osmotic laxatives;
Stimulant laxatives;
Secretagogues;
Chloride-channel activators; and
Guanylate cyclase-C agonists.

The patent did not prevent development of a cathartic compound outside its structural genus. A competitor could seek to avoid the claim by using a non-15-keto analog, a non-16-halogen analog, a different prostaglandin architecture, or a non-prostaglandin cathartic mechanism.

What generic launch risks exist today?

The patent creates no current generic launch risk by itself.

A product developer should instead assess:

Unexpired compound patents;
Formulation and dosage patents;
Method-of-use patents;
FDA-approved labeling;
Regulatory exclusivity;
Pediatric exclusivity;
Orphan-drug exclusivity;
Patent-term extensions;
State-law licensing restrictions; and
Manufacturing process rights.

For a product that contains a compound within the expired genus, the key present question is whether another patent covers the specific active ingredient or its approved use. U.S. Patent 5,317,032 cannot independently support an injunction against a post-2011 launch.

How does this patent compare with a modern drug patent?

U.S. Patent 5,317,032 differs from modern pharmaceutical patent portfolios in three important respects.

First, it relies on a broad use claim rather than a layered estate of composition, formulation, dosing, manufacturing, and method-of-use claims.

Second, its term is governed by the historical 17-year-from-issuance framework rather than the modern 20-year-from-effective-filing-date framework.

Third, the claim does not identify a commercial product or dosage regimen. Modern Orange Book strategies typically rely on product-specific claims and detailed labeling-linked method claims. [3, 4]

What is the geographic coverage?

The patent covered conduct within the United States. It did not automatically create rights in Europe, Japan, Canada, or other jurisdictions.

International protection would have required corresponding national or regional patents. The supplied U.S. claims do not establish:

Foreign filing dates;
Foreign grant status;
Foreign expiration dates;
Patent-family members; or
Foreign litigation.

The U.S. patent’s expiration did not determine the status of any foreign counterpart.

Key Takeaways

U.S. Patent 5,317,032 is a method-of-use patent for catharsis using 15-keto-16-halogen PGA, PGE, or PGF analogs.
Claim 1 is broad but requires the specific 15-keto-16-halogen prostaglandin framework and enumerated unsaturation and substitution patterns.
Claims 2 through 7 narrow the halogen, alkyl, alkoxy, positional, and carbonyl limitations.
The patent does not claim a prostaglandin compound, formulation, synthesis method, or manufacturing process per se.
The patent issued on May 31, 1994 and ordinarily expired on May 31, 2011.
It presents no current Paragraph IV, Orange Book, injunction, or generic-launch barrier.
Commercial risk today depends on separate patents covering a specific active ingredient, formulation, manufacturing route, or approved indication.
The claim text supplied does not establish a commercial product, licensee, litigation history, or foreign patent family.

FAQs

Does U.S. Patent 5,317,032 cover all prostaglandin laxatives?

No. It covers only cathartic use of the specified 15-keto-16-halogen PGA, PGE, or PGF genus and its permitted esters and salts.

Can a company sell a compound that falls within the patent’s chemical genus?

Yes, as a general matter, because the U.S. patent has expired. Historical infringement could still depend on conduct occurring before expiration and on the exact product and use.

Does the patent cover lubiprostone?

The supplied claims do not identify lubiprostone, and the claim’s 15-keto-16-halogen prostaglandin limitations should not be assumed to cover lubiprostone without a structure-based comparison.

Does the patent protect a sustained-release cathartic formulation?

No specific sustained-release technology appears in the supplied claims. The claims require a pharmaceutically acceptable carrier but do not recite a release mechanism or excipient system.

Is a separate patent search required for a specific prostaglandin cathartic product?

Yes. This expired method patent does not resolve rights covering the product’s exact chemical structure, formulation, manufacturing process, approved indication, or foreign markets.

References

United States Patent and Trademark Office. (1994). U.S. Patent No. 5,317,032.
35 U.S.C. § 154. Patent term and adjustment provisions.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations.
21 U.S.C. § 355(j). Abbreviated applications and patent certifications.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Japan	62-250163	Oct 02, 1987

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	78465	⤷ Start Trial
Australia	2292088	⤷ Start Trial
Australia	609883	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,317,032

Summary for Patent: 5,317,032