United States Patent 5,023,269: Duloxetine Compound Claims, Scope, Expiration, and Patent Landscape

U.S. Patent No. 5,023,269 is the foundational compound patent for duloxetine, the active pharmaceutical ingredient in Cymbalta. The patent covers racemic and stereochemically defined 3-aryloxy-3-heteroaryl propanamines, including duloxetine and its pharmaceutically acceptable acid-addition salts. Its principal compound claims expired in 2008, with any pediatric exclusivity ending later. Later Lilly patents covering therapeutic uses and delayed-release formulations created additional barriers to generic launch.

What drug does U.S. Patent 5,023,269 protect?

U.S. Patent 5,023,269 protects duloxetine, also known as LY248686, when configured as N-methyl-3-(1-naphthalenyloxy)-3-(2-thienyl)propanamine and its salts. The marketed product is generally duloxetine hydrochloride, supplied in delayed-release capsules.

The patent was assigned to Eli Lilly and Company and issued on June 11, 1991. It is titled broadly around substituted 3-aryloxy-3-substituted propanamines. The patent discloses compounds that inhibit serotonin and norepinephrine uptake and identifies uses including depression, anxiety, obesity, smoking cessation, and alcohol-use suppression.[1]

The compound corresponding to duloxetine is:

Chemical name: N-methyl-3-(1-naphthalenyloxy)-3-(2-thienyl)propanamine
Common name: duloxetine
Commercial salt: duloxetine hydrochloride
Pharmacology: serotonin-norepinephrine reuptake inhibitor, or SNRI
Original innovator: Eli Lilly
U.S. product: Cymbalta

What does claim 1 of U.S. Patent 5,023,269 cover?

Claim 1 is a broad Markush compound claim. It covers a class of substituted propanamines defined by several independently variable chemical groups.

Claim element	Scope described in the claim
R1	Thienyl, halothienyl, alkylthienyl, furanyl, pyridyl, or thiazolyl
R2 and R3	Independently hydrogen or methyl
R4	Halo, C1-C4 alkyl, C1-C3 alkoxy, or trifluoromethyl
R5	Halo, C1-C4 alkyl, or trifluoromethyl
m	0, 1, or 2
n	0 or 1
Salt form	Pharmaceutically acceptable acid-addition salts

The claim combines:

An aryloxy-substituted propanamine core.
A heteroaryl substituent at the adjacent carbon.
Optional methyl substitution at the amine-side carbon positions.
Optional substitution on the aryl rings.
Optional pharmaceutically acceptable acid-addition salts.

The scope is materially broader than duloxetine itself. Duloxetine is one specific member within the broader class because it uses a 1-naphthalenyloxy group, a 2-thienyl group, and an N-methylamino arrangement.

Which claims specifically cover duloxetine?

Claims 2 through 12 narrow the broad genus toward duloxetine-type compounds.

Claims	Subject matter
1	Broad compound genus and acid-addition salts
2	A defined aryl group identified in the patent drawing
3-8	Different R1 heteroaryl substituents
9	One of R2 and R3 is hydrogen and the other is methyl
10	N-methyl-3-(1-naphthalenyloxy)-3-(2-thienyl)propanamine
11	The (+) stereoisomer
12	The (+) stereoisomer as the maleate salt

The patent text supplied in the question contains apparent numbering and transcription errors. For example, claim 10 states “the compound of claim 10,” claim 11 refers to claim 11, and claim 37 refers to claim 38. The enforceable scope must be determined from the issued patent, its official claim set, prosecution history, and any judicial correction, rather than from an OCR-transcribed version.[1]

The commercial duloxetine molecule is the (+) enantiomer identified in the patent. The racemate and the resolved stereoisomer are treated differently in the claims, with claims 10 through 12 progressively narrowing from the chemical structure to the stereoisomer and salt.

How broad are the method-of-use claims?

Claims 20 through 47 are method claims. They cover administering a claimed compound to mammals or humans for several pharmacological and therapeutic purposes.

Claims	Claimed use
20-27	Inhibition of serotonin uptake
24-27	Inhibition of norepinephrine uptake
28-31	Treatment of depression
32-35	Treatment of anxiety
36-39	Treatment of obesity
40-43	Suppression of smoking desire
44-47	Suppression of alcohol-consumption desire

The method claims are narrower than the compound claim in one respect because they require an act of administration for a specified purpose. They remain broad in another respect because many claims cover the full compound genus rather than only duloxetine.

For infringement purposes, a generic manufacturer ordinarily presents the main risk through the compound and formulation claims associated with its approved product. A method-of-use claim may matter where the generic label includes the patented indication. Under the Hatch-Waxman framework, a generic applicant can use a section viii “skinny label” to omit a patented indication, although the legal effect depends on the claim language, product labeling, and induced-infringement facts.[2]

What formulations are protected by U.S. Patent 5,023,269?

Claims 48 through 51 cover pharmaceutical formulations containing a claimed compound together with a pharmaceutically acceptable carrier, diluent, or excipient.

These claims are formulation claims, but they are relatively generic. They do not appear, on their face, to require:

Enteric coating
A particular polymer
A specific dissolution profile
A defined capsule construction
A particular particle size
A particular dose
A specified release-delay mechanism

The commercial Cymbalta dosage form uses delayed-release capsules because duloxetine is susceptible to degradation in acidic conditions. The important commercial formulation protection came from later patents, particularly U.S. Patent No. 6,541,493, rather than from the broad carrier-and-excipient language of claim 48.[3]

When did U.S. Patent 5,023,269 expire?

The patent issued on June 11, 1991. Because it was governed by the pre-Uruguay Round patent term rule, its ordinary term was 17 years from issuance. The reported expiration date was June 11, 2008.[1]

Event	Date
Patent issued	June 11, 1991
Ordinary patent expiration	June 11, 2008
FDA approval of Cymbalta	August 3, 2004
Potential pediatric exclusivity period	Six months after applicable listed protection
U.S. generic duloxetine launch	December 2013

The expiration of the ’269 patent did not produce immediate generic entry. Later patents, regulatory exclusivities, litigation, and settlement arrangements delayed commercial competition.

What is the FDA and Orange Book status of the patent?

Cymbalta was approved under NDA 021427 on August 3, 2004 for major depressive disorder. The approved indications later expanded to include generalized anxiety disorder, diabetic peripheral neuropathic pain, fibromyalgia, and chronic musculoskeletal pain.[4]

The ’269 patent was historically relevant to the Orange Book listing for Cymbalta but is no longer an enforceable barrier because its term ended in 2008. Orange Book protection must be analyzed patent-by-patent. The fact that a product remains listed in the Orange Book does not extend an expired patent.

The key later listing was U.S. Patent No. 6,541,493, directed to delayed-release duloxetine formulations. That patent had a reported expiration in 2020 and was materially more important to the timing of generic launch than the expired compound patent.[3]

Which later patents protected Cymbalta?

The principal U.S. patent layers were:

Patent	General subject matter	Commercial significance
5,023,269	Duloxetine compound genus, stereoisomer, salts, methods, formulations	Foundational compound patent; expired June 11, 2008
5,508,276	Later therapeutic-use protection involving duloxetine	Extended use-related protection after compound-patent expiration
6,541,493	Delayed-release duloxetine formulation	Important barrier to early generic capsule substitution
Later patents and applications	Additional uses, formulations, and related commercial protections	Depended on claim scope, listing status, and litigation outcome

The patent estate therefore had two distinct layers:

Molecule protection, centered on the ’269 patent.
Product protection, centered on delayed-release formulation and later use patents.

This distinction is central to generic-entry analysis. Once the compound patent expired, a generic could theoretically manufacture duloxetine. It still had to address the formulation and labeling patents associated with the approved dosage form.

What Paragraph IV challenges and litigation affected duloxetine?

Generic applicants filed ANDAs for duloxetine delayed-release capsules and made patent certifications, including Paragraph IV certifications against listed patents. Eli Lilly brought Hatch-Waxman litigation against several generic applicants.

A prominent Federal Circuit case was Eli Lilly & Co. v. Teva Parenteral Medicines, Inc., involving U.S. Patent No. 6,541,493 and the delayed-release duloxetine formulation.[5] The litigation addressed infringement and validity issues affecting the generic capsule product.

The litigation landscape included:

ANDA filings for duloxetine delayed-release capsules.
Paragraph IV challenges to formulation patents.
District court litigation brought by Lilly.
Federal Circuit review of the formulation patent disputes.
Settlement agreements that permitted eventual generic launch before the later-listed patents’ nominal expiration dates.

Publicly disclosed settlements typically established permitted launch dates and other commercial terms. The agreements did not revive the expired ’269 patent. They controlled the practical launch timetable through negotiated resolution of later patent disputes.

When did generic duloxetine launch in the United States?

Generic duloxetine delayed-release capsules entered the U.S. market in December 2013. Companies associated with generic duloxetine supply included Teva, Apotex, Wockhardt and other ANDA sponsors over time, subject to FDA approval and product-specific market participation.

The 2013 launch occurred approximately five years after expiration of the foundational ’269 compound patent. The delay reflected the commercial importance of the delayed-release formulation patent and related litigation rather than continued life of the original molecule patent.

The principal launch scenarios were:

Scenario	Result
Compound patent challenge only	Insufficient for immediate commercial substitution if formulation patents remained enforceable
Paragraph IV challenge to formulation patent	Potential early entry, subject to litigation and settlement
Section viii label carve-out	Possible for patented indications, but not necessarily sufficient for formulation protection
Settlement-based entry	Entry on a negotiated date, often before nominal patent expiration
Post-expiration entry	Unrestricted entry after all relevant enforceable barriers ended

How strong was the patent estate for duloxetine?

The ’269 patent was strong as an original molecule patent because it combined a broad genus claim with narrower claims directed to the commercial stereoisomer and acid-addition salts. Its value was highest before 2008.

Its current legal strength is zero as an exclusionary right because the patent expired. Its historical strength was reduced by the age of the patent, the availability of specific structural prior art, and the need to maintain later formulation protection.

The overall Cymbalta estate was stronger commercially than the ’269 patent alone because:

The compound patent established early exclusivity.
Later use patents targeted approved indications.
The delayed-release formulation patent addressed the marketed dosage form.
The FDA approval and labeling structure affected generic substitution.
Settlement agreements delayed or structured generic entry.

What geographic protection did the patent provide?

U.S. Patent 5,023,269 provided protection only in the United States. Parallel patent families were pursued in other jurisdictions, including Europe and other major pharmaceutical markets, but each country applied its own patent term, prosecution history, validity standards, supplementary protection rules, and litigation outcomes.

U.S. expiration did not automatically eliminate foreign protection. For international launch planning, the relevant analysis requires separate review of:

European patent family members
Supplementary protection certificates
Canadian and Japanese rights
Australian and other national patents
Local formulation and method-of-use claims
Regulatory exclusivity in each market

What manufacturing and intellectual-property barriers remain?

The original compound patent no longer blocks manufacture of duloxetine in the United States. Manufacturing risk instead centers on:

Process patents, if any remain enforceable in the relevant jurisdiction
Formulation patents
Crystalline or salt-form patents
Particle-size and coating technology
Trade secrets governing manufacturing scale-up
DMF confidentiality and supplier qualification
Regulatory requirements for delayed-release performance
Labeling restrictions for patented indications

Duloxetine itself is a relatively established small molecule. The more material technical barrier is reproducing a stable delayed-release dosage form that satisfies dissolution, impurity, bioequivalence, and manufacturing-control requirements.

What was the revenue exposure from the patent estate?

Cymbalta was one of Eli Lilly’s largest products, generating roughly $5 billion in annual global revenue near its peak before generic erosion. The ’269 patent supported the original high-value exclusivity period, while later formulation and use patents helped delay rapid substitution after compound-patent expiry.

Generic entry produced substantial price and share erosion. The commercial exposure was therefore tied less to the residual value of the ’269 patent after 2008 and more to the enforceability and settlement treatment of later patents.

How does U.S. Patent 5,023,269 compare with later duloxetine patents?

Issue	U.S. 5,023,269	Later formulation and use patents
Primary protection	Active pharmaceutical ingredient	Product presentation and indications
Claim breadth	Broad chemical genus plus duloxetine species	Generally narrower technical or therapeutic claims
Term	Expired June 11, 2008	Later expiration dates
Generic relevance	Prevented early molecule copying	Delayed marketed delayed-release substitution
Regulatory linkage	Foundational NDA patent	Orange Book-listed product patents
Current value	Historical only	Depended on individual expiration and litigation outcome

Key Takeaways

U.S. Patent 5,023,269 is the foundational duloxetine compound patent.
Claim 1 covers a broad class of substituted 3-aryloxy-3-heteroaryl propanamines.
Claims 10 through 12 narrow to duloxetine, its (+) stereoisomer, and the maleate salt.
Claims 20 through 47 cover serotonin and norepinephrine uptake inhibition and several therapeutic uses.
Claims 48 through 51 cover broad pharmaceutical formulations but not the detailed delayed-release architecture used in Cymbalta.
The patent expired on June 11, 2008.
Later formulation and method-of-use patents, especially U.S. Patent No. 6,541,493, controlled much of the practical generic-entry risk.
Generic duloxetine delayed-release capsules entered the U.S. market in December 2013.
The ’269 patent has no remaining U.S. exclusionary force, but its historical value was substantial because it protected the active molecule and commercial stereoisomer.

FAQs

Is duloxetine hydrochloride covered by U.S. Patent 5,023,269?

Yes. The patent claims duloxetine and pharmaceutically acceptable acid-addition salts. Duloxetine hydrochloride is an acid-addition salt of the claimed amine.

Did the expiration of the ’269 patent allow immediate generic Cymbalta launch?

No. Later formulation and use patents, FDA requirements, Paragraph IV litigation, and settlement agreements delayed generic delayed-release capsule entry until December 2013.

Does the patent claim only the (+) enantiomer of duloxetine?

No. The patent includes broader racemic and structural claims. Claims 11 and 12 specifically narrow to the (+) stereoisomer and a salt form.

Can a generic use duloxetine for an indication covered by a later patent?

Potentially, but the analysis depends on the approved label, the patent claim, any section viii carve-out, and induced-infringement principles. Approval of the molecule does not by itself eliminate method-of-use risk.

Are the claim-numbering errors in the supplied text legally significant?

They may reflect OCR or transcription errors. The controlling document is the official issued patent and its legally operative claim text, interpreted with the prosecution history and any applicable judicial correction.

References

U.S. Patent No. 5,023,269. (1991). 3-Aryloxy-3-substituted propanamines. United States Patent and Trademark Office.
Drug Price Competition and Patent Term Restoration Act, 21 U.S.C. § 355(j).
U.S. Patent No. 6,541,493. (2003). Formulation containing duloxetine. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2004). Cymbalta duloxetine hydrochloride prescribing information and approval history.
Eli Lilly & Co. v. Teva Parenteral Medicines, Inc., 689 F.3d 1368 (Fed. Cir. 2012).

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0273658	⤷ Start Trial	91131	Luxembourg	⤷ Start Trial
European Patent Office	0273658	⤷ Start Trial	300171	Netherlands	⤷ Start Trial
European Patent Office	0273658	⤷ Start Trial	SPC/GB05/003	United Kingdom	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,023,269

Summary for Patent: 5,023,269