United States Patent 4,590,213: Scope, Claims, Expiration, and Fluoxetine Patent Landscape

U.S. Patent No. 4,590,213 covered methods of treating human anxiety with fluoxetine, norfluoxetine, or pharmaceutically acceptable salts. Its broadest claim reached either compound without limiting route, dosage, formulation, or specific anxiety disorder. The patent issued on May 27, 1986, and its 17-year pre-URAA term expired on May 27, 2003. The claims therefore no longer create an enforceable U.S. exclusion right.[1][2]

The patent remains relevant for historical freedom-to-operate analysis, patent-family reconstruction, generic-launch history, and interpretation of the early fluoxetine estate. It does not currently block manufacture, sale, prescribing, or off-label use of fluoxetine or norfluoxetine in the United States.

What does U.S. Patent 4,590,213 cover?

U.S. Patent 4,590,213 covers a therapeutic method rather than a chemical compound, formulation, manufacturing process, or dosage form. The patent claims administration of fluoxetine or norfluoxetine to a human patient suffering from anxiety.[1]

The independent claim is Claim 1:

A method for treating anxiety in a human subject in need of such treatment comprising administration of an effective amount of fluoxetine, norfluoxetine, or a pharmaceutically acceptable salt thereof.

The claim has five principal elements:

A method of treatment.
A human subject.
A subject in need of treatment.
Anxiety as the condition being treated.
Administration of an effective amount of fluoxetine, norfluoxetine, or a pharmaceutically acceptable salt.

The claim does not require:

Oral administration.
A particular dosage.
Fluoxetine hydrochloride.
A capsule, tablet, solution, or other formulation.
Monotherapy.
A specific anxiety diagnosis.
A particular treatment duration.
FDA approval for the anxiety indication.

The phrase “effective amount” is a functional limitation. The administered quantity must be sufficient to treat anxiety in the relevant patient. A nominal administration that has no therapeutic effect would not satisfy the limitation, although infringement analysis would depend on the facts and applicable claim-construction principles.

How do Claims 1 through 9 differ?

Claims 2 through 9 narrow the alternatives, route, salt, and dosage contained in Claim 1.

Claim	Subject matter	Key limitation
1	Fluoxetine or norfluoxetine	Human anxiety treatment; effective amount; compound or salt
2	Fluoxetine	Excludes norfluoxetine
3	Fluoxetine	Oral administration
4	Fluoxetine	Fluoxetine hydrochloride
5	Fluoxetine	20-80 mg daily
6	Fluoxetine	60-80 mg daily
7	Norfluoxetine	Excludes fluoxetine
8	Norfluoxetine	Oral administration
9	Norfluoxetine	Norfluoxetine hydrochloride

What is the scope of Claim 1?

Claim 1 is the broadest and commercially most significant claim. It covers administration of either fluoxetine or norfluoxetine, including their pharmaceutically acceptable salts, for treating anxiety in a human.

Because Claim 1 does not specify route or dose, it potentially reaches oral, parenteral, and other routes, provided the treatment otherwise satisfies the claim. It also does not require fluoxetine hydrochloride. A different pharmaceutically acceptable salt could fall within the claim if it was administered in an effective amount for anxiety treatment.

The claim is directed to treatment of anxiety generally. It does not expressly distinguish generalized anxiety disorder, panic disorder, social anxiety disorder, adjustment-related anxiety, or another recognized diagnostic category.

What additional protection do Claims 2 through 6 provide?

Claims 2 through 6 create a progressively narrower fluoxetine sub-combination:

Claim 2 limits the compound to fluoxetine or a salt.
Claim 3 requires oral administration.
Claim 4 requires fluoxetine hydrochloride.
Claim 5 requires a daily dosage of 20-80 mg.
Claim 6 narrows the dosage to 60-80 mg daily.

Claim 6 is a subset of Claim 5. A 60 mg daily regimen falls within both claims. An 80 mg daily regimen also falls within both. A 40 mg daily regimen falls within Claim 5 but not Claim 6.

The dose limitations apply to the daily dosage level, not necessarily to the strength of an individual tablet or capsule. A 20 mg capsule administered twice daily could satisfy a 40 mg daily dosage limitation if the other claim elements were met.

What is the scope of Claims 7 through 9?

Claims 7 through 9 cover norfluoxetine separately from fluoxetine:

Claim 7 covers norfluoxetine or its pharmaceutically acceptable salts.
Claim 8 requires oral administration.
Claim 9 requires norfluoxetine hydrochloride.

These claims do not include a daily dosage limitation. Norfluoxetine was the active metabolite of fluoxetine and had a substantially longer half-life than the parent compound. The patent therefore attempted to protect both administration of the marketed parent drug and use of its metabolite.

When did U.S. Patent 4,590,213 expire?

U.S. Patent 4,590,213 expired on May 27, 2003, based on the pre-URAA patent term of 17 years from issuance.[1][2]

Event	Date
U.S. patent issued	May 27, 1986
Governing term for this patent	17 years from issuance
Expiration	May 27, 2003
Current enforceability	Expired

The patent predates the Uruguay Round Agreements Act term change that generally applies a 20-year term measured from the earliest effective nonprovisional filing date. Under the transition rules, older patents such as this one generally retained the 17-years-from-issuance rule unless the newer term was longer.[2]

There is no current U.S. patent enforcement right under the claims quoted by the user. Patent expiration eliminates the right to prevent conduct that would otherwise infringe. It does not eliminate the patent document, its prosecution history, or its value as prior-art evidence.

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

The patent was part of the historical U.S. intellectual-property environment surrounding Prozac, the original fluoxetine product marketed by Eli Lilly and Company. The FDA-approved Prozac labeling identified fluoxetine hydrochloride for major depressive disorder and other approved indications, including obsessive-compulsive disorder, bulimia nervosa, panic disorder, and premenstrual dysphoric disorder, depending on the applicable labeling version.[3]

The patent’s anxiety claim was broader than the approved indications identified in the Prozac label. A method patent does not itself establish FDA approval for the claimed use. Fluoxetine could be prescribed off-label for anxiety, but the FDA labeling and patent scope were separate legal and regulatory issues.

The FDA Orange Book historically identified patents associated with approved drug products, including patents relating to active ingredients, formulations, and methods of use. Orange Book listings do not extend patent terms, validate claims, or make an expired patent enforceable. Current generic products containing fluoxetine hydrochloride are approved through abbreviated new drug applications and are not blocked by the expiration of U.S. Patent 4,590,213.[4]

Norfluoxetine was not the commercial active ingredient in Prozac and was not generally positioned as an independently approved FDA drug product. Consequently, the norfluoxetine claims were more important as a patent-risk and research-protection tool than as a direct Orange Book barrier to a marketed norfluoxetine product.

What patents formed the broader fluoxetine patent estate?

The broader fluoxetine estate included compound, use, formulation, polymorph, and regulatory patents. U.S. Patent 4,590,213 was a method-of-use patent within that estate.

Patent category	Representative subject matter	Commercial relevance
Chemical compound	Fluoxetine and related phenoxyphenyl propylamines	Basic active-ingredient protection
Method of use	Anxiety and other psychiatric disorders	Indication-specific protection
Formulation	Fluoxetine hydrochloride dosage forms and pharmaceutical compositions	Product and dosage-form protection
Solid-state technology	Crystalline or polymorphic forms of fluoxetine hydrochloride	Manufacturing and product-quality protection
Regulatory patents	Approved indications and use codes	ANDA certification and launch timing

The foundational fluoxetine compound patent, U.S. Patent No. 4,314,081, was issued to Eli Lilly and Company and covered fluoxetine-related chemical matter.[5] That patent expired before U.S. Patent 4,590,213. Later fluoxetine patents included patents associated with approved uses and solid-state forms, including U.S. Patent No. 5,427,800, which was litigated in connection with generic Prozac competition.[6]

The commercial significance of U.S. Patent 4,590,213 therefore depended on the interaction between it and later patents. Once the compound patent expired, a generic manufacturer could generally seek approval to market fluoxetine, subject to any unexpired method-of-use, formulation, polymorph, or regulatory patents.

Which companies challenged the Prozac patent estate?

Barr Laboratories was a leading generic challenger in the Prozac patent litigation. In Eli Lilly & Co. v. Barr Laboratories, Inc., the Federal Circuit addressed Lilly’s patent position concerning fluoxetine hydrochloride and generic competition.[6]

The litigation is commonly associated with later fluoxetine patent protection, particularly U.S. Patent No. 5,427,800, rather than with a current enforcement action under the expired claims of U.S. Patent 4,590,213. The case illustrates the commercial strategy used in the Prozac market: generic applicants challenged later patents after the basic compound patent had expired, while the brand holder asserted secondary patents involving product form and related technology.

A Paragraph IV certification would have been relevant only while a listed patent remained unexpired and enforceable. A Paragraph IV challenge to an expired patent cannot support a current statutory 30-month stay or a present infringement action based on that patent.[7]

What was the impact of Paragraph IV challenges and generic entry?

The expiration of the primary fluoxetine compound protection opened the market to ANDA applicants. Generic applicants could rely on the innovator’s clinical data through the abbreviated pathway and certify against listed patents under the Hatch-Waxman framework.[7]

For an anxiety-related use, the key legal distinction was between:

A product patent or compound patent.
A method-of-use patent covering anxiety.
A label that included or omitted the patented indication.
A generic product approved for only non-patented uses through a section viii statement.
A patent that had already expired.

The fluoxetine market demonstrates why method-of-use patents do not always prevent generic product entry. A generic applicant may enter for non-patented indications while using labeling strategies that omit a patented use, subject to the statutory requirements and the facts surrounding the patent and proposed label.

Because U.S. Patent 4,590,213 expired in 2003, it no longer creates a Paragraph IV launch risk. Any historic settlement involving Prozac or fluoxetine would have to be analyzed against the particular patent asserted, the settlement date, the generic applicant, and the agreed entry date. The existence of a Prozac patent settlement does not establish that Patent 4,590,213 remained enforceable after its expiration.

How strong was the patent estate for fluoxetine?

U.S. Patent 4,590,213 was commercially broad when unexpired but technically vulnerable to several validity and scope issues.

Claim breadth

Claim 1 had broad therapeutic coverage because it did not limit the anxiety condition, route, formulation, or dose. Its principal limitations were the identity of the active compound and the requirement that the subject have anxiety.

Enablement and written description

The patent claimed both fluoxetine and norfluoxetine. A validity analysis would examine whether the specification adequately described and enabled the full scope of both compounds, their salts, and their use for anxiety. Broad therapeutic claims covering multiple compounds can raise written-description and enablement questions, particularly where the disclosure contains limited clinical evidence.

Definiteness

“An effective amount” is common in pharmaceutical method claims. Its enforceability depends on whether the specification and ordinary medical practice provide an objective basis for identifying a therapeutically effective amount. Claims 5 and 6 reduce this issue by specifying daily dosage ranges for fluoxetine.

Anticipation and obviousness

A challenger could examine earlier disclosures of fluoxetine, norfluoxetine, psychiatric treatment, and related antidepressant uses. The legal question would be whether a single prior-art reference disclosed every claim element for anticipation, or whether the claimed anxiety treatment would have been obvious in view of the prior art for obviousness purposes.[8]

Enforceability

Potential enforceability issues would include inequitable conduct, prosecution disclosure obligations, inventorship, and claim interpretation. Those issues have no current commercial effect because the patent expired in 2003.

What generic entry risks exist for fluoxetine today?

There is no current generic-entry risk arising from U.S. Patent 4,590,213. Fluoxetine hydrochloride is available from multiple generic manufacturers, and the product has long been subject to generic competition through the FDA’s ANDA system.[4]

Current commercial risks would instead relate to:

Manufacturing cost and supply reliability.
FDA manufacturing compliance.
Product recalls.
Active pharmaceutical ingredient sourcing.
Bioequivalence and dissolution performance.
State substitution rules.
Competition among generic fluoxetine suppliers.
Any separate, unexpired patent covering a new formulation, delivery system, or combination product.

A new formulation using fluoxetine would require a separate patent analysis. Patent 4,590,213 does not protect a delivery system, extended-release formulation, combination therapy, salt-selection strategy, or manufacturing process independent of the claimed anxiety treatment.

Does the patent create biosimilar risk?

No. Fluoxetine is a small-molecule drug, not a biologic. Biosimilar approval under section 351(k) of the Public Health Service Act does not apply. Fluoxetine competition proceeds through generic-drug pathways, principally ANDAs under section 505(j) of the Federal Food, Drug, and Cosmetic Act.[7]

Norfluoxetine also does not create a biosimilar issue. If developed as a new small-molecule drug product, it would be evaluated under a small-molecule NDA or applicable abbreviated pathway, not the biosimilar framework.

What is the geographic coverage of U.S. Patent 4,590,213?

The patent covered conduct within the United States, including U.S. manufacture, use, sale, offers for sale, and importation to the extent those activities implicated the asserted method claims. It did not directly provide patent protection in Europe, Canada, Japan, or other jurisdictions.

Foreign protection would require separate national or regional patents. A U.S. patent expiration date does not establish the expiration date of a corresponding foreign patent. For current global freedom-to-operate work, the relevant analysis would include national patent registers, continuation applications, divisional patents, SPCs, and local term-adjustment rules.

Key Takeaways

U.S. Patent 4,590,213 claimed treatment of human anxiety with fluoxetine, norfluoxetine, or pharmaceutically acceptable salts.
Claim 1 was broad and did not limit route, dosage, formulation, or specific anxiety disorder.
Claims 2 through 6 narrowed the invention to fluoxetine, oral administration, fluoxetine hydrochloride, and 20-80 mg or 60-80 mg daily dosing.
Claims 7 through 9 covered norfluoxetine, including oral norfluoxetine hydrochloride.
The patent issued May 27, 1986, and expired May 27, 2003.
The patent no longer creates a U.S. infringement, Paragraph IV, Orange Book, or generic-launch barrier.
Fluoxetine is a small molecule and has generic competition, not biosimilar competition.
Later fluoxetine patents, including formulation and polymorph patents, were more relevant to the timing of generic Prozac entry.
Any current patent risk must come from a separate, unexpired patent.

FAQs About U.S. Patent 4,590,213

Can a doctor still prescribe fluoxetine for anxiety?

Yes. Patent 4,590,213 does not restrict prescribing because it expired in 2003. Prescribing decisions remain subject to medical judgment and the FDA-approved labeling for the relevant product.

Did Patent 4,590,213 cover generalized anxiety disorder specifically?

No specific anxiety subtype appears in the quoted claims. The language covers “anxiety” generally, subject to the other claim elements and the scope supported by the patent specification.

Did the patent cover Prozac capsules?

The patent did not claim a capsule, tablet, or specific dosage form as such. It claimed methods of administering the active compound for anxiety. The product could fall within a method claim only when used in the claimed treatment method during the patent term.

Did the patent cover combination treatment with fluoxetine?

The claims require administration of an effective amount of fluoxetine or norfluoxetine but do not expressly require monotherapy. A combination regimen could potentially have fallen within the claims if the claimed compound was administered for treating anxiety and the other elements were met.

Could a company commercialize norfluoxetine based on the expiration of this patent?

Expiration removes this patent as a barrier, but it does not establish FDA approval, clinical safety, bioequivalence, manufacturing compliance, or freedom from other unexpired patents. Norfluoxetine would require its own regulatory and patent assessment.

References

United States Patent and Trademark Office. (1986). U.S. Patent No. 4,590,213: Treatment of anxiety with fluoxetine and norfluoxetine.
35 U.S.C. § 154(c)(1). Patent term transition provisions for applications filed before June 8, 1995.
U.S. Food and Drug Administration. (2023). Prozac (fluoxetine hydrochloride) prescribing information.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations (Orange Book).
United States Patent and Trademark Office. (1982). U.S. Patent No. 4,314,081: N-substituted-3-phenyl-3-(substituted phenoxy)propylamines.
Eli Lilly & Co. v. Barr Laboratories, Inc., 251 F.3d 955 (Fed. Cir. 2001).
Drug Price Competition and Patent Term Restoration Act of 1984, 21 U.S.C. § 355(j); 35 U.S.C. § 271(e).
35 U.S.C. §§ 102, 103, 112.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	2645784	⤷ Start Trial
Australia	556476	⤷ Start Trial
Germany	3413093	⤷ Start Trial
Germany	3467704	⤷ Start Trial
Denmark	113284	⤷ Start Trial
Denmark	166479	⤷ Start Trial
European Patent Office	0123469	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,590,213

Summary for Patent: 4,590,213