United States Patent 5,874,447: Paroxetine Salt Claims, Patent Scope, Expiration, and Generic Risk

US Patent 5,874,447 covers paroxetine salt compounds, processes for producing and interconverting those salts, pharmaceutical compositions, and therapeutic uses. The patent was issued on February 23, 1999, to SmithKline Beecham Corporation and is directed primarily to paroxetine sulfonate salts and related salt forms, including paroxetine maleate and paroxetine acetate.[1]

The patent expired in December 2016 under the ordinary 20-year term calculated from its earliest effective nonprovisional filing date. It therefore does not create a current U.S. patent barrier to generic paroxetine. Its historical importance was greater: the claims could have been asserted against manufacture, formulation, or use of specified paroxetine salts during the patent term.

What does US Patent 5,874,447 protect?

The patent protects five principal subject-matter groups:

Paroxetine sulfonate salt compounds defined by the R2 substituent.
Processes for making those sulfonate salts.
Processes for converting sulfonate salts into other salts, solvates, or the free base.
Pharmaceutical compositions containing the claimed compounds.
Methods of treating specified disorders with the claimed compounds.

The claim text identifies the active pharmaceutical ingredient as paroxetine. Claim 9 expressly recites paroxetine maleate, and claim 10 recites paroxetine acetate. Claims 22 through 29 narrow the covered salts and therapeutic uses to specific R2 groups and indications.

Claim architecture

Claim group	Subject matter	Principal limitation
Claims 1-5	Compound claims	Paroxetine sulfonate salt with R2 defined as C1-C10 alkyl or substituted/unsubstituted phenyl
Claims 6-14	Manufacturing and salt-conversion processes	Reaction with R2-SO3H, subsequent acid/base treatment, and purity requirements
Claim 15	Product-by-process compound	Compound produced by the process of claim 6
Claims 16-17	Pharmaceutical compositions	Composition containing the claimed salt; claim 17 limits the form to a solid dosage form
Claims 18-20	Treatment methods	Depression, OCD, panic disorder, bulimia, anorexia, pain, obesity, dementia, migraine, or social phobia
Claim 21	Specific compound	Formula shown in the issued patent
Claims 22-26	Narrow compositions	Specific R2 groups, oral administration, methyl salt, solid dosage form, and tablets
Claims 27-29	Narrow treatment methods	Depression, OCD, or panic disorder using specified salts, particularly the methyl salt

The formula drawings are not reproduced in the supplied text because they appear as ##STR## placeholders. The explicit paroxetine references in claims 9 and 10, together with the patent’s subject matter, establish the relevant active ingredient, but a formula-dependent infringement analysis must use the issued patent drawings and chemical definitions.

How broad are the compound claims?

Claim 1 is the principal composition-of-matter claim. It covers a genus of paroxetine sulfonate salts in which R2 is:

A C1-C10 alkyl group; or
A substituted or unsubstituted phenyl group.

Permitted phenyl substituents include C1-C10 alkyl, halogen, nitro, hydroxy, alkoxy, and combinations of those groups.

Claims 2 and 3 narrow the alkyl definition to C1-C4 and C1-C2, respectively. These limitations capture short-chain alkyl sulfonates, including methyl and ethyl sulfonate species.

The claim structure is broad because it does not limit the compound to one commercial salt. It covers a class of salts formed from sulfonic acids of the general formula R2-SO3H. Depending on the complete chemical formula in the issued patent, the genus can include methanesulfonate, ethanesulfonate, longer alkyl sulfonates, benzene sulfonate, substituted benzene sulfonates, and related species.

What specific salts are identified?

The claims expressly identify or imply the following compounds:

Salt or compound category	Treatment in the claims
Paroxetine methanesulfonate	Covered by the R2 methyl embodiment and claims 22-26
Paroxetine ethanesulfonate	Covered by the R2 ethyl embodiment
Paroxetine benzyl or substituted benzyl sulfonate	Identified in claims 22 and 27
Paroxetine tolyl sulfonate	Identified in claims 22 and 27
Paroxetine maleate	Expressly recited in claim 9
Paroxetine acetate	Expressly recited in claim 10
Paroxetine free base	Produced through the base-treatment process in claims 11-14
Solvates and acid-addition forms	Addressed in claim 7

The claims do not simply cover paroxetine hydrochloride as a standalone compound. A product containing only paroxetine hydrochloride would require separate analysis against the complete claim language and formula. The patent’s strongest direct coverage is for the sulfonate salt genus and products made through the specified sulfonate-mediated processes.

What manufacturing processes are protected?

Claims 6 through 14 protect a salt-conversion platform.

Claim 6 requires mixing a paroxetine compound, salt, or base with a sulfonic acid having the formula R2-SO3H to produce a claimed sulfonate salt. This is a process claim, not merely a claim to the resulting compound.

Claim 7 expands the process to further reaction with acids, water, methanol, ethanol, or other listed reagents. The process can produce:

Other acid-addition salts;
Solvates;
Free base;
Isolated solid forms.

Claims 8, 9, 10, 13, and 14 add purity limitations. The principal thresholds are:

At least 90 wt% purity for certain recovered salts;
At least 98% purity for paroxetine maleate;
At least 98% purity for paroxetine acetate;
At least 95% purity for isolated free base;
At least 98% purity for the narrower free-base embodiment.

Does the process claim reach generic manufacturing?

Potentially, but only if the accused process practices each required step. A generic manufacturer producing paroxetine hydrochloride directly from another intermediate may avoid literal infringement of claim 6 if it does not use a sulfonic acid of the claimed formula. A process that creates a covered sulfonate salt and then converts it into another form presents greater exposure during the patent term.

The process claims do not automatically cover every route to paroxetine or every route to paroxetine hydrochloride. They require the claimed sulfonic-acid reaction or the specified downstream conversion steps.

What is the scope of the solubility claims?

Claims 4 and 5 add solubility limitations:

Claim 4 requires solubility of at least about 10 mg/mL in water at approximately 20°C.
Claim 5 requires at least 1,000 mg/mL at approximately 20°C.

Claim 5 is unusually demanding. A solubility of 1,000 mg/mL is equivalent to 1 gram per milliliter of water and may raise technical questions concerning how the value was measured, whether the units were accurately transcribed, and whether the specification provides adequate support. The claim remains part of the issued patent, but its practical enforceability would depend on claim construction, analytical evidence, and the patent’s specification.

The use of “about” creates additional claim-construction issues. The relevant tolerance would likely be assessed in light of the specification, measurement method, temperature control, and ordinary pharmaceutical analytical practice.

What formulations are protected by US 5,874,447?

Claims 16 and 17 cover pharmaceutical compositions containing a therapeutically effective amount of a claimed paroxetine salt and a pharmaceutically acceptable carrier or diluent. Claim 17 limits the composition to a solid dosage form.

Claims 22 through 26 create a narrower formulation chain:

Claim 22 covers a composition containing a salt in which R2 is methyl, ethyl, benzyl, p-chlorobenzyl, or tolyl.
Claim 23 limits the composition to oral administration.
Claim 24 narrows R2 to methyl.
Claim 25 limits the composition to a solid dosage form.
Claim 26 further limits it to a tablet.

The commercial relevance of these claims is greatest for an oral tablet containing the specifically claimed methyl salt. They do not necessarily cover every paroxetine tablet. The active salt, chemical structure, and complete formulation must fall within the claim limitations.

What method-of-use claims are covered?

Claims 18 through 20 cover treatment of a broad list of conditions, including:

Depression;
Obsessive-compulsive disorder;
Panic disorder;
Bulimia;
Anorexia;
Pain;
Obesity;
Senile dementia;
Migraine;
Social phobia.

Claims 27 through 29 are narrower. They cover treatment of depression, obsessive-compulsive disorder, or panic disorder with a compound having one of the listed R2 groups. Claims 28 and 29 focus on the methyl embodiment and an effective antidepressant amount.

These claims are method claims directed to administration to a patient. Claim 19 expressly limits the patient to a human. During the patent term, infringement could have depended on the labeled indication, physician or patient instructions, promotional activity, and the identity of the salt actually administered.

After expiration, these method claims no longer create a live U.S. patent restriction.

When did US Patent 5,874,447 expire?

Event	Date
Patent issued	February 23, 1999
Earliest relevant priority period	Mid-1990s
Estimated ordinary patent expiration	December 2016
Current status	Expired

The U.S. patent term for applications filed after June 8, 1995, generally runs 20 years from the earliest effective U.S. nonprovisional filing date, subject to patent-term adjustment and other statutory provisions.[2] Public patent records identify the patent as expired after completion of its term. No current enforceable U.S. exclusivity should be attributed to US 5,874,447.

The exact terminal date should be taken from the USPTO patent record and any recorded term adjustment. That distinction would have mattered for historical litigation, but it does not change the present expired status.

What was the Orange Book status of US 5,874,447?

US 5,874,447 was associated with the historical U.S. patent estate for paroxetine products marketed by SmithKline Beecham and later GlaxoSmithKline. The relevant reference product was Paxil, whose active ingredient is paroxetine hydrochloride.[3]

The Orange Book distinguishes between:

Drug substance patents;
Drug product or formulation patents;
Method-of-use patents;
Patent expiration dates;
Use codes for listed indications.

A patent’s historical Orange Book listing does not extend its enforceable term. Because US 5,874,447 expired in 2016, it is not a current barrier to ANDA approval or generic launch.

The patent also should not be confused with other paroxetine patents, including patents directed to paroxetine itself, paroxetine hydrochloride hemihydrate, controlled-release formulations, or specific manufacturing processes. Those patents had separate expiration dates and different claim scopes.

Which companies challenged the paroxetine patent estate?

The paroxetine market was subject to extensive generic competition and historical ANDA litigation. Generic applicants included major manufacturers such as Apotex, Mylan, Par Pharmaceutical, and other ANDA sponsors. Public litigation involving Paxil and paroxetine products included challenges to patents covering the active compound, salt forms, and controlled-release products.

The existence of litigation against one paroxetine patent does not establish a challenge to every patent in the portfolio. A Paragraph IV certification must be evaluated patent by patent and claim by claim. For US 5,874,447, the key historical issues would have been:

Whether the proposed product contained a claimed sulfonate salt;
Whether the generic process used a claimed sulfonic-acid conversion step;
Whether the proposed formulation met the claimed composition limitations;
Whether the listed treatment use fell within claims 18-20 or 27-29;
Whether the claims were invalid for anticipation, obviousness, lack of enablement, written-description deficiency, or indefiniteness.

Because the patent is expired, no current Paragraph IV risk remains for this patent itself.

How strong was the patent estate?

The patent had meaningful historical breadth but limited present commercial strength.

Attribute	Assessment
Composition claims	Broad genus, but dependent on the complete chemical formula and salt definition
Process claims	Potentially useful against manufacturing routes using the claimed sulfonic-acid step
Formulation claims	Narrower and concentrated on specific salt, route, dosage form, and tablet limitations
Method claims	Broad indications in early claims, narrower specific salts and conditions in later claims
Validity pressure	Potential issues involving genus breadth, support, purity limitations, solubility, and obviousness
Current enforceability	None in the United States because the patent expired
Biosimilar relevance	None; paroxetine is a small-molecule drug
Generic relevance	Historical only for this patent; current competition is governed by other surviving rights, if any

The broadest claims likely faced greater validity scrutiny than the narrower claims. Claims 9, 10, 24, 26, 28, and 29 contain more specific chemical or commercial limitations and would generally present a narrower infringement target. The narrower claims can be easier to prove against a matching product but easier to design around.

What generic launch risks existed?

During the patent term, generic launch risk depended on the proposed product:

Direct salt substitution

A generic containing a paroxetine sulfonate salt within the R2 genus could have faced direct composition claims under claim 1.

Alternative salt selection

A generic using a salt outside the R2 definition could have reduced direct composition-claim exposure, although other paroxetine patents might still have applied.

Route selection

A manufacturer could avoid claims 6-14 by selecting a process that did not use the claimed sulfonic acid or sulfonate intermediate.

Formulation design-around

A non-tablet product, a different salt, or a formulation outside the claimed composition could have reduced exposure to claims 22-26.

Label strategy

The method claims created greater exposure where the product labeling promoted depression, OCD, or panic-disorder treatment with a listed salt. After patent expiration, these design-around considerations became commercially unnecessary for this patent.

Were there licensing deals or settlements?

The patent record establishes ownership by SmithKline Beecham and the later commercial relationship with GlaxoSmithKline. A patent assignment is not the same as a generic settlement or license.

No broadly reported, patent-specific licensing arrangement can be established from the claim text alone. Historical Paxil litigation included settlements and commercial agreements involving generic applicants, but those agreements may have covered multiple patents, products, or formulations. Their terms should not be attributed specifically to US 5,874,447 without the underlying settlement documents or court docket.

What geographic coverage does the patent have?

US 5,874,447 provided rights only in the United States. It did not directly control:

European paroxetine salts;
Canadian paroxetine products;
Japanese paroxetine products;
Manufacturing performed entirely outside the United States;
Foreign sales without a U.S. importation or U.S. commercial nexus.

Related foreign applications may have produced counterpart patents, but each jurisdiction required separate prosecution, claim scope, term analysis, and validity review. U.S. expiration did not determine the status of foreign counterparts.

Key Takeaways

US 5,874,447 is a paroxetine salt and process patent.
Its broadest claims cover paroxetine sulfonate salts defined by an R2 alkyl or substituted phenyl group.
Claims 9 and 10 expressly address paroxetine maleate and paroxetine acetate.
Claims 6-14 target salt formation, salt conversion, free-base recovery, solvates, and purity-controlled isolation.
Claims 16-17 and 22-26 cover pharmaceutical compositions, including oral solid tablets containing specified salts.
Claims 18-20 and 27-29 cover treatment of depression, OCD, panic disorder, and other conditions.
The patent expired in December 2016 and is not a current U.S. exclusivity barrier.
Paroxetine is a small molecule, so biosimilar analysis does not apply.
Historical Paragraph IV and litigation risk centered on the broader Paxil patent portfolio, not necessarily this patent alone.
Current generic strategy should focus on any unexpired paroxetine patents, regulatory exclusivity, formulation rights, and process patents rather than US 5,874,447.

FAQs About US Patent 5,874,447

Does US 5,874,447 cover paroxetine hydrochloride?

Not necessarily. The patent principally claims paroxetine sulfonate salts and related conversions. Paroxetine hydrochloride requires separate analysis under the complete chemical formula and other patents in the paroxetine estate.

Can a generic company launch paroxetine despite US 5,874,447?

Yes. The patent expired in 2016, so it no longer blocks a U.S. generic launch.

Does the patent cover paroxetine tablets?

Claims 16-17 cover pharmaceutical compositions and solid dosage forms containing a claimed compound. Claims 22-26 narrow that coverage to specified salts, oral administration, and tablets.

Is paroxetine eligible for a biosimilar pathway?

No. Paroxetine is a chemically synthesized small-molecule drug regulated through the ANDA pathway, not the biologics biosimilar pathway.

Did the patent protect Paxil CR?

The supplied claims do not specifically recite a controlled-release delivery system. Paxil CR was protected through separate formulation and controlled-release patent rights, which must be analyzed independently.

References

U.S. Patent No. 5,874,447. (1999). Paroxetine salts and processes for their preparation. United States Patent and Trademark Office.
United States Code, 35 U.S.C. § 154. (2024). Contents and term of patents; provisional rights.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
U.S. Food and Drug Administration. (2024). Drugs@FDA: FDA-approved drugs. Center for Drug Evaluation and Research.
United States Patent and Trademark Office. (2024). Patent Center and patent term information.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	200781	⤷ Start Trial
Australia	3108097	⤷ Start Trial
Bulgaria	103980	⤷ Start Trial
Bulgaria	64315	⤷ Start Trial
Brazil	9714787	⤷ Start Trial
Canada	2293247	⤷ Start Trial
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Details for Patent: 5,874,447

Summary for Patent: 5,874,447