United States Patent 3,862,319: Scope, Claims, Piroxicam Coverage, and Patent Landscape

United States Patent No. 3,862,319 is an early oxicam patent directed to 1,2-benzothiazine carboxamides and their use as therapeutic agents. The supplied claims cover substituted benzothiazine-3- and -4-carboxamides, including piroxicam and multiple related analogues. The patent issued in 1975 and, under the pre-1995 United States patent-term rule, expired in January 1992. It no longer creates a patent barrier to U.S. manufacture, sale, or use.

The principal commercial compound identifiable in the supplied claims is piroxicam, covered expressly by claim 17. The patent is historically important but has no current Orange Book, Paragraph IV, biosimilar, or generic-entry blocking effect.

What patent is United States Patent 3,862,319?

United States Patent 3,862,319 concerns substituted 1,2-benzothiazine derivatives, commonly referred to as oxicam compounds. The claimed structures contain:

A fused benzothiazine ring system.
A 1,1-dioxide sulfonamide group.
A carboxamide substituent at either the 3- or 4-position.
Variable aryl or heteroaryl groups designated R2.
Alkyl or hydrogen substitution designated R3.
A claimed therapeutic method incorporated through claim 1.

The patent issued on January 21, 1975. It belongs to the first generation of oxicam anti-inflammatory patent families associated with piroxicam and structurally related nonsteroidal anti-inflammatory drugs. The patent document is the controlling source for its exact specification, prosecution history, inventorship, assignee, and claim language. [1]

What compounds do claims 2 through 22 cover?

Claims 2 through 13 are genus claims. They cover categories of compounds defined by the nature of R2 and R3. Claims 14 through 22 are narrower species claims directed to named chemical compounds.

Claim	Core ring system	R2 or named substituent	R3 or N-substitution	Claim type
2	4-oxo-3-carboxamide	Phenyl	C1-C3 alkyl	Genus
3	4-oxo-3-carboxamide	Chlorophenyl	C1-C3 alkyl	Genus
4	4-oxo-3-carboxamide	Dichlorophenyl	C1-C3 alkyl	Genus
5	4-oxo-3-carboxamide	Phenyl	Hydrogen	Genus
6	4-oxo-3-carboxamide	2-Thiazolyl	C1-C3 alkyl	Genus
7	4-oxo-3-carboxamide	Pyridyl	C1-C3 alkyl	Genus
8	4-oxo-3-carboxamide	Methyl-2-pyridyl	C1-C3 alkyl	Genus
9	3-oxo-4-carboxamide	Phenyl	C1-C3 alkyl	Genus
10	3-oxo-4-carboxamide	Chlorophenyl	C1-C3 alkyl	Genus
11	3-oxo-4-carboxamide	Pyridyl	C1-C3 alkyl	Genus
12	3-oxo-4-carboxamide	Bromophenyl	C1-C3 alkyl	Genus
13	3-oxo-4-carboxamide	Naphthyl	C1-C3 alkyl	Genus
14	4-oxo-3-carboxanilide	Phenyl anilide	2-Methyl	Species
15	4-Hydroxy-3-carboxamide	2-Thiazolyl	2-Methyl	Species
16	3-Oxo-4-carboxanilide	4-Bromophenyl	2-Methyl	Species
17	4-Hydroxy-3-carboxamide	2-Pyridyl	2-Methyl	Species
18	4-Hydroxy-3-carboxamide	4,5-Dimethyl-2-thiazolyl	2-Methyl	Species
19	4-Hydroxy-3-carboxamide	4-Methyl-2-pyridyl	2-Methyl	Species
20	4-Hydroxy-3-carboxamide	6-Methyl-2-pyridyl	2-Methyl	Species
21	4-Hydroxy-3-carboxamide	5-Chloro-2-pyridyl	2-Methyl	Species
22	4-Hydroxy-3-carboxamide	5-Bromo-2-pyridyl	2-Methyl	Species

The compounds in claims 2 through 13 are defined by chemical classes rather than by individual compound names. Their scope depends on the precise definitions of R2, R3, the ring numbering, and the therapeutic limitation in claim 1.

Does United States Patent 3,862,319 cover piroxicam?

Yes. Claim 17 expressly identifies piroxicam under its chemical name:

4-hydroxy-2-methyl-N-(2-pyridyl)-2H-1,2-benzothiazine-3-carboxamide-1,1-dioxide.

That structure corresponds to piroxicam, the active ingredient in Feldene. Piroxicam is an oxicam-class NSAID used primarily for osteoarthritis and rheumatoid arthritis. [2]

Claim 17 is narrower than a broad chemical genus because it identifies one specific compound. A product containing piroxicam would fall within claim 17 only if the method limitations inherited from claim 1 were also satisfied. The claim is a method claim, not a standalone composition claim.

This distinction matters:

A composition claim can cover the compound itself.
A method claim covers use of the compound in the claimed treatment.
A manufacturing process claim covers making the compound by the claimed process.
Claim 17, as supplied, is limited to the claimed method of use.

The missing text of claim 1 prevents a complete construction of the method limitation. Claims 2 through 22 expressly depend on claim 1, so each includes every limitation of claim 1.

How broad are the genus claims?

Claims 2 through 13 use structural categories that extend beyond piroxicam.

Claims 2 through 8: 4-oxo-3-carboxamide series

These claims cover compounds in which the benzothiazine core has a 4-oxo group and a 3-carboxamide. The R2 group may be phenyl, chlorophenyl, dichlorophenyl, thiazolyl, pyridyl, or methyl-substituted pyridyl. R3 is an alkyl group containing one to three carbon atoms, except claim 5, which allows hydrogen.

The claim language potentially covers methyl, ethyl, and propyl substitution, subject to the definitions and structural formula in claim 1. Claim 17 represents the hydroxy tautomeric or corresponding named form of the 4-oxo-3-carboxamide class with a 2-pyridyl amide and a 2-methyl substituent.

Claims 9 through 13: 3-oxo-4-carboxamide series

These claims reverse the functional arrangement. The compounds contain a 3-oxo group and a 4-carboxamide. The R2 groups include phenyl, chlorophenyl, pyridyl, bromophenyl, and naphthyl.

This series is chemically distinct from the piroxicam structure in claim 17. A compound satisfying the 3-oxo-4-carboxamide architecture would not fall within claim 17, although it could fall within claims 9 through 13 if the method limitation were met.

What is the legal significance of claims 14 through 22?

Claims 14 through 22 are species claims that narrow the broader structural classes. Their legal value would historically have been strongest against use of the specifically identified compounds, particularly where a defendant’s product or clinical use matched the claim 1 treatment limitation.

The species claims include:

A methyl-substituted carboxanilide.
Thiazolyl analogues.
Pyridyl analogues.
Halogenated pyridyl analogues.
Methyl-substituted pyridyl analogues.
A bromophenyl analogue.

Claim 17 has the greatest commercial relevance because it identifies piroxicam. Claims 19 through 22 cover close pyridyl analogues that may have been investigated as oxicam candidates but do not, based solely on the supplied claim language, become piroxicam merely because they share the same benzothiazine core.

The claims do not expressly recite:

A particular dosage strength.
A tablet, capsule, injectable, gel, or topical formulation.
A salt, hydrate, solvate, polymorph, or crystal form.
A specific manufacturing process.
A particular pharmaceutical excipient.
A controlled-release or enteric-release delivery system.

When did United States Patent 3,862,319 lose exclusivity?

The patent issued January 21, 1975. Because it was filed and issued under the former United States patent-term system, its ordinary term was 17 years from grant. The expected expiration date was January 21, 1992. [1]

Event	Date or status
Patent issued	January 21, 1975
Applicable term	17 years from grant
Expected expiration	January 21, 1992
Current status	Expired
Current blocking effect	None in the United States

The patent predates the 20-year-from-earliest-effective-filing-date rule established by the Uruguay Round Agreements Act. It also predates modern patent-term adjustment and patent-term extension practice. No current patent-term extension is relevant to the 1975 patent.

What was the FDA and Orange Book status of piroxicam?

Piroxicam was approved in the United States as Feldene, sponsored by Pfizer, under NDA 018023. FDA approval occurred in 1982. The product was approved for symptomatic treatment of osteoarthritis and rheumatoid arthritis. [2]

The Orange Book historically listed patents associated with approved piroxicam products where applicable. Patent listings for the original product cannot extend beyond the enforceable life of the listed patent. Once United States Patent 3,862,319 expired in 1992, it ceased to provide a basis for blocking an ANDA applicant.

FDA approval and patent protection are separate systems:

FDA approval establishes regulatory authorization.
Orange Book listing identifies patents submitted for an approved small-molecule product.
Patent expiration ends enforceable exclusion.
Regulatory exclusivity may expire independently of patent rights.

Piroxicam is a small molecule, so biosimilar regulation does not apply. Generic applicants use the ANDA pathway, not the biosimilar pathway under the Public Health Service Act. [3]

What Paragraph IV challenges affected piroxicam?

A Paragraph IV certification is relevant when an ANDA applicant asserts that an Orange Book-listed patent is invalid, unenforceable, or will not be infringed. [4]

For United States Patent 3,862,319, a current Paragraph IV challenge is legally immaterial because the patent expired decades ago. Any historical Paragraph IV dispute would have depended on:

Whether the patent was listed for the relevant NDA.
Whether the patent remained unexpired when the ANDA was submitted.
Whether the applicant challenged the patent under Paragraph IV.
Whether the patent holder filed an infringement action within the statutory 45-day period.
Whether litigation triggered a 30-month stay.

No present-day generic launch risk can be attributed to this patent. Any commercial restriction on a piroxicam generic would have to arise from a different unexpired patent, regulatory exclusivity, manufacturing issue, supply constraint, or market strategy.

What formulations are protected by this patent?

The supplied claims do not contain formulation claims. They are method claims directed to use of defined benzothiazine compounds. On the supplied language, the patent does not separately claim:

Immediate-release tablets.
Capsules.
Injectable formulations.
Topical formulations.
Transdermal systems.
Sustained-release systems.
Specific particle sizes.
Solid-state forms.
Particular excipient combinations.

A formulation could have been implicated indirectly if it were used to practice the claimed therapeutic method during the patent term. That would not convert the patent into a formulation patent.

The distinction is commercially important. A later formulation patent could have protected a dosage form even after the underlying compound patent expired. Such a later patent would need separate analysis based on its claims, filing date, term, and Orange Book listing.

How does this patent compare with later oxicam patent estates?

Product or class	Relationship to US 3,862,319	Current patent relevance
Piroxicam	Expressly identified in claim 17	Patent 3,862,319 expired
Isoxicam-type analogues	Structurally related oxicam compounds	Separate patent and regulatory analysis required
Tenoxicam	Later thienothiazine oxicam	Not covered merely by sharing the oxicam pharmacophore
Meloxicam	Later oxicam with different substitution pattern	Separate later patent estate
Generic piroxicam	Product corresponding to claim 17 compound	No current risk from US 3,862,319

Piroxicam, tenoxicam, and meloxicam should not be treated as one patent family. Similar pharmacology or an oxicam core does not establish literal infringement. Claim scope turns on the required atoms, substituents, positions, and method limitations.

What manufacturing and IP barriers remain for piroxicam?

United States Patent 3,862,319 no longer creates a manufacturing barrier. A current manufacturer would instead assess:

Freedom to operate for the synthetic route.
Process patents filed after 1975.
Solid-state, salt, hydrate, or polymorph rights.
Impurity-control and purification patents.
Formulation patents.
Regulatory requirements for an ANDA.
Active pharmaceutical ingredient supplier qualification.
Pharmacopoeial and stability specifications.
International patent rights outside the United States.

A process that produces piroxicam may be commercially available while still requiring independent review of later process patents in jurisdictions where those patents remain active. The expired compound and method claims do not immunize a manufacturer from infringement of a separate later process or formulation patent.

What licensing deals and litigation affect this patent?

The patent record alone does not establish a current licensing obligation. The patent was historically associated with the commercial development of piroxicam by Pfizer, but ownership, licensing, and commercialization arrangements must be separated from the patent’s claim scope.

No current litigation can be based on an expired United States patent. Historical infringement litigation, if any, would not revive enforceability after expiration. Settlement agreements also cannot extend the statutory patent term against the public, although confidential commercial arrangements may have governed historical generic entry.

How strong is the patent estate today?

The estate is commercially weak in the United States because the identified patent expired in 1992.

Risk category	Assessment
Compound patent risk	None from US 3,862,319
Method-of-use risk	None from US 3,862,319
Formulation risk	Not addressed by supplied claims
Biosimilar risk	Not applicable
Paragraph IV risk	Historical only
Generic-entry risk	No current risk from this patent
Manufacturing risk	Requires separate later-process review
Foreign territorial risk	Requires country-by-country review
Piroxicam commercial relevance	Historical and scientific, not exclusivity-blocking

The patent remains relevant as prior art and as evidence of the early oxicam chemical genus. It does not support a current U.S. exclusivity position.

Key Takeaways

United States Patent 3,862,319 covers methods involving substituted 1,2-benzothiazine carboxamides.
Claim 17 expressly covers piroxicam by chemical name.
Claims 2 through 13 are broader genus claims covering phenyl, halophenyl, pyridyl, thiazolyl, and naphthyl analogues.
Claims 14 through 22 are narrower species claims.
All supplied claims depend on claim 1, so its treatment limitation is required.
The patent issued in 1975 and expired approximately January 21, 1992.
The patent contains no supplied formulation, process, dosage-form, or biologic claims.
Piroxicam is subject to the generic ANDA pathway, not biosimilar regulation.
No current Paragraph IV, litigation, settlement, or Orange Book risk arises from this expired patent.
Later process, formulation, solid-state, and foreign patents require separate freedom-to-operate analysis.

FAQs

Does claim 17 cover Feldene?

Yes. Claim 17 identifies piroxicam, the active ingredient in Feldene, by its chemical name. The method limitation of claim 1 must also be satisfied.

Can an expired method patent block a piroxicam generic?

No. United States Patent 3,862,319 expired in 1992 and cannot now block a piroxicam generic in the United States.

Are claims 9 through 13 directed to piroxicam?

No. Claims 9 through 13 cover the 3-oxo-4-carboxamide series. Piroxicam is identified in claim 17 as a 4-hydroxy-3-carboxamide compound.

Does the patent cover meloxicam?

The supplied claims do not identify meloxicam. Structural similarity to piroxicam is insufficient to establish literal claim coverage.

Can a later piroxicam formulation patent remain enforceable?

Yes. A later patent directed to a formulation, solid form, manufacturing process, or delivery system could have a separate term and scope, even though United States Patent 3,862,319 has expired.

References

United States Patent No. 3,862,319. (1975, January 21). 1,2-Benzothiazine carboxamide derivatives and therapeutic methods. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (n.d.). Drugs@FDA: Feldene (piroxicam), NDA 018023. https://www.accessdata.fda.gov/scripts/cder/daf/
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. https://www.fda.gov/drugs/drug-approvals-and-databases
U.S. Food and Drug Administration. (n.d.). ANDA submissions: Patent certification requirements and Paragraph IV certifications. https://www.fda.gov/drugs/guidance-compliance-regulatory-information-drugs

Details for Patent: 3,862,319

Summary for Patent: 3,862,319