United States Drug Patent 6,562,861: Claim Scope, Peramivir Coverage, Expiration, and Patent Landscape

U.S. Patent No. 6,562,861 is a composition-of-matter patent covering cyclopentane neuraminidase inhibitors, including the peramivir chemical class. The patent issued May 13, 2003, and its claims include broad chemical genera, specifically enumerated intermediates and stereoisomers, pharmaceutical compositions, and methods for treating influenza. The patent is expired under the ordinary U.S. patent term, so it does not currently block generic development or commercial manufacture. Peramivir remains a small-molecule drug regulated through the ANDA pathway, not the biosimilar pathway.

What drug does U.S. Patent 6,562,861 protect?

The patent principally covers cyclopentane-based influenza neuraminidase inhibitors associated with peramivir, also known as BCX-1812 and RWJ-270201. Peramivir is marketed in the United States as Rapivab by BioCryst Pharmaceuticals.

The clinically relevant peramivir structure is a stereochemically defined cyclopentane carboxylic acid containing:

A cyclopentane ring;
A carboxylic acid group;
A guanidino or amino-imino substituent;
A hydroxyl group;
An acylamino-substituted alkyl side chain;
Defined relative and absolute stereochemistry.

The patent does not claim only one commercial active ingredient. It covers a broad family of related cyclopentane derivatives, including protected intermediates, esters, acids, amino compounds, guanidino compounds, azido precursors, sulfonate derivatives, unsaturated analogues, stereoisomers, and pharmaceutically acceptable salts.

When was U.S. Patent 6,562,861 filed and when did it expire?

Item	Information
Patent number	U.S. 6,562,861
Technology	Cyclopentane neuraminidase inhibitors
Patent type	U.S. utility patent
Issue date	May 13, 2003
Listed assignee	BioCryst Pharmaceuticals, Inc.
U.S. therapeutic target	Influenza virus neuraminidase
Nominal term	20 years from the earliest effective U.S. nonprovisional filing
Nominal expiration	2019, based on the U.S. filing timeline
Current status	Expired
FDA exclusivity type	Small-molecule drug exclusivity, not biologic exclusivity

The patent issued before approval of Rapivab in 2014. Any remaining term at the time of approval could have been relevant to peramivir commercialization, but the patent has since expired. Patent term extension under 35 U.S.C. § 156 would have required an approved regulatory extension. The Orange Book, rather than the patent document alone, is the controlling source for any listed drug patent and regulatory exclusivity analysis.[1][2]

How many claims does U.S. Patent 6,562,861 contain?

The patent contains 41 claims in the claim set supplied.

Claim group	Claims	Subject matter
Broad chemical genus	1-6	Formula-defined cyclopentane compounds and salts
Enumerated compounds	7-8	Long lists of specifically identified compounds
Individual compounds	9-39	Named stereoisomers, esters, acids, amino compounds, and guanidino analogues
Pharmaceutical composition	40	Neuraminidase-inhibiting composition
Treatment method	41	Treatment of influenza infection

Claims 2 through 6 narrow claim 1 by defining alkyl, alkylene, aromatic, cycloalkyl, acid, and salt substituents. Claims 7 through 39 move from a broad structural genus to specifically named compounds. Claims 40 and 41 extend the patent beyond the molecule itself to pharmaceutical use.

What is the scope of claim 1?

Claim 1 is a broad Markush composition-of-matter claim. It covers compounds represented by multiple formulae, with substituent definitions that permit substantial variation around the cyclopentane scaffold.

The principal scope elements are:

A cyclopentane-based molecular framework represented by the referenced formulae.
A variable Z group that can include carbon, nitrogen, carbonyl-related, heteroatom-substituted, and sulfur-containing arrangements.
An R1/R9 substitution pattern containing acidic, polar, ionic, or salt-forming groups.
An R2 substituent containing acylamino, thiocarbonylamino, sulfonamido, urea, sulfonyl, sulfoxide, or sulfone functionality.
R3 and R8 substituents that can contain carbonyl, ester, ether, amine, hydroxyl, heterocyclic, amidino, and guanidino-related functionality.
R4 substituents that can contain alcohol, ether, amino, amidino, guanidino, nitrile, or azide functionality.
Alkyl, alkylene, aromatic, cyclic, and heterocyclic substituents.
Pharmaceutically acceptable salts.

The claim is structurally broad because it covers both the final active-acid compounds and chemically related derivatives. It also permits numerous protecting-group and prodrug-like forms, including esters and tert-butoxycarbonyl-protected amino or guanidino groups.

What are the main claim-construction limitations?

The broadest claim is limited by several material requirements:

The compound must satisfy one of the stated formulae.
The defined substituent options must be selected from the recited alternatives.
At least one of R2, R3, and R8 must be other than hydrogen.
The compound must have the specified U and p relationship where applicable.
Salt coverage applies only to pharmaceutically acceptable salts.
The chemical identity must meet the structural and stereochemical requirements imposed by the formula and dependent claims.

The missing structural drawings in the supplied text are significant for literal claim analysis. Terms such as U, Z, R1, R2, R3, R4, R8, R9, R10, R11, R12, and R13 cannot be mapped definitively to a commercial compound without the patent’s original figures and specification. The textual claim transcription also contains apparent typographical and numbering defects.

Does the patent specifically cover peramivir?

Yes, the claim architecture is directed to the peramivir family, and the individual compound claims cover structures that correspond to the key peramivir stereochemical and functional-group arrangements.

The closest commercial-asset claim categories are:

Claims 8, 13, 14, 20, 21, and 22, which cover carboxylic acid compounds with amino or guanidino functionality;
Claims 9 through 12, which cover methyl and ethyl ester forms of hydroxycyclopentane derivatives;
Claims 15, 16, 27, 28, 34, and 35, which cover amino-imino and N-methylamino-imino derivatives;
Claims 17 through 19, which cover unsaturated cyclopentene analogues;
Claims 40 and 41, which cover pharmaceutical compositions and influenza treatment methods.

The strongest commercial relevance is concentrated in the narrowly defined stereoisomeric compounds with:

A cyclopentane carboxylic acid;
A 4-amino or 4-guanidino group;
A 2-hydroxyl group in the hydroxy series;
A 3-substituted acylamino alkyl side chain;
The specific peramivir stereochemistry.

What formulations are protected by U.S. Patent 6,562,861?

Claim 40 covers a pharmaceutical composition containing:

A pharmaceutically acceptable carrier; and
An amount of a claim 1 compound effective to inhibit influenza virus neuraminidase.

The claim does not recite a particular dosage form, excipient, concentration, container, route, or manufacturing process. On its face, it can reach oral, parenteral, liquid, solid, or other pharmaceutical presentations if they contain a qualifying compound and carrier.

The claim is not a detailed formulation claim. It does not expressly require:

Intravenous administration;
A particular buffer;
A specific pH;
A defined concentration;
A particular stabilizer;
A lyophilized product;
A controlled-release system;
A sterile manufacturing process.

For Rapivab, the commercially important product is an intravenous peramivir formulation. A later patent directed specifically to concentration, stability, sterile preparation, container closure, or administration conditions could provide separate protection even after expiration of the composition-of-matter patent. Such later patents would need to be analyzed independently from U.S. 6,562,861.

What method-of-use patents does U.S. Patent 6,562,861 contain?

Claim 41 covers a method of treating influenza virus infection by administering an effective amount of a claim 1 compound with a pharmaceutically acceptable carrier.

The claim is broad in therapeutic scope. It does not limit treatment to:

Influenza A or influenza B;
A particular viral strain;
Adults or pediatric patients;
Uncomplicated or complicated influenza;
Hospitalized patients;
A specified dose;
A specified infusion duration;
Prophylaxis rather than treatment;
A defined treatment window.

The claim’s practical scope depends on whether the accused product contains a compound within claim 1 and whether the use is treatment of influenza infection. A generic peramivir product could implicate the method claim if the relevant patent were still enforceable. Because the patent is expired, claim 41 no longer creates a live U.S. patent barrier.

How strong is the patent estate for peramivir?

The patent was strong as an early composition-of-matter patent because it combined a broad genus with an extensive list of specific compounds and stereoisomers. Its commercial value came from the breadth of the chemical disclosure and the inclusion of compounds close to the eventual clinical candidate.

Its current strength is materially lower because the patent has expired.

Strength factor	Assessment
Core composition coverage	Historically strong
Stereochemical coverage	Strong in claims 7-39
Salt coverage	Broad but dependent on underlying compound
Formulation coverage	Limited; generic carrier language
Method-of-use coverage	Broad treatment claim
Manufacturing coverage	Not the principal claim focus
Current enforceability	None after expiration
Generic blocking value	None in the United States
Freedom-to-operate relevance	Historical and technical only

The long lists in claims 7 and 8 do not automatically make every listed chemical a marketed drug. They function as closed selections from the disclosed compounds and can be useful for identifying the inventors’ preferred stereochemical and functional-group combinations.

What is the Orange Book status of peramivir?

Rapivab is an FDA-approved small-molecule antiviral product. FDA approved peramivir injection on December 19, 2014, for treatment of acute uncomplicated influenza in patients 2 years and older who had been symptomatic for no more than two days, subject to the approved labeling at the relevant time.[3]

Because peramivir is a chemical drug, an applicant seeking approval of a therapeutically equivalent generic would use an ANDA under section 505(j) of the Federal Food, Drug, and Cosmetic Act. A biosimilar application under section 351(k) would not apply.

The relevant Orange Book questions are:

Whether U.S. 6,562,861 was listed against Rapivab;
Whether any later patents were listed;
Whether the listed patents have expired;
Whether any pediatric or regulatory exclusivity remains;
Whether an ANDA applicant has filed a Paragraph IV certification.

The original patent’s expiration removes it as a current barrier. FDA approval of Rapivab does not itself establish continuing patent exclusivity.[1][3]

Which companies are challenging U.S. Patent 6,562,861?

No current Paragraph IV challenge can target an expired patent as a meaningful litigation barrier. Publicly visible generic competition for peramivir would instead focus on any later-expiring Orange Book patents, product-specific exclusivity, manufacturing patents, and supply-chain constraints.

The relevant commercial parties are:

Company	Role
BioCryst Pharmaceuticals	Peramivir developer and U.S. rights holder for Rapivab
Shionogi	Commercial and development collaborator in certain peramivir markets
Generic manufacturers	Potential ANDA applicants for peramivir injection
Contract manufacturers	Potential holders or users of process and sterile manufacturing know-how

The patent number itself is not a current basis for a Paragraph IV launch strategy because its term has ended.

What patent litigation and settlement agreements affect peramivir?

U.S. 6,562,861 does not present a current litigation risk after expiration. A complete current litigation assessment would require checking:

Federal district court complaints and docket outcomes;
PTAB proceedings;
Orange Book patent listings;
FDA Paragraph IV litigation notices;
Patent assignments and terminal disclaimers;
Any settlement or license agreements covering later patents.

The commercial impact of a historical license is separate from patent enforceability. A license can govern know-how, territories, supply, royalties, or regulatory rights after a patent expires, but an expired patent cannot independently support an injunction against a generic entrant.

What generic entry risks exist for peramivir?

Peramivir generic entry has a lower patent risk from U.S. 6,562,861 but may face non-patent barriers.

Patent-related risks

Later formulation patents;
Process or crystallization patents;
Salt or solid-state patents;
Container and sterile-fill patents;
Patent claims directed to dosing or specific patient populations;
Unlisted foreign patents in export markets.

Regulatory and commercial risks

Bioequivalence for an intravenous product;
Sterility and injectable manufacturing compliance;
Limited influenza-treatment demand outside seasonal outbreaks;
Commercial scale and inventory economics;
Procurement contracts and government stockpiling;
Supply reliability during influenza surges.

Peramivir is an injectable antiviral, so generic competition may be constrained by manufacturing and demand economics even where the core compound patent is expired.

How does peramivir compare with oseltamivir and zanamivir?

Drug	Active ingredient	Route	Primary patent risk today	Generic or alternative status
Rapivab	Peramivir	Intravenous	Core compound patent expired; later rights require separate review	ANDA pathway
Tamiflu	Oseltamivir phosphate	Oral	Core patents expired in the United States	Multiple generics
Relenza	Zanamivir	Inhaled	Core patents expired; device and formulation issues may remain	Generic substitution more complex
Xofluza	Baloxavir marboxil	Oral	Later-generation composition and method patents	Patent estate more relevant to current entry

Peramivir’s principal differentiation is intravenous delivery. That makes its regulatory and manufacturing profile more important than the expired composition-of-matter patent.

What is the geographic patent coverage?

U.S. 6,562,861 provides rights only in the United States. Patent protection in Europe, Japan, Australia, Canada, and other jurisdictions depends on separate national or regional family members and their individual expiration, maintenance, opposition, and litigation histories.

A U.S. expiration does not establish worldwide freedom to operate. It does establish that the patent cannot currently prevent U.S. manufacture, sale, use, or importation of a covered compound.

Key Takeaways

U.S. Patent 6,562,861 is a cyclopentane neuraminidase-inhibitor patent associated with the peramivir family.
Claims 1-6 cover a broad chemical genus.
Claims 7-39 cover numerous named compounds, stereoisomers, esters, acids, intermediates, and salts.
Claim 40 covers pharmaceutical compositions.
Claim 41 covers treatment of influenza infection.
The patent issued May 13, 2003, and expired under the ordinary U.S. patent term in 2019.
Peramivir is an FDA-approved small-molecule drug marketed as Rapivab.
Generic peramivir would proceed through the ANDA pathway, not the biosimilar pathway.
The expired patent no longer creates a U.S. Paragraph IV or launch barrier.
Current risk must focus on later formulation, process, manufacturing, and Orange Book-listed patents.
The patent’s historical composition-of-matter strength does not translate into current enforceability.

FAQs

Does U.S. Patent 6,562,861 cover Rapivab?

Yes. The patent covers the peramivir chemical family, including stereochemically defined cyclopentane acids and related amino and guanidino derivatives.

Can a company launch generic peramivir after expiration of this patent?

Yes, subject to FDA approval, applicable Orange Book patents, regulatory exclusivity, sterile manufacturing requirements, and commercial supply conditions.

Is peramivir a biologic requiring a biosimilar application?

No. Peramivir is a chemically synthesized small molecule. A generic applicant would use the ANDA pathway.

Does claim 40 cover intravenous peramivir?

Claim 40 is broad enough to cover a pharmaceutical composition containing a qualifying compound and carrier, but it does not expressly require intravenous administration or the specific Rapivab formulation.

Are the protected compounds limited to the exact stereoisomer of peramivir?

No. The patent claims multiple stereoisomers and structurally related compounds. The most relevant commercial coverage is found in the claims reciting the specific hydroxycyclopentane, amino, guanidino, carboxylic-acid, and side-chain configurations associated with peramivir.

References

U.S. Patent and Trademark Office. (2003). U.S. Patent No. 6,562,861, Cyclopentane derivatives as neuraminidase inhibitors.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
U.S. Food and Drug Administration. (2014). Rapivab (peramivir injection) prescribing information. BioCryst Pharmaceuticals, Inc.
U.S. Food and Drug Administration. (2024). Drugs@FDA: Rapivab application and approval history.
BioCryst Pharmaceuticals, Inc. (2015). Annual report and intellectual-property disclosures.

PCT Information
PCT Filed	December 17, 1998	PCT Application Number:	PCT/US98/26871
PCT Publication Date:	July 08, 1999	PCT Publication Number:	WO99/33781

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	016162	⤷ Start Trial
Austria	425955	⤷ Start Trial
Australia	2200199	⤷ Start Trial
Brazil	9813480	⤷ Start Trial
Canada	2315262	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,562,861

Summary for Patent: 6,562,861