US Patent 9,907,859: ST-246 Injectable Formulation Claims, Scope, Expiration and Competitive Patent Landscape

US Patent No. 9,907,859 protects methods of treating orthopoxvirus infections, including eczema vaccinatum, with a liquid formulation of ST-246, the active ingredient in tecovirimat, combined with hydroxypropyl-beta-cyclodextrin and/or sulfobutyl-ether-beta-cyclodextrin. The most commercially important claims are the intravenous-use claims covering 50 to 500 mg per administration, including a 300 mg dose, treatment courses of 7 to 30 days, and prolonged or twice-daily infusions.

The patent is assigned to SIGA Technologies, Inc. Its protection is directed primarily to clinical use of a parenteral tecovirimat formulation rather than to the broad chemical composition of tecovirimat itself. The patent is particularly relevant to intravenous TPOXX because the FDA-approved injection uses a cyclodextrin-containing aqueous formulation and is administered by intravenous infusion.

What does US Patent 9,907,859 protect?

The patent protects a treatment method with four required elements:

A subject has an orthopoxvirus infection or eczema vaccinatum.
The subject receives a liquid pharmaceutical formulation.
The formulation contains a therapeutically effective amount of ST-246.
The formulation contains hydroxypropyl-beta-cyclodextrin, sulfobutyl-ether-beta-cyclodextrin, or both, plus one or more pharmaceutically acceptable ingredients.

Claim 1 is the independent claim. Claims 2 through 5 narrow the administration route. Claims 6 through 14 focus on intravenous dosing, treatment duration, infusion duration and administration frequency.

Claim group	Protected subject matter	Commercial relevance
Claim 1	Liquid ST-246 formulation with HP-beta-CD and/or SBE-beta-CD for orthopoxvirus or eczema vaccinatum	Establishes the principal method-of-treatment scope
Claims 2-4	Parenteral, oral or topical administration	Broad route alternatives
Claim 5	Intravenous administration	Directly relevant to IV tecovirimat
Claims 6-8	50-500 mg, 200-400 mg, or approximately 300 mg per IV session	Dose-specific protection
Claims 9-10	Treatment for 7-30 days or 7-15 days	Duration-specific protection
Claims 11 and 14	Infusion sessions lasting 2-24 hours or 2-12 hours	Administration-process protection
Claims 12-13	50-500 mg per day and two sessions per day	Daily-dose and frequency protection

The claims are method claims. They do not, on their face, claim every liquid formulation containing tecovirimat, nor do they claim ST-246 as a molecule. An accused product must be used in a manner that satisfies the claim limitations.

How should claim 1 be interpreted?

Claim 1 has broad formulation and administration language but a defined disease and excipient combination.

ST-246 requirement

ST-246 is the development code for tecovirimat, also known as SIGA-246. The claim requires a therapeutically effective amount, which is a functional limitation. The formulation must contain enough active ingredient to treat the claimed infection.

Cyclodextrin requirement

The claim requires hydroxypropyl-beta-cyclodextrin, sulfobutyl-ether-beta-cyclodextrin, or both. These excipients are solubilizing agents used to improve the aqueous formulation of poorly water-soluble compounds.

The phrase "and/or" means that a formulation containing either specified cyclodextrin can fall within the claim. A formulation containing both also falls within the claim. A formulation using a different solubilizer without either claimed cyclodextrin would not satisfy this limitation.

Disease limitation

The treatment must concern an orthopoxvirus infection or eczema vaccinatum. Orthopoxviruses include smallpox, monkeypox, cowpox and related viruses. The claim does not expressly limit treatment to variola virus or monkeypox.

The disease limitation matters in infringement analysis. A formulation administered for an unrelated viral disease would not meet the express therapeutic-use limitation, even if it contained ST-246 and the claimed excipients.

What do claims 2 through 5 add?

Claims 2 through 5 create route-specific versions of claim 1.

Claim 2 covers parenteral administration. Intravenous administration is a form of parenteral administration, but claim 2 is broader than claim 5 because it is not limited to the intravenous route.

Claim 3 covers oral administration. This route overlaps with oral tecovirimat capsules in principle, provided the liquid formulation and cyclodextrin limitations are satisfied.

Claim 4 covers topical administration. The claim does not require a particular topical site, vehicle or concentration.

Claim 5 specifically covers intravenous administration and is the principal claim for the commercial IV formulation. An IV product can potentially fall within both claims 2 and 5, but claim 5 supplies the more detailed downstream limitations for dose, duration and infusion timing.

What intravenous dosing is protected by US 9,907,859?

The IV claims create a layered dose range.

Claim	IV limitation
Claim 5	Any intravenous administration of the claimed formulation
Claim 6	Approximately 50-500 mg per single IV session
Claim 7	Approximately 200-400 mg per single IV session
Claim 8	Approximately 300 mg per single IV session
Claim 12	Approximately 50-500 mg per day
Claim 13	Two IV sessions per day
Claim 14	Each of two daily sessions lasts approximately 2-12 hours

The dependent claims are cumulative. For example, a method using approximately 300 mg per IV session, administered over 6 hours, for 10 days would implicate claim 8, claim 10 and claim 11, assuming all other limitations are met.

The claims use approximate ranges. Courts generally assess the meaning of "about" in view of the specification, technical context and prosecution history. A dose slightly outside a stated range may still present risk, particularly under the doctrine of equivalents, but literal infringement analysis begins with the numerical limitation as construed.

How does the patent compare with the FDA-approved TPOXX injection?

The FDA approved TPOXX capsules in 2018 and TPOXX injection in 2022. The injection contains tecovirimat in an aqueous formulation with hydroxypropyl-beta-cyclodextrin and is administered intravenously. The FDA label identifies a 200 mg dose administered by IV infusion over six hours every 12 hours for patients who cannot take oral therapy, subject to weight-based and clinical considerations.[1]

The label's formulation and administration profile align closely with the technical subject matter of US 9,907,859:

TPOXX injection attribute	Relationship to patent claims
Tecovirimat active ingredient	Satisfies ST-246 limitation
Liquid formulation	Satisfies liquid-formulation limitation
Hydroxypropyl-beta-cyclodextrin	Satisfies specified cyclodextrin limitation
Intravenous administration	Falls within claim 5
200 mg per dose	Falls within claim 6 and claim 7 ranges
Every 12 hours	Consistent with claim 13's two-session daily limitation
Six-hour infusion	Falls within claims 11 and 14

The 200 mg labeled IV dose is within the claimed 50-500 mg and 200-400 mg ranges. It is not the approximately 300 mg embodiment in claim 8. A marketed use can infringe broader dependent claims even when it does not meet a narrower dose claim.

What is the patent's expiration date?

US 9,907,859 claims priority to an early filing directed to parenteral ST-246 formulations. Its nominal patent term runs from the earliest effective nonprovisional filing date and is projected to expire in January 2029, subject to any applicable patent-term adjustment or terminal-disclaimer treatment recorded by the USPTO.[2]

The practical exclusivity timeline is:

Event	Date or status
Priority period	2009-era priority for parenteral ST-246 formulation technology
Patent issuance	March 6, 2018
FDA approval of oral TPOXX	July 2018
FDA approval of TPOXX injection	June 2022
Projected patent expiration	January 2029, subject to USPTO term calculation
Regulatory exclusivity	Separate from patent term and dependent on FDA-granted exclusivity periods

FDA approval does not extend the patent automatically. A patent-term extension under 35 U.S.C. § 156 would require a qualifying regulatory application and an issued extension certificate. The Orange Book and USPTO records control the operative expiration date and any extension.[2,3]

What is the Orange Book status of US 9,907,859?

The relevant regulatory question is whether US 9,907,859 is listed for the approved TPOXX dosage form and whether its listing covers the injection, capsules or both.

The Orange Book distinguishes approved product information from patent information. A listed patent may cover:

The active ingredient;
A drug product or formulation;
A method of use;
A specific dosage form or route.

For an IV formulation, US 9,907,859 is most relevant as a method-of-use and formulation-related patent. Its strongest overlap is with the approved injection, not necessarily with every oral tecovirimat product.

An ANDA applicant challenging a listed patent would generally address the patent through a Paragraph IV certification. If the NDA holder receives timely notice of a Paragraph IV certification and files suit within the statutory period, FDA approval can be stayed for up to 30 months under the Hatch-Waxman framework.[4]

Are there known Paragraph IV challenges to TPOXX?

No material public Paragraph IV litigation involving US 9,907,859 is established in the supplied record. TPOXX has a specialized public-health market, and the commercial incentive for an immediate generic IV challenge is lower than for a high-volume chronic-use drug.

A generic applicant would face several barriers:

The approved IV formulation is technically specific.
The method claims combine formulation, disease, route and dosing limitations.
The market is primarily government procurement rather than routine retail dispensing.
A generic could need to manage labeling designed to avoid inducing infringement.
The Orange Book listing and any use codes would determine the scope of an ANDA certification.

The absence of a known Paragraph IV case does not eliminate future challenge risk. A generic could pursue a Paragraph IV certification, a section viii statement for carved-out methods, or a separate 505(b)(2) strategy depending on the proposed formulation and labeling.

What patent litigation affects SIGA and tecovirimat?

The principal public SIGA litigation was SIGA Technologies, Inc. v. PharmAthene, Inc., involving contractual obligations concerning development and commercialization of SIGA's smallpox antiviral technology. The Delaware Supreme Court affirmed an award relating to PharmAthene's breach of obligations associated with a license agreement.[5]

That dispute was not a direct validity challenge to US 9,907,859. It is relevant because it confirms the commercial value of SIGA's tecovirimat intellectual property and the company's willingness to enforce contractual and technology rights.

No major reported validity decision is identified here that invalidates the claims of US 9,907,859. The patent therefore remains commercially relevant through its remaining term, subject to ordinary claim-construction, validity and infringement defenses.

How strong is the patent estate for IV tecovirimat?

The patent has meaningful strength against an IV tecovirimat product that copies the approved product profile.

Strengths

The independent claim combines active ingredient, liquid formulation, excipient and disease use.
The claim covers both hydroxypropyl-beta-cyclodextrin and sulfobutyl-ether-beta-cyclodextrin.
Claim 5 reaches intravenous treatment directly.
The dose ranges cover the 200 mg IV dose used in the FDA-approved product.
The infusion-duration claims cover a six-hour infusion.
The two-sessions-per-day claim corresponds to the labeled every-12-hour schedule.

Vulnerabilities

The claims are method claims rather than broad composition claims.
A challenger could contest written description, enablement or obviousness based on earlier ST-246 formulation and dosing disclosures.
The specification and prosecution history will control the construction of "about," "therapeutically effective amount" and the cyclodextrin limitations.
A non-infringing formulation could use a different solubilization system.
A competing product could seek a different dose, route or treatment schedule.
The patent's remaining term is materially shorter than a newly issued formulation patent.

Overall, the patent is strongest against a product that reproduces the TPOXX injection's excipient, IV route, repeated-dose regimen and infusion profile. It is weaker against oral products, alternative liquid formulations and products with materially different dosing instructions.

What manufacturing and formulation barriers exist?

The principal technical barrier is aqueous delivery of tecovirimat at a clinically useful concentration. Cyclodextrins improve solubility, but parenteral products must also meet requirements for:

Sterility;
Endotoxin control;
Stability;
Particulate matter;
Container compatibility;
Infusion-site tolerability;
Dilution and administration instructions;
Manufacturing consistency at commercial scale.

A competitor could attempt a design-around using a different cyclodextrin, cosolvent, surfactant, lipid system, salt form or prodrug. That strategy would need to avoid both the literal claim limitations and equivalents-based infringement. It would also require a separate FDA development and approval pathway.

Because the claims cover treatment methods, a manufacturing design-around does not automatically eliminate risk. A product using a different formulation could still implicate the patent if it uses ST-246 in a liquid formulation with one of the claimed cyclodextrins.

How does US 9,907,859 compare with core tecovirimat patents?

US 9,907,859 should be separated from three other patent categories:

Patent category	Typical subject matter	Relevance
Core compound patents	Tecovirimat chemical structure and antiviral activity	Protect the active ingredient itself
Broad antiviral-use patents	Treatment of orthopoxvirus infections with tecovirimat	Cover disease use across dosage forms
Formulation and dosing patents	Liquid delivery, cyclodextrins, IV dosing and infusion schedules	Targeted by US 9,907,859

The commercial value of US 9,907,859 depends on the status of the broader tecovirimat estate. If core compound claims have expired or are invalid, a formulation and method patent can still delay an IV generic. Conversely, expiration of US 9,907,859 would not necessarily eliminate all barriers if separate active-ingredient, method-of-use or formulation patents remain enforceable.

What generic-entry scenarios exist?

IV generic before January 2029

A generic applicant would likely face an Orange Book patent challenge if the patent is listed against the relevant approved product. The applicant could file Paragraph IV certification and litigate validity or non-infringement.

IV generic after patent expiration

After expiration, the patent would no longer block an otherwise approvable generic based on the claimed method. Other listed patents, regulatory exclusivity and manufacturing requirements could still affect timing.

Oral generic

An oral generic faces a different risk profile. Claims 1 and 3 can reach oral liquid formulations containing the specified cyclodextrins, but the claims do not automatically cover every oral capsule or tablet. The relevant Orange Book patents and use codes must be reviewed separately.

Alternative IV formulation

An alternative IV formulation using no hydroxypropyl-beta-cyclodextrin or sulfobutyl-ether-beta-cyclodextrin may avoid literal infringement of claim 1. The product would still need to address other patents, FDA requirements and potential equivalents arguments.

What is the geographic coverage?

US 9,907,859 is enforceable only in the United States. Foreign counterparts, if granted, require separate analysis of:

National-phase status;
Claim scope;
Patent-term adjustment or supplementary protection;
Patent-term extensions;
Local validity standards;
Regulatory approval and linkage rules.

A US patent does not block manufacture, sale or use outside the United States. It can, however, affect products imported into the United States or supplied under US government procurement programs.

Key Takeaways

US 9,907,859 is a SIGA patent focused on liquid ST-246 treatment methods using specified cyclodextrins.
The patent's most important commercial claims cover IV tecovirimat.
The 200 mg IV dose, six-hour infusion and twice-daily schedule associated with TPOXX align with multiple patent limitations.
The patent is projected to expire in January 2029, subject to the USPTO's operative term calculation and any extension.
The patent is not a broad claim to the tecovirimat molecule.
Generic risk is highest for an IV product that copies the TPOXX injection formulation and labeled administration schedule.
A Paragraph IV challenge would likely focus on obviousness, written description, enablement, claim construction and non-infringement.
Biosimilar law is not applicable because tecovirimat is a small-molecule drug. The relevant pathway is an ANDA or, in some cases, a 505(b)(2) application.
The patent should be analyzed with the separate core-compound, method-of-use and formulation patents covering TPOXX.

FAQs About US Patent 9,907,859

Does US 9,907,859 claim the tecovirimat molecule itself?

No. The claims cover treatment methods using ST-246 in a liquid formulation with specified cyclodextrins. They do not constitute a broad composition-of-matter claim to tecovirimat.

Does the patent cover oral TPOXX capsules?

Not automatically. The patent can reach an oral liquid formulation satisfying the claim limitations, but a conventional capsule or tablet would not meet the liquid-formulation requirement.

Does a 200 mg IV dose fall within the patent?

Yes. A 200 mg IV dose falls within the approximately 50-500 mg range in claim 6 and the approximately 200-400 mg range in claim 7, assuming the other claim limitations are met.

Is a biosimilar filing required to compete with TPOXX?

No. Tecovirimat is a small molecule. A competitor would generally use the ANDA pathway or, depending on the product, a 505(b)(2) application rather than a biosimilar application.

Can a generic avoid the patent by using a different solubilizer?

Potentially. A formulation that does not contain hydroxypropyl-beta-cyclodextrin or sulfobutyl-ether-beta-cyclodextrin may avoid the express cyclodextrin limitation, but it would require analysis of other patents and the doctrine of equivalents.

References

U.S. Food and Drug Administration. (2022). TPOXX (tecovirimat) injection prescribing information. FDA.
United States Patent and Trademark Office. (2018). U.S. Patent No. 9,907,859, parenteral formulations of ST-246. USPTO Patent Center.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA, Center for Drug Evaluation and Research.
21 U.S.C. § 355(j); 35 U.S.C. § 271(e).
SIGA Technologies, Inc. v. PharmAthene, Inc., 67 A.3d 330 (Del. 2013).

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Siga Technologies	TPOXX	tecovirimat	SOLUTION;INTRAVENOUS	214518-001	May 18, 2022		RX	Yes	Yes	⤷ Start Trial	⤷ Start Trial				TPOXX IS INDICATED FOR THE TREATMENT OF HUMAN SMALLPOX DISEASE IN ADULTS AND PEDIATRIC PATIENTS WEIGHING AT LEAST 3 KG	⤷ Start Trial
>Applicant	>Tradename	>Generic Name	>Dosage	>NDA	>Approval Date	>TE	>Type	>RLD	>RS	>Patent No.	>Patent Expiration	>Product	>Substance	>Delist Req.	>Patented / Exclusive Use	>Submissiondate

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	082566	⤷ Start Trial
Argentina	122178	⤷ Start Trial
Australia	2011285871	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 9,907,859

Which drugs does patent 9,907,859 protect, and when does it expire?

Summary for Patent: 9,907,859