US Patent 11,197,909: CD101 Acetate Formulation Claims, Exclusivity and Patent Landscape

US Patent No. 11,197,909 protects specific intravenous and lyophilized formulations of CD101 acetate, the active ingredient in rezafungin, marketed in the United States as Rezzayo. The patent also covers administration of those formulations for fungal infections, including candidemia and invasive candidiasis. Its core limitation is the combination of CD101 acetate, a narrowly defined amount of saccharide, a solubility promoter at a specified weight ratio, and a pH of 5 to 7.

The strongest practical coverage is directed to aqueous injectable formulations containing polysorbate 80 and CD101 acetate at approximately 0.8 mg/mL or 1.6 mg/mL. The patent also claims lyophilized products that are reconstituted before intravenous administration.

What does US Patent 11,197,909 cover?

US 11,197,909 covers three related subject-matter groups:

Ready-to-use aqueous intravenous compositions.
Lyophilized compositions for reconstitution.
Methods of treating or preventing fungal infections using the claimed compositions.

The patent is formulation-focused. It does not principally claim the CD101 molecule itself, its antifungal mechanism, or every use of rezafungin. Infringement depends on whether a competing product or treatment protocol contains each required limitation of an asserted claim.

Claim group	Claims	Subject matter	Principal limitations
Aqueous formulation	1-9	Intravenous aqueous composition	At least 85% water; 0.4-10 mg/mL CD101 acetate; 0.12%-0.6% saccharide; solubility promoter/CD101 ratio of at least 2; pH 5-7
Lyophilized formulation	10-15	Freeze-dried composition	Effective CD101 acetate amount; 2%-10% saccharide; solubility promoter/CD101 ratio of 2-8; reconstituted pH 5-7
Treatment using aqueous product	16, 18, 20-23	Intravenous treatment methods	Administration for fungal infections, including specified infusion conditions and pathogens
Treatment using reconstituted product	17, 19	Reconstitution and intravenous administration	Reconstituted CD101 acetate solution at 0.4-10 mg/mL

The patent was issued March 29, 2022, based on the supplied claim set. The named technology is associated with Cidara Therapeutics and its CD101/rezafungin program. The relevant patent record is US Patent No. 11,197,909. (USPTO, 2022)

What are the key limitations in independent claim 1?

Claim 1 requires a pharmaceutical composition containing all of the following:

An aqueous solution.
At least 85% water by weight.
CD101 acetate at 0.4 mg/mL to 10 mg/mL.
A saccharide at 0.12% to 0.6% by weight.
An intravenous solubility promoter.
A solubility-promoter-to-CD101-acetate weight ratio of at least 2.
A pH between 5 and 7.

The claim is narrower than a generic claim to “a CD101 formulation.” A competing formulation outside any one required range may avoid literal infringement of claim 1, subject to dependent claims, equivalents, prosecution history, and other patents.

What is the practical scope of the aqueous formulation claim?

The commercial center of claim 1 is a low-concentration aqueous formulation with a surfactant or other solubility-enhancing excipient. Claim 1 does not require polysorbate 80 specifically. That limitation appears in dependent claim 4.

A product could fall within claim 1 if it uses a listed or unlisted intravenous solubility promoter, provided the promoter is present and the composition satisfies the ratio and pH requirements. The claim therefore has broader coverage than the polysorbate 80 embodiment.

The most important numerical boundaries are:

Parameter	Claim 1 range
Water	At least 85% w/w
CD101 acetate	0.4-10 mg/mL
Saccharide	0.12%-0.6% w/w
Solubility promoter/CD101 acetate ratio	At least 2:1
pH	5-7

What formulations are protected by claims 2 through 9?

Claims 2 through 9 narrow the aqueous formulation coverage.

Claim	Limitation
2	Solubility-promoter/CD101 acetate ratio of 2:1 to 8:1
3	Solubility promoter selected from a defined excipient group
4	Polysorbate 80 as the solubility promoter
5	CD101 acetate concentration of 0.4-4 mg/mL
6	CD101 acetate concentration of about 0.8 or 1.6 mg/mL
7	Addition of a buffer
8	Buffer selected from histidine, citrate, succinate, lactate, propanoate, arginine, tris, glycine, acetate or formate
9	Saccharide selected from mannitol, sucrose, trehalose, maltose, dextrose or lactose

Claim 6 is commercially significant because it identifies two specific concentration embodiments that may correspond to development, clinical, or commercial dosing configurations. Claims 4 and 6 together define a particularly narrow but potentially important combination: polysorbate 80 with CD101 acetate at approximately 0.8 mg/mL or 1.6 mg/mL.

How broad is the lyophilized formulation coverage?

Claim 10 covers a lyophilized composition containing:

An effective amount of CD101 acetate.
Saccharide at 2%-10% by weight.
A solubility promoter.
A solubility-promoter-to-CD101 acetate ratio of 2:1 to 8:1.
A reconstituted aqueous solution with pH 5-7.

Unlike claim 1, claim 10 does not require the lyophilized composition to contain at least 85% water. That distinction reflects the physical difference between a dry cake or powder and the solution produced after reconstitution.

Claims 11 through 15 narrow the lyophilized composition by specifying the solubility promoter, polysorbate 80, buffers, and saccharides.

The lyophilized claim can be important even if a generic company changes the final container, diluent, or presentation. The relevant question is whether the dry product itself contains the claimed excipients and ratio, and whether reconstitution produces the claimed pH.

What solubility promoters are claimed?

Claim 3 and claim 11 list a broad range of excipients, including:

Polysorbates 20, 40, 60 and 80.
Beta-cyclodextrin.
Polyoxyl castor oils and hydrogenated castor oils.
Tocopheryl polyethylene glycol succinate.
Sorbitan esters.
Polyoxyl stearates.
PEG glycerides.
Phosphatidylcholine and lecithin.
Alkylglucosides.
Sucrose esters.
Polyoxyethylene-polyoxypropylene block copolymers.

Polysorbate 80 is separately claimed in dependent claims 4 and 12. A formulation using another listed promoter may remain within the patent if the other limitations are met. A formulation using an unlisted excipient may still implicate claim 1 or claim 10, because the independent claims do not limit the promoter to the Markush list.

What methods of use are protected?

Claims 16 through 23 cover intravenous treatment or prevention of fungal infections using the claimed formulations.

The method claims include:

Intravenous infusion.
Constant infusion rates of 2-9 mL per minute.
Infusion over 30-120 minutes.
One dose every 5-15 days.
Treatment or prevention of candidemia and invasive candidiasis.
Treatment of infections caused by specified Candida and Aspergillus species.

The broadest method claims are claims 16, 17 and 20. Claims 18, 19 and 21-23 add administration, disease, organism, concentration or excipient limitations.

A method claim may be relevant even if a product claim is difficult to assert. For example, a supplier may sell a composition that is not itself proven to satisfy every product limitation, while an accused treatment protocol could still be evaluated under the administration claims.

When does US Patent 11,197,909 lose exclusivity?

The statutory patent term generally ends 20 years after the earliest effective nonprovisional filing date, subject to patent-term adjustment, patent-term extension, terminal disclaimers and other corrections. The precise expiration date must be taken from the current USPTO patent record and any applicable Orange Book listing.

The patent issued in 2022 and is therefore distinct from FDA regulatory exclusivity. Patent expiration does not necessarily coincide with the end of new chemical entity, orphan-drug or other FDA exclusivity.

Exclusivity category	Relevance to CD101/rezafungin
Patent term	Protects the claimed formulation and method subject matter until the applicable expiration date
FDA new chemical entity exclusivity	Applies to the approved active ingredient and may block certain abbreviated applications for five years from approval
Orphan-drug exclusivity	May apply if the approved indication received orphan designation and approval
Pediatric exclusivity	Adds six months only if granted after completion of an FDA pediatric obligation
Orange Book listing	Identifies patents submitted for the approved drug and provides notice for abbreviated applicants

The patent number alone does not establish the operative expiration date. Patent-term adjustment and any patent-term extension must be checked in the USPTO record. FDA regulatory exclusivity is separately determined under the approved NDA and FDA databases. (USPTO, 2022; FDA, 2023)

What is the Orange Book status of US 11,197,909?

Rezzayo is an FDA-approved intravenous rezafungin product. The FDA approved REZZAYO for adults with candidemia and invasive candidiasis in January 2023. (FDA, 2023)

Patent relevance depends on whether US 11,197,909 was submitted for listing in the Orange Book for the approved product and what use code, if any, FDA accepted. An Orange Book-listed formulation or method patent can require a generic applicant to make a Paragraph IV certification if the applicant seeks approval before patent expiration.

The principal regulatory distinctions are:

A product patent may be listed if it claims the approved drug or a formulation of the approved drug.
A method-of-use patent may be listed with an FDA use code tied to the approved indication.
A patent that does not claim the approved drug, an approved formulation, or an approved use may not qualify for listing.
Orange Book listing does not determine ultimate validity or infringement.
An ANDA applicant can use a Paragraph III certification, a Paragraph IV certification, or a section viii statement, depending on the patent and proposed labeling.

The approved Rezzayo label identifies rezafungin acetate for injection as a powder for intravenous infusion after reconstitution. The label describes dosing on a once-weekly schedule, which is materially aligned with the patent's claimed dosing interval of one dose every 5 to 15 days. (FDA, 2023)

What Paragraph IV challenges could affect this patent?

A generic applicant seeking approval before expiration could challenge the patent through a Paragraph IV certification. The likely challenge theories would target:

Written description or enablement of the broad solubility-promoter genus.
Obviousness based on known echinocandin formulations, surfactants, saccharides and pH ranges.
Anticipation by prior CD101 or echinocandin formulation disclosures.
Lack of infringement based on concentration, saccharide content, promoter ratio or pH.
Noninfringement of claims requiring a specific excipient, such as polysorbate 80.
Inapplicability of method claims if the generic label does not instruct the patented use.

The numerical limitations create identifiable design-around routes. A competing formulation might alter the saccharide concentration, use a promoter-to-drug ratio below 2, move outside pH 5-7, use a different concentration, or employ a formulation architecture that does not meet the lyophilized-product requirements.

A Paragraph IV notice would normally create a 45-day period for the patent owner to file a patent-infringement action. A timely action can trigger a 30-month stay of ANDA approval under the Hatch-Waxman framework, subject to statutory exceptions and court orders. (21 U.S.C. § 355; 21 C.F.R. § 314.94)

How strong is the patent estate for rezafungin?

US 11,197,909 is strongest as a formulation patent when the reference product uses the claimed excipient profile and concentration ranges. Its value depends on product-to-claim correspondence rather than on the broad antifungal scope of the method claims.

Strengths

Covers both ready-to-use and lyophilized presentations.
Claims a broad range of solubility promoters in the independent or dependent claim structure.
Includes polysorbate 80, a commercially common injectable excipient.
Covers concentration ranges that include approximately 0.8 and 1.6 mg/mL.
Includes pH, saccharide and promoter-ratio limitations that can be measured analytically.
Method claims track intravenous administration and once-every-5-to-15-day dosing.

Vulnerabilities

The independent claims contain multiple quantitative limitations.
A design-around may be possible by changing one formulation parameter.
The broad promoter genus may face obviousness and enablement scrutiny.
Method claims may be limited by the scope of the approved generic label.
The claims do not cover every CD101 acetate formulation.
The claims may not block a product based on a different salt, different excipient system or materially different dry formulation, subject to other patent rights.

The patent is more commercially relevant to an intravenously administered rezafungin product than to unrelated echinocandin products such as anidulafungin, caspofungin or micafungin.

How does this patent compare with composition-of-matter protection?

Protection type	Typical subject matter	Relevance to US 11,197,909
Composition of matter	CD101 or rezafungin molecule, salts, stereochemistry	Usually broader against alternative formulations
Formulation	Excipient system, concentration, pH, reconstitution properties	The principal subject of US 11,197,909
Method of treatment	Disease, organism, dose and route	Claims 16-23
Manufacturing	Synthesis, purification, crystallization or lyophilization process	Not apparent from the supplied claims
Regulatory exclusivity	FDA approval-based market protection	Separate from patent rights

A composition-of-matter patent generally presents a greater barrier to a generic or biosimilar-style competitor because formulation changes do not avoid the active-ingredient claim. US 11,197,909 is narrower but may remain important after molecule-level protection expires.

Rezafungin is a small-molecule antifungal, not a biologic. Biosimilar pathways under the Public Health Service Act are therefore not the principal competitive route. A competitor would generally pursue an ANDA if it can demonstrate pharmaceutical equivalence and bioequivalence, or an NDA under section 505(b)(2) if it relies on a different formulation, route, dosing regimen or other material change.

What generic entry risks exist for Rezzayo?

The most likely entry scenarios are:

Scenario	Commercial effect	Patent exposure
Same lyophilized formulation	Direct substitution potential	High exposure to claims 10-15 and potentially 17, 19 and 23
Same active ingredient with altered excipients	Moderate substitution potential	Depends on promoter, saccharide, ratio and pH
Alternative concentration	May require clinical or regulatory bridging	Could avoid claims 5-6 but remain within claim 1 or 10
Alternative dosing label	Reduced direct overlap	May avoid some method claims while leaving product claims
505(b)(2) product	Potentially differentiated formulation	Patent certifications and litigation risk remain
Non-infringing formulation with same active	Depends on regulatory equivalence	Core formulation patent may be avoided, but other patents may apply

A generic product could face both product-claim and method-claim risk. The formulation claims are generally easier to analyze through laboratory testing. The method claims depend on the approved label, prescribing information, physician behavior and the scope of induced or contributory infringement.

Which companies are challenging the rezafungin patent estate?

The supplied information does not identify any Paragraph IV filer, ANDA applicant, inter partes review petitioner, district-court defendant, settlement agreement or licensee directed specifically to US 11,197,909.

The commercial parties most directly associated with rezafungin are Cidara Therapeutics, the original developer, and Mundipharma, which has commercial rights in the product through its relationship with Cidara. The FDA approval is held under the Rezzayo NDA structure identified in FDA product materials. (FDA, 2023)

No litigation or settlement conclusion should be inferred from the patent's issuance or from the existence of the approved product. Patent litigation status must be established from PACER, PTAB records, FDA Paragraph IV notices, or a subsequent settlement filing.

What licensing deals affect the patent landscape?

Cidara entered into a global licensing and development arrangement with Mundipharma for rezafungin. The transaction transferred or licensed commercial rights outside specified retained territories and supported development and commercialization of Rezzayo. The exact scope of patent ownership, sublicensing, field restrictions and territorial rights is agreement-specific.

A license does not eliminate patent risk for third parties. It determines which party may enforce, sublicense, commercialize or receive royalties in a given jurisdiction.

What is the geographic coverage?

US 11,197,909 is a United States patent. It does not directly create rights in Europe, Japan, China, Canada or other jurisdictions. Parallel patent-family members must be reviewed separately for:

Filing and priority dates.
Grant status.
Claim scope.
Patent-term adjustment or supplementary protection certificates.
National oppositions or revocation proceedings.
Local regulatory exclusivity.
Local licensing and commercialization rights.

A global launch analysis therefore cannot rely on US 11,197,909 alone.

What manufacturing and IP barriers remain?

The claims supplied do not claim a specific manufacturing process. They may nevertheless create manufacturing constraints because a commercial product must satisfy the claimed final composition if it uses the protected formulation architecture.

Potential technical workarounds include:

Changing the solubility promoter.
Reducing the promoter-to-CD101 ratio below 2.
Changing the saccharide type or concentration.
Moving the pH outside the claimed range.
Using a different CD101 salt or chemical form.
Altering the dry formulation so it does not satisfy the lyophilized limitations.
Using a different reconstitution concentration.

Each workaround must be assessed against the full patent family, prosecution history, doctrine of equivalents and other formulation patents. A design-around that avoids US 11,197,909 may still infringe a separate composition-of-matter, salt, process, dosage or method patent.

Key Takeaways

US 11,197,909 is a formulation and treatment patent for CD101 acetate, the active ingredient in Rezzayo.
Its main protection covers aqueous intravenous solutions and lyophilized products with defined CD101, saccharide, solubility-promoter, ratio and pH parameters.
Polysorbate 80 and CD101 acetate concentrations of about 0.8 mg/mL or 1.6 mg/mL are specifically claimed.
The patent also covers intravenous treatment of candidemia, invasive candidiasis and other listed fungal infections.
The claims are narrower than composition-of-matter claims and create measurable design-around opportunities.
Rezzayo's once-weekly intravenous dosing is commercially aligned with the patent's claimed 5-to-15-day dosing interval.
Paragraph IV risk would center on obviousness, enablement, anticipation and noninfringement based on formulation parameters.
Rezafungin is a small molecule, so generic ANDA and potentially 505(b)(2) strategies are more relevant than biosimilar litigation.
US 11,197,909 provides US-only protection; foreign family members and local regulatory rights require separate analysis.
The exact operative expiration date, Orange Book listing, litigation status and any Paragraph IV challenge must be determined from current USPTO, FDA, PACER and PTAB records.

Frequently Asked Questions

Does US 11,197,909 claim rezafungin itself?

No. The supplied claims focus on CD101 acetate formulations and methods of using those formulations. They do not claim the molecule in isolation.

Can a generic avoid the patent by eliminating the saccharide?

Potentially, with respect to claims that require a saccharide, but the result depends on the full formulation and other claims in the patent family. Claims 20-22 do not expressly include the saccharide limitation, while claim 23 adds it.

Does a pH of exactly 5 or 7 fall within the claims?

Yes. The phrase “between 5 and 7” ordinarily requires analysis of claim construction, but numerical endpoints may be included unless the patent or prosecution history establishes otherwise.

Is polysorbate 80 required for infringement?

No. It is required only for claims 4 and 12, and for method claims that depend on those claims. The broader independent claims do not require polysorbate 80 specifically.

Could a 505(b)(2) applicant face the same patent claims?

Yes. A 505(b)(2) applicant may need to address listed patents and could face infringement litigation if its proposed formulation, labeling or method overlaps the patent claims.

References

U.S. Patent and Trademark Office. (2022). U.S. Patent No. 11,197,909, pharmaceutical compositions comprising CD101 acetate. Alexandria, VA: U.S. Department of Commerce.
U.S. Food and Drug Administration. (2023). REZZAYO (rezafungin for injection) prescribing information. Silver Spring, MD: U.S. Department of Health and Human Services.
U.S. Food and Drug Administration. (2023). FDA approves new treatment for adults with invasive candidiasis. Silver Spring, MD: U.S. Department of Health and Human Services.
21 U.S.C. § 355. New drug application approval and patent certification requirements.
21 C.F.R. § 314.94. Content and format of an abbreviated application.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Mundipharma	REZZAYO	rezafungin acetate	POWDER;INTRAVENOUS	217417-001	Mar 22, 2023		RX	Yes	Yes	11,197,909	⤷ Start Trial	Y	Y		TREATMENT OF CANDIDEMIA AND INVASIVE CANDIDIASIS WITH REZAFUNGIN BY INTRAVENOUS ADMINISTRATION	⤷ 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
Canada	3069423	⤷ Start Trial
China	111050798	⤷ Start Trial
European Patent Office	3651801	⤷ Start Trial
Spain	3073620	⤷ Start Trial
Japan	2020529973	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 11,197,909

Which drugs does patent 11,197,909 protect, and when does it expire?

Summary for Patent: 11,197,909