US Patent 10,660,907: Spironolactone Liquid Formulation Scope, Patent Landscape, and Generic Entry Risk

US Patent 10,660,907 protects a ready-to-use aqueous spironolactone formulation using xanthan gum within a defined concentration range, subject to a 12-month stability requirement. The strongest commercial coverage is concentrated in the 0.5% w/v spironolactone formulation, equivalent to 25 mg/5 mL, with approximately 0.25% w/v xanthan gum, selected excipients, controlled pH, rapid content uniformity after shaking, and specified PET amber bottles. The patent does not claim spironolactone generally, tablets, capsules, reconstituted powders, or a manufacturing process.

The patent creates a formulation-based barrier for products resembling CaroSpir, the FDA-approved spironolactone oral suspension marketed by CMP Pharma, Inc. It does not prevent a generic competitor from pursuing a materially different liquid formulation unless the competing product still satisfies every limitation of an asserted claim or falls within the doctrine of equivalents.

What does US Patent 10,660,907 protect?

The patent protects a ready-to-use liquid formulation containing:

Claim element	Scope
Active ingredient	Spironolactone
Spironolactone concentration	About 0.20% to about 1.0% w/v in claim 1
Preferred concentration	About 0.3% to 0.8% w/v, or 0.4% to 0.6% w/v
Narrow commercial concentration	About 0.5% w/v
Suspending agent	Xanthan gum at about 0.18% to 0.36% w/v
Preferred xanthan gum range	About 0.20% to 0.32% w/v
Vehicle	Sufficient amount of water
Excipient	At least one pharmaceutically acceptable excipient
Stability	100% +/- 10% labeled spironolactone content after about 12 months at 25 +/- 2 degrees C and 40 +/- 5% relative humidity
Packaging	Enclosed bottle in certain dependent claims
Bottle material	Polyethylene terephthalate with amber colorant
Bottle size	4 oz. or 16 oz.
pH	4.5 to 5.5 in the narrower claims
Mixing performance	Approximately 100% labeled content achieved within about 10 seconds of shaking

The claims are formulation and packaging claims. They are not claims to a method of treating heart failure, hypertension, edema, or primary hyperaldosteronism.

How are the claims structured?

What is the broadest independent claim?

Claim 1 is the principal composition claim. It requires all of the following:

A ready-to-use liquid formulation.
Spironolactone at about 0.20% to about 1.0% w/v.
Xanthan gum at about 0.18% to about 0.36% w/v.
A pharmaceutically acceptable excipient.
Water as the vehicle.
The specified 12-month stability result.

The stability limitation is material. A formulation that satisfies the concentration ranges but does not maintain 90% to 110% labeled spironolactone content under the specified conditions may fall outside literal claim 1, subject to the evidentiary record and claim construction.

Which claims cover the likely commercial strength?

Claims 10 through 16 are the most commercially focused group. They narrow the formulation to:

About 0.5% w/v spironolactone.
About 0.25% w/v xanthan gum.
Selected excipient categories.
Defined excipient concentration ranges.
A pH of 4.5 to 5.5.
A buffer concentration of about 10 mM to 100 mM.
A citrate buffer as one narrower option.

At 0.5% w/v, the formulation contains 5 mg/mL, or 25 mg in 5 mL. That concentration corresponds to the labeled strength of CaroSpir oral suspension.

What do the bottle claims add?

Claims 4, 7, 17, and 18 cover an enclosed bottle containing formulations falling within specified composition claims. Claims 8 and 18 require a bottle comprising:

Polyethylene terephthalate; and
An amber colorant.

Claims 9 and 19 narrow the package to 4-ounce or 16-ounce volume.

These claims create packaging coverage, but they do not independently protect a bottle containing any spironolactone liquid. The bottle must contain the claimed formulation.

What formulations are protected by US 10,660,907?

The core protected formulation is an aqueous, ready-to-use suspension rather than a tablet, capsule, dry powder, or liquid concentrate intended for dilution.

The claim set covers a range of xanthan gum concentrations. A product with 0.25% w/v xanthan gum and 0.5% w/v spironolactone is directly within the narrowest commercial composition claims, assuming the other limitations are satisfied.

Claim 13 identifies several excipient categories:

Excipient category	Claimed range
Anti-foaming agent	0.2% to 0.6% w/v
Preservative	0.125% to 0.250% w/v
Dispersing agent	1.8% to 2.4% w/v
Sweetening agent	0.04% to 0.6% w/v
Flavoring agent	0.1% to 0.5% w/v
Buffer	Amount sufficient to maintain pH 4.5 to 5.5

Claim 14 lists acetate, aconitate, glutarate, glutamate, malate, succinate, tartrate, citrate, and phosphate buffers. Claim 16 specifically identifies citrate buffer.

The language permits a formulation containing one listed excipient or a combination, depending on how the “selected from the group consisting of” language is construed in the context of the specification and prosecution history.

How strong is the patent estate for spironolactone suspension products?

What are the principal strengths?

The patent has several meaningful enforcement strengths:

It covers the likely commercial 25 mg/5 mL concentration.
It combines active, suspending agent, vehicle, and stability limitations.
It includes narrower claims directed to pH, buffers, excipients, mixing time, and packaging.
The claimed xanthan gum range is relatively specific.
Commercial products often use standardized excipient systems and container configurations, making formulation discovery possible through product testing and regulatory disclosures.
The rapid uniformity limitation in claim 20 may be useful where the product label requires shaking before administration.

What are the principal weaknesses?

The estate also has design-around vulnerabilities:

No claim covers all spironolactone liquids.
Xanthan gum is required in the independent claim.
A formulation using a different suspending agent may avoid literal infringement.
A formulation outside the claimed xanthan gum range may avoid literal infringement.
The claims contain functional stability and uniformity limitations that may require testing.
The bottle claims are dependent and do not materially expand composition coverage.
The patent does not claim the therapeutic use of spironolactone.
The claims do not cover tablets, capsules, injectable products, or dry formulations.

A competing product using, for example, a different polymeric suspending system could present a substantial non-infringement position. That position would depend on whether the formulation nevertheless contains xanthan gum as a minor excipient and whether the accused product meets the “about” ranges.

When does US Patent 10,660,907 lose exclusivity?

The patent issued on June 2, 2020. Its patent-family priority is associated with the spironolactone suspension formulation filings leading to the CMP Pharma product family. The nominal 20-year patent-term date for the family is October 31, 2034, before any patent-term adjustment or terminal-disclaimer analysis.

Event	Date or status
Earliest relevant family priority	October 31, 2013
US patent grant	June 2, 2020
Nominal patent-term endpoint	October 31, 2034
FDA approval of CaroSpir NDA 209127	2017
Small-molecule regulatory exclusivity	Expired before the patent term
Patent protection	Extends beyond regulatory exclusivity

The precise expiration date for enforcement purposes must account for any patent-term adjustment shown in the USPTO record. Patent expiration also does not eliminate other unexpired patents in the same product family.

What is the Orange Book status of US 10,660,907?

CaroSpir is an FDA-approved spironolactone oral suspension associated with NDA 209127. The FDA-approved label identifies the product as a 25 mg/5 mL oral suspension and requires shaking before use.[2]

Orange Book treatment must be analyzed at the NDA level. A formulation patent is eligible for listing only if it meets the FDA’s patent-listing standards and is submitted by the NDA holder. The existence of US 10,660,907 does not, by itself, establish that every claim is currently listed in the Orange Book.

For generic-entry analysis, the relevant records are:

The current Orange Book patent-and-exclusivity data for NDA 209127.
The patent declaration submitted with any ANDA.
Any Paragraph IV notice.
FDA’s patent-listing and delisting history.
Any patent-term adjustment or terminal-disclaimer information.

The patent’s commercial relevance is high even if only selected claims are listed because an ANDA applicant may still face infringement exposure under unlisted claims in district court.

Which companies are challenging the spironolactone suspension patent?

No challenger, Paragraph IV notice, district-court complaint, or settlement agreement is established by the patent claims supplied here. The patent itself contains no litigation history.

A generic applicant seeking approval of an equivalent spironolactone suspension would generally evaluate:

Paragraph IV invalidity arguments.
Non-infringement based on a different suspending agent.
Non-infringement based on xanthan gum outside the claimed range.
Failure of the claimed stability or shaking-performance limitations.
Invalidity based on anticipation or obviousness.
Written-description and enablement challenges to the full concentration ranges.
Claim-construction arguments concerning “ready-to-use,” “about,” and functional stability language.

A Paragraph IV certification would create the possibility of a 30-month FDA stay if the NDA holder or patent owner filed suit within the statutory period.[4]

What generic launch scenarios exist?

Scenario 1: Same 25 mg/5 mL formulation

A product matching 0.5% w/v spironolactone, approximately 0.25% w/v xanthan gum, a pH of 4.5 to 5.5, and the claimed excipient system would face the highest infringement risk. Claims 1, 10 through 16, and 20 would be the principal exposure points.

Scenario 2: Different suspending polymer

Replacing xanthan gum with another suspending agent could avoid the central composition claims if xanthan gum is absent. The applicant would still need to address pharmaceutical equivalence, physical stability, dose uniformity, preservative performance, and FDA product-quality requirements.

Scenario 3: Xanthan gum outside the claimed range

A product using xanthan gum below 0.18% or above 0.36% w/v could present a literal non-infringement position. The word “about” creates a boundary dispute risk, particularly where the concentration is close to a claimed endpoint.

Scenario 4: Alternative dosage form

Tablets, capsules, powders, and extemporaneously prepared suspensions are outside the literal subject matter of these claims. They may compete with CaroSpir clinically but would not ordinarily practice the claimed ready-to-use liquid formulation.

Does the patent create biosimilar risk?

No. Spironolactone is a small-molecule drug. The relevant competitive pathway is an ANDA for a generic drug, not a biosimilar application under the Biologics Price Competition and Innovation Act.

The main regulatory and commercial issues are pharmaceutical equivalence, bioequivalence where required, container-closure compatibility, suspension uniformity, stability, preservative effectiveness, and labeling.

What patent litigation and settlement issues matter?

The patent claims do not disclose any settlement agreement or license. A settlement involving an ANDA applicant would typically address:

Earliest agreed generic launch date.
Whether the launch is authorized or at risk.
Patent claim carve-outs.
Supply or licensing terms.
Covenants not to sue.
Acceleration provisions if the patents are invalidated.
Treatment of later-issued continuation patents.

Any settlement date should be tested against the patent term, FDA exclusivity, and the existence of related patents. A settlement concerning US 9,901,561, for example, would not automatically resolve separate claims in US 10,660,907 unless the agreement expressly covers the continuation or patent family.

How does US 10,660,907 compare with competing spironolactone products?

Product or format	Formulation type	Direct exposure to US 10,660,907
CaroSpir	Ready-to-use 25 mg/5 mL oral suspension	High
Generic equivalent suspension	Ready-to-use liquid	Potentially high
Compounded spironolactone suspension	Variable liquid formulation	Depends on xanthan gum and claim limitations
Aldactone tablets	Solid oral dosage form	Low or none under these claims
Spironolactone capsules	Solid oral dosage form	Low or none
Dry powder for reconstitution	Not ready-to-use before reconstitution	Generally outside literal scope
Alternative-polymer suspension	Ready-to-use liquid	Potentially reduced exposure

The patent’s economic value is therefore concentrated in the commercial suspension segment, not the broader spironolactone market.

What geographic coverage does the patent provide?

US 10,660,907 provides rights only in the United States. Parallel foreign applications or granted patents must be analyzed separately. US patent rights can affect:

Manufacture in the United States.
Importation of an infringing product.
Commercial sale in the United States.
Offers for sale in the United States.
Certain activities tied to ANDA development under the Hatch-Waxman safe harbor.

The patent does not independently block sales in Canada, Europe, Japan, or other jurisdictions.

Key Takeaways

US 10,660,907 is a formulation patent directed to ready-to-use aqueous spironolactone suspensions.
The core range is 0.20% to 1.0% w/v spironolactone and 0.18% to 0.36% w/v xanthan gum.
The commercially important embodiment is approximately 0.5% w/v spironolactone with approximately 0.25% w/v xanthan gum.
Narrow claims add excipient ranges, pH 4.5 to 5.5, buffer concentration, citrate buffer, rapid shake uniformity, and PET amber bottles.
The nominal patent-term endpoint is October 31, 2034, subject to USPTO term adjustments and related-family analysis.
Generic risk is highest for a product matching the CaroSpir formulation and lower for a suspension using a different polymer or materially different xanthan gum concentration.
The patent does not cover spironolactone tablets, capsules, general therapeutic use, or all liquid formulations.
No litigation, Paragraph IV challenge, or settlement is established by the supplied claim text.
Biosimilar analysis is not applicable because spironolactone is a small molecule.

FAQs

Does US 10,660,907 cover a spironolactone tablet?

No. The claims require a ready-to-use liquid formulation. A conventional tablet does not satisfy that dosage-form limitation.

Can a generic use xanthan gum and avoid the patent?

Possibly, but only if the product falls outside the claimed xanthan gum ranges or otherwise avoids another required limitation. A formulation using xanthan gum at approximately 0.25% w/v would be within the central claimed range.

Is a 25 mg/5 mL spironolactone suspension automatically infringing?

No. Strength alone is insufficient. Infringement depends on the complete formulation, including xanthan gum concentration, water vehicle, excipients, stability performance, and applicable dependent-claim limitations.

Does an amber PET bottle create independent patent protection?

No. The bottle limitations are dependent on the claimed formulation. An amber PET package without the claimed liquid composition does not independently practice the bottle claims.

Can a compounded suspension compete with CaroSpir?

Yes, subject to applicable FDA compounding rules, state law, product quality requirements, and patent risk. A compounded product using the claimed spironolactone and xanthan gum ranges could raise infringement issues.

References

United States Patent No. 10,660,907, “Spironolactone liquid formulation,” issued June 2, 2020. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2017). CaroSpir (spironolactone) oral suspension prescribing information. NDA 209127.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. FDA.
21 U.S.C. § 355(j), Abbreviated new drug applications and patent certifications.

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Cmp Dev Llc	CAROSPIR	spironolactone	SUSPENSION;ORAL	209478-001	Aug 4, 2017	AB	RX	Yes	Yes	10,660,907	⤷ Start Trial	Y				⤷ 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	3003028	⤷ Start Trial
European Patent Office	3368045	⤷ Start Trial
Morocco	43132	⤷ Start Trial
World Intellectual Property Organization (WIPO)	2017075463	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 10,660,907

Which drugs does patent 10,660,907 protect, and when does it expire?

Summary for Patent: 10,660,907