United States Patent 11,389,461: Spironolactone Liquid Formulation Scope, Claims and Patent Landscape

United States Patent No. 11,389,461 protects a ready-to-use aqueous spironolactone suspension defined by a tightly integrated formulation profile: approximately 5 mg/mL micronized spironolactone, xanthan gum-controlled viscosity, glycerin as the dispersing agent, citrate buffering, and an acidic pH between 4.5 and 5.5. The dependent claims narrow particle size, excipient concentration, viscosity, buffer composition, and twelve-month stability.

The patent is commercially relevant to liquid spironolactone products, particularly the 5 mg/mL oral suspension marketed as CaroSpir. A competing product can avoid literal infringement only by omitting or moving outside at least one limitation of every asserted independent claim, subject to claim construction and the doctrine of equivalents.[1,2]

What formulation does United States Patent 11,389,461 protect?

The two independent claims, claims 1 and 12, cover substantially the same formulation architecture.

Limitation	Claim 1	Claim 12	Commercial significance
Dosage form	Ready-to-use liquid formulation	Ready-to-use liquid formulation	Targets a product supplied without reconstitution
Active ingredient	Micronized spironolactone	Micronized spironolactone	Captures particle-engineered suspension products
Spironolactone concentration	About 5 mg/mL	About 5 mg/mL	Corresponds to a 25 mg/5 mL presentation
Suspending agent	Xanthan gum	Xanthan gum	Controls sedimentation and rheology
Viscosity	100-300 cP	100-300 cP	Creates a functional rheological limitation
Dispersing agent	Glycerin, 18-24 mg/mL	Dispersing agent consisting of glycerin, 18-24 mg/mL	Claim 12 has a potentially narrower closed limitation
Buffer	Citrate buffer	Citrate buffer	Controls formulation pH
pH	4.5-5.5	4.5-5.5	Limits the formulation to an acidic range
Vehicle	Water	Water	Excludes nonaqueous dosage forms

Claims 1 and 12 are composition claims, not method-of-treatment claims. They do not require a particular patient population, dose, administration route, indication, or clinical outcome. Infringement therefore turns primarily on the composition supplied or manufactured.

The claims do not expressly require a particular container, dosing syringe, flavor, preservative, manufacturing process, or commercial label. Those characteristics may affect infringement only if they alter one of the claimed formulation limitations.

How do claims 1 and 12 differ?

Claim 12 adds the phrase “a dispersing agent consisting of glycerin.” This creates a possible distinction from claim 1.

Claim 1 requires glycerin in the specified concentration but does not expressly state that glycerin is the only dispersing agent. Claim 12 characterizes glycerin as a dispersing agent “consisting of glycerin.” Under ordinary patent construction principles, “consisting of” is a closed transitional phrase. It may exclude another ingredient performing the claimed dispersing-agent function, while still permitting excipients that perform unrelated functions.[3]

A formulation containing glycerin and a second ingredient expressly used as a dispersing agent may therefore present a stronger noninfringement position against claim 12 than against claim 1. That position would depend on the specification, prosecution history, and the court’s construction of “dispersing agent.”

Claims 1 and 12 also create redundancy. Their near-duplicate structure gives the patent owner two independent claim formats covering the same commercial product class. A challenge invalidating one independent claim would not necessarily eliminate the other.

What particle-size range is protected?

Claims 2, 3, 13, 14 and 26, 30 narrow the active ingredient to micronized spironolactone with specified median volume particle sizes.

Claims	Particle-size limitation
2, 13	Median volume particle size not more than about 9.6 micrometers
3, 14	About 3.6 to about 9.6 micrometers
26, 30	About 3.6 micrometers

The particle-size limitations are important because spironolactone has low aqueous solubility. Reducing particle size can improve suspension uniformity, dissolution behavior, dose withdrawal, and content uniformity. The patent does not claim micronization in the abstract. It claims micronized spironolactone within a formulation that also satisfies the concentration, viscosity, pH, buffer and glycerin limitations.

A competitor using particles above approximately 9.6 micrometers could avoid the dependent particle-size claims, but it could still infringe claims 1 or 12 if all independent-claim limitations are met. Conversely, a competitor using particles below 3.6 micrometers may fall outside claims 3, 14, 26 and 30 while remaining within claim 2 if the “not more than about 9.6 micrometers” limitation applies.

The measurement method matters. “Median volume particle size” is not interchangeable with number-average particle size, surface-area diameter, or a different particle-size statistic. Laser diffraction settings, dispersion medium, agglomeration control, and sample preparation can materially affect the reported result.

What xanthan gum and viscosity ranges are claimed?

The independent claims require xanthan gum in an amount sufficient to produce a viscosity of 100 to 300 cP. The dependent claims add the following ranges:

Claims	Xanthan gum or viscosity limitation
4, 15	Xanthan gum, 1.3-3.6 mg/mL
5, 16	Xanthan gum, 1.8-3.6 mg/mL
25, 29	Xanthan gum, 1.3-3.0 mg/mL
10, 21	Viscosity, 130-170 cP
23, 27	Viscosity, 120-170 cP
24, 28	Viscosity, 150-170 cP

The viscosity ranges overlap substantially:

100-300 cP: broadest independent-claim range
120-170 cP: narrower
130-170 cP: narrower
150-170 cP: narrowest

A product measuring 160 cP falls within all of these viscosity ranges. A product measuring 125 cP falls within the 100-300 cP and 120-170 cP ranges but not the 130-170 cP or 150-170 cP ranges.

Viscosity is typically method-dependent. Temperature, spindle, shear rate, equilibration time, sample age, and instrument configuration can affect the result. A patent dispute would likely focus on the specification’s measurement protocol and whether the claim requires a particular test method.

The claims also create a potential formulation-design constraint. Xanthan gum and particle size are not independent variables in practice. Changing xanthan concentration can alter sedimentation, syringeability, pourability, redispersibility and viscosity. A design-around that changes xanthan concentration may still remain inside the independent 100-300 cP limitation.

What glycerin concentrations are protected?

Claims 1 and 12 require glycerin at 18-24 mg/mL. Claims 6 and 17 narrow the range to 18-22 mg/mL.

At 5 mg/mL spironolactone, the claimed glycerin concentration is approximately 0.36% to 0.48% w/v if expressed as a mass-per-volume percentage. The narrower 18-22 mg/mL range is approximately 0.36% to 0.44% w/v.

Glycerin has a dual formulation role. It can assist wetting and dispersion of hydrophobic spironolactone particles and can modify the physical properties of the suspension. Because the claim expressly recites a quantitative glycerin range, a product using a materially different wetting or dispersing system may have a potential design-around route.

That route is not automatically sufficient. A formulation with glycerin at 17 mg/mL may avoid the literal 18-24 mg/mL limitation, but “about 5 mg/mL” and other approximate terms may be construed with an allowed tolerance. Commercial specifications, batch variability, analytical error and prosecution history would be relevant.

What citrate buffer and pH limitations apply?

The claims require a citrate buffer maintaining pH between 4.5 and 5.5. Claims 7 and 18 specify a buffer concentration of approximately 10-100 mM. Claims 8 and 19 narrow pH to 4.8-5.2.

Claim 9 recites:

Citric acid: 1.7-2.4 mg/mL
Sodium citrate: 3.6-4.8 mg/mL

Claim 20 contains similar language but uses “and/or” between the citric acid and sodium citrate ranges. That drafting difference may create claim-construction and clarity issues. Claim 9 more naturally requires both components in their respective ranges. Claim 20 could be argued to cover one component, the other component, or both, depending on the specification and prosecution record.

The pH limitation is central. A formulation at pH 5.0 falls within the independent and narrower pH claims. A formulation at pH 5.6 may avoid the literal pH range but could raise questions about measurement accuracy, product drift and the meaning of “about.” A noncitrate buffer, such as phosphate or acetate, could avoid the citrate-buffer limitation, although a court would assess whether the substitute performs a substantially identical function in substantially the same way under the doctrine of equivalents.

What stability property is claimed?

Claims 11 and 22 require spironolactone content of 100% ±10% of labeled content after storage for 12 months at 25°C and 40% relative humidity.

This is a product-performance limitation. It may require proof through stability data or testing showing that the formulation retains 90-110% of labeled spironolactone under the specified conditions.

The supplied text states “25±° C.” The claim as reproduced appears incomplete because the tolerance after the plus/minus sign is absent. The issued patent should control the operative temperature limitation.

The stability claims are narrower than claims 1 and 12. A product meeting the formulation composition but lacking the claimed stability result may still infringe the independent claims, while avoiding claims 11 and 22 if the stability limitation is not satisfied.

How many patents cover the formulation?

The supplied material establishes one patent with 30 claims. It does not establish the number of related continuation, divisional, foreign or Orange Book-listed patents in the family.

The claim set has two independent claims and 28 dependent claims. Its effective coverage is concentrated in five technical dimensions:

Active-ingredient concentration and micronization.
Xanthan-gum concentration and viscosity.
Glycerin concentration and dispersing function.
Citrate-buffer composition and pH.
Stability under defined storage conditions.

The estate is therefore formulation-specific rather than molecule-wide. Spironolactone itself is an established active ingredient. Patent value depends on whether a competing liquid product needs the claimed combination to achieve acceptable dose uniformity, physical stability and commercial usability.

What is the FDA and Orange Book relevance?

CaroSpir is an FDA-approved spironolactone oral suspension supplied at 25 mg/5 mL, equivalent to 5 mg/mL.[2] The dosage form and concentration correspond closely to the architecture recited in Patent 11,389,461.

For an approved drug product, Orange Book relevance depends on whether the patent is listed against the applicable NDA and whether the listing remains active in the current Orange Book. The supplied claim text alone does not establish the patent’s present listing status, delisting status, or any pediatric-exclusivity adjustment.[4]

A generic applicant submitting an ANDA for an equivalent spironolactone oral suspension could address listed patents through:

Paragraph I certification, if no patent is listed;
Paragraph II certification, if the patent has expired;
Paragraph III certification, accepting approval only after patent expiration; or
Paragraph IV certification, asserting that the patent is invalid, unenforceable or not infringed.[5]

A Paragraph IV notice can trigger patent litigation under 21 U.S.C. § 355(j)(5)(B)(iii). A successful suit may produce a 30-month stay of approval, subject to statutory exceptions and litigation developments.[5]

When does Patent 11,389,461 lose exclusivity?

The patent’s exact expiration date cannot be established from the claim text. Patent term generally runs 20 years from the earliest effective U.S. nonprovisional filing date, subject to patent-term adjustment, patent-term extension, terminal disclaimers and other statutory adjustments.[6]

The relevant timeline must distinguish:

Event	Legal effect
Patent expiration	Ends ordinary patent exclusion rights
FDA regulatory exclusivity expiration	Ends the applicable approval-based restriction
Paragraph IV filing	May initiate litigation before patent expiration
30-month stay	Can delay ANDA approval, not necessarily commercial launch after expiration
Patent-term adjustment	Can extend the nominal 20-year term
Terminal disclaimer	Can limit a patent’s term to another patent’s expiration

FDA exclusivity and patent term are separate. An approved liquid spironolactone product may have no meaningful remaining regulatory exclusivity even while formulation patents remain enforceable.

What generic entry risks exist?

The principal generic-entry risk is a formulation-specific Paragraph IV challenge. A generic applicant may attempt to avoid the patent by changing one or more of the following:

Design-around variable	Potential effect
Use a noncitrate buffer	May avoid citrate-buffer limitations
Use xanthan gum outside the claimed range	May avoid dependent claims, but not necessarily independent viscosity claims
Target viscosity below 100 or above 300 cP	May avoid the independent claims
Use glycerin outside 18-24 mg/mL	May avoid a core quantitative limitation
Use a different dispersing agent	May be more effective against claim 12
Use nonmicronized or differently sized spironolactone	May avoid particle-size-dependent claims
Change concentration from approximately 5 mg/mL	May avoid the central concentration limitation
Use a dry powder for reconstitution	May avoid “ready-to-use” liquid limitations

The strongest design-around opportunities are likely to involve a noncitrate buffer, a different suspending system, or a materially different viscosity profile. The commercial tradeoff is that these changes may affect suspension quality, dose uniformity and patient usability.

How strong is the patent estate?

The patent has moderate formulation-protection strength and limited molecule-level breadth.

Strengths

The independent claims combine multiple quantitative and functional limitations.
The 5 mg/mL concentration aligns with a commercially useful product presentation.
The claims cover both broad and narrower viscosity ranges.
Particle size, rheology, buffer chemistry and stability are linked in a coherent formulation strategy.
Claims 1 and 12 provide partially overlapping independent-claim coverage.

Vulnerabilities

The claims may face obviousness challenges based on combining known spironolactone micronization, xanthan suspensions, glycerin dispersion and citrate buffering.
“About” ranges may create boundary disputes.
Viscosity and particle-size measurements may vary by analytical method.
The claim set is vulnerable to a product that changes the buffer system or dispersing agent.
Claims 11 and 22 may raise enablement, written-description or proof-of-performance questions if stability data do not support the full formulation scope.
Claim 20’s “and/or” language may create indefiniteness or construction disputes.

The patent’s practical strength is greatest against a product that closely copies the commercial formulation. It is weaker against a technically differentiated suspension that maintains spironolactone dose uniformity through a different excipient and rheology system.

What patent litigation or settlement agreements affect the patent?

The supplied information does not identify a Paragraph IV notice, ANDA litigation docket, settlement agreement, license, covenant not to sue, or authorized-generic arrangement involving Patent 11,389,461.

A complete litigation assessment would require matching the patent to PACER or district-court filings, FDA Paragraph IV notices where available, USPTO assignment records, and the current Orange Book. The claim text alone does not establish whether the patent has been litigated, licensed or challenged.

What licensing and commercial exposure are relevant?

The commercial exposure is concentrated in the oral-liquid spironolactone segment rather than the broader spironolactone market. A patent dispute would be most material to:

The NDA holder of an approved spironolactone suspension.
Generic applicants seeking an ANDA for a therapeutically equivalent oral suspension.
Compounding pharmacies and specialty manufacturers supplying liquid spironolactone.
Companies developing pediatric or geriatric liquid dosage forms.
Manufacturers seeking an authorized-generic or private-label supply arrangement.

Tablets and capsules using spironolactone do not ordinarily practice the “ready-to-use liquid formulation” limitations. They may compete commercially without implicating these claims, although separate patents or regulatory exclusivities could apply.

What geographic coverage does the patent provide?

Patent 11,389,461 provides U.S. rights only. Foreign protection would require separate national or regional patents in the relevant jurisdictions. The U.S. claims do not directly restrict manufacture, sale or use outside the United States unless the conduct has a U.S. statutory nexus.

For international launch planning, the relevant questions are whether corresponding applications issued in Europe, Canada, Japan, Australia or other target markets and whether those rights remain pending or enforceable. The U.S. patent number does not establish foreign-family status.

Key Takeaways

Patent 11,389,461 is a formulation patent directed to a 5 mg/mL ready-to-use liquid spironolactone suspension.
The core combination is micronized spironolactone, xanthan gum, glycerin, citrate buffer, water and pH 4.5-5.5.
The principal dependent limitations address particle size, viscosity, excipient concentration, buffer concentration, pH and stability.
Claims 1 and 12 are overlapping independent claims; claim 12 may be narrower because it defines glycerin as the dispersing agent consisting of glycerin.
The patent does not broadly cover spironolactone, tablets, capsules or every liquid spironolactone product.
A generic using a noncitrate buffer, alternative dispersing agent or materially different rheology may have a credible design-around strategy.
FDA approval and Orange Book listing must be analyzed separately from patent enforceability and expiration.
The exact patent expiration date, current Orange Book status, licensing record, Paragraph IV activity and litigation history are not established by the supplied claim text.

Frequently Asked Questions

Does a 5 mg/mL spironolactone suspension automatically infringe Patent 11,389,461?

No. It must also satisfy the claimed micronization, xanthan-gum, viscosity, glycerin, citrate-buffer, pH and water-vehicle limitations, unless a court applies the doctrine of equivalents.

Can a spironolactone suspension avoid the patent by using phosphate buffer?

Potentially. A phosphate-buffered formulation would not literally contain the claimed citrate buffer, but infringement would depend on the full claim language, the patent specification and any doctrine-of-equivalents analysis.

Does using a different suspending agent avoid the claims?

Usually it would avoid the literal xanthan-gum limitation. The formulation would still need to be evaluated against other patents and against any equivalence argument.

Are spironolactone tablets covered by this patent?

Not by the supplied claims. The claims require a ready-to-use liquid formulation and a water vehicle.

Can an ANDA applicant launch before patent expiration?

A Paragraph IV certification can support an early launch strategy, but the patent holder may sue and obtain a statutory stay of FDA approval. Commercial launch risk depends on litigation, settlement, patent validity, infringement, and any applicable exclusivity.

References

United States Patent No. 11,389,461, claims 1-30. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2017). CaroSpir (spironolactone) oral suspension prescribing information.
35 U.S.C. §§ 112, 271.
U.S. Food and Drug Administration. Approved drug products with therapeutic equivalence evaluations (Orange Book).
21 U.S.C. § 355(j).
35 U.S.C. § 154.

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	11,389,461	⤷ 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: 11,389,461

Which drugs does patent 11,389,461 protect, and when does it expire?

Summary for Patent: 11,389,461