Scope, Claims, and U.S. Patent Landscape for Drug Patent US 11,529,333

US 11,529,333 claims a specific liquid oral suspension formulation of zonisamide with tight quantitative excipient ranges, defined pH, defined stability, and an impurity specification. The claim set is built to cover both a “core” formulation (Claim 1) and multiple common formulation variants through dependent claims (buffer systems, sweeteners, flavors, preservative lists, and tighter impurity limits), plus a representative “fully specified” composition in Claim 13.

What is the claimed invention under US 11,529,333?

The invention is a liquid oral pharmaceutical suspension of zonisamide at about 20 mg/mL, using a suspending system of xanthan gum plus a defined cellulose combination, buffered to an acidic pH window, preserved, and demonstrated stable for storage conditions consistent with ICH accelerated testing.

Core formulation requirements (Claim 1)

Claim 1 requires, in combination:

Drug
- Zonisamide: about 20 mg/mL
Suspending agent system
- Xanthan gum: about 2 mg/mL to about 3.5 mg/mL
- Cellulose combination: about 20 mg/mL of a combination of
  - microcrystalline cellulose and
  - sodium carboxymethylcellulose
Buffers
- One or more buffering agents (buffer species are further constrained in Claim 2 and Claim 12)
Excipients
- One or more pharmaceutically acceptable excipients, where the excipients comprise a preservative.
pH
- Suspension has pH 3.5 to 5.0
Stability
- Stable for at least 6 months when stored at 40°C / 25% relative humidity
Preservative presence
- Preservative is required by Claim 1, and Claim 4 narrows acceptable preservative chemistries.

Variant coverage via dependent claims

The patent then “fans out” into typical oral formulation design variables while preserving the core quantitative and functional constraints:

Buffer agent selection (Claim 2; and specific buffer pair in Claim 12)
Sweetening and flavoring packages (Claims 3, 5, 6, 7, 8)
Vehicle choices (Claim 9)
Preservative selection (Claim 4)
Impurity performance (Claims 10 and 11)
A specific example-level composition (Claim 13)

What do the independent and dependent claims cover, claim-by-claim?

Claim 1: The independent “composition and performance” claim

Claim 1 is the primary infringement anchor. It ties together:

Drug level (zonisamide about 20 mg/mL)
Suspender system (xanthan gum 2 to 3.5 mg/mL plus microcrystalline cellulose + sodium carboxymethylcellulose about 20 mg/mL)
Buffer and preservative inclusion
pH 3.5 to 5.0
Stability: 6 months at 40°C / 25% RH
Implicit product qualification by the pH and stability functional requirement

Notably, Claim 1 does not itself list the preservative chemicals, buffer species, or flavor/sweetener species. Those are handled by dependent claims.

Claim 2: Buffer agent genus

Claim 2 selects buffering agents from a closed list:

Sodium acetate
Sodium citrate
Ammonium sulfate
Sodium phosphate
Disodium hydrogen phosphate
Potassium citrate
Citric acid monohydrate
Trisodium citrate dihydrate
Combinations thereof

This claim is narrower than Claim 1 because it limits the allowed buffer chemistries.

Claim 3: Addition of standard organoleptic/vehicle components

Claim 3 allows further excipients:

One or more sweetening agents
One or more flavoring agents
One or more vehicles
Combinations

This claim expands scope to formulations that keep Claim 1’s core quantitative constraints while adding typical oral formulation ingredients.

Claim 4: Preservative selection list (closed list)

Claim 4 restricts “the preservative” to specific options (or combinations):

Benzyl alcohol
Chloro-butanol
Chloro-cresol
Alkyl esters of paraben
Phenol
Phenyl ethanol
Propylene glycol
Chloroform
Benzoic acid
Potassium sorbate
Sodium benzoate
Combinations

This is a closed selection dependent on Claim 1’s requirement that the excipients comprise a preservative.

Claim 5: Sweetener list (closed list)

Claim 5 narrows sweeteners to:

Sucralose
Sucrose
Glycerol
Liquid glucose
Sorbitol
Maltitol
Saccharin sodium
Aspartame
Combinations

Claim 6: Flavoring ingredient class

Claim 6 limits flavors to:

Essential oils
Fruit flavors
Combinations

Claim 7: Essential oils subset (closed list)

Claim 7 specifies essential oils from:

Peppermint oil
Orange oil
Lemon oil
Combinations

Claim 8: Fruit flavor subset (closed list)

Claim 8 specifies fruit flavors from:

Peppermint flavour
Raspberry flavour
Strawberry flavour
Tutti-fruit flavour
Combinations

Claim 9: Vehicle type

Claim 9 constrains vehicles to:

An aqueous vehicle selected from:
- purified water
- hydro alcoholic
- a polyhydric alcohol
- a buffer
- combinations

This claim operationalizes Claim 3’s vehicle concept and narrows formulation physical construction.

Claim 10: Impurity performance I (tight “single and total” limits)

Claim 10 adds quantitative impurity thresholds:

Single max impurity: 0.06% or less
Total impurities: 0.10% or less

This claim is an additional performance-based qualifier layered on top of Claim 1.

Claim 11: Impurity performance II (impurity A and total)

Claim 11 further tightens/targets specific impurity reporting:

Impurity A: less than 0.05%
Total impurity: less than 0.25%

This indicates the specification contains at least two impurity metrics: “impurity A” and “total impurity,” each with distinct cutoffs.

Claim 12: Specific buffer pairing (citric acid + trisodium citrate dihydrate)

Claim 12 narrows buffering agents to:

Citric acid monohydrate and
tri-sodium citrate dihydrate

This is a specific embodiment locked to a particular buffer system.

Claim 13: A fully specified formulation instance (example-level “comprising”)

Claim 13 compiles the core components into a specific quantitative recipe:

Zonisamide: about 20 mg/mL
Xanthan gum: about 3.5 mg/mL
Microcrystalline cellulose + sodium carboxymethylcellulose: about 20 mg/mL
Sodium benzoate: about 1.0 mg/mL
Buffers: citric acid monohydrate + tri-sodium citrate dihydrate
Plus:
- one or more sweetening agents
- one or more flavoring agents
Purified water

This claim is both narrower (because it pins quantities for xanthan gum and benzoate and identifies the buffer pair) and broader in an “open” sense due to “comprising,” while still tethered to the core structure of Claim 1.

What is the effective claim scope for competitors? (formulation design “do’s and don’ts”)

Because Claim 1 contains multiple hard constraints (zonisamide concentration, suspension system ranges, pH, stability, preservative inclusion), the infringement risk is highest for products that satisfy all of those elements simultaneously. The dependent claims then create additional infringement paths if a competitor’s formulation matches the listed species and impurity targets.

Key “gates” in Claim 1

A competitor must generally avoid at least one of the following gates to reduce risk:

Zonisamide concentration deviates from about 20 mg/mL
Xanthan gum is outside about 2 to about 3.5 mg/mL
Cellulose combination deviates from about 20 mg/mL
pH outside 3.5 to 5.0
No preservative or a preservative that does not fall under the dependent preservative claim (Claim 4) if it is asserted
Stability fails (less than 6 months at 40°C/25% RH)
Impurity performance not meeting Claims 10/11 (if those claims are asserted)

Additional narrowing in dependent claims (species coverage)

Even if a product hits the Claim 1 core, the dependent claims can still be asserted if the formulation uses:

A buffer from Claim 2’s list (or specifically citric acid monohydrate + trisodium citrate dihydrate per Claim 12)
A preservative from Claim 4’s list
Sweeteners from Claim 5’s list
Flavors from Claims 6-8’s lists
A vehicle constrained by Claim 9

How does the impurity/quality layer change the landscape?

Claims 10 and 11 are structured as product-by-process/product-by-attribute performance limitations. They matter for competitive freedom because they connect formulation stability and composition to impurity outcomes.

Impurity thresholds (as claimed)

Claim	Metric	Limit
10	Single max impurity	≤ 0.06%
10	Total impurities	≤ 0.10%
11	Impurity A	< 0.05%
11	Total impurity	< 0.25%

Interpretation for landscape: if a generic or follow-on manufacturer uses the same excipient system and achieves the same performance, it may be difficult to design around the impurity limits without changing the chemistry or process to change degradation pathways and impurity profiles.

What is the overall patent landscape picture in the US (based on this claim set)?

This patent is a formulation patent focused on a zonisamide liquid suspension. The claim system indicates a strategy typical for “line-of-sight” barriers against:

early generics that rely on different suspending systems or pH windows
“me-too” formulations that match the active concentration but diverge on buffer/preservative/sweetener/flavor combinations
products that fail storage stability and impurity targets

Practical landscape segments (what others typically do)

From the claim structure, the competitive perimeter is split into:

Core formulation lock-in
- Quantitative suspending system + pH + stability at 40°C/25% RH
Preservative and buffer selection
- Species-constrained in dependent claims
Organoleptic package
- Species constrained in dependent claims
Quality metrics
- Impurity windows constrain “same formulation, different manufacturing” unless impurity profile is also shifted

Where are the highest-risk overlaps for a zonisamide liquid oral suspension product?

The risk is highest if a competitor’s product (i) is designed to be liquid suspension, (ii) uses xanthan gum in the claimed range, (iii) uses the specific cellulose combination at about 20 mg/mL, (iv) targets pH 3.5-5.0, (v) includes a preservative that fits Claim 4, and (vi) demonstrates at least 6 months stability at 40°C / 25% RH, with impurity profiles that do not exceed the tight limits in Claims 10 or 11 if those are asserted.

The “most literal” overlap is with an embodiment matching Claim 13:

zonisamide 20 mg/mL
xanthan gum 3.5 mg/mL
cellulose combination 20 mg/mL
sodium benzoate 1.0 mg/mL
citric acid monohydrate + tri-sodium citrate dihydrate buffer
purified water base
plus sweeteners and flavors

What are the scope boundaries for a design-around strategy? (Claim-structured)

A formulation designer typically looks for non-overlapping changes, and the claim set points to the most surgical levers:

pH window change: Claim 1 requires pH 3.5 to 5.0
suspending system shift:
- xanthan gum outside 2 to 3.5 mg/mL, or
- cellulose combination not about 20 mg/mL
stability profile change: Claim 1 requires stability at least 6 months at 40°C/25% RH
preservative selection:
- Claim 4 provides a closed list; using a preservative outside that list may avoid dependent-claim coverage (but still must satisfy Claim 1’s requirement that a preservative is present)
buffer system:
- Use buffers not listed in Claim 2, or at least not the citric acid + trisodium citrate combination of Claim 12
impurity profile change:
- Engineering to exceed impurity thresholds would avoid Claims 10 and 11, though it would likely be unacceptable from a regulatory standpoint

Key Takeaways

US 11,529,333 claims a zonisamide liquid oral suspension at about 20 mg/mL with a defined suspending system: xanthan gum (2 to 3.5 mg/mL) plus microcrystalline cellulose/sodium carboxymethylcellulose (about 20 mg/mL).
The formulation must have pH 3.5 to 5.0 and be stable for at least 6 months at 40°C/25% RH.
Dependent claims tightly constrain buffer chemistry (including a specific citric acid + trisodium citrate dihydrate system), preservatives (closed list), sweeteners, and flavor oils/fruit flavors.
Two additional layers set impurity performance limits (Claims 10 and 11) that can bar near-identical formulations if impurity outcomes track the claimed profile.
Claim 13 is a close-to-literal “implementation” recipe that concentrates risk for competitors using the same excipient quantities and buffer/preservative pairings.

FAQs

1) Does Claim 1 cover any preservative or only certain ones?

Claim 1 requires that the excipients “comprise a preservative,” but it does not limit the preservative to a specific list. The preservative list appears in dependent Claim 4.

2) What is the pH requirement and how tight is it?

Claim 1 requires pH 3.5 to 5.0, which is a narrow acidic window for oral suspensions.

3) Is the stability requirement a “data” limitation or just a formulation goal?

It is a stated requirement: the suspension is “stable for at least 6 months when stored at 40°C and 25% relative humidity.”

4) What impurity constraints are claimed?

Claim 10 limits single max impurity to 0.06% and total impurities to 0.10%. Claim 11 limits impurity A to <0.05% and total impurity to <0.25%.

5) Which dependent claims most directly control “me-too” product design?

Claim 2 (buffers), Claim 4 (preservatives), Claims 5-8 (sweeteners and flavors), Claim 9 (vehicle type), and Claims 10-11 (impurity performance) are the most direct constraints beyond Claim 1’s core quantitative and functional requirements.

References

[1] US Patent 11,529,333 (claims as provided by the user).

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate
Azurity	ZONISADE	zonisamide	SUSPENSION;ORAL	214273-001	Jul 15, 2022		RX	Yes	Yes	11,529,333	⤷ 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
European Patent Office	3668508	⤷ Start Trial
World Intellectual Property Organization (WIPO)	2019038584	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 11,529,333