United States Patent 9,173,851: Scope, Claim Architecture, and Landscape for Delayed-Release Cysteamine Beads
United States Patent 9,173,851 claims a capsule-compatible delayed-release cysteamine bead formulation defined by (i) bead size distribution, (ii) an enteric membrane with defined dissolution pH and membrane loading, (iii) a specific cysteamine bitartrate-containing core with binder, and (iv) human in vivo exposure targets at 600 mg free cysteamine base in fasted healthy subjects. The claims are tight on formulation and on the pharmacokinetic (PK) outcomes.
What is claimed in US 9,173,851? (Core formulation and performance limits)
Claim 1 is the dominant independent claim
Claim 1 defines a pharmaceutical dosage form comprising:
A. Dosage form type
- “Delayed-release cysteamine beads”
- Beads administered “in a capsule” to fasted healthy normal subjects at 600 mg free cysteamine base
B. Bead structure
- Core particle comprising:
- cysteamine bitartrate and a binder
- Enteric membrane surrounding the core particle
C. Physical particle size distribution
- Beads have distribution in a range of:
- about 0.7 mm to about 2.8 mm
D. Enteric membrane dissolution behavior
- Enteric membrane begins to dissolve within:
- pH range about 4.5 to about 6.5
E. Enteric membrane loading
- Enteric membrane amount is:
- about 25% to about 35% by weight
- based on the weight of core particles
F. In vivo PK performance constraints
Upon administration in capsule to fasted healthy normal subjects at 600 mg free cysteamine base, the formulation provides:
- (a) Mean Cmax oral dosing:
- 2.3 ± 0.6 mg/L, or
- 80% to 125% of that range
- (b) Mean AUC (0-inf_D) oral dosing:
- 0.84 ± 0.19 min·mg/L/mg, or
- 80% to 125% of that range
These PK limits appear to operate as formulation-defining functional results anchored to a specific dose and dosing condition.
How do dependent claims narrow the scope?
Claim set 2 to 4: cysteamine composition in the core
- Claim 2: cysteamine (as free base) comprises:
- at least 10 wt.% of the core particle.
- Claim 3: cysteamine is:
- cysteamine bitartrate (or pharmaceutically acceptable salt thereof where the salt is cysteamine bitartrate).
- Claim 4: cysteamine bitartrate comprises:
- at least 50 wt.% of the core particle.
Practical consequence: if a competitor uses a different salt (not cysteamine bitartrate) or a core with materially lower bitartrate loading, it is outside these dependent claim constraints.
Claim 5: capsule shell impact and bioequivalence relationship
- Claim 5: beads in a capsule shell are bioequivalent to beads without a capsule shell, measured for:
- mean Cmax and mean AUC (0-inf_D) in the fasted, 600 mg free base condition.
Practical consequence: Claim 5 attempts to prevent design-around arguments based on whether the capsule shell changes absorption.
Claim 6: a specific enteric material dissolution pH
- Claim 6: enteric membrane comprises an enteric material that begins to dissolve at:
- about pH 5.5 in aqueous solution.
Practical consequence: this narrows Claim 1’s broader “begins to dissolve within pH 4.5 to 6.5” into a more specific enteric chemistry or grade.
Claims 7 and 8: tighter recitation of the PK numbers
- Claim 7 repeats Claim 1 PK targets using the point values:
- mean Cmax: 2.3 mg/L
- mean AUC (0-inf_D): 0.84 min·mg/L/mg
- Claim 8 repeats the PK targets with the “80% to 125%” equivalence bands.
Practical consequence: Claim 7 and 8 reduce interpretive disputes about whether the broader “range of 2.3 ± 0.6” is equivalent to the narrower point value with an 80% to 125% band.
What is the enforceable claim scope in plain technical terms?
Claim 1 is a multi-parameter formulation claim with functional PK limitations
To practice Claim 1, a product must align on all (or at least each required dependent limitation if that claim is asserted):
- Cysteamine bead delayed-release system
- Core: mixture of cysteamine bitartrate + binder
- Enteric membrane: surrounding core
- Bead size distribution: 0.7 to 2.8 mm
- Enteric dissolution start pH: 4.5 to 6.5
- Enteric membrane loading: 25% to 35% by weight (relative to core)
- Clinical PK at 600 mg free base (fasted; capsule dosing):
- Cmax mean 2.3 ± 0.6 mg/L and/or within 80%–125%
- AUC (0-inf_D) mean 0.84 ± 0.19 min·mg/L/mg and/or within 80%–125%
Enforcement implication: Even if a competitor matches the chemistry and physical parameters, a failure to hit the human PK target band can be used to argue non-infringement.
How does the PK language change the patent landscape vs. typical formulation patents?
Most formulation patents define composition and manufacturing parameters. Here, Claim 1 includes human bio-performance ranges tied to:
- dosing matrix (capsule)
- condition (fasted)
- dose (600 mg free cysteamine base)
- exposure metrics (mean Cmax and mean AUC 0-inf_D)
That structure creates two landscape effects:
1) Design-arounds face a “performance gate”
A developer can alter:
- binder type
- bead geometry distribution
- enteric polymer grade
- coating method
But the product must still produce exposure within the claimed band. This raises the cost of iterative reformulation.
2) Bioequivalence and variability become claim-relevant
Claim 5 explicitly addresses whether capsule presence changes bioequivalence outcomes. That indicates the patent owner anticipates arguments that the capsule shell alters absorption kinetics.
Where is the “hard boundary” for design-around? (Parameter checklist)
A competitor looking for a non-infringing formulation must evaluate at least these boundaries:
| Claim element |
Claimed boundary |
Design-around direction that risks still landing in scope |
| Bead size distribution |
0.7 mm to 2.8 mm |
Changing size distribution can still land within the range |
| Enteric dissolution start |
pH 4.5 to 6.5 |
Using the same polymer at different thickness may still meet the pH band |
| Enteric coating level |
25% to 35% w/w vs core |
Changing coating level may push outside, but may affect PK |
| Enteric composition (dependent claim) |
begins dissolving at pH ~5.5 |
Many enteric materials are designed around ~5.5 onset |
| Core composition |
cysteamine bitartrate + binder |
Different salt or reduced bitartrate loading targets Claims 3-4 |
| Core cysteamine loading (dependent) |
free base ≥ 10 wt.% |
If bitartrate is dominant, free base wt.% depends on definition |
| Human PK (Claim 1) |
mean Cmax 2.3 ± 0.6 mg/L |
Even close Cmax may still infringe if within 80%-125% band |
| Human PK (Claim 1) |
mean AUC 0.84 ± 0.19 min·mg/L/mg |
AUC is typically more sensitive to release kinetics |
How to position this patent in a competitive landscape for cysteamine products
Strategic read-through: this patent targets a delayed-release bead approach
The claims are written around:
- delayed-release bead formulation
- enteric coating dissolution near intestinal pH
- controlled release to hit specific systemic exposure
Business implication: any competitor seeking to commercialize cysteamine as a delayed-release bead dosage form with enteric-coated particle cores must treat US 9,173,851 as a central barrier.
Likely landscape segments by risk level (infringement exposure logic)
| Segment |
Typical approach |
Infringement risk against US 9,173,851 |
| “Enteric-coated cysteamine bead with bitartrate core” |
Similar core salt + binder + enteric polymer coating |
High, if size, coating level, and PK overlap |
| “Enteric-coated beads with different salt” |
Different cysteamine salt or different core active |
Medium on independent claim; lower on dependent Claims 3-4 |
| “Delayed-release cysteamine not bead-based” |
Different dosage technology (e.g., matrix, osmotic, liquids) |
Lower on structural claim elements, but still must meet PK if asserted creatively |
| “Beads with shifted size/coating/enteric onset” |
Adjust manufacturing parameters |
Medium to high until PK is proven outside band |
What does Claim 5 imply about capsule shell dependence?
Claim 5 is an explicit control point: it requires bioequivalence between:
- beads administered inside a capsule shell
- beads administered without a capsule shell
That does two things for landscape mapping:
- It reduces the credibility of “capsule shell is the release driver” as a non-infringement theory.
- It tightens the formulation-to-outcome link: the beads themselves are the relevant absorption determinant, not merely the container.
What are the likely claim construction pressure points?
1) Interpretation of bead “distribution of particle sizes”
The claim uses “distribution” and a size range. This suggests:
- not a single nominal size
- but an engineered distribution that includes particles within the stated range.
For freedom-to-operate screening, the key is not merely median size but distribution profile.
2) “Enteric membrane begins to dissolve within pH range 4.5 to 6.5”
This anchors dissolution onset to pH behavior. Since dissolution depends on:
- polymer grade
- plasticizers
- coating thickness
- coating integrity
the competitor must test dissolution onset under relevant aqueous conditions.
3) PK band as a claim delimiter
If a product generates mean exposure outside the claimed ranges, it can avoid Claim 1. If it falls within, it is exposed.
Landscape action points for R&D and licensing
1) Treat human PK targets as primary design constraints
If the goal is to reduce infringement exposure, reformulation must be coupled to:
- early PK screening to measure Cmax and AUC under the same test conditions (fasted, 600 mg free base, capsule handling).
2) Define “core” composition strategy up front
Since dependent claims lock:
- cysteamine bitartrate identity
- bitartrate wt.% ≥ 50
- free base wt.% ≥ 10 (Claim 2)
a developer can lower exposure by moving away from those core definitions. This is a faster route than trying to escape all physical and performance parameters.
3) Enteric dissolution onset is not just polymer selection
Claim 6 narrows to pH ~5.5 onset for one dependent version, but Claim 1 already covers the broad pH band. Adjusting coating thickness and binder matrix can shift dissolution. That likely changes PK, bringing performance back into the infringement discussion.
Key Takeaways
- US 9,173,851 is a formulation-and-performance patent: it covers enteric-coated cysteamine beads defined by structure (core + enteric membrane), physical size distribution, enteric dissolution onset pH, coating loading, and human PK ranges at 600 mg free cysteamine base in fasted subjects.
- Claim 1 is the main barrier because it combines multiple formulation parameters with mean Cmax and AUC banding.
- Dependent claims tighten core salt and loading (cysteamine bitartrate and wt.% thresholds) and specify enteric dissolution at pH ~5.5.
- Capsule shell dependency is addressed in Claim 5 via bioequivalence, limiting container-based design-around arguments.
- Competitive risk is highest for products that are enteric-coated cysteamine bead systems using a cysteamine bitartrate core and that generate exposures near 2.3 mg/L Cmax and 0.84 AUC (0-inf_D) under fasted dosing.
FAQs
1) What product attributes are required to meet the core of Claim 1?
Delayed-release cysteamine beads with a cysteamine bitartrate + binder core, an enteric membrane, bead size distribution 0.7 to 2.8 mm, enteric dissolution start pH 4.5 to 6.5, enteric coating level 25% to 35% by weight (core basis), and fasted PK at 600 mg free base with mean Cmax and AUC within the claimed ranges.
2) Does the patent require the dose to be 600 mg free cysteamine base?
Yes. The claimed performance is tied to administration at 600 mg free cysteamine base in fasted healthy normal subjects and the resulting mean Cmax and mean AUC (0-inf_D).
3) How can a competitor reduce risk related to dependent Claims 3 and 4?
By avoiding a cysteamine bitartrate core and/or reducing cysteamine bitartrate wt.% below the claimed threshold (Claim 4 requires ≥50 wt.%).
4) Can changing the capsule shell avoid infringement?
Claim 5 requires bioequivalence between beads administered in a capsule shell and without a capsule shell, so a capsule-based change is unlikely to eliminate exposure if beads themselves match the other limitations.
5) What parameters are most likely to drive non-infringement in practice?
The most decisive are usually the enteric dissolution behavior, enteric membrane loading, bead size distribution, and especially whether the product delivers mean Cmax and AUC within the specific Claim 1 bands under the claimed dosing conditions.
References
[1] United States Patent No. 9,173,851. “Delayed-release cysteamine beads” (claims provided in user prompt).
