United States Patent 8,252,328 (Sufentanil Bioadhesive Oral Transmucosal Tablet): Claim Scope and Patent Landscape
What does US 8,252,328 claim cover at the core (independent claim 1)?
US 8,252,328 claims an oral transmucosal sufentanil bioadhesive tablet defined by a combination of (i) dose, (ii) bioadhesive/transmucosal delivery performance, and (iii) physical form and composition uniformity.
Independent Claim 1 elements (combined limitations):
- Drug: from about 2.5 to about 100 micrograms of sufentanil
- Form: bioadhesive tablet with bioadhesive material and pharmaceutically acceptable excipients
- Adherence/route behavior: adherence to oral mucosa during drug delivery such that the majority of drug is delivered across oral mucosa
- Reduced oral reflex and swallowing: minimal saliva response and minimal swallowing of drug
- Form/size constraint: substantially homogeneous composition with volume from about 3.0 to about 15.0 microliters (µL)
This claim is not a generic “sublingual/buccal sufentanil” claim. It is narrowed by the tablet being bioadhesive with specific delivery behavior plus substantially homogeneous composition and tight volume range.
What are the main claim “knobs” that broaden or narrow coverage?
Below are the claim families that define the technical scope beyond claim 1. In each case, dependent claims add a measurable performance property, a mechanistic excipient system, or a physical characteristic.
1) Disintegration / erosion time windows
- Claim 2: complete erosion evident visually in ~30 seconds to ~15 minutes
- Claims 13-15: disintegration time windows linked to pharmacokinetic timing and “therapeutic time ratio”
- Claim 13: disintegration ~30 sec to ~30 min; 50% Cmax at ~10 to ~30 min
- Claim 14: disintegration ~15 min to ~8 hours; 50% Cmax at ~10 to ~100 min
- Claim 15: disintegration ~15 min to ~8 hours; therapeutic time ratio ~0.3 to ~2.0
Landscape implication: the patent covers multiple kinetic profiles (fast-erosion vs slower/hydrating/eroding kinetics), but always under the claim 1 umbrella of bioadhesive, transmucosal majority delivery, minimal reflexes, and the stated volume/homogeneity constraint.
2) Bioavailability and exposure variability targets
- Claims 6-8: bioavailability thresholds for single or repeated oral transmucosal dosing
- Claim 29: bioavailability >90%
- Claim 18: bioavailability coefficient of variation <40%
- Claims 23-25: oral bioavailability reported as 12.2% (average), with dependent tailoring for dose:
- Claim 24: tablet comprises 10 µg
- Claim 25: tablet comprises 15 µg
Landscape implication: this is a claim set that ties performance to specific PK and variability metrics, which can restrict design-arounds if competing products do not meet those endpoints.
3) PK onset timing (Tonset) and early exposure
- Claim 9: 50% of Cmax occurs ~10 to ~30 minutes
- Claim 19: Tonset ~3 to ~30 minutes
- Claim 13 and Claim 14 also embed 50% Cmax timing constraints in relation to disintegration.
4) Exposure geometry via half-life windows
- Claim 21: half-life 30 minutes to 4 hours
- Claim 22: half-life 100 to 300 minutes (i.e., ~1.7 to ~5 hours)
5) “Therapeutic time ratio” performance metric
- Claim 10: therapeutic time ratio 0.5 to 2.0
- Claim 15: therapeutic time ratio 0.3 to 2.0
6) Route fraction absorbed through oral mucosa
- Claim 11: absorbed via oral mucosa selected from a tiered list:
- ≥55%, ≥60%, ≥65%, ≥70%, ≥75%, ≥80%, ≥85%, ≥90%, ≥95%, ≥98%, ≥99% of drug in the tablet
- Claim 12: at least 60% total drug absorbed via oral transmucosal route
- Claim 20: at least 65%
- Claim 11 plus 12/20 hardens the “majority delivery” concept in claim 1 into a quantitative route absorption fraction.
7) Hydrogel vs non-hydrogel eroding tablet
- Claim 4: tablet becomes a hydrogel upon contact with aqueous fluid
- Claim 5: tablet is an eroding tablet where upon aqueous contact, the surface hydrates and erodes without formation of hydrogel
Landscape implication: the claim set explicitly contemplates two distinct wetting/transition behaviors, which increases coverage for formulation approaches that either (i) form hydrogel-like matrices or (ii) erode without a hydrogel phase.
8) Excipients that couple disintegration kinetics and drug release
- Claim 27: further includes excipients that affect both disintegration kinetics and drug release
- Claim 28: excipient system is crosslinked sodium carboxy methylcellulose
- Claim 30-31: same concept, with crosslinked sodium carboxy methylcellulose again
Landscape implication: the patent includes a formulation-science “handle” for design-around. If a competitor uses a different gel former/disintegrant system, they may avoid the dependent excipient-specific claims, but they still face claim 1 (bioadhesive, homogeneous, volume range, majority transmucosal delivery with minimal reflex/swallowing).
9) Bioadhesive content and adhesion force
- Claim 33: bioadhesive material 1% to 40% w/w
- Claim 34: attachment force 0.03 to 0.18 N/cm² on porcine mucosa substrate in vitro
- Claim 35: repeats the 1% to 40% w/w constraint
How broad is the dose and physical form coverage?
Dose coverage
- Claim 1: 2.5 to 100 µg sufentanil
- Claim 3: 2.5 to 40 µg
- Claim 16-17: 2.5 to 15 µg
This creates layered coverage:
- The broadest dose boundary is claim 1.
- Several dependent claims narrow to the lower-dose region.
Tablet volume boundary
- Claim 1: 3.0 to 15.0 µL volume
- “Substantially homogeneous composition” is required.
This is a strong physical limitation that competitors can’t ignore if they aim for different tablet geometries, densities, or multilayer structures.
What claim coverage is likely to be most enforceable in practice?
From a litigation perspective, the “tightest” and most objectively measurable limitations tend to anchor enforceability:
- Bioadhesive tablet volume (3.0 to 15.0 µL) and homogeneity (Claim 1)
- Quantitative route absorption fraction (Claim 11, Claim 12, Claim 20)
- Erosion/disintegration endpoints (Claim 2, Claims 13-15)
- PK timing (Tonset and 50% Cmax windows) (Claims 9, 13, 14, 19)
- Adhesion force window on porcine mucosa (Claims 34-35)
Claim 4-5 (hydrogel vs non-hydrogel) and the crosslinked sodium carboxy methylcellulose dependent claims create additional formulation-specific hooks, but claim 1 is the enforcement backbone.
Design-around pressure points (where competitors can fail)
Likely high-risk deviations
- Leaving the defined volume range (3 to 15 µL) or using non-homogeneous / multilayer tablet structures that defeat “substantially homogeneous composition.”
- Changing delivery mode such that majority of drug is not delivered across oral mucosa (including if swallowing rises beyond the patent’s “minimal saliva response and minimal swallowing of drug” concept).
- Missing quantitative performance thresholds:
- Bioavailability targets (e.g., >70%, >85%, >90%)
- Route fraction absorbed via oral transmucosa (e.g., ≥70%, ≥85%, ≥95%)
- Tonset and 50% Cmax timing ranges
- Attachment force in the porcine mucosa window
Potential lower-risk deviations
- Using different excipients may reduce exposure to the crosslinked sodium carboxy methylcellulose dependent claims, but it does not remove exposure to claim 1’s functional and physical limitations.
Patent landscape: what this patent blocks and what it leaves open
What US 8,252,328 covers
US 8,252,328 targets a specific product class:
- Sufentanil at microgram doses
- in a bioadhesive oral transmucosal tablet
- with controlled volume, homogeneity, and fast or extended disintegration profiles
- delivering mostly across oral mucosa
- with defined PK outcomes and measurable bioadhesion/erosion behavior
Where the landscape remains open
Even with a strong claim 1, the landscape can still have room around it, mainly because the independent claim is still a set of constraints rather than a single broad concept like “any buccal sufentanil tablet.” Competitors with sufficiently different tablet engineering may avoid meeting one or more constraints:
- tablet volume/homogeneity
- majority transmucosal delivery performance
- reflex/swallowing behavior tied to the bioadhesive adherence
- quantitative absorption, bioavailability, PK timing, or adhesion force
Practical freedom-to-operate mapping (claim-to-platform matching)
A competitor product that differs on any one of the following may not infringe claim 1, even if it is a “bioadhesive oral transmucosal sufentanil” formulation:
| Claim 1 / core limitation |
What to match in a competitor product |
| Sufentanil dose |
2.5 to 100 µg |
| Tablet is bioadhesive and homogenous |
“substantially homogeneous composition” |
| Tablet volume |
3.0 to 15.0 µL |
| Majority delivery via oral mucosa |
quantitative route delivery supports “majority across oral mucosa” |
| Minimal saliva response and swallowing |
formulation and clinical behavior align with low swallowing |
| Sustained adherence |
adheres during drug delivery period |
Key Takeaways
- US 8,252,328 claim 1 is narrow by engineering constraints: sufentanil microdose (2.5 to 100 µg) plus substantially homogeneous tablet at 3.0 to 15.0 µL, with performance requiring majority oral mucosal delivery and minimal saliva response/minimal swallowing.
- Dependent claims expand the enforceable perimeter through measurable endpoints: erosion/disintegration timelines, bioavailability thresholds, route absorption fractions, PK timing (Tonset and 50% Cmax windows), half-life windows, therapeutic time ratio, and in vitro adhesion force.
- Formulation-science hooks exist: hydrogel vs non-hydrogel eroding behaviors and crosslinked sodium carboxy methylcellulose as an excipient system tied to disintegration and drug release.
- Design-around risk concentrates on objective constraints: tablet volume/homogeneity, adhesion/erosion behavior, and quantitative transmucosal absorption and PK outcomes.
FAQs
1) Is US 8,252,328 only about hydrogel-forming tablets?
No. It covers both hydrogel-forming (Claim 4) and eroding tablets without hydrogel formation (Claim 5), while still requiring claim 1’s core bioadhesive and delivery behavior.
2) Does the patent cover multiple sufentanil dose ranges?
Yes. Claim 1 spans 2.5 to 100 µg, with dependent claims narrowing to 2.5 to 40 µg and 2.5 to 15 µg.
3) What is the most constraining physical parameter in the independent claim?
Tablet volume (3.0 to 15.0 µL) plus substantially homogeneous composition.
4) Which dependent claims add quantitative performance standards that are likely central in infringement analysis?
Bioavailability thresholds (Claims 6-8, 29), route absorption fractions (Claims 11-12, 20), disintegration/erosion windows (Claims 2, 13-15), and PK timing metrics (Claims 9, 13-14, 19).
5) Can a competitor avoid dependent claims about crosslinked sodium carboxy methylcellulose?
It may reduce exposure to those dependent claims, but it does not eliminate risk under claim 1 if the competitor still meets the independent claim’s bioadhesion, volume/homogeneity, and transmucosal delivery performance limitations.
References
[1] United States Patent No. 8,252,328. (Claims provided by user text).
