United States Patent 5,965,161: Scope, Claim Coverage, and US Patent Landscape for Extruded Multiparticulate Opioid Sustained-Release Particles

The US patent 5,965,161 claims an extruded, non-spheroidal, multiparticulate sustained-release oral dosage form built from extruded particles with (i) an opioid analgesic dispersed in a matrix of one or more water-insoluble retardants and (ii) a water-insoluble binder, where particles are strand-cut and provided as unit doses (including gelatin capsules). The claim set also covers multiparticulate sustained-release methods (extrusion, heating, strand formation, cooling, cutting, unit-dose division), method-of-treatment use, and formulation/process parameters (particle dimensions, retardant/binder classes, opioid lists, drug loading ranges, and feeding/metering variants).

What does US Patent 5,965,161 claim for extruded multiparticulate sustained-release opioids?

Answer: It claims sustained-release oral dosage forms and particles made by extruding a homogeneous matrix of an opioid (or other active agent class) with water-insoluble retardants plus a water-insoluble binder, then cutting strands into non-spheroidal cylindrical particles of defined size, with in vitro release over at least about 6 hours (and a separate claim targeting 12–24 hours).

Core product claim architecture (unit dose + extruded particles)

The principal claim set is structured around four nested elements:

Unit dose containing a plurality of extruded, non-spheroidal particles
Particle composition: opioid dispersed in a matrix of retardant(s) + water-insoluble binder
Particle morphology/geometry:
- length about 0.1 mm to 12 mm
- diameter about 0.1 mm to 5 mm (with later variants narrowing to 3 mm)
Release performance: release of opioid over at least about 6 hours (with an additional claim extending to 12–24 hours)

Independent claim focal points (what limits infringement)

Even without construing claim language in litigation-style detail, the infringement “center of mass” is clear from the limitations:

Extrusion + strand cutting requirement: “mixed… in an extruder… extruding… to form strands… cutting… into extruded particles.” This distinguishes over pelletization/granulation systems not built via extrusion and strand cutting.
Non-spheroidal particles of defined dimensions: design-around can target particle shape or dimension outside ranges (or argue nonconformance).
Water-insoluble binder present in the opioid particle claims: claims 1 and 3 require a water insoluble binder (claim 28 makes it optional).
Matrix system: one or more retardants and binder classes are broadly defined but tethered to water-insoluble excipient categories.

Which opioid analgesics are explicitly covered in the claim lists?

Answer: The claims include extensive explicit opioid lists, with further dependent claims limiting to numeric drug-loading ranges for specific opioids.

Claim 1 opioid list (representative, broad explicit coverage)

Claim 4 and claim 20 enumerate many opioids in a single list. The coverage includes (among others): buprenorphine, fentanyl, hydrocodone, hydromorphone, morphine, oxycodone, oxymorphone, tramadol, and many additional named opioids, salts, and mixtures.

Numeric potency ranges (drug loading limits)

Three dependent coverage anchors in claim 1:

Hydromorphone loading range: 2 mg to 64 mg (claim 5)
Morphine loading range: 5 mg to 800 mg (claim 6)
Oxycodone loading range: 5 mg to 400 mg (claim 7)

These ranges are not generic “amount” placeholders; they create a measurable boundary for unit-dose strength formulations.

Particle-retardant-binder selection effects

Dependent claims further narrow excipient selections, for example:

Retardant examples: ethylcellulose, acrylic polymers, hydroxyalkylcelluloses (claims 8, 33, 34, 52, 24)
Binder examples: stearyl alcohol, stearic acid, waxes, hydrogenated fats (claims 10–11, 41, 45, 32, 36, 55–56)

This matters because a competitor can attempt to maintain extrusion/strand-cut particle morphology while shifting retardant or binder systems to exit the claim classes.

What particle dimensions and morphology does the patent require?

Answer: Non-spheroidal, strand-cut particles with length 0.1–12 mm and diameter 0.1–5 mm are required for the base opioid unit-dose claims; other claims narrow diameter or extend release time.

Dimensional limitations by claim group

Claim 1 / opioid unit dose particles:
- length 0.1–12 mm
- diameter 0.1–5 mm
- release ≥ 6 hours
Claim 12 (gelatin capsule unit dose): same general dimensions but explicitly includes hydroxyalkycellulose and stearic acid with diameter 0.1–5 mm
Method claims: diameter ranges sometimes tighten (e.g., claim 18 uses diameter 0.1–3 mm)
Extended-release claim (claim 28): diameter constrained to 0.1–3 mm and release ≥ 12–24 hours

“Non-spheroidal” as a practical design-around lever

The patent does not demand “cylindrical” in claim 1, but does constrain it to non-spheroidal geometry. The method claims explicitly target “generally cylindrically-shaped particles,” strengthening that geometry if you are practicing the disclosed method.

What retardants and water-insoluble binders are covered?

Answer: The claim set covers water-insoluble retardants (including ethylcellulose, acrylic polymers, hydroxyalkylcelluloses) and water-insoluble binders chosen from a broad fatty/wax/polymer list; dependent claims add specific exemplars like stearic acid and paraffin.

Retardant categories

Claim 1: “one or more retardants” (broad)
Claim 8: retardant selected from acrylic polymers and hydroxyalkylcelluloses
Claim 9: acrylic polymers defined by acrylic acid/methacrylic acid ester monomer family
Claim 24: method claim specifies acrylic polymers and hydroxyalkylcelluloses
Claim 52: method specifies water-insoluble retardant as ethylcellulose
Claim 34: unit dose where retardant is hydroxyalkylcellulose

Water-insoluble binder categories

Claim 10: binder selected from fatty alcohols, hydrogenated fats, fatty acid glycerides, hydrocarbons, waxes, hydrophobic/hydrophilic hydrocarbon-backbone polymers, fatty acid esters, and mixtures
Claim 11: stearic acid, stearyl alcohol, water-insoluble waxes, mixtures
Claim 41: binder is stearic acid
Claim 45: binder is stearic acid or stearyl alcohol
Claim 32: hydrogenated fats exemplars (hydrogenated vegetable oil, hydrogenated castor oil), waxes water-insoluble
Claim 35: paraffin identified as example wax

Capsule-specific binder/excipient stack

Claim 12 adds a specific capsule formulation:

gelatin capsule containing particles with:
- retardants: ethylcellulose and/or acrylic polymers
- binder: stearic acid
- hydroxyalkylcellulose present
- strands extruded and cut

This creates a fairly tight formulation envelope if a capsule product uses the same excipient stack.

How broad is the “active agent” coverage beyond opioids?

Answer: Claim 2 is a sustained-release particle claim covering a wide set of non-opioid actives (disinfecting agents, repellents, pesticides, fertilizers, dyes, fragrances, etc.) dispersed in a water-insoluble retardant matrix with a water-insoluble binder and strand-cut particle geometry.

Claim 2 active agent categories (non-opioid)

Claim 2 expands the “sustained-release particle” concept to:

disinfecting agents, cleansing agents, deodorants, fragrances, dyes
animal repellents, insect repellents
fertilizing agents, pesticides, herbicides, fungicides
plant growth stimulants

So, the particle platform is not limited to opioid drugs in a generic sense; it is limited by particle geometry, extrusion/strand cutting process, and the specified excipient categories.

What formulation claims cover extended release and feeding-fasting effects?

Answer: Claim 28 targets a unit dose opioid sustained-release oral dosage form “having substantially no feeding-fasting effect,” with release over 12–24 hours, diameter 0.1–3 mm, and optional water-insoluble binder.

Claim 28 key differences vs. claim 1

Compared to claim 1 (6+ hours; diameter up to 5 mm; binder required), claim 28:

extends release to 12–24 hours
tightens diameter to 0.1–3 mm
makes binder optional (“optional water insoluble binder”)
imposes a behavioral/bioperformance concept: “substantially no feeding-fasting effect,” which can be used in infringement to tie the excipient/process stack to food effect performance

Because this claim is broader in binder presence (optional) but narrower in release endpoint and diameter, it can capture different formulation optimizations.

What methods-of-preparation are claimed (extrusion, heating, strand cutting)?

Answer: The patent claims multiple multiparticulate sustained-release manufacturing workflows centered on feeding/metering into an extruder, heating the homogeneous mixture, extruding to strands, cooling, cutting into particles, and dividing into unit doses.

Main method claim (claim 15) workflow

Claim 15 is a manufacturing method requiring:

feeding powder active + water-insoluble retardant into extruder
mixing to homogeneous mixture
heating in extruder
extruding strands
cooling strands
cutting into cylindrically shaped particles (0.1–12 mm length; 0.1–5 mm diameter)
dividing into unit doses
excipient ratio: retardant/active sufficient for ≥ 6-hour release in aqueous fluid

Dependent modifications include:

gelatin capsule unit dose (claim 16)
heating range prior to extrusion: 30°C to 200°C (claim 17)
specific active agent opioid lists (claim 19 and 20)
specific strength ranges for hydromorphone/morphine/oxycodone (claims 21–23)
selection of retardant and binder (claims 24–26)
feeding binder into extruder and mixing binder into homogeneous mixture (claim 26)

Direct metering variant (claim 27)

Claim 27 provides an alternative process:

directly metering into extruder retardant + active agent
heating, extruding strands
cooling, cutting into particles (diameter tightened to 0.1–3 mm)
dividing into unit doses

Further dependents (claims 30–31) add direct metering of binder and/or excipients.

What method-of-treatment claims exist?

Answer: Claim 18 claims a method of treating a patient with the sustained-release multiparticulate opioid formulation, using the same manufacturing workflow steps and release-time limitation to link manufacturing parameters to therapeutic administration.

Method-of-treatment constraints

same extrusion, heating, cooling, cutting, unit-dose division steps
diameter capped to 0.1–3 mm in claim 18
excipient ratio must be sufficient for ≥ 6-hour release during administration

Claim 18 is significant in enforcement because it allows a medical-use pathway if a practitioner uses a product made by the claimed steps and administers it in a way meeting the release requirement.

What is the key scope split between “required binder” and “optional binder”?

Answer: Claim 1 requires a water-insoluble binder. Claim 28 makes the binder optional.

Practical implications for product engineering

A competitor attempting to avoid claim 1 can attempt to eliminate a “water insoluble binder” class component if claim 28 still captures their product via optional binder language.
Conversely, if a competitor includes a water-insoluble binder, they can be captured under claim 1 if particle geometry and release requirements also match.

How many distinct claim themes exist in US 5,965,161?

Answer: Five major themes are claimed in parallel:

Opioid sustained-release unit doses (extruded, non-spheroidal, strand-cut particles)
Particle platform for non-opioid active agents
Capsule-specific opioid formulation (gelatin capsule; stearic acid; hydroxyalkylcellulose)
Manufacturing methods (extruder-based homogeneous mixing, heating, strand cutting, unit-dose division)
Method of treatment (administration with release-time tied to manufacturing/excipient ratio)

What patent landscape questions should be answered around this patent (freedom-to-operate inputs)?

Answer: The enforceable value of US 5,965,161 in a freedom-to-operate review will turn on (i) whether competitors’ products are made via extrusion and strand cutting with the same geometry, (ii) whether they use the claimed excipient classes (water-insoluble retardants and binders), and (iii) whether they achieve the claimed release windows (≥6 hours vs ≥12–24 hours) and, in claim 28, “substantially no feeding-fasting effect.”

Design-around levers created by claim text

Particle shape: convert from non-spheroidal to other morphologies outside the claim’s “non-spheroidal” limitation (fact-dependent)
Geometry outside ranges: length and diameter outside the explicit windows
Process not strand-cut extrusion: avoid extrusion-to-strands-to-cut workflow
Excipient substitution: use retardants/binders outside the listed classes (or change their “water insoluble” functional characterization)
Release target: produce shorter/longer release than claimed windows, or argue release is not “over at least about” thresholds
Food effect: avoid the formulation behavior in claim 28 (but infringement may still be argued by product-specific food-effect data)

US 5,965,161 claim-by-claim “coverage map” (what blocks and what remains open)

Answer: Below is a structured mapping of the claim set to practical product/process attributes.

Claim group	What it covers	Hard limitations likely tested
1 (unit dose, opioid)	Extruded non-spheroidal particles in unit dose; sustained release ≥6h	extrusion mixing, strand cutting, particle dimensions (0.1–12 mm length; 0.1–5 mm diameter), opioid dispersed in retardant matrix with water-insoluble binder, release ≥6h
2 (particle, non-opioid actives)	Sustained-release extruded particles for broad active agents	same particle/process and excipient stack structure; sustained release in matrix
3 (unit dose formulation)	Similar to claim 1 with specific retardant/binder choices	retardants: ethylcellulose/acrylic polymers; binder classes specified; release ≥6h
4,19,20 (opioid selection lists)	Explicit opioid enumeration	opioid is within list (or salt/mixture)
5–7,21–23 (dosage strength ranges)	Specific strength windows for select opioids	unit dose amounts within stated ranges
8,24,33,34,52 (retardant subtypes)	Acrylic polymers, hydroxyalkylcelluloses, ethylcellulose	retardant must fall within recited families/classes
10–11,32,35 (binder subtypes)	fatty alcohols, hydrogenated fats, waxes, stearic acid/stearyl alcohol, paraffin example	binder category must match and be water insoluble
12 (gelatin capsule)	Capsule embodiment with stearic acid + hydroxyalkylcellulose	gelatin capsule with specified excipient stack and particle geometry; extrusion/strand cutting
13–14 (retardant % w/w)	Retardant loading ranges	particles contain 1–99% or 5–95% retardant
15–17 (method prep; heating)	manufacturing method for ≥6h release	extruder feed/mix/heating 30–200°C, cooling, cutting, unit-dose division; ratio sufficient for release
18 (method of treatment)	administering patient after such formulation	diameter 0.1–3 mm; release ≥6h
26,27,30–31 (binder/excipient metering variants)	process variants with binder/excipients metering	specific procedural variation steps

Key takeaways

US 5,965,161 is centered on an extrusion-based, strand-cut, non-spheroidal multiparticulate sustained-release platform for opioids, with a defined particle geometry (0.1–12 mm length; 0.1–5 mm diameter in core claims), release performance (≥6 hours; claim 28 targets ≥12–24 hours), and excipient architecture (water-insoluble retardants plus a water-insoluble binder, with binder optional in claim 28).
The enforceable boundaries are driven by (i) the extrusion-to-strands-to-cut workflow, (ii) particle morphology/dimensions, and (iii) excipient class selection (retardant and binder lists) paired with the release requirement.
The opioid scope is broadened by long explicit opioid lists and tightened by numeric unit-dose strength ranges for hydromorphone, morphine, and oxycodone.
The same platform is claimed for non-opioid actives (claim 2), meaning the patent’s concept scope can be broader than the opioid market segment, subject to the same particle/process and excipient category limitations.
Claim 28 introduces a food-effect performance hook (“substantially no feeding-fasting effect”), which can be material for commercial differentiation and enforcement against formulations targeting reduced food impact.

FAQs

1) What formulation elements must be present to infringe US 5,965,161 claim 1?
A unit dose with multiple non-spheroidal extruded particles made by extruding a homogeneous matrix in an extruder and cutting strands, where the opioid is dispersed in a retardant matrix and includes a water-insoluble binder, with particles sized within the claimed ranges and releasing the opioid over at least about 6 hours.

2) Do the claims cover both hydromorphone and morphine, and what do the loading ranges mean?
Yes. Hydromorphone is limited to 2–64 mg per unit dose (claims 5 and 21) and morphine to 5–800 mg per unit dose (claims 6 and 22). These ranges are strength-limiting dependent claims that matter for unit-dose composition and labeling.

3) What’s different about claim 28 versus claim 1?
Claim 28 targets ≥12–24 hour release, tighter diameter (0.1–3 mm), and “substantially no feeding-fasting effect,” and it makes the water-insoluble binder optional.

4) Is the manufacturing method claim broader than the product claim?
The method claims require the same extrusion-based strand formation and cutting into cylindrically shaped particles with unit-dose division, and they tie the excipient ratio to achieving at least about 6 hours release in aqueous fluid. Scope is therefore closely coupled to the product architecture.

5) Does the patent cover non-opioid sustained-release particles?
Yes. Claim 2 covers sustained-release extruded particles for many non-opioid active agent categories (disinfecting agents, pesticides, repellents, dyes, and others) using the same strand-cut particle platform structure with water-insoluble retardants and water-insoluble binders.

References

United States Patent and Trademark Office. US Patent 5,965,161. “Extruded sustained-release oral dosage form and method of making same.” (Claim text provided in prompt).

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Details for Patent: 5,965,161

Summary for Patent: 5,965,161