US Patent 5,202,128: What Is Claimed, How Broad It Is, and Where It Sits in the Landscape

US Drug Patent 5,202,128 claims a pH-dependent, sustained-release pellet architecture with a three-component coating system designed to start release slowly in the stomach and then release faster in the intestines, using acid-soluble/insoluble polymer behavior across pH 1–7.5. The claims also lock in specific polymer classes, quantitative coating ranges, and multiple drug/indication-dependent fallbacks centered on morphine acid addition salts, especially morphine sulfate, for analgesia (including acute and chronic pain).

Because the text you provided enumerates claims 1–26 (and contains internal numbering issues in places), the analysis below focuses strictly on the scope those claims state: independent composition claim 1, dependent claim sets 2–17, drug-specific claim 10–17, and method claims 18–26.

What Is the Core Claim Architecture in Claim 1?

Independent composition claim 1

Claim 1 defines a pH-dependent sustained release pharmaceutical pellet composition with:

1) Core element

Contains a therapeutically effective amount of at least one active ingredient
Active ingredient constraint: aqueous solubility ≥ 1 in 30

2) Coating on the core Coating must contain components (a), (b), (c) with weight percentages by weight based on total weight of components (a), (b), and (c):

(a) Matrix polymer
- ≥ 35 wt%
- Insoluble at pH 1 to 7.5
- Controls release rate in stomach and intestines
(b) Enteric polymer
- 1 to 30 wt%
- Substantially insoluble at pH 1 to 4
- Delays release in stomach
- Soluble at pH 6 to 7.5
- Designed not to substantially delay release in intestines
(c) Acid-activated soluble compound
- 1 to 60 wt%
- Soluble at pH 1 to 4
- Enables initiation of release in the stomach

3) Functional ratio limitation The “ratio of components (a), (b), and (c)” is required to be effective so that:

Initiation of release in stomach occurs at a slow rate
Release in intestines occurs at a rate faster than in stomach
Overall provides therapeutically effective amount over a predetermined interval at a predetermined dosage and interval

This claim is a functional-quantitative blend: it combines strict polymer/pH definitions with performance intent (stomach slower than intestine).

How Broad Is Claim 1 on the Drug Substance and Product Use?

Active ingredient scope

Claim 1 is drug-flexible by design:

It covers “at least one active ingredient” meeting aqueous solubility ≥ 1 in 30
It does not require opioids in claim 1

Claim set then narrows in later claims:

Claim 3 lists major drug categories (see below)
Claim 10 hard-codes morphine acid addition salt in the core
Claims 18–23 define the method for pain treatment using the pellet

Dosage interval

The independent composition claim 1 does not specify duration. The method claims 20 specify approximately 8 to 24 hours for the predetermined interval.

What Are the Major Dependent Claim “Add-On” Limiters?

Claim 2: Polymer species lists for (a), (b), (c)

Claim 2 narrows the coating by specifying eligible polymers for each component:

(a): ethyl cellulose; quaternary ammonium acrylic or methacrylic polymer; acrylic/methacrylic ester copolymer; mixtures
(b): cellulose acetate phthalate; hydroxypropyl methylcellulose phthalate; polyvinyl acetate phthalate; methacrylic acid:acrylic acid ester copolymer; hydroxypropyl methylcellulose acetate succinate; shellac; cellulose acetate trimellitate; mixtures
(c): polyvinylpyrrolidone; hydroxypropyl cellulose; hydroxypropyl methylcellulose; PEG MW 1700–20,000; polyvinyl alcohol and monomers; mixtures

This claim shifts from class-based constraints to named species, improving enforceability when an accused product uses these exact polymers.

Claim 7: Narrower coating percentage bounds

Claim 7 adds specific ranges for the coating composition:

(a) 35–75 wt%
(b) 2–20 wt%
(c) 15–50 wt%

This is a meaningful tightening relative to claim 1’s broader ranges (notably claim 1’s (a) is “≥35”, (b) is “1–30”, (c) is “1–60”).

Claim 8: Plasticizer and filler options

Claim 8 allows formulation components beyond the core (a)-(c) system:

Plasticizer: up to 50% of coating
- Examples: diethyl phthalate; triethyl citrate; triethyl acetyl citrate; triethyl acetin; tributyl citrate; PEG MW 200–<1700; glycerol
Filler: up to 75% of coating
- Examples: silicon dioxide; titanium dioxide; talc; alumina; starch; kaolin; polacrilin potassium; powdered cellulose; microcrystalline cellulose

The key legal effect: it does not remove the (a)-(c) constraints; it expands permissible formulation latitude while staying inside claim 1/2/7 type boundaries.

Claim 9: A structured numeric sub-range (but with formatting artifacts)

Claim 9 appears to define another narrower set of ranges:

component (a) 35 to 70%
component (b) 4 to 20%
component (c) 15 to 35%
plasticizer 4 to 30% (Formatting in your text is imperfect, but the numeric bounds are clear.)

Claims 15–16: Species-specific morphine coating refinements

Claims 15 and 16 effectively restate the claim 2 polymer lists and apply them in the morphine-specific framework:

Claim 15 specifies eligible polymers for (a), (b), (c)
Claim 16 narrows coating percentage:
- (a) 35–75 wt%
- (b) 2–20 wt%
- (c) 15–40 wt%

Claim 17: A very specific example-like composition

Claim 17 (numbering appears inconsistent in your paste, but it is stated as dependent on claim 49 in the text) provides a specific:

PEG (MW 1700–20,000) 15–40%
ethyl cellulose 45–65%
methacrylic acid:acrylic ethyl ester 1:1 copolymer 4–20% This is narrower and likely intended to cover a representative embodiment.

Where Does Morphine Take Over: Claims 10–17

Claim 10: Core specifies morphine acid addition salt

Claim 10 replaces generic active ingredient language with:

Core contains a therapeutically effective amount of an acid addition salt of morphine
Coating system remains the same (a)-(c) framework with identical pH/solubility logic

Claim 11: morphine sulphate

Claim 11 narrows the salt to:

morphine sulphate

Claim 12: stomach vs intestine release rate ratio

Claim 12 sets an explicit performance metric:

Rate of release in intestine is 1.2 to 3 times greater than the rate of release in stomach

This can materially increase infringement risk for products using the same polymer framework but achieving different kinetic ratios.

Claim 13–14: plasma fluctuation minimization + exposure window

Claim 13:

“minimizes fluctuations in the morphine compound concentration in the plasma”

Claim 14:

time concentration ≥75% of maximum is at least 3 hours

These performance metrics are likely used to demonstrate sustained-release behavior in vivo and support non-obviousness/utility.

Claim 18: method claim (composition into therapy)

Claim 18 ties the pellet to treatment of:

“pain associated with a condition” in a patient
via administration at predetermined dosage and interval

Claim 19–20: pain scope and dosing interval

Claim 19: pain conditions relate to acute and chronic pain
Claim 20: predetermined interval is approximately 8 to 24 hours
Claim 20 also states the composition is in a unit dosage form

Claims 21–23: morphine salt variants

Claim 21: acid addition salt of morphine (general)
Claim 22: morphine sulphate
Claim 23: morphine hydrochloride

Claims 24–26: composition/method repeats with added “matrix polymer composed of…”

Claims 24 and 25 are composition claims that restate claim 1 and claim 10 respectively but add the constraint that (a) matrix polymer is composed of:

ethyl cellulose
quaternary ammonium acrylic or methacrylic polymer
acrylic or methacrylic ester copolymer (or mixtures)

Claims 26 restates method claim 18 in a similar way.

What Is the Drug Category Breadth in Claim 3–6?

Claim 3: active ingredient categories

Claim 3 lists active ingredients with high aqueous solubility (as required by claim 1) grouped by class, including:

antihistamines, antibiotics, antituberculosis agents
cholinergic agents, antimuscarinics
sympathomimetics, sympatholytic agents
autonomic drugs
iron preparations, haemostatics
cardiac drugs
antihypertensive agents, vasodilators
NSAIDs
opiate agonists, anticonvulsants, tranquilizers
stimulants, barbiturates, sedatives
expectorants, antiemetics, gastrointestinal drugs
heavy metal antagonists, antithyroid agents
genitourinary smooth muscle relaxants
vitamins

Claim 4: opiate agonists narrowed to specific salts

Claim 4 narrows “opiate agonist” to salts of:

codeine
dextromoramide
hydrocodone
hydromorphine
pethidine
methadone
morphine
propoxyphene

Claim 5–6: dissolution profile and plasma fluctuation

Claim 5:

two dissolution profiles:
- pH 1–4 (“first”)
- pH about 7.5 (“second”)
each is at least equal to the minimum dissolution required to provide substantially the same bioavailability as immediate release

Claim 6:

in use, minimizes plasma concentration fluctuations

These claims do not mention morphine specifically, but they apply to any active ingredient falling into the claim tree.

Claim Scope Map: What Must an Accused Product Contain?

Composition infringement logic (practical)

A product is most exposed to the strictest independent-to-dependent chain when it meets:

1) Pellet dosage form 2) Core containing a therapeutically effective amount of an active with aqueous solubility ≥ 1 in 30 (or morphine salt, in claim 10 onward) 3) Coating with pH-behavior defined polymers:

matrix polymer insoluble across pH 1–7.5 (≥35 wt%)
enteric polymer insoluble pH 1–4 but soluble pH 6–7.5 (1–30 wt%)
acid-soluble initiator soluble pH 1–4 (1–60 wt%) 4) Functional ratio to get slower stomach release and faster intestinal release 5) For morphine-specific dependent claims, also meet:
morphine acid addition salt (and specific salt type for claims 11, 22, 23)
release rate ratio 1.2–3x (claim 12)
plasma metric thresholds (claims 13–14) 6) If the claims are asserted in the narrower coating species range, also match:
the named polymers in claim 2/15 and the numeric coating ranges in claim 7/9/16/17

Where the claim is likely hardest to design around

The pH windows are broad (pH 1–4 vs 6–7.5) but the combination is specific: enteric insoluble at pH 1–4 and soluble at pH 6–7.5, plus an additional acid-soluble initiator in controlled amounts.
The coating must control both initiation and rate differential between stomach and intestine.
For morphine analgesia products, additional metrics (1.2–3x intestinal release and ≥3 hours above 75% Cmax) raise the bar.

Patent Landscape Positioning: What This Patents Do to Freedom-to-Operate

Without bibliographic metadata for the related family (assignee, priority, expiration calculations, cited references, continuations), the landscape read remains structural: US 5,202,128 is an enabling “platform” claim for pellet-based pH-dependent sustained release with a specific polymer triad.

Landscape implications for other pH-dependent SR products

This patent’s independent claim 1 is a compositional constraint claim more than a method claim. It will typically collide with:

pellet or multiparticulates using pH-responsive polymers with defined insolubility/solubility windows
formulations mixing insoluble matrix polymers with enteric coatings and acid-soluble components to tune early release

Landscape implications for opioid modified-release products

The dependent claim chain around morphine sulphate and morphine hydrochloride creates an opioid-specific foothold in addition to the general chemistry scope:

claim 10 (morphine acid addition salt)
claim 11 (morphine sulphate)
claim 23 (morphine hydrochloride)

For morphine, the scope tightens further with measurable release and plasma fluctuation requirements (claims 12–14, and 13/14).

Landscape implications for “high solubility” actives

Claim 1 and claim 3’s category list targets actives with high aqueous solubility (≥1 in 30). Many sustained-release designs avoid high-solubility actives or require different release mechanisms; this patent frames the opposite by requiring solubility above the threshold and still controlling pH behavior.

Risk Hotspots by Claim Layer

Claim layer	What it adds	Why it matters for FTO
Claim 1	(a) ≥35% insoluble pH 1–7.5 + (b) 1–30% enteric insoluble pH 1–4 but soluble pH 6–7.5 + (c) 1–60% soluble pH 1–4, plus functional stomach slow and intestine faster	Defines the “triad” that many pH-tuned SR coatings attempt
Claim 2	Named polymer species for each component	If an accused formulation uses the same species, the claim narrows and infringement risk rises
Claim 7/9/16	Tightened numeric ranges	Narrows design-around space where formulators tune within the broader claim 1 boundaries
Claim 10–14	Morphine acid addition salt + kinetic and plasma metrics	Adds objective bio-performance constraints and opioid specificity
Claim 3–6	High-solubility active categories + dissolution profile thresholds	Helps broaden enforceability across many drug classes beyond opioids

Key Takeaways

US 5,202,128 is a pH-dependent sustained-release pellet platform built on a three-part coating triad: insoluble matrix polymer (pH 1–7.5) plus enteric polymer (insoluble pH 1–4, soluble pH 6–7.5) plus acid-soluble initiator (soluble pH 1–4).
Claim 1’s scope is broad on active ingredient selection (solubility ≥ 1 in 30) but strict on polymer pH behavior and the stomach slower vs intestine faster release outcome.
The patent tightens substantially in the opioid branch: morphine acid addition salts (including morphine sulphate and morphine hydrochloride) and measurable outcomes including intestinal release 1.2–3x stomach and a ≥3 hour window above 75% of Cmax.
From an FTO standpoint, the most actionable design-around pressure points are:
- removing or replacing the acid-soluble initiator (c) in the defined pH 1–4 solubility manner,
- changing polymer behavior so the enteric component does not match the pH 1–4 vs pH 6–7.5 solubility pattern, and
- for morphine, failing to meet the explicit kinetic/plasma metrics if the claims are asserted.

FAQs

1) What is the main novelty claimed in US 5,202,128?
A pH-dependent sustained-release pellet coating that combines an insoluble matrix polymer (insoluble across pH 1–7.5) with a true enteric polymer (insoluble pH 1–4 but soluble pH 6–7.5) and a component soluble at pH 1–4 to initiate stomach release, then achieve faster intestinal release.

2) Does claim 1 require morphine?
No. Claim 1 covers any active ingredient with aqueous solubility ≥ 1 in 30; morphine is introduced in the dependent claim chain starting at claim 10.

3) What polymer classes does the patent allow for the coating?
Claim 2 (and claim 15 for the morphine branch) names eligible polymers for each coating component: ethyl cellulose and other specific matrix-formers for (a), multiple phthalate/succinate/shellac-type enteric polymers for (b), and PVP/HPC/PEG/PVA-type acid-soluble initiators for (c).

4) Is there an explicit stomach-to-intestine release ratio requirement?
Yes, but only in the morphine branch: claim 12 requires intestinal release rate 1.2 to 3 times the stomach release rate.

5) Does the patent include a plasma concentration performance threshold for morphine?
Yes. Claim 14 requires the time concentration stays at or above 75% of maximum to be at least 3 hours.

References

[1] US Patent 5,202,128 (claims text as provided in prompt).

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Australia	PJ2192	Jan 06, 1989

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	133862	⤷ Start Trial
Austria	167629	⤷ Start Trial
Australia	4773290	⤷ Start Trial
Australia	617573	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 5,202,128