Patent 4,721,619 landscape: scope of claims, likely infringement factors, and US controlled-release diltiazem competitors
United States Patent 4,721,619 claims a controlled-absorption, pH-independent oral diltiazem formulation built around (1) a diltiazem/organic-acid/lubricant pellet core and (2) a multi-layer membrane with defined water-insoluble vs water-soluble polymer ratios engineered to hit a specific 12-hour in vitro dissolution pattern. Dependent claims narrow the formulation to specific organic acids, lubricants, polymer classes, and capsule dosage form, and a polymer architecture tied to copolymers of acrylic/methacrylic acid esters with different water permeability.
What is the scope of US Patent 4,721,619 controlled-absorption diltiazem claims?
The independent claim (claim 1) is a formulation claim that requires every limitation simultaneously:
Claim 1 essential elements (all must be present)
- Controlled absorption diltiazem for oral administration
- Active: diltiazem or a pharmaceutically acceptable salt
- Pellet core composition
- Diltiazem (or salt) associated with an organic acid
- Plus a lubricant
- Multi-layer membrane surrounding the pellet core
- Membrane contains:
- Major proportion: water-insoluble film-forming polymer
- Minor proportion: water-soluble film-forming polymer
- Layer count and ratio of soluble/insoluble polymer are “effective” to obtain controlled release over 12 hours
- pH-independent dissolution
- Release rate is measured in vitro as dissolution of the pellet
- The rate is “substantially pH independent”
- Numeric dissolution pattern in US Pharmacopeia basket assembly (USP XX)
- 0 to 10% released after 2 hours
- 10 to 30% after 4 hours
- 20 to 40% after 6 hours
- 50 to 80% after 8 hours
- 85 to 100% after 12 hours
- Controlled absorption timeframe
- Controlled absorption is tied to the 12-hour dissolution profile.
Key claim interpretation pressure points
- “Substantially pH independent”: validity and infringement often turn on whether the accused product’s release profile changes materially across pH conditions used in the patent’s measurement framework.
- USP XX basket assembly: numeric dissolution windows reduce ambiguity. If a product’s dissolution profile falls outside one or more windows, literal infringement is less likely.
- “Multi-layer membrane”: a single-layer film can be a non-infringement design-around if the claim requires multiple layers structurally.
- Soluble/insoluble polymer ratio and “effective” layers: doctrine of equivalents risk exists, but dependent claims and the explicit structure of major/minor polymer proportions increase the value of literal comparisons.
Which limitations in claim 1 drive infringement risk for generic or reformulated diltiazem?
12-hour in vitro dissolution pattern is the highest-friction element
A challenger typically compares dissolution data generated using the same or substantially similar apparatus and test conditions. The claim’s windows are broad but not infinite.
Practical infringement screen using the claim’s windows
- If a competitor’s pellet shows, for example, >30% by 4 hours or <50% by 8 hours, it likely misses at least one required limitation.
- If dissolution is pH-dependent, it can miss the “substantially pH independent” requirement even if the 12-hour endpoint is similar.
Multi-layer membrane construction
The claim ties controlled release to:
- the number of layers, and
- the ratio of water-soluble vs water-insoluble polymers.
A design-around that uses a different membrane architecture (e.g., different layer count, different polymer distribution across layers, or a different release mechanism) can avoid structural equivalence arguments if it is clear in composition and manufacturing.
Pellet core: organic acid + lubricant association
The claim requires the diltiazem core has:
- diltiazem (or salt) associated with an organic acid, and
- a lubricant.
Products that change the acid system (different acids, no acid association, or use of alternative excipient strategies) can reduce literal overlap. However, “organic acid” is broad in claim 1, which makes design-around harder unless the formulation avoids “organic acid” association entirely.
What formulations are covered in dependent claims 2 to 10?
Dependent claims progressively constrain the claim 1 structure.
Claim 2: organic acid selection and ratio
- Organic acid is selected from:
- fumaric acid
- malic acid
- succinic acid
- Ratio of diltiazem : organic acid is 19:1 to 1:1.
Scope impact: If an accused product uses a different acid (e.g., tartaric, citric, adipic) it may not fall within claim 2, but it could still fall within claim 1 unless the acid requirement in claim 1 is met (claim 1 only needs “an organic acid,” not a specific list).
Claim 3: lubricant selection and ratio
- Lubricant selected from:
- sodium stearate
- magnesium stearate
- talc
- Ratio of diltiazem : lubricant is 5:1 to 100:1.
Scope impact: Like claim 2, claim 3 constrains only the dependent claim. It does not limit claim 1.
Claim 4: core layering with polymeric material
Requires:
- core comprises (a) a powder mixture of:
- diltiazem (or salt)
- specified organic acid group (fumaric/malic/succinic)
- lubricant
- plus (b) a polymeric material:
- major water soluble polymer
- minor water insoluble polymer
- and the core has layers of powder mixture and polymeric material superimposed so the polymeric material amount is sufficient to coat the powder mixture.
Scope impact: This is a structural/process-adjacent limitation that may distinguish pellet manufacturing strategies. If a competitor uses different pelletization/diffusion methods without this superimposed layering structure, dependent claim 4 is vulnerable.
Claims 5 to 7: specific polymer lists
- Claim 5 water soluble polymer:
- polyvinyl alcohol
- polyvinylpyrrolidone
- hydroxypropylmethylcellulose
- Claim 6 water insoluble polymer:
- polyvinyl chloride
- shellac
- polyurethane
- ethylcellulose
- Claim 7 ties these lists to the membrane components (insoluble is from the insoluble list; soluble from the soluble list).
Scope impact: These lists can be used as a detailed infringement map, especially for capsule pellet variants built around known film formers.
Claims 8 and 9: acrylic/methacrylic ester copolymer architecture
- Claim 8 (core polymeric material):
- major proportion: copolymer of acrylic and methacrylic acid esters that is freely permeable to water
- minor proportion: same type copolymer slightly permeable to water
- Claim 9 (membrane composition):
- major proportion: slightly permeable copolymer
- minor proportion: freely permeable copolymer
- Both claims focus on permeability class inversion between core and membrane.
Scope impact: This is a sophisticated formulation feature. If a competitor uses different permeability polymers (or reverses proportions without meeting “major/minor” and “slightly/freely permeable” mapping), it can be a meaningful non-infringement lever for dependent claims.
Claim 10: capsule dosage form
- “A capsule comprising pellets according to claim 1.”
Scope impact: This is a dosage-form claim tied to capsule delivery of the pellets that meet claim 1.
How do USP XX dissolution windows function as claim boundaries?
The claim uses USP XX basket assembly and provides release ranges at fixed times. This is a classic “numerical limitation” structure.
Dissolution pattern as a binary gate
A product can miss claim 1 if it:
- Releases too fast in early stages (e.g., outside 0–10% after 2 hours),
- Releases too slowly in mid stages (e.g., below 20–40% at 6 hours),
- Or fails to release sufficiently by 12 hours (outside 85–100%).
“Substantially pH independent” makes cross-media testing relevant
Even if timepoints match, pH dependence can break the limitation. Practically, disputes typically focus on whether the dissolution rate is materially different across pH buffers in the in vitro protocol used to generate the data.
What patent landscape does US 4,721,619 imply for controlled-release diltiazem capsules and pellets?
Only the claim text is provided. No file history, specification details, family members, forward citations, or Orange Book listings were supplied. Under those constraints, a complete, accurate landscape of specific related US patents and assignees cannot be produced here without fabricating record-level details.
What can be stated from the claim scope alone is the likely competitive perimeter in freedom-to-operate terms:
Core design space likely targeted by the estate
- Diltiazem pellets for oral controlled absorption
- Pellet core incorporating organic acid association
- Multi-layer polymer membranes tuned with:
- water-insoluble vs water-soluble film formers
- layer count and polymer ratio
- Release governed by pH-independent dissolution with a 12-hour USP basket pattern
- Polymer classes include:
- stearate/talc lubricated cores
- soluble polymers: PVA, PVP, HPMC
- insoluble polymers: PVC, shellac, polyurethane, ethylcellulose
- permeability-defined acrylic/methacrylic ester copolymers
Most common infringement arguments a generic or reformulator would face
- Their pellets contain the same acid association and lubricants
- Their membrane uses both soluble and insoluble polymers with “major/minor” proportions
- Their release profile matches the numeric dissolution windows
- Their dissolution is pH independent and uses USP basket conditions.
Most plausible design-around themes
- Switch to a non-infringing acid system or remove acid association.
- Replace soluble/insoluble film former pairing with a different release-control mechanism (e.g., matrix diffusion rather than membrane-controlled release).
- Use a different membrane architecture (not multi-layer, different layer sequence, different permeation polymer distribution).
- Achieve similar 12-hour endpoints but move the timepoint distribution outside one or more numeric bands.
- Introduce measurable pH dependence to avoid the “substantially pH independent” requirement.
Does 4,721,619 cover method-of-use claims or only formulations?
Based on the provided claim set, the patent is directed to:
- a formulation (pellet with coated multi-layer membrane)
- and a capsule comprising those pellets.
There is no method-of-use claim text supplied. As written, the coverage is composition and dosage form, anchored to in vitro dissolution performance.
What generic entry risks exist for products matching the 12-hour dissolution pattern?
For any competitor trying to sell a controlled-release diltiazem capsule or pellet formulation in the US, the risk is highest when they:
- tune their formulation to produce a USP basket dissolution profile that falls within the claim’s timepoint windows, and
- use a membrane system with both:
- a major insoluble film former component and
- a minor soluble film former component, with multiple layers.
Risk decreases when a product:
- is demonstrably pH dependent,
- uses a different core or membrane construction that does not meet multi-layer structural requirements,
- or fails one or more dissolution-timepoint windows.
Key Takeaways
- US 4,721,619 claims a diltiazem (salt) pellet with an organic acid + lubricant core and a multi-layer membrane engineered to produce substantially pH-independent dissolution matching a 12-hour USP XX basket profile.
- The numerical dissolution ranges at 2, 4, 6, 8, and 12 hours are central infringement boundaries.
- Dependent claims lock in specific acid and lubricant lists, specific polymer lists, and an acrylic/methacrylic copolymer water-permeability architecture (core vs membrane proportion inversion).
- The likely competitive perimeter is controlled-release diltiazem pellets built with soluble/insoluble membrane pairs and tuned to the same timepoint dissolution windows.
FAQs
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What happens if a diltiazem controlled-release product matches the 12-hour percent released but differs at the 8-hour window?
It likely misses at least one required claim element because claim 1 requires multiple fixed-time dissolution bands simultaneously.
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Can a product avoid claim coverage by using different water-soluble polymers than PVA, PVP, or HPMC?
It may avoid dependent claims 5 and 7, but claim 1 could still read if the membrane uses a water-soluble film-forming polymer in the defined major/minor architecture.
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Does the patent require a specific number of membrane layers?
Claim 1 requires “the number of layers…effective to permit release” over 12 hours with the specified profile; the exact layer count is not stated in the claim excerpt, but “multi-layer membrane” is required structurally.
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Is the organic acid limitation narrow enough to design around?
Claim 2 is narrow (fumaric/malic/succinic), but claim 1 is broad (“organic acid”). Full avoidance depends on whether the formulation still uses an organic acid association.
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How does “substantially pH independent” affect enforcement?
Even if dissolution at one pH matches, material pH-dependent release can defeat the claim’s pH independence limitation.
References
- United States Patent 4,721,619, claims 1–10 (provided claim text in prompt).
