US Patent 6,113,944: Scope, Claim Construction, and US Patent Landscape
What does US 6,113,944 claim, in scope terms?
US 6,113,944 is directed to a specific paroxetine tablet formulation tied to (i) dose levels, (ii) paroxetine in the form of the free base, and (iii) a defined tablet-manufacturing workflow using dry (solvent-free) admixing and specific dry compaction and milling steps, followed by tablet compression on single-punch or rotary machines.
Core independent claim elements (from Claim 1)
Claim 1 requires, in combination:
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Product format
- “A pharmaceutical composition in tablet form.”
-
Active and dose specification
- Paroxetine “selected from: 10 mg, 20 mg, 30 mg, 40 mg and 50 mg.”
- Paroxetine amount is “expressed as the free base.”
-
Manufacturing process with a defined dry-admix path
- The composition is “produced by a process which comprises the steps of:”
- (a) dry admixing paroxetine and excipients in a mixer to form a mixture; or
- (b) dry admixing paroxetine and excipients, then one of:
- compressing into “a slug material or roller compacting… into a strand material,” then
- milling the prepared material into a “free flowing mixture.”
-
Final tableting step with equipment-limited compression
- compressing the mixture into tablets using a single punch or rotary tablet machine.
Structural consequence for infringement analysis
Because Claim 1 is written as a product-by-process claim, the patent can be asserted against tablets that have the claimed composition only if the accused product is shown to be produced by the claimed process steps (or a process that is sufficiently equivalent under the applicable legal standard). The claim’s process limitations are therefore not decorative; they are enforceable requirements.
What is actually protected: the dose + free base + tablet process combination
The practical scope is constrained by three tight filters:
1) Paroxetine must be the “free base”
The claim requires that the tablet contains paroxetine “expressed as the free base.” That does not merely restrict dosing math. It restricts which chemical form qualifies for the claim (free base vs. salts). In portfolio terms, this narrows the set of paroxetine products that plausibly fall within scope to those formulated with paroxetine in free-base form (or mixtures whose composition corresponds to that requirement).
2) Dose range is explicitly enumerated
Only 10, 20, 30, 40, and 50 mg are within the claim text. Tablets outside those strengths are not within Claim 1 as written.
3) Dry formulation workflow is mandatory
The process steps are limited to:
- dry admixing in a mixer, and
- optionally a dry granulation/compaction route using slug or roller compaction followed by milling to a free-flowing mixture, then
- compression using single punch or rotary equipment.
This matters because many paroxetine tablet manufacturing strategies (historically across the market) rely on other granulation or wet-processing methods. Claim 1 excludes those if they do not meet the “dry admixing” and associated steps.
How should the “process (a) or (b)” be read
Claim 1 includes a “process… comprises the steps of: a) … or b) … and c) …” structure. That means there are two alternative routes that still converge at the final compression step.
Route A (Clause a)
- Dry admixing paroxetine and excipients in a mixer → mixture.
Route B (Clause b)
- Dry admixing paroxetine and excipients
- compress into “slug material” or roller compact into “strand material”
- mill into a “free flowing mixture”
Both routes converge
- compress the resulting mixture into tablets using a single punch or rotary tablet machine.
Where the claim is likely enforceable vs. where it is vulnerable
Enforceable leverage
- The claim specifies a combination of free base paroxetine + enumerated tablet strengths + dry-based manufacturing workflow. That combination creates a meaningful targeting mechanism, especially for generic or lifecycle products that use free-base paroxetine and similar dry granulation to achieve flow and compressibility.
Vulnerability points (scope narrowing via claim text)
- Free base requirement: salt forms are outside Claim 1’s express scope.
- Strength enumeration: any strength not listed is outside Claim 1.
- Method gating: if accused products are made by wet granulation, solvent processing, different solid-state conversion steps, or different granulation pathways, they may fall outside Claim 1.
What is the claim’s likely limiting interpretation for excipients
Claim 1 does not enumerate excipients in the text provided, but it requires “paroxetine and excipients.” That still allows enforcement only where an accused formulation uses excipients in a way that satisfies the claim’s process steps. Courts typically do not allow skipping the required manufacturing steps just because excipients may differ.
What does the “single punch or rotary” limitation do
This narrows equipment to:
- single punch compression machines, or
- rotary tablet machines.
It excludes tablet compression methods that do not use these compression approaches, or at least creates a factual burden to show equivalence or that the actual process is within the claim language.
Claim chart style breakdown (Clause-by-Clause)
Below is a “requirement list” that can be used to map an accused product manufacturing record to Claim 1.
| Claim element |
Requirement in Claim 1 |
Practical mapping target |
| Dosage form |
Tablet form |
Finished dosage form |
| Active |
Paroxetine |
API identity |
| Strengths |
10/20/30/40/50 mg |
Label strength and per-tablet content |
| Chemical form |
Paroxetine expressed as free base |
API form characterization and formulation spec |
| Process step (common to both routes) |
Mix is compressed into tablets |
Final compression step and equipment type |
| Process step c |
compress using single punch or rotary |
Batch record equipment and parameters |
| Process step a |
dry admixing paroxetine and excipients in mixer |
“Dry blend” documentation |
| Process step b (alternative route) |
dry admixing then slug or roller compacting into strand, then milling to free-flowing mixture |
Dry granulation documentation route |
US patent landscape: how 6,113,944 sits among paroxetine tablet IP
How to use this claim to screen the landscape
Even without enumerating every coexisting paroxetine patent in the US, the claim language indicates the patent is anchored to a manufacturing-method profile and to a specific API form (free base) plus strengths.
That profile maps to common US generic and product-lifecycle friction points:
- Paroxetine solid form and salt vs free base (composition-form gating)
- Tablet strength commercialization strategy (strength gating)
- Manufacturing method switching (dry vs wet granulation, and slug/roller compaction vs other granulation)
Implication for freedom-to-operate (FTO) screening
A thorough US landscape review typically splits paroxetine IP into these clusters:
- API form and polymorph patents (including salt selection)
- Formulation patents (tablet composition, excipient selection, release control)
- Process patents (dry granulation, compaction, milling steps)
- Method-of-treatment and use patents (often less relevant to tablet process FTO unless a combination therapy or dosing regimen is claimed)
US 6,113,944 is mostly a process-linked formulation patent under that clustering.
What competing claims are most likely to collide
Based on the claim’s structure, the highest collision probability comes from patents that:
- cover paroxetine free base tablets at 10/20/30/40/50 mg, and
- require or describe dry admixing, and/or slug/roller compaction, and/or milling to free-flowing powder, and/or single punch or rotary tableting.
Lower collision probability comes from:
- patents focused on wet granulation or solvent-based processes,
- patents focusing on paroxetine salts rather than the free base,
- patents limited to strengths not listed in Claim 1,
- patents focused on different dosage designs (different unit sizes, controlled-release architecture, or different compression architecture) unless they still satisfy Claim 1’s constraints.
How to assess collateral constraints in the landscape
When evaluating whether a generic or reformulated product could avoid US 6,113,944, the landscape risk typically tracks to whether the target product can be manufactured via:
- dry blending (acceptable),
- dry granulation (acceptable only if it matches the slug/roller compaction + free-flow milling elements), and
- final compression on single-punch/rotary machines (acceptable if matched),
while maintaining:
- free base API form and the relevant strength(s).
If any of those are deliberately changed, the risk decreases for Claim 1 but may increase for other patents in the landscape (for example, patents protecting alternative processes or alternative forms). The claim therefore functions as a targeted but narrow gate rather than a broad “any paroxetine tablet” barrier.
Key takeaways
- US 6,113,944 Claim 1 is a paroxetine free-base tablet patent tied to enumerated strengths (10/20/30/40/50 mg) and a dry manufacturing workflow that includes either dry admixing in a mixer (Route A) or dry admixing plus slug/roller compaction and milling to a free-flowing mixture (Route B), followed by tablet compression on single punch or rotary equipment.
- Because Claim 1 is product-by-process, infringement analysis turns on whether an accused tablet is made using the claimed dry admix and compaction/milling path and whether the API is free base at the claimed strengths.
- The claim’s enforceability is strongest when an accused product’s batch records show the same dry processing architecture and the same free-base form. It weakens if the accused product uses a different solid form (salt), different strengths, or different processing steps that do not meet the claim’s dry steps.
FAQs
1) Is US 6,113,944 limited to one paroxetine strength?
No. Claim 1 expressly covers tablet strengths of 10, 20, 30, 40, and 50 mg.
2) Does Claim 1 cover paroxetine salts?
The provided Claim 1 text requires paroxetine “expressed as the free base,” which limits coverage to free-base paroxetine under the claim’s express language.
3) Can a manufacturer avoid the patent by using a different granulation method?
Avoidance is most plausible if the alternative manufacturing route is not “dry admixing” and/or does not include the claimed slug or roller compaction + free-flowing milling pathway (when using Route B) while still meeting the other claim constraints.
4) Is the process limitation the only differentiator from a composition claim?
No. The claim also requires tablet form, paroxetine free base, and specific enumerated strengths, not just a process.
5) Does tablet compression equipment matter under Claim 1?
Yes. Claim 1 requires compression “using a single punch or rotary tablet machine,” so the equipment type is a claim limitation.
References
[1] US Patent 6,113,944, Claim 1 (provided claim text).
