US Patent 5,985,321: Soft Gelatin Capsule with Cyclosporin A and 1,2-Propyleneglycol in Shell and Fill
What is covered by US 5,985,321 (claim scope)
US Patent 5,985,321 claims soft gelatin capsule technology that fixes a specific excipient architecture: 1,2-propylene glycol (PG) is present in the shell at encapsulation and after drying, and the liquid filling contains cyclosporin A (CsA) plus PG in a carrier medium.
Core independent claim (Claim 1)
Claim 1 requires all of the following in combination:
- Soft gelatin capsule with:
- At time of encapsulation, the shell comprises:
- gelatin
- 1,2-propylene glycol
- The filling comprises:
- cyclosporin A
- 1,2-propylene glycol
- a carrier medium
- After drying, the shell comprises:
- 2 to 40% by weight 1,2-propylene glycol
This establishes the main claim posture: bi-layer excipient placement (PG in shell and filling) plus a quantitative dried-shell PG window.
Claim fall-through: quant windows expand but remain within PG-in-shell
Claims 2 and 12 to 13 tighten dried-shell PG:
- Claim 2: shell after drying has 5-40% PG
- Claim 12: shell after drying has 5-32% PG
- Claim 13: shell after drying has 10-32% PG
Claims 3, 14, and 17 define shell formulation at the gelatin-composition stage:
- Claim 3: shell is produced from a gelatin composition comprising 1-35% PG
- Claim 14: same architecture as Claim 1, plus shell gelatin composition comprising 1-35% PG
- Claim 17: shell produced from gelatin composition comprising 4-30% PG
Claims 4 to 5 define an excipient ratio:
- Claim 4: weight ratio 1,2-propylene glycol : gelatin = 1:1 to 1:47
- Claim 5: ratio is 1:1 to 1:4
Claim fall-through: additional optional functional elements
From Claim 6 onward, the claims layer add-ons that do not remove the core structure:
- Claim 6: shell further comprises plasticizers and optionally auxiliary agents
- Claim 7: filling includes a lipophilic component
- Claim 8: filling includes a surfactant
- Claim 9: filling forms an emulsion on mixing with water
- Claim 10: filling is a microemulsion preconcentrate
- Claim 11: filling includes ethanol as a cosolvent
- Claim 15: shell further comprises glycerol at encapsulation (for Claim 14 dependent path)
- Claim 16: filling is a microemulsion preconcentrate (for Claim 14 dependent path)
What the claims do not require
Based solely on the claim text provided, the invention scope does not explicitly require:
- A specific brand name of CsA, crystal form, or polymorph
- A specific shell drying method, time, temperature, or residual moisture
- A defined microemulsion composition outside “microemulsion preconcentrate” (Claim 10/16) and generic components like surfactant/cosolvent (Claims 8/11)
- Specific types of plasticizers or auxiliary agents beyond being “plasticizers” and “optionally auxiliary agents”
What are the claim “pressure points” for enforcement
For freedom-to-operate analysis and infringement risk, the practical leverage points are the elements that must match numerically or categorically:
1) Dried-shell PG content (2-40% by weight)
Claim 1 binds the product state after drying. This is a clear quant constraint. Any design-around must address the measured dried-shell PG level:
- Hardest discriminator: 2-40% by weight PG (Claim 1)
- Narrowers: 5-40% (Claim 2), 5-32% (Claim 12), 10-32% (Claim 13)
2) Presence of PG in both shell and filling
Even if dried-shell PG is in range, absence of PG in the filling would fall outside the independent claim as written.
- Claim 1 requires filling contains:
3) Shell composition at encapsulation and at formulation
Two separate constraints exist:
- At encapsulation, shell includes gelatin + PG.
- From a gelatin composition perspective, PG content is defined:
- 1-35% (Claim 3 and Claim 14)
- 4-30% (Claim 17)
These tie to process design. If a competitor uses a different shell formulation at encapsulation stage but ends with dried PG in-range, claim coverage becomes fact-dependent around what “at the time of encapsulation” means operationally.
4) Microemulsion preconcentrate vs broader “forms an emulsion”
The dependent claims create multiple entry points for accused products:
- Broad functional: filling capable of forming an emulsion on mixing with water (Claim 9)
- More specific composition class: microemulsion preconcentrate (Claim 10 and Claim 16)
If a competitor uses a self-emulsifying system but does not meet a microemulsion preconcentrate classification, Claim 10/16 may not land even if Claim 9 could.
5) Ratio window (PG:gelatin)
Claims 4 and 5 create broad and narrow ratio corridors:
- 1:1 to 1:47 (Claim 4)
- 1:1 to 1:4 (Claim 5)
Given Claim 4’s very wide ceiling, this ratio element often won’t limit infringement unless the competitor’s formulation pushes far outside typical gelatin/PG ranges.
What is the likely claim map across product designs
Using the claim structure, infringement risk clusters into four design archetypes. Each archetype corresponds to how easily a product fits Claim 1 versus dependent claims.
Archetype A: PG-in-shell + PG-in-fill with dried-shell PG 2-40%
- Matches Claim 1 directly if:
- shell has gelatin + PG at encapsulation
- filling has CsA + PG in a carrier medium
- shell after drying has 2-40% PG by weight
This archetype is the highest-risk for enforcement.
Archetype B: PG-in-shell + PG-in-fill but dried-shell PG below 2%
- Likely avoids Claim 1 by failing the dried-shell constraint.
- May still intersect dependents if dried-shell is 5-40% etc, but lower than 2% would typically avoid all those.
Archetype C: PG only in shell OR only in fill
- If filling lacks PG, independent claim fails.
- If shell lacks PG at encapsulation, independent claim fails.
This is a clean design-around if practical.
Archetype D: PG in both but filling is not microemulsion-related
- Still potentially infringing Claim 1 (since microemulsion is only in dependents).
- Dependent claims 10/16 may not apply, but Claim 1 likely still does.
How dependent claims expand coverage
The dependents primarily add “formulation optionality” while preserving the core:
- Shell modifiers: plasticizers and glycerol (Claims 6 and 15)
- Fill composition cues:
- lipophilic component (Claim 7)
- surfactant (Claim 8)
- ethanol cosolvent (Claim 11)
- microemulsion preconcentrate (Claims 10 and 16)
- emulsion-forming behavior (Claim 9)
This matters because many CsA soft-gelatin products use surfactants/cosolvents and microemulsion-like systems. The patent’s novelty is framed around PG placement and quantified shell PG retention after drying, not around adding a particular emulsifier.
What is the patent landscape positioning (technical neighborhood and competitive design space)
Within the provided claim set, US 5,985,321 sits in a technical neighborhood defined by:
- Soft gelatin capsule drug delivery
- Cyclosporin A oral formulation
- Solubilization and emulsification systems
- PG as a key excipient in gelatin shells and as a component of the liquid formulation
- Microemulsion preconcentrates and self-emulsifying behavior
From a landscape standpoint, this patent’s “moat” is narrower than generic CsA soft-gel inventions because it anchors on the quantitative PG content after drying and requires PG in both shell and filling. That anchor typically forces competitors either to:
1) replicate the PG distribution (high exposure), or
2) alter the excipient system so dried-shell PG falls outside 2-40%, or
3) remove PG from the fill or shell (high reformulation effort).
Practical infringement checklist for US 5,985,321
A product is at highest risk if it satisfies all of the independent-claim elements:
- Soft gelatin capsule with shell + liquid fill
- At encapsulation, shell contains gelatin + 1,2-propylene glycol
- Filling contains:
- cyclosporin A
- 1,2-propylene glycol
- carrier medium
- After drying, shell contains 2-40% by weight 1,2-propylene glycol
Secondary checks (dependent claims) if the above is met:
- Dried-shell PG 5-40% (Claim 2)
- Dried-shell PG 5-32% (Claim 12), or 10-32% (Claim 13)
- Gelatin composition PG 1-35% (Claim 3, 14) or 4-30% (Claim 17)
- PG:gelatin ratio within 1:1 to 1:4 or 1:1 to 1:47 (Claims 5 or 4)
- Shell includes plasticizers (Claim 6) and/or glycerol (Claim 15)
- Fill includes lipophilic component, surfactant, ethanol (Claims 7-8 and 11)
- Fill behaves as emulsion-former (Claim 9) or is microemulsion preconcentrate (Claims 10 and 16)
Design-around pathways implied by the claim text
These options follow directly from claim constraints and are actionable for formulation and analytical development:
- Shift dried-shell PG below 2%: targets the key numerical barrier in Claim 1.
- Remove PG from the fill: breaks Claim 1’s “filling comprises 1,2-propylene glycol” requirement.
- Remove PG from the shell at encapsulation: breaks Claim 1’s “shell comprises gelatin and 1,2-propylene glycol” requirement.
- Keep PG only in one location: shell-only or fill-only avoids the “both shell and filling” requirement.
- If microemulsion components are used, do not treat it as a safe harbor; microemulsion is not needed for Claim 1 coverage.
Key takeaways
- US 5,985,321’s independent claim is built around a specific excipient architecture: 1,2-propylene glycol in both shell and filling, coupled to a quantified dried-shell retention of PG (2-40% by weight).
- Dependent claims broaden enforcement vectors through dried-shell narrower windows, gelatin composition PG ranges, PG:gelatin ratios, and fill functional/formulation traits (lipophilic component, surfactant, ethanol, emulsion-forming capability, and microemulsion preconcentrate).
- The main competitive risk is not “microemulsion vs not,” but where PG sits and how much remains in the shell after drying.
FAQs
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What is the single most important numerical constraint in US 5,985,321?
The shell’s 1,2-propylene glycol content after drying, defined as 2-40% by weight in Claim 1.
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Does the patent require the filling to be a microemulsion preconcentrate?
No. Microemulsion preconcentrate appears in dependent claims (Claims 10 and 16), while Claim 1 only requires a carrier medium with cyclosporin A and PG.
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Can a product infringe if the filling has no 1,2-propylene glycol?
No, because Claim 1 requires the filling comprises cyclosporin A and 1,2-propylene glycol.
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How do Claims 12 and 13 change the dried-shell PG requirement?
Claim 12 tightens to 5-32%, and Claim 13 tightens further to 10-32% after drying.
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Is Claim 1 limited to a particular shell or fill composition beyond PG and CsA?
It is not. Beyond the core requirements (gelatin + PG in shell, CsA + PG in fill, and dried-shell PG 2-40%), the other components are introduced as optional dependents (plasticizers, glycerol, surfactant, ethanol, lipophilic components).
References
[1] US Patent 5,985,321. Claims 1-17 (as provided in the prompt).
