United States Patent 5,989,581: What the Claims Cover and How the Landscape Shapes Freedom to Operate

What is US Patent 5,989,581 claiming in plain technical terms?

US 5,989,581 claims a bilayer (core and skin) thermoplastic polymer drug delivery system designed to provide direct release of a steroidal progestogenic compound and a steroidal estrogenic compound from the same compartment(s), using controlled solubility/supersaturation in the core and permeability through the skin.

The system structure and release logic repeat across the independent concept (Claim 1) and the more specific vaginal ring implementations (Claims 2 and 5 to 11):

At least one compartment with:
- a thermoplastic polymer core containing a mixture of:
- progestogenic steroid compound (example given: etonogestrel)
- estrogenic steroid compound (example given: ethinylestradiol)
- a thermoplastic polymer skin that is permeable to both compounds
Core formulation constraints:
- the progestogen is present at a defined supersaturation degree in the polymer core:
- 1 to about 6 times the weight amount required to reach saturation concentration at 25°C
- the estrogen concentration in the core is lower than the progestogen concentration
Specific delivery geometry:
- in narrower claims, the delivery system is substantially ring-shaped for vaginal administration
Specific polymer identity constraints:
- skin and/or core use ethylene-vinylacetate (EVA) copolymer
Specific composition and polymer property windows:
- defined progestogen:estrogen weight ratios
- defined drug loading % ranges for etonogestrel and ethinylestradiol
- defined EVA skin thickness and vinyl acetate content
- defined EVA core vinyl acetate content

This is a claims-driven formulation of a controlled diffusion, polymer-permeability delivery system where the progestogen release behavior is governed by supersaturation and the skin governs release kinetics via permeability.

What does Claim 1 cover, and what are the critical limitations?

Claim 1 is the core independent claim. Its constraints form the baseline infringement envelope.

Claim 1 key elements

Device architecture
- “at least one compartment”
- thermoplastic polymer core
- thermoplastic polymer skin covering the core
Drug mixture in the core
- core has a mixture of:
  - “a steroidal progestogenic compound”
  - “a steroidal estrogenic compound”
- the ratio is by weight and “allows a direct release” of both compounds in physiologically required amounts
Supersaturation requirement for the progestogen
- the progestogenic compound is “initially dissolved” in the core
- with “a degree of supersaturation” of:
  - 1 to about 6 times the amount by weight needed to obtain saturation concentration in the polymer core at 25°C
Relative concentration constraint
- estrogenic compound is dissolved at lower concentration than the progestogenic compound
Skin permeability requirement
- “thermoplastic skin being permeable for” both progestogenic and estrogenic compounds

Claim 1 critical points that drive infringement

A product must have both:
- core + skin polymer structure
- both steroid classes in the core
The progestogen must be in the core at a supersaturation degree within 1 to 6x the 25°C saturation concentration in that core polymer.
The estrogen must be lower concentration than the progestogen.
The skin must be permeable to both drugs (not merely a barrier).

Any design that breaks one of these constraints (especially supersaturation range or core/skin structure) narrows or eliminates direct claim fit.

How do Claims 2 and 5 narrow to vaginal rings?

Claim 2

Adds: “substantially ring-shaped form”
Intended for vaginal administration
The mixture of progestogenic and estrogenic compounds is delivered

Claim 5

Also specifies “substantially ring-shaped form” and vaginal administration
Reasserts the core + skin structure
Adds a more specific numeric ratio window:
- 10 parts progestogenic compound to 1.5 to 5 parts estrogenic compound
Reasserts the supersaturation requirement for the progestogen:
- 1 to about 6 times saturation concentration at 25°C
Reasserts skin permeability for both drugs

So, Claims 2 and 5 move from “therapeutic drug delivery system” to a ring geometry and a tight numeric steroid ratio.

What is the scope on polymer selection (EVA) across dependent claims?

The EVA limitation is introduced and repeated as narrowing specificity.

Claim 3

At least the skin material comprises ethylene-vinylacetate copolymer.

Claim 6

Extends EVA to both core and skin:
- core EVA: “ethylene-vinylacetate copolymer”
- skin EVA: “ethylene-vinylacetate copolymer”
Adds specific drugs:
- progestogen: etonogestrel
- estrogen: ethinylestradiol
Adds a ratio and explicit weight percentages:
- ratio: 10 parts etonogestrel to 2 to 4 parts ethinylestradiol
- core composition windows:
- etonogestrel: 0.3 up to about 1% by weight
- ethinylestradiol: 0.05 to about 0.3% by weight

Note: Claim 6 contains a redundant line “the thermoplastic polymer used for the skin material is an ethylene-vinylacetate copolymer” repeated. Practically, it still narrows to EVA skin and EVA core.

Claims 8 to 10 add EVA physical property windows

Claim 8:
- Skin is EVA with:
- thickness: 40 to 300 μm
- vinyl acetate content: 5 to 15%
Claim 9:
- narrower skin window:
- thickness: 80 to 150 μm
- vinyl acetate content: 9 to 10%
Claim 10:
- Core material is EVA with vinyl acetate content:
- 25 to 35% vinyl acetate content

These EVA ranges are likely the most design-influencing constraints for a Freedom-to-Operate design review because they map directly onto manufacturable material parameters and can be measured.

What specific drug ratio and drug loading windows are claimed?

The patent builds multiple “layers” of numeric constraints:

Ratio windows

Claim 5: progestogen:estrogen = 10 : (1.5 to 5)
Claim 6: 10 : (2 to 4)
Claim 7: 10 : (2 to 3) and weight % examples

Drug loading windows (explicit core % by weight)

Claim 6:
- etonogestrel: 0.3 to about 1.0%
- ethinylestradiol: 0.05 to about 0.3%
Claim 7:
- ratio: 10 : (2 to 3)
- etonogestrel: 0.5% and 1.0% (two specific values)
Claim 11:
- etonogestrel: 0.55 to 0.8%
- ethinylestradiol: 0.12 to 0.18%

Supersaturation remains the “release physics” constraint

Across Claims 1 and 5, the progestogen is the element tied to the supersaturation range:

Supersaturation degree: 1 to about 6x saturation concentration at 25°C
Estrogen is lower concentration than progestogen (Claims 1 and 5 frame it this way, while Claims 6 and 7 give numeric ratio and numeric composition windows).

How broad is the independent concept vs how narrow are the “EVA + ring + explicit formulation” claims?

Breadth ranking (conceptual)

Claim 1 is broadest because it:
- does not require ring geometry
- does not require EVA specifically
- does not require a specific pair of steroid drugs (uses general “steroidal progestogenic” and “steroidal estrogenic” compounds)
- only specifies polymer architecture, supersaturation range, relative estrogen concentration, and skin permeability
Claims 2 and 5 reduce scope by requiring:
- ring-shaped vaginal administration
- numeric progestogen:estrogen ratio window
Claims 3, 6, 8, 9, 10, 11 reduce scope further by requiring:
- EVA for skin (and in Claim 6 for core too)
- explicit drug pair (etonogestrel and ethinylestradiol)
- explicit polymer property windows (skin thickness, vinyl acetate content)
- explicit core EVA vinyl acetate content
- explicit drug loading % windows and/or specific ratio subranges

Practical implication

A product that matches Claim 1’s core features (bilayer polymer system with progestogen supersaturation in a specific window and a permeable skin) can still avoid later dependent claims by changing one or more of:

steroid identities
ring geometry
EVA material selection
skin thickness and vinyl acetate content
core vinyl acetate content
drug loading windows

But if a product matches both the core supersaturation requirement and the EVA ring formulation windows (notably Claims 6 to 11), the overlap tightens substantially.

What does the overall claim set imply about the patent’s inventive focus?

The claim language ties together three causally linked variables:

Supersaturation of progestogen in the core polymer (defined 1 to 6x saturation at 25°C)
Skin permeability that allows diffusion of both progestogen and estrogen through a polymer skin layer
Numeric drug ratio and concentration windows that maintain “physiologically required amounts” and control release balance

Even without external context, the structure suggests the inventive hook is not only co-delivery but co-delivery with a defined supersaturation condition plus controlled polymer skin properties to tune release.

What is the patent landscape posture for US 5,989,581?

The prompt provides only claim text; it does not provide bibliographic data (filing date, assignee, priority, other family members), nor citation lists, nor prosecution history. Without that metadata, a full landscape map (near-citations, family members, continuation status, active/inactive status, and claim construction patterns across related patents) cannot be produced accurately.

Freedom-to-operate (FTO) lens: which design changes most likely reduce risk?

Given the claim structure, risk reduction concentrates on breaking one of the numbered limitations below.

Highest-impact “avoid” levers

Supersaturation of the progestogen in the core
- Claims require 1 to about 6x saturation at 25°C.
Core + skin architecture
- Claims require a thermoplastic polymer core with a thermoplastic polymer skin covering it, where the skin is permeable to both drugs.
Skin material parameters (if practicing within the EVA subspace)
- Skin thickness: 40 to 300 μm (narrower: 80 to 150 μm)
- Skin vinyl acetate content: 5 to 15% (narrower: 9 to 10%)
Core EVA vinyl acetate content (if practicing within the EVA subspace)
- core vinyl acetate: 25 to 35%
Drug ratio and loading windows (if co-delivering etonogestrel + ethinylestradiol)
- ratio windows in dependent claims: 10 : (1.5 to 5), 10 : (2 to 4), 10 : (2 to 3)
- etonogestrel and ethinylestradiol weight % ranges: 0.3 to ~1.0% and 0.05 to ~0.3%, plus narrower ranges in Claims 7 and 11.

Claim-to-design matrix

Design element	Claim locations	Numeric / defining scope
Bilayer polymer compartment	1, 2, 5	core + skin; skin permeable to both drugs
Progestogen supersaturation in core	1, 5	1 to about 6x saturation at 25°C
Estrogen lower concentration than progestogen	1	estrogen concentration < progestogen concentration
Ring-shaped vaginal administration	2, 5	“substantially ring-shaped” for vaginal administration
Progestogen:estrogen weight ratio	5, 6, 7	5: 10:(1.5 to 5); 6: 10:(2 to 4); 7: 10:(2 to 3)
Drug identities	6, 7, 11	progestogen = etonogestrel, estrogen = ethinylestradiol
Core drug loading	6, 11, 7	6: etonogestrel 0.3 to ~1.0%, ethinylestradiol 0.05 to ~0.3%; 11: etonogestrel 0.55 to 0.8%, ethinylestradiol 0.12 to 0.18%
EVA skin polymer	3, 8, 9	skin EVA; thickness 40-300 μm; vinyl acetate 5-15%; narrower: 80-150 μm and 9-10%
EVA core polymer	6, 10	core EVA; vinyl acetate content 25-35%
Example etonogestrel values	7	0.5% and 1.0% (with ratio constraints)

Key Takeaways

US 5,989,581 claims a bilayer thermoplastic polymer drug delivery device with:
- a core containing both a progestogenic and an estrogenic steroid, and
- a permeable skin over the core that releases both compounds.
The most distinctive limitation is the progestogen supersaturation in the polymer core: 1 to about 6 times saturation concentration at 25°C.
Dependent claims narrow strongly to vaginal rings and, in later layers, to EVA-based cores and skins with specific vinyl acetate contents, skin thickness windows, and drug ratio/loading ranges (including etonogestrel and ethinylestradiol).
For FTO design planning, the highest-leverage non-infringement routes are to adjust:
- progestogen supersaturation range,
- core/skin architecture,
- and, if using EVA ring concepts, the vinyl acetate and thickness windows and the etonogestrel/ethinylestradiol ratio and loading.

FAQs

1) Is ring geometry required for all claims in US 5,989,581?

No. Ring-shaped, vaginal administration language appears in Claims 2 and 5. Claim 1 covers the delivery system structure without requiring a ring form.

2) What controls the progestogen release in the claim language?

The claims tie progestogen behavior to its initial supersaturation degree in the thermoplastic core, defined as 1 to about 6 times the 25°C saturation concentration.

3) Does the patent require EVA in the skin and core?

Not in Claim 1. EVA is required in narrower dependent claims, with Claim 3 requiring EVA for at least the skin, and Claim 6 requiring EVA for both core and skin.

4) Are the steroid identities fixed in the broad claim?

No. Claim 1 uses generic “steroidal progestogenic compound” and “steroidal estrogenic compound.” Specific identities (etonogestrel/ethinylestradiol) appear in dependent claims.

5) Which numerical constraints are most likely to be measured in product testing?

For EVA ring embodiments, the most measurable constraints are:

skin thickness (e.g., 40-300 μm or narrower 80-150 μm),
vinyl acetate content in skin (e.g., 5-15% or narrower 9-10%),
vinyl acetate content in core (25-35%),
and core drug loading % and progestogen:estrogen ratio (notably in Claims 6, 7, 11).

References

[1] United States Patent 5,989,581. Drug delivery system (claim set provided in prompt).

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
	97201098	Apr 11, 1997

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	011709	⤷ Start Trial
Austria	211646	⤷ Start Trial
Australia	6075198	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,989,581

Summary for Patent: 5,989,581