United States Patent 5,164,190: Scope of Claims and Patent Landscape for Subsaturated Transdermal Hydrophobic Drug Delivery

What is the core invention in US 5,164,190?

US 5,164,190 claims transdermal drug administration systems and methods that use a drug reservoir holding a hydrophobic drug in a carrier at a subsaturated condition (below saturation), then maintain subsaturation during wear to keep drug skin flux elevated over a prolonged period.

The invention is defined by a flux advantage relative to the same carrier when saturated with drug, measured over at least about 60% of the diffusion time period. The claims require:

Prolonged delivery time: at least about one day (and dependent claims specify 1 to 14 days).
Subsaturation: the drug is below saturation at the start and remains subsaturated thereafter for at least about 60% of the time period.
Flux uplift: drug skin flux during the subsaturation period is at least about 25% greater than flux when the carrier is saturated with drug, over at least about 60% of the time period.
Hydrophobic drug eligibility: includes low water solubility drugs, and dependent claims list specific steroids and other hydrophobic exemplars.
Device architecture: reservoir in drug delivery communication with skin, with carrier and optionally permeation enhancer, plus adhesive means to maintain skin contact.

What do the independent claims cover?

H2: Claim 1 (device)

Claim 1 covers a device for transdermal diffusion delivery of a hydrophobic drug for at least about one day, comprising:

1) Reservoir with:

drug dissolved in a carrier
the amount and solubility of the drug in the carrier defining a subsaturation condition sufficient to provide:
- drug skin flux over at least about 60% of the time period, where flux is:
- at least about 25% greater than flux when the carrier is saturated.

2) Means for maintaining the reservoir in drug delivery communication with skin.

The claim is tightly tied to a quantified performance relationship: subsaturation yields improved flux versus saturation during most of the wear period.

H2: Claim 13 (method of administering)

Claim 13 covers an administration method defined by the same performance logic:

Place a reservoir with hydrophobic drug dissolved in carrier in communication with unbroken skin.
Maintain drug concentration below saturation at the start and maintain subsaturation thereafter for at least about 60% of the time period.
This produces flux over at least about 60% of the time period that is at least about 25% greater than flux when the carrier concentration is saturated.

H2: Claim 18 (method of increasing flux)

Claim 18 is a “functional method” framed as a strategy to increase flux:

For prolonged diffusion delivery above saturation flux, you keep the reservoir drug concentration below saturation at the start and maintain subsaturation for at least about 60% of the time period.
Target outcome: at least about 25% greater flux than saturated condition over at least about 60% of the time period.

Practical consequence: Claims 13 and 18 cover method steps that directly correspond to the device feature of Claim 1, but they focus on the concentration management strategy (subsaturation maintenance), not necessarily on specific adhesive or polymer selection.

What are the key limiting parameters that define infringement risk?

H2: The flux comparison is the legal fulcrum

The claims repeatedly anchor patent scope to a side-by-side comparison:

Benchmark condition: “flux provided when the carrier is saturated with drug.”
Accused/claimed condition: “subsaturated” carrier maintained over most of the time period.

This means a transdermal system that only provides sustained delivery without proving the 25%+ flux advantage relative to saturated carrier is outside the asserted claim logic. The flux benchmark also narrows the scope against systems where flux is merely stabilized, delayed, or equivalent.

H2: The subsaturation duration requirement

Both device and methods require maintaining subsaturation for at least about 60% of the time period. This introduces a claim structure that is not satisfied if the reservoir transitions quickly to saturation early in wear.

H2: “At least about 60%” and “at least about 25%”

The language uses “at least about,” which typically broadens the tolerance for measurement variability. However, it still requires compliance with:

at least about 60% of the wear period in a subsaturated state (or equivalent subsaturation condition meeting the flux uplift requirement), and
at least about 25% flux increase versus saturated carrier over at least about 60% of the time period.

H2: Concentration bands tied to saturation concentration

Dependent Claim 10 defines a quantitative subsaturation window:

concentration in the carrier is about 20% to about 80% of the saturation concentration over at least about 60% of the time period.

Dependent Claims 17 and 22 repeat the same window in method claims.

This concentration band is a high-value claim subset for both enforcement and freedom-to-operate (FTO) design.

How broad is the drug scope?

H2: Hydrophobic drug definition (solubility threshold)

Claim 3 limits hydrophobicity through a solubility test:

hydrophobic drug has solubility in water at room temperature < 50 μg/mL.

This excludes many moderately soluble drugs and pushes scope toward true hydrophobics.

H2: Exemplified steroid list

Claim 4 lists:

estradiol, progesterone, testosterone, norethindrone acetate, medroxyprogesterone acetate.

Claim 14 and Claim 19 repeat the same list for method claims.

Effect on landscape: Even though the independent claims are not limited to those steroids, many real-world transdermal products in the steroid space will be compared against these dependent claim embodiments.

How broad is the carrier and formulation scope?

H2: Two carrier classes

Claim 6 allows solid carriers and lists:

polyacrylate, polymethacrylate, silicone polymer, polyalkyloxide, natural rubber, synthetic rubber.

Claim 7 allows fluid carriers and lists:

alcohol, alcohol-water mixture, low molecular weight polymer.

These lists are broad in both chemical category and formulation function (solid vs fluid reservoirs).

H2: Drug solubility in carrier

Claim 8 defines a reservoir solubility range:

solubility of the drug in the carrier in the range of 1 to 500 mg/mL.

This further narrows the chemical compatibility zone.

H2: Permeation enhancer optionality

Claim 2 adds:

reservoir also contains a permeation enhancer.

This is a permissive dependent claim: it expands device embodiments but does not restrict the independent claim (unless prior art arguments hinge on enhancer-related performance).

What is the “prolonged time” scope?

H2: Minimum and dependent duration

Independent claims require at least about one day (Claims 1, 13, 18).
Dependent Claim 5 specifies 1 to 14 days.

The patent’s practical enforceability will often track actual patch wear times.

Claim-by-claim scope map (what each dependent claim adds)

Claim	Adds/limits	Scope impact
2	permeation enhancer present	Adds device embodiments with enhancer; independent scope already covers subsaturation + flux uplift
3	drug water solubility < 50 μg/mL	Narrows to hydrophobic candidates meeting test
4	drug is one of specified steroids	Narrows to exemplars for dependent coverage
5	time period 1 to 14 days	Limits duration window in dependent case
6	solid carrier polymer types	Narrows carrier materials in dependent embodiment
7	fluid carrier solvent/polymer types	Narrows liquid carrier system options
8	drug solubility in carrier 1 to 500 mg/mL	Establishes concentration-solubility compatibility band
9	flux uplift 25% to 400% over saturated	Adds an explicit numerical range for improved flux
10	initial-to-majority concentration 20% to 80% of saturation over 60%+ of time	Defines a direct engineering design window
11	maintaining means is adhesive carrier	Narrows architecture
12	basal adhesive layer / overlay / peripheral ring	More specific patch geometry and adhesive structure
14	method with specified steroids	Method subset
15	method with specified solid carriers	Method subset
16	method with specified fluid carriers	Method subset
17	maintain concentration 20% to 80% of saturation over 60%+ time	Method subset with engineering band
18	method of increasing flux (performance framed)	Independent method strategy claim
19	method with specified steroids	Method subset
20	method with specified solid carriers	Method subset
21	method with specified fluid carriers	Method subset
22	maintain concentration 20% to 80% of saturation over 60%+ time	Method subset with engineering band

Where does the claim language create enforceability leverage?

H2: “At least about 60% of said time period” links performance to kinetics

The claim does not just ask for average flux over the entire period. It requires the subsaturated condition to persist for most of the time period, and flux advantage to be observed over that same majority.

This can be used in enforcement to argue that a competitor’s formulation transitions to saturation too quickly, eliminating the required performance window.

H2: “Drug skin flux” is a measurable endpoint

Both the device and methods use “drug skin flux” as the metric tied to the subsaturation strategy. That supports experimental comparability in litigation and in FTO validation.

H2: Reservoir concentration management becomes the infringement trigger

A competitor may use the same drug and a similar carrier class but avoid infringement by designing a system whose reservoir concentration does not remain in the claimed subsaturation band (or does not achieve the required flux uplift compared with saturated carrier).

In practice, the subsaturation band (20% to 80% of saturation for 60%+ of time) is the most operationally relevant element for testing.

How would this patent likely sit in the transdermal performance landscape?

H2: It targets the saturation-limitation problem

Conventional reservoir transdermal delivery often relies on maintaining a saturated or near-saturated drug concentration in the reservoir. This patent instead claims the counter-strategy: maintain subsaturation and still exceed saturated flux during most of the wear period.

That design principle is the distinctive hook that separates the claimed technology from many saturation-based steady-state reservoir concepts.

H2: It spans both solid and fluid reservoir platforms

Because the claims cover both solid and fluid carriers, the patent landscape risk is not limited to polymer-matrix patches alone. It reaches reservoir-type systems that can be engineered to manage drug concentration below saturation.

H2: It has both device and method coverage

Device claim (1) covers patch architecture conceptually anchored by adhesive means and reservoir placement.
Method claims (13 and 18) cover administration steps based on concentration state management.

For landscape mapping, this means a competitor cannot avoid risk solely by changing device structure if the method or concentration management strategy is effectively used.

What would a practical FTO screen look like against this claim set?

H2: Binary decision points

A candidate transdermal product or development program is most likely in-scope if all of these are met:

1) Hydrophobic drug with water solubility at room temperature < 50 μg/mL (Claim 3 as a dependent embodiment; conceptually indicates intended chemical class). 2) Reservoir drug concentration is below saturation at start and remains subsaturated for at least about 60% of the wear time. 3) The resulting skin flux over at least about 60% of the wear time is at least about 25% higher than the flux when the carrier is saturated with the drug (same drug/carrier system under comparison conditions). 4) Carrier and reservoir architecture support diffusion-mediated transdermal administration for at least about one day.

H2: High-probability design windows from dependent claims

Programs that tune reservoir concentration into the 20% to 80% of saturation band for 60%+ of wear time are closer to Claim 10/17/22.

Similarly, patch systems with typical adhesive-backed reservoirs will frequently satisfy the “means for maintaining communication with skin” limitation (Claim 11/12).

Key takeaways

US 5,164,190 claims transdermal diffusion systems that deliver hydrophobic drugs by maintaining subsaturation (below saturation) for at least 60% of a prolonged wear period, producing at least 25% higher skin flux versus a saturated carrier benchmark over the same majority of time.
The invention scope is defined less by specific drug or polymer and more by performance math: subsaturation state + sustained majority duration + flux uplift versus saturation.
Dependent claims add concrete engineering constraints: 20% to 80% of saturation concentration (for 60%+ of time), specified steroid candidates, and broad lists of solid and fluid carriers.
For landscape and FTO purposes, the primary infringement levers are: (1) the subsaturation duration, and (2) demonstrable flux superiority relative to saturated-carrier controls.

FAQs

H2: What is the main performance requirement in US 5,164,190?

The claims require that when a reservoir drug concentration is kept below saturation and maintained subsaturated for at least about 60% of the wear period, the drug skin flux over that same majority period is at least about 25% greater than the flux obtained when the carrier is saturated with the drug.

H2: Does the patent require a specific drug?

No. The independent claims require a hydrophobic drug. Dependent claims specify examples including estradiol, progesterone, testosterone, norethindrone acetate, and medroxyprogesterone acetate, and also define hydrophobicity as water solubility < 50 μg/mL at room temperature.

H2: What carrier types are covered?

Both solid and fluid carriers are covered. Solid carriers listed include polyacrylate, polymethacrylate, silicone polymer, polyalkyloxide, natural rubber, synthetic rubber. Fluid carriers listed include alcohol, alcohol-water mixtures, low molecular weight polymers.

H2: Are adhesive-backed patch structures within scope?

Yes. The claims include “means for maintaining” reservoir-skin communication and dependent claims specify adhesive-based configurations, such as an adhesive carrier, basal adhesive layer, overlay, or peripheral adhesive ring.

H2: How does the patent treat concentration control?

It requires subsaturation at the start and maintenance thereafter for at least 60% of the time period. Dependent claims provide a specific engineering band: maintaining drug concentration at about 20% to about 80% of saturation concentration over at least about 60% of the time period.

References

[1] United States Patent 5,164,190. (Claims as provided in prompt text).

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Summary for Patent: 5,164,190