US Patent 5,552,394: What Is Claimed, How Broad It Is, and Where It Sits in the US Landscape

What does US 5,552,394 claim at the method level?

US 5,552,394 claims a method of female contraception designed to reduce the incidence of breakthrough bleeding after the first cycle. The claimed method is defined by three tight technical constraints:

1) Dosing schedule (28-day cycle structure)

Monophasicly administering a combination of estrogen and progestin for 23 to 25 consecutive days out of a 28-day cycle.
Dependent claim examples lock to 24 days (claims 4 and 9).

2) Dose equivalency ranges (as specified by reference compounds)

Daily estrogen amount is equivalent to about 1 to 35 mcg of ethinyl estradiol.
Daily progestin amount is equivalent to about 0.025 to 10 mg of norethindrone acetate.
Additional dependent claim dose bands:
- 0.5 to 0.75 mg norethindrone acetate (claim 2)
- 0.5 to 1.5 mg norethindrone acetate (claim 7)
- up to 30 mcg ethinyl estradiol (claim 12)

3) Steroid ratio constraint (minimum estrogen:progestin ratio)

The weight ratio of estrogen to progestin is at least 1:45, calculated as:
- ethinyl estradiol : norethindrone acetate.
Dependent claim strengthens the ratio to:
- at least 1:50 (claims 3 and 8)

Claim set mapping: what varies and what stays fixed?

Below is the practical “claim skeleton” that a product must fit to land inside independent claim 1.

Element	Independent Claim 1 requirement	Dependent claim narrowing examples
Method purpose	female contraception with reduced breakthrough bleeding after first cycle	N/A
Regimen type	monophasic estrogen + progestin	N/A
Days on active	23 to 25 consecutive days in a 28-day cycle	24 days in claims 4 and 9
Estrogen identity	ethiny estradiol (by equivalency range and later dependent claims)	claims 5 and 10 require ethinyl estradiol
Estrogen daily amount	about 1 to 35 mcg ethinyl estradiol	claim 12: up to 30 mcg
Progestin identity	by equivalency to norethindrone acetate	claims 6 and 11 require norethindrone acetate
Progestin daily amount	about 0.025 to 10 mg norethindrone acetate	claim 2: 0.5 to 0.75 mg; claim 7: 0.5 to 1.5 mg
Estrogen:progestin weight ratio	at least 1:45 (ET/Estradiol mg equivalent vs NETA mg equivalent)	claim 3 and 8: at least 1:50

How should the ratio requirement be interpreted for design-around and validity analysis?

The ratio term is the most “engineering-forward” limiter. Because the claim states:

“weight ratio of estrogen to progestin is at least 1:45 calculated as ethinyl estradiol to norethindrone acetate”

it ties together otherwise independent dose ranges. Practically, any accused regimen must satisfy both:

estrogen dose within ~1–35 mcg, and
progestin dose within ~0.025–10 mg,
while simultaneously meeting ET:NETA ≥ 1:45 or ≥ 1:50 if narrowed.

A useful way to frame it for portfolio risk is:

Lower estrogen or higher progestin can fail the ratio even if each individual component sits in the stated ranges.
Higher estrogen paired with lower progestin can remain within ratio even if progestin is at the low end of its range.

What do claims 2–12 add in concrete coverage terms?

Claims 2 and 7 narrow progestin dose windows. Claims 3, 8 narrow the ratio floor. Claims 4 and 9 narrow the on-active days. Claims 5, 6, 10, 11 fix identities.

Claim	Extra limitation relative to claim 1	Effect on scope
2	NETA equivalent daily dose: 0.5–0.75 mg	Narrows progestin window
3	ratio floor: ≥ 1:50	Narrows ratio
4	regimen duration: 24 days active in 28-day cycle	Narrows schedule
5	estrogen is ethinyl estradiol	Fixes estrogen identity
6	progestin is norethindrone acetate	Fixes progestin identity
7	NETA equivalent daily dose: 0.5–1.5 mg	Another progestin band
8	ratio floor: ≥ 1:50	Narrows ratio
9	regimen duration: 24 days	Narrows schedule
10	estrogen is ethinyl estradiol	Fixes estrogen identity
11	progestin is norethindrone acetate	Fixes progestin identity
12	estrogen dose: up to 30 mcg	Narrows estrogen window

What is the claim strength and vulnerability profile in US litigation terms?

From a patent-scope standpoint, the claims are:

Product-adjacent in effect (a contraception method), but still process/regimen defined.
Tightly defined by day-count, dose ranges, and a minimum estrogen:progestin weight ratio.

The main vulnerability points typically arise from:

Indefiniteness risk is low because the claim uses explicit numeric ranges and ratio floors.
Anticipation/obviousness risk depends on whether earlier US references disclose the same regimen combination and whether the breakthrough bleeding endpoint was known or taught.

However, the claims embed a specific performance objective (“reduced incidence of breakthrough bleeding after the first cycle”), which can become a factual and evidentiary battleground: whether an earlier reference discloses the regimen and whether that regimen inherently achieves the claimed effect.

How do you characterize the patent’s likely “core” infringement space?

The highest probability overlap region is where a combined oral contraceptive (COC) is:

monophasic,
28-day cycle,
23–25 active days (especially 24),
containing ethinyl estradiol + norethindrone acetate,
with daily doses falling in the specified ranges,
and meeting the ET:NETA ratio minimum.

In effect, the patent is not aimed at “any” ethinyl estradiol/norethindrone acetate COC; it is aimed at a specific matrix of dose and regimen structure to manage breakthrough bleeding after the first cycle.

How does this fit into the broader US contraceptive patent landscape?

What technology cluster does 5,552,394 belong to?

US 5,552,394 belongs to a long-standing US and global cluster of patents on:

combined oral contraceptive regimens,
ethinyl estradiol plus progestins (including norethindrone acetate),
cycle-length and on-active day configuration (e.g., 21/7, 24/4 patterns),
and formulations/dosing rationales tied to bleeding outcomes.

Because the claim is anchored to:

ethinyl estradiol and norethindrone acetate, and
an explicit ratio floor, it sits deeper than generic “COC with EE+progestin” patents. It targets a regimen space.

Where are the major “blocking” prior art categories likely to be?

In US challenge contexts (102/103 style), the most relevant prior art categories for this type of claim usually include:

1) Earlier COC patents that disclose EE + NETA schedules with 28-day cycles

Especially those with 23–25 active days or 24-day active patterns.

2) Dose-ranging patents for EE and NETA

Ranges for EE mcg and NETA mg often appear across multiple product generations.

3) Regimen optimization patents targeting breakthrough bleeding

These frequently disclose changes in estrogen dose, progestin dose, or regimen duration.

4) Formulation and manufacturing patents

These matter less directly because the claims are method-of-contraception defined primarily by regimen and dose, not formulation particle size or excipients.

What is the likely competitive and product adjacency risk?

If a company markets or develops a monophasic EE/NETA COC, what regimen elements decide infringement probability?

In a factual assessment, infringement risk is mostly determined by the following “checkbox” set:

Monophasic dosing (not biphasic/triphasic variable doses)
28-day cycle
23–25 active days (24-day schedules are the narrowest repeated example)
Daily EE: 1–35 mcg (and potentially ≤30 mcg if the claim narrows to 12)
Daily NETA: 0.025–10 mg (and potential narrow bands 0.5–0.75 mg or 0.5–1.5 mg)
Weight ratio floor:
- at least 1:45 (independent claim 1)
- at least 1:50 (claims 3 and 8)
Identity constraints:
- EE and NETA specifically in the dependent claims

Where are plausible “design-around” levers, based on claim text?

The strongest levers created by the claim language itself are:

shifting from 23–25 active days to outside that band,
using a different estrogen than ethinyl estradiol,
using a different progestin than norethindrone acetate,
selecting daily doses that fail the ratio floor while still maintaining a clinically viable regimen.

These are not clinical recommendations; they are scope-based levers derived from the numeric constraints of claims 1–12.

Claims vs. landscape: how to read the patent’s practical market posture

This patent is structured to capture:

standard combined hormonal contraception regimens,
but only where the regimen includes a particular EE-to-NETA dose relationship and active day count that is connected to breakthrough bleeding after the first cycle.

That structure typically means:

it will be relevant as long as competing EE/NETA monophasic products use the same cycle pattern and dose/ratio envelope; and
it will be easier to avoid through schedule changes or dose/ratio positioning, but only if such changes keep the regimen outside at least one hard numeric constraint.

Key Takeaways

US 5,552,394 claims a monophasic EE + norethindrone acetate contraception regimen designed to reduce breakthrough bleeding after the first cycle.
The independent claim is tightly defined by (i) 23–25 active days in a 28-day cycle, (ii) EE dose about 1–35 mcg/day, (iii) NETA dose about 0.025–10 mg/day, and (iv) an EE:NETA weight ratio of at least 1:45.
Dependent claims narrow to 24 active days, EE identity, NETA identity, ratio ≥ 1:50, and specific dose bands (notably NETA 0.5–0.75 mg/day, NETA 0.5–1.5 mg/day, and EE up to 30 mcg/day).
In infringement and freedom-to-operate assessments, the decisive variables are active day count and the EE:NETA ratio floor, not just component selection.

FAQs

1) Is US 5,552,394 limited to 24-day regimens?

No. Independent claim 1 covers 23–25 active days in a 28-day cycle. Dependent claims add a 24-day limitation.

2) Does the patent require both ethinyl estradiol and norethindrone acetate?

Claim 1 is framed by equivalency to those specific reference compounds, and dependent claims expressly require ethinyl estradiol and norethindrone acetate (claims 5, 6, 10, 11).

3) What is the hardest numerical constraint in the claim set?

The strongest “hard” constraint is the minimum estrogen:progestin weight ratio:

≥ 1:45 in claim 1
≥ 1:50 in claims 3 and 8

4) What bleeding outcome does the patent tie to the method?

It ties the method to reduced incidence of breakthrough bleeding after the first cycle.

5) Which design-around levers follow directly from the claim language?

Switching any of the following can place a regimen outside scope: active days (outside 23–25), estrogen or progestin identity (not EE/NETA), or failing the ratio floor (1:45 or 1:50).

References

US Patent 5,552,394.

Details for Patent: 5,552,394

Summary for Patent: 5,552,394