US Patent 3,666,858: Claim Scope, Expiration, and Levonorgestrel Patent Landscape

US Patent 3,666,858 is an early hormonal-contraceptive patent covering compositions and oral administration methods using the steroid identified in the claims as 13β-ethyl-17α-ethynyl-17β-hydroxygon-4-en-3-one, generally associated with levonorgestrel or a closely defined norgestrel stereochemical form. The patent also contains separate growth-stimulation claims for different steroid compounds and a gynecomastia-treatment method.

The patent issued on May 30, 1972. Assuming the standard pre-Uruguay Round patent term of 17 years from issuance and no unusual term adjustment, the patent expired on May 30, 1989. It therefore presents no current US patent barrier to generic or branded products containing the claimed steroid.

What compound does US Patent 3,666,858 cover?

The contraceptive compound recited in claims 2 through 6 and 9 through 13 is:

13β-ethyl-17α-ethynyl-17β-hydroxygon-4-en-3-one

That nomenclature corresponds to the steroid commonly known as levonorgestrel when the specified stereochemistry is applied. Norgestrel is the racemic mixture of the two relevant enantiomers, while levonorgestrel is the biologically active levo-isomer. Patent and regulatory analysis must therefore distinguish between:

Name	Relationship to the claimed steroid
Levonorgestrel	Specific stereochemical form generally associated with the claimed structure
Norgestrel	Racemic mixture containing levonorgestrel and the opposite enantiomer
D-norgestrel	Historical terminology for levonorgestrel
LNG	Common abbreviation for levonorgestrel

The chemical name in the supplied claims contains typographical or OCR-style inconsistencies, including “17 eta” in claim 2. Claim 2 otherwise uses the 17β-hydroxy designation used in the other contraceptive claims.

What are the principal claim categories in US Patent 3,666,858?

The supplied claims divide into five legal categories:

Female reproductive-health compositions.
Contraceptive compositions.
Growth-stimulation methods using different steroids.
Oral contraceptive methods.
A male gynecomastia-treatment method.

The patent does not operate as a single broad claim to every use of levonorgestrel. Each claim includes specific elements involving the active ingredient, dosage, route, indication, combination partner, or treatment schedule.

How broad is claim 2 for reproductive dysfunctions?

Claim 2 covers a pharmaceutical composition containing an effective amount of the specified steroid and a pharmaceutically acceptable carrier. The composition must be useful for:

Cyclic control in a female mammal;
Amenorrhea;
Dysmenorrhea; or
Functional uterine bleeding.

The claim has no express numerical dose limitation. Its scope is therefore broader than claim 3 with respect to quantity, but it remains limited by the listed reproductive indications and by the requirement for a pharmaceutically acceptable carrier.

Claim 2 is a composition claim, not a pure compound claim. A product would need to contain the specified active ingredient in a pharmaceutical composition. The claim does not expressly require oral administration, although claim 9 separately imposes that route for the corresponding method.

What does claim 3 add?

Claim 3 depends on claim 2 and limits the amount of the steroid to approximately 2.5 mg to approximately 25 mg.

The claim therefore requires:

Element	Requirement
Active ingredient	13β-ethyl-17α-ethynyl-17β-hydroxygon-4-en-3-one
Indication	Cyclic control or listed reproductive dysfunction
Form	Composition
Carrier	Pharmaceutically acceptable carrier
Amount	Approximately 2.5 mg to approximately 25 mg

A formulation outside that dosage range could still fall within claim 2 if it satisfied the broader “effective amount” limitation.

What contraceptive compositions are covered by claims 4 through 6?

Claim 4: 0.015 mg to 10 mg

Claim 4 covers a composition useful for preventing conception in a female mammal containing approximately 0.015 mg to approximately 10 mg of the active steroid.

Claim 5: 0.015 mg to 1 mg

Claim 5 narrows claim 4 to approximately 0.015 mg to approximately 1 mg. Because it depends on claim 4, the composition must still be directed to contraception and include a pharmaceutically acceptable carrier.

Claim 6: Levonorgestrel with ethynyl estradiol

Claim 6 covers a contraceptive composition containing:

An effective amount of the specified steroid; and
Up to approximately 0.05 mg of ethynyl estradiol.

This is a combination claim. It does not require a particular amount of the progestin, other than an amount effective to prevent conception, but it caps the estrogen component at approximately 0.05 mg.

The claim language does not expressly require a particular ratio, tablet schedule, or formulation technology. It is directed to the presence of the two hormonal components in a contraceptive composition.

What methods are covered by claims 9 through 13?

Claim 9: Oral reproductive-health treatment

Claim 9 covers orally administering a pharmaceutically effective amount of the specified steroid for:

Cyclic control;
Amenorrhea;
Dysmenorrhea; or
Functional uterine bleeding.

Compared with claim 2, claim 9 changes the category from composition to method and adds oral administration.

Claim 10: Daily contraception at 0.015 mg to 10 mg

Claim 10 covers orally administering the steroid at an effective amount of approximately 0.015 mg to approximately 10 mg per day for preventing conception.

The claim requires:

A female mammal;
Oral administration;
Daily dosing;
A dose within the stated range; and
Contraceptive effectiveness.

Claim 11: Continuous low-dose contraception

Claim 11 narrows the daily amount to approximately 0.015 mg to approximately 1 mg and requires administration on a continuous basis.

The “continuous basis” limitation distinguishes this claim from a method that uses the same ingredient intermittently or only during part of a menstrual cycle.

Claim 12: Cyclic combination therapy

Claim 12 covers orally administering the steroid in an effective contraceptive amount together with up to approximately 0.05 mg of ethynyl estradiol per day on a cyclic basis.

This claim is narrower than claim 10 in several respects:

Limitation	Claim 10	Claim 12
Oral administration	Yes	Yes
Contraceptive use	Yes	Yes
Ethynyl estradiol	Not required	Required, up to 0.05 mg/day
Schedule	Daily	Cyclic
Progestin dose	0.015 mg to 10 mg/day	Effective amount, no stated numerical range

Claim 13: Gynecomastia in males

Claim 13 covers administering an effective amount of the steroid to a male human for control of gynecomastia.

This is a method-of-use claim. It does not specify:

Dose;
Route;
Treatment duration;
Formulation;
Combination therapy; or
Disease severity.

The claim is narrower than a general treatment claim because it is limited to male humans and gynecomastia.

What do claims 7 and 8 cover?

Claims 7 and 8 do not concern the contraceptive steroid recited in the other supplied claims.

Claim	Compound	Claimed use
7	13β,17α-diethyl-17β-hydroxygon-4-en-3-one	Stimulating growth in a mammal
8	13β-ethyl-17β-hydroxygon-4-en-3-one 17-decanoate	Stimulating growth in a mammal

These claims should be analyzed separately from the levonorgestrel claims. They are method claims directed to growth stimulation and require administration of the specified alternative steroid.

Their presence indicates that the patent specification likely disclosed a family of related 13β-ethyl gonane compounds, but the supplied claims do not establish that the contraceptive steroid and the growth-stimulation steroids are legally interchangeable.

How many patents cover the contraceptive compound?

US Patent 3,666,858 is one historical patent in the broader norgestrel and levonorgestrel estate. Its relevant claim groups cover therapeutic compositions and methods rather than a presently enforceable compound monopoly.

The commercial patent landscape later shifted toward:

Specific formulations;
Combination oral contraceptives;
Intrauterine delivery systems;
Emergency-contraception products;
Extended-release dosage forms;
Drug-device combinations;
Manufacturing and purification processes; and
Product-specific labeling or method-of-use claims.

The key distinction is between the expired foundational patent and later patents directed to particular products or delivery systems. A later formulation patent could remain relevant after expiration of the foundational steroid patent, but it could not restore exclusivity over the active ingredient itself.

When did US Patent 3,666,858 lose exclusivity?

The patent issued on May 30, 1972. Under the pre-1995 US patent term applicable to this type of patent, the ordinary term was 17 years from issuance. The expected expiration date was therefore:

Event	Date
Patent issued	May 30, 1972
Standard 17-year expiration	May 30, 1989
Current enforceability	Expired

The patent predates the Hatch-Waxman framework and the modern patent-term system. Patent-term extension under 35 U.S.C. § 156 was not generally available for an ordinary early-1970s patent in the manner available to certain later pharmaceutical patents. The patent cannot support a current Paragraph IV challenge or an enforceable injunction against a modern levonorgestrel generic.

What is the Orange Book status of this patent?

US Patent 3,666,858 is not a current Orange Book exclusivity asset. The Orange Book lists patents submitted for approved drug products, but an expired 1972 patent has no continuing period of enforceable exclusivity.

Current Orange Book analysis must be conducted at the product level. Relevant products may include:

Levonorgestrel oral contraceptives;
Emergency-contraception tablets;
Levonorgestrel-releasing intrauterine systems;
Combination oral contraceptives containing estrogen and a progestin; and
Other approved products using levonorgestrel or related progestins.

A product may have later formulation, device, or method-of-use patents even though the compound patent in US 3,666,858 has expired. The patent therefore should not be treated as evidence that any particular modern branded product is patent-free.

Which products and therapeutic uses are commercially relevant?

Levonorgestrel has been used in several FDA-regulated categories:

Category	Representative use
Oral contraception	Daily progestin-containing contraceptives
Emergency contraception	Single-dose oral levonorgestrel products
Intrauterine systems	Local release for contraception and heavy menstrual bleeding
Combination contraceptives	Levonorgestrel with ethinyl estradiol
Reproductive disorders	Historical and current hormonal-treatment applications

FDA-approved emergency contraception products containing levonorgestrel include Plan B One-Step and generic equivalents. Levonorgestrel-releasing intrauterine systems are regulated as drug-device combination products and have separate product-specific patent considerations. FDA approval, labeling, and exclusivity data are maintained through FDA drug databases and product records.[2][3]

Are biosimilar risks relevant?

No. Levonorgestrel is a chemically synthesized small molecule, not a biologic. The relevant competitive pathways are:

Abbreviated New Drug Application, or ANDA, filings;
Drug-device combination-product submissions;
OTC monograph or prescription-to-OTC pathways where applicable;
Paragraph IV certifications against unexpired listed patents; and
Conventional generic competition after patent and regulatory exclusivity expiration.

Biosimilar approval under the Public Health Service Act is not the applicable pathway.

What Paragraph IV challenges affect this patent?

US Patent 3,666,858 cannot support a current Paragraph IV challenge because it expired decades ago. A generic applicant would not need to certify that the patent is invalid or will not be infringed in order to enter the market today.

Paragraph IV litigation may still arise against later patents covering:

A branded levonorgestrel product;
An intrauterine delivery device;
A specific release profile;
A formulation excipient system;
A combination product;
A method of treating a labeled condition; or
A manufacturing process.

The existence of a Paragraph IV dispute involving a later levonorgestrel product would not revive or extend the term of US Patent 3,666,858.

What formulation and manufacturing barriers remain?

The patent claims supplied do not contain a manufacturing-process claim. They do not expressly claim:

Particle-size control;
Crystallinity;
Polymorphs;
Impurity limits;
Granulation;
Coating;
Extended release;
Intrauterine polymer matrices;
Drug-device integration; or
Specific synthetic intermediates.

The principal post-expiration barriers are therefore regulatory and technical rather than attributable to this patent. For oral products, manufacturing complexity is generally lower than for levonorgestrel intrauterine systems. Device products require additional control over polymer composition, drug loading, release kinetics, sterility, insertion performance, and long-term stability.

How strong is the patent estate?

Strength of US Patent 3,666,858

Factor	Assessment
Claim breadth	Moderate within the specified therapeutic and contraceptive categories
Compound coverage	No standalone compound claim shown in the supplied claims
Dosage coverage	Broad in claims 2 and 4; narrower in dependent claims
Route coverage	Oral administration expressly required in claims 9 through 12
Combination coverage	Claim 6 and claim 12 cover ethynyl estradiol combinations
Manufacturing coverage	None shown in the supplied claims
Current enforceability	None; patent expired
Biosimilar relevance	None
Generic entry relevance	Historical only
Current litigation value	None as an enforceable patent

The patent was commercially important as an early disclosure of contraceptive and therapeutic applications for the compound, but its present legal strength is zero because the patent term ended in 1989.

What generic launch scenarios existed historically?

Before expiration, the patent could have affected products using the specified steroid for the claimed indications, dose ranges, or schedules. Potential infringement theories would have depended on the exact product and conduct:

A tablet containing the steroid in the claimed amount could implicate claims 4 or 5.
A combination tablet containing the steroid and up to 0.05 mg ethynyl estradiol could implicate claim 6.
A daily oral contraceptive regimen could implicate claim 10.
A continuous low-dose regimen could implicate claim 11.
A cyclic combination regimen could implicate claim 12.
A labeled gynecomastia treatment could implicate claim 13.

After May 30, 1989, those claims no longer blocked commercial launch. Any later launch risk would have depended on separate patents, regulatory exclusivity, trademarks, trade dress, product-specific device rights, or manufacturing know-how.

What litigation and settlement agreements affect the patent?

The supplied record does not identify a current litigation or settlement dispute involving US Patent 3,666,858. Because the patent expired in 1989, it is not a viable basis for present-day infringement litigation.

Historical settlement agreements involving later contraceptive products, branded manufacturers, or device patents should not be attributed to this patent without a case-specific record. Any current dispute involving levonorgestrel is more likely to concern a later product patent or a drug-device combination than US Patent 3,666,858.

Key Takeaways

US Patent 3,666,858 covers compositions and treatment methods involving a levonorgestrel-associated steroid.
Claims 2 through 6 address reproductive-health and contraceptive compositions.
Claims 9 through 12 cover oral contraceptive and reproductive-treatment methods.
Claim 13 covers treatment of gynecomastia in male humans.
Claims 7 and 8 cover different steroids for growth stimulation.
The patent issued May 30, 1972 and ordinarily expired May 30, 1989.
It does not provide current US exclusivity for levonorgestrel products.
No biosimilar pathway applies because levonorgestrel is a small molecule.
Current commercial risk lies in later formulation, device, manufacturing, and product-specific patents.
A current Paragraph IV certification would target later unexpired patents, not this expired patent.
The supplied claims show no standalone compound claim and no manufacturing-process claim.

FAQs About US Patent 3,666,858 and Levonorgestrel

Is US Patent 3,666,858 still enforceable?

No. Its standard pre-1995 patent term ended in 1989.

Does the patent cover Plan B?

The patent historically covers contraceptive use of the claimed steroid, but it does not currently block Plan B or generic levonorgestrel products because the patent expired before those products reached their modern commercial status.

Does the patent cover a levonorgestrel intrauterine device?

The supplied claims do not expressly claim an intrauterine device, polymer reservoir, or controlled-release system. Later device patents must be analyzed separately.

Can a generic manufacturer rely on this patent’s expiration?

Yes. The expiration removes this patent as a blocking US patent. The manufacturer must still assess later listed patents, FDA requirements, trademarks, and product-specific regulatory obligations.

Is norgestrel legally identical to levonorgestrel under these claims?

Not necessarily. The claims use stereochemical nomenclature. Levonorgestrel is a specific stereoisomer, while norgestrel generally refers to a racemic mixture. Chemical identity should be determined from the complete patent specification and applicable analytical standards.

References

United States Patent and Trademark Office. (1972). US Patent No. 3,666,858.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations: Orange Book.
U.S. Food and Drug Administration. (n.d.). Drugs@FDA: FDA-approved drugs.
U.S. Code, 35 U.S.C. §§ 154, 156, 271, and 355.
U.S. Food and Drug Administration. (n.d.). Abbreviated new drug application approvals and patent certification requirements.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Belgium	716736	⤷ Start Trial
Cyprus	658	⤷ Start Trial
Denmark	130949	⤷ Start Trial
United Kingdom	1204171	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 3,666,858

Summary for Patent: 3,666,858