United States Drug Patent 4,377,584: Claim Scope, Expiration, and Patent Landscape

US 4,377,584 is an early Merck patent directed to a broad genus of 4-aza steroid compounds, their pharmaceutically acceptable salts, therapeutic uses, testosterone-5α-reductase inhibition, and pharmaceutical compositions. The patent issued March 22, 1983, and its original United States patent term expired in 2000 or 2001, depending on the applicable term calculation and patent-term adjustment record. It is no longer an enforceable barrier to generic development.

The claims have historical importance because they cover the chemical class that produced clinically relevant 5α-reductase inhibitors, including compounds associated with benign prostatic hyperplasia and androgen-related disorders. The patent does not, by itself, establish current exclusivity for any marketed product. Later patents, particularly method-of-use and formulation patents, determined the commercial exclusivity of specific products.

What does US Patent 4,377,584 cover?

The patent covers four related subject-matter categories:

Claim category	Claims	Scope
Chemical compounds	1-13	Broad genus and selected steroid species
Treatment of hyperandrogenic conditions	14-15	Parenteral treatment of acne, seborrhea, female hirsutism and benign prostatic hypertrophy
Testosterone-5α-reductase inhibition	16-17	Administration of covered compounds to inhibit the enzyme
Pharmaceutical compositions	18-19	Covered compounds combined with a pharmaceutically acceptable carrier

Claim 1 is the principal composition-of-matter claim. Claims 2 through 13 narrow the genus to defined substituent combinations and named steroid compounds. Claims 14, 16 and 18 independently claim therapeutic use and pharmaceutical-composition concepts rather than merely depending on the compound claims.

The patent is therefore not limited to a single active pharmaceutical ingredient. It claims a chemically diverse steroid platform.

How broad is claim 1 of US 4,377,584?

Claim 1 is a Markush claim covering multiple variations at the steroid nucleus and side-chain positions.

Its principal variables are:

A: alternative steroid-ring or unsaturated-ring structures.
B: nitrogen-containing substituents, including aza, alkylated aza, amino, cyano and quaternary ammonium arrangements.
R1: hydrogen, alkyl, alkenyl, alkynyl, amino-substituted groups or cyano.
R', R" and R"': hydrogen, methyl and hydroxyl configurations.
Z: multiple 17-position substituent arrangements.
R8: hydrogen, hydroxyl, alkyl, amino, substituted amino, cyclic amino or ether groups.
R9 and R10: hydrogen, alkyl, cycloalkyl, phenyl or heterocyclic amino substituents.
R11 and R12: hydrogen, alkali metals, alkyl, benzyl, acyl, benzoyl, cycloalkylcarbonyl and alkoxycarbonyl groups.
R13: alkyl or amino substituents.
Pharmaceutical salts.

This drafting strategy attempts to capture both the steroid nucleus and a large range of 17-position carboxamide, ester, ether, amino and related derivatives. The claim also allows alternative partial structures, increasing the number of possible constitutional and stereochemical embodiments.

What chemical features define the protected genus?

The common technical concept is a steroid framework containing a 4-aza or related nitrogen substitution pattern, combined with modifications that affect 5α-reductase inhibition and androgen metabolism.

The claim set reaches:

Saturated and unsaturated steroid frameworks.
4-aza and 4-substituted-4-aza systems.
17-position carboxamides and related derivatives.
Ester and ether substituents.
Cyano and tetrazolyl derivatives.
Quaternary ammonium salts.
Compounds bearing tertiary, secondary or cyclic amino groups.
Pharmaceutically acceptable salts.

The claim is chemically broad, but its enforceability depends on whether a defendant's compound satisfies every structural limitation in the selected claim. A compound that falls outside the claimed steroid skeleton, nitrogen placement, stereochemistry or permitted substituent definitions would not infringe claim 1.

Which claims are narrow species claims?

Claims 2 through 13 narrow the broad genus. The most commercially relevant narrowing features are the 4-methyl, 4-amino and 17-carbamoyl substitutions.

Claim	Subject matter
2	A restricted structural subgroup with R1 as hydrogen, methyl or amino and a specified T group
3	R1 as methyl with ethyl carbamoyl or diethylcarbamoyl substitution
4	17β-N,N-diethylcarbamoyl-4-methyl-4-aza-5α-androstan-3-one
5	17β-N,N-diethylcarbamoyl-4-aza-5α-androstan-3-one
6	17β-N,N-diethylcarbamoyl-4-amino-4-aza-5α-androstan-3-one
7	4-aza-5α-20-spiroxan-3-one
8	4-methyl-4-aza-5α-20-spiroxan-3-one
9	17β-N-ethylcarbamoyl-4-methyl-4-aza-5α-androst-3-one
10	4-methyl-4-aza-5α-pregnane-3,20-dione
11	20-hydroxymethyl-4-methyl-4-aza-5α-pregnane-3-one
12	17β-carbomethoxy-4-methyl-4-aza-5α-androstan-3-one
13	17β-N-octylcarbamoyl-4-methyl-4-aza-5α-androstane-3-one

Claims 4 through 13 are materially easier to analyze for literal infringement because they identify individual compounds. They also have a narrower validity profile. A species claim can survive invalidity challenges even if a broader genus claim is vulnerable, provided the specific compound is novel, nonobvious and adequately disclosed.

What methods of treatment are protected?

Claim 14 covers parenteral administration of the claimed compounds to treat:

Acne vulgaris.
Seborrhea.
Female hirsutism.
Benign prostatic hypertrophy.

The claim requires three central elements:

A patient in need of treatment.
Parenteral administration.
A therapeutically effective amount of a compound within the claimed genus.

The parenteral limitation narrows the claim. Oral administration alone would not satisfy the express administration route in claim 14. Depending on claim construction, injection, infusion and other non-gastrointestinal delivery routes would generally be the principal forms targeted.

Claim 15 narrows claim 14 to a smaller structural subgroup. It does not create a freestanding use right for compounds outside the specified formula.

What does claim 16 cover?

Claim 16 is a separate method claim directed to inhibiting testosterone-5α-reductase. It does not expressly repeat the disease list from claim 14. Its required elements are:

A patient in need of testosterone-5α-reductase inhibition.
Administration of a therapeutically effective amount.
A compound within the stated steroid genus.

This claim is potentially broader in therapeutic purpose than claim 14 because it is framed around enzyme inhibition rather than named diseases. It remains subject to the structural limitations of the compound formula.

Claim 17 narrows claim 16 to the specified subgroup.

What do the pharmaceutical-composition claims cover?

Claim 18 covers a pharmaceutical composition containing:

A pharmaceutically acceptable carrier; and
A compound within the broad formula.

Claim 19 narrows the composition to the smaller compound subgroup.

These claims can reach tablets, capsules, injectable preparations, solutions, suspensions and other dosage forms if the composition contains a covered compound and an acceptable carrier. The claims do not appear, based on the supplied text, to require a particular dosage, release profile, excipient, particle size, coating or manufacturing process.

That distinction matters. Claim 18 is a compound-plus-carrier claim, not a modern formulation claim directed to a specific controlled-release system or bioavailability-enhancing composition.

When did US 4,377,584 lose exclusivity?

US 4,377,584 was granted under the pre-Uruguay Round patent-term regime, under which United States utility patents generally ran for 17 years from grant. The patent issued on March 22, 1983. Its ordinary term therefore ran to March 22, 2000, subject to any applicable adjustment, disclaimer or statutory calculation.

Commercial and regulatory databases commonly associate the patent with an expiration date in 2000 or 2001. That difference reflects historical term calculations and database treatment of the patent record. Regardless of the precise historical date, the patent expired more than two decades ago and does not provide current United States exclusivity.

Was pediatric exclusivity relevant?

No current patent barrier can be attributed to pediatric exclusivity under this patent. Pediatric exclusivity adds six months to certain listed patents after qualifying FDA action; it does not revive an expired composition-of-matter patent indefinitely. Any pediatric extension would have been time-limited and would not alter the present status of US 4,377,584.

What was the FDA and Orange Book significance?

US 4,377,584 is associated with the early patent estate for 5α-reductase inhibitor products, but Orange Book status must be assessed at the product level.

The FDA Orange Book lists patents identified by an NDA holder for a specific approved drug. A patent may be relevant to a compound historically used in a product without remaining listed or enforceable today. Orange Book listing does not extend patent term and does not independently establish infringement.

For a product such as finasteride, the principal commercial exclusivity was supported by later patents directed to approved indications, particularly androgenic alopecia and benign prostatic hyperplasia. The early patent should not be treated as the sole patent determining generic launch timing.

What was the Paragraph IV impact?

A generic applicant may file an ANDA with a Paragraph IV certification asserting that an Orange Book-listed patent is invalid, unenforceable or not infringed. For an expired patent, the relevant certification is generally not a live Paragraph IV dispute because the applicant does not need to challenge an enforceable term.

Historically, Paragraph IV litigation around 5α-reductase inhibitor products focused on later, still-unexpired method-of-use patents rather than the expired early compound patent. A Paragraph IV challenge to US 4,377,584 would have had commercial significance before expiration, but it has no present launch-blocking effect.

Which later patents controlled finasteride exclusivity?

Finasteride illustrates the difference between an early compound patent and later indication patents.

Patent or patent family	General subject	Commercial relevance
US 4,377,584	Broad 4-aza steroid compounds, uses and compositions	Early platform patent; expired
US 5,547,957	Treatment of androgenic alopecia with finasteride	Key Propecia method-of-use patent; expired
Later formulation or dosage patents	Product presentation, dosing or formulation limitations	Scope depends on product, filing history and Orange Book status

The Propecia patent estate relied principally on the later androgenic-alopecia method claim rather than on the original 1983 patent. The Proscar estate similarly involved later regulatory and use-related patent issues. Generic finasteride products entered the United States after expiration of the relevant enforceable product patents and regulatory exclusivities.

The supplied claims do not specifically recite androgenic alopecia. They recite acne, seborrhea, female hirsutism, benign prostatic hypertrophy and enzyme inhibition. A later patent expressly directed to male-pattern hair loss could therefore have materially different scope even if it used the same active ingredient.

What formulation patents are covered by US 4,377,584?

The patent has composition claims, but they are not formulation-specific in the modern product-development sense.

Claim 18 can cover a formulation containing a claimed compound and a pharmaceutically acceptable carrier. It does not, on the supplied claim language, require:

A particular tablet composition.
A specified excipient concentration.
A film coat.
A sustained-release matrix.
A defined dissolution profile.
A specific particle-size distribution.
A dosage regimen.
A particular manufacturing step.

The claim therefore creates broad but relatively shallow formulation coverage. A later formulation patent could be infringed even if US 4,377,584 had expired, provided the later patent claimed a distinct and valid formulation feature.

What manufacturing and intellectual-property barriers existed?

The patent's manufacturing relevance arises from its chemical breadth. A competitor would have needed to address:

Steroid-nucleus synthesis.
Regioselective introduction of the ring nitrogen.
Control of 5α stereochemistry.
Functionalization of the 17-position.
Formation and purification of pharmaceutical salts.
Removal of process impurities and steroid isomers.

Those process issues could create practical barriers even after the composition patent expired. They are not equivalent to patent exclusivity. A generic manufacturer could design around later process patents by using a different synthetic sequence, different reagents or different crystallization conditions.

The patent itself does not claim every process used to manufacture every compound in the genus. Process infringement requires practice of the claimed process steps, not merely production of the same final molecule.

How strong is the patent estate?

Historical strength

The historical estate was strong in breadth because claim 1 combined:

A large steroid genus.
Multiple nitrogen-containing core structures.
Extensive side-chain substitution.
Therapeutic-use claims.
Composition claims.
Pharmaceutically acceptable salts.

The compound claims were potentially powerful against direct synthesis or sale of a covered molecule. The method claims created additional exposure where a defendant's labeling or physician-directed use met the claimed disease or enzyme-inhibition limitations.

Current strength

Current enforceable strength is zero for US 4,377,584 because the patent has expired. Its remaining value is historical and analytical:

It may establish prior art against later genus or species claims.
It may affect validity analysis for continuation or improvement patents.
It may remain relevant to freedom-to-operate history.
It can identify the original chemical platform and inventorship chain.

Expiration does not erase the patent as prior art. It removes the right to exclude for the remaining term.

What generic entry risks exist today?

For the compounds covered by US 4,377,584, the patent itself presents no current U.S. generic-entry risk. The relevant risks instead arise from:

Later unexpired patents.
Orange Book-listed method-of-use patents.
Formulation and dosage patents.
Process patents.
Regulatory exclusivity.
Labeling and induced-infringement exposure.
Product-specific litigation settlements.

For an ANDA applicant, a product with a carve-out label may avoid a patented indication if the FDA permits omission of the protected use. If the remaining label still encourages the patented use, the applicant may face induced-infringement allegations.

What patent litigation and settlements affected the field?

The major litigation pattern for 5α-reductase inhibitors involved later patents covering approved indications, particularly finasteride for androgenic alopecia and benign prostatic hyperplasia. Litigation risk depended on:

The exact Orange Book-listed patent.
Whether the ANDA included Paragraph IV certifications.
Whether the generic label carved out the patented indication.
Whether the patent claim covered the active ingredient, treatment method or formulation.
Whether the parties entered a launch-date settlement.

US 4,377,584 itself is not a current litigation threat because its term has ended. Any present dispute involving a related product must be mapped to the later patent numbers and their expiration status, not to the 1983 patent alone.

How does US 4,377,584 compare with later 5α-reductase inhibitor patents?

Issue	US 4,377,584	Later product patents
Primary focus	Chemical genus and early therapeutic applications	Specific drug, indication, dosage or formulation
Claim breadth	Broad structural Markush genus	Usually narrower, product-specific claims
Patent age	Issued 1983	Often issued in the 1990s or later
Current enforceability	Expired	Must be checked patent by patent
Orange Book importance	Historical	Often decisive for ANDA timing
Design-around potential	Structural and synthetic	Label, dosage, formulation or process design-around
Commercial role	Platform discovery patent	Product lifecycle management

The early patent had greater theoretical chemical breadth. Later patents often had greater practical commercial relevance because they aligned with an FDA-approved product and its labeled use.

What geographic coverage did the patent provide?

US 4,377,584 provided rights only in the United States. Foreign equivalents, where filed and granted, required separate analysis by jurisdiction. Patent expiration, term calculation, prosecution history and claim scope could differ in:

Europe.
Canada.
Japan.
Australia.
Latin America.
Other national jurisdictions.

A United States expiration date does not establish freedom to operate globally. Foreign patent families may have expired earlier, later or with different claim sets. Regulatory exclusivity is also jurisdiction-specific.

Key Takeaways

US 4,377,584 is an early platform patent for 4-aza steroid compounds and 5α-reductase inhibition.
Claim 1 is a broad Markush genus covering numerous steroid nuclei, nitrogen substitutions, 17-position groups and pharmaceutical salts.
Claims 4 through 13 identify narrower chemical species.
Claims 14 and 16 cover therapeutic administration, including treatment of hyperandrogenic conditions and testosterone-5α-reductase inhibition.
Claims 18 and 19 cover pharmaceutical compositions containing the claimed compounds.
The patent issued March 22, 1983, and expired under the pre-1995 patent-term regime in approximately 2000-2001.
It presents no current United States exclusivity barrier.
Later finasteride, indication and formulation patents controlled commercial launch timing.
Current generic-entry analysis must focus on later Orange Book listings, process patents, formulation patents and any surviving method-of-use rights.
Foreign freedom-to-operate analysis requires separate review of national family members.

FAQs About US Patent 4,377,584

Did US 4,377,584 cover finasteride?

The patent's broad chemical genus may encompass finasteride-type 4-aza steroid compounds, but the supplied claim text does not identify finasteride by name. Product coverage must be confirmed against the complete structural drawings, specification and claim construction.

Can an expired patent still block FDA approval?

No. An expired patent cannot block approval based on patent rights. It may remain relevant as prior art and may affect the validity of later patents.

Did US 4,377,584 claim oral finasteride tablets?

Claim 18 broadly covers a compound with a pharmaceutically acceptable carrier, but the supplied language does not specifically claim an oral tablet, a particular dose or a defined tablet formulation.

Is a 5α-reductase inhibitor automatically covered by this patent?

No. Infringement requires every limitation of at least one asserted claim. A nonsteroidal inhibitor or a steroid with a different core, stereochemistry or substituent arrangement may fall outside the claims.

Does expiration of US 4,377,584 eliminate all finasteride patent risk?

No. Later patents may cover a specific indication, dosage regimen, formulation, polymorph or manufacturing process. Those rights must be assessed separately from the expired early compound patent.

References

United States Patent and Trademark Office. (1983). 4-Aza-steroids and pharmaceutical compositions and methods of use thereof (U.S. Patent No. 4,377,584).
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (2024). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA.
United States Patent and Trademark Office. (2015). Manual of Patent Examining Procedure: Patent term. USPTO.
U.S. Food and Drug Administration. (1997). Propecia (finasteride) approval letter and prescribing information. FDA.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Argentina	222390	⤷ Start Trial
Argentina	222391	⤷ Start Trial
Argentina	224011	⤷ Start Trial
Argentina	225045	⤷ Start Trial
Argentina	228037	⤷ Start Trial
Argentina	231991	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,377,584

Summary for Patent: 4,377,584