U.S. Patent 5,998,427: Claim Scope, Dutasteride Coverage, Expiration, and Patent Landscape

U.S. Patent 5,998,427 covers a broad genus of 4-aza steroid compounds that inhibit 5-alpha-reductase, including dutasteride and related analogues. Its strongest protection was the compound coverage in claims 1 and 19. Claims 11 through 17 extended protection to pharmaceutical formulations, manufacturing processes, enzyme inhibition, and treatment of androgen-mediated diseases. The patent was filed on June 17, 1996, issued on December 7, 1999, and expired on June 17, 2016, based on the 20-year U.S. patent term.[1]

The patent no longer creates an active U.S. exclusionary right. Its historical importance remains high because it covered the active pharmaceutical ingredient used in Avodart and related dutasteride products.

What drug does U.S. Patent 5,998,427 protect?

The patent protects 4-aza-5-alpha-androstane and 4-aza-5-alpha-androstene derivatives containing a substituted phenylcarbamoyl group at the 17-beta position.

The most commercially important compound is dutasteride:

17-beta-N-(2,5-bis-trifluoromethylphenylcarbamoyl)-4-aza-5-alpha-androst-1-en-3-one.

Dutasteride inhibits both type 1 and type 2 5-alpha-reductase. The enzyme converts testosterone to dihydrotestosterone, or DHT. The corresponding commercial product is Avodart, approved by the FDA for the treatment of symptomatic benign prostatic hyperplasia, or BPH.[2]

Core structural elements

The independent compound claim requires:

Structural element	Claim requirement
Steroid nucleus	4-aza steroid framework
C1-C2 bond	Single or double bond
R1	Hydrogen or methyl
R2	Hydrogen or methyl
R3	Substituted phenylcarbamoyl group
R6	Trifluoromethyl, substituted phenyl, or branched C4-C7 alkyl
R7/R8	One defined substituent and one hydrogen or halogen
X	Hydrogen or halogen
Pharmaceutical form	Compound or pharmaceutically acceptable solvate

The claim language reaches substantially more compounds than dutasteride alone. It covers alternative aryl substituents, tert-butyl analogues, methyl-substituted steroid analogues, saturated and unsaturated compounds, and halogen-substituted variants.

How broad is claim 1 of U.S. Patent 5,998,427?

Claim 1 is a genus claim. It covers a large Markush class defined by multiple independently variable substituents.

Its breadth comes from four features:

The C1-C2 bond can be saturated or unsaturated.
R1 and R2 can independently be hydrogen or methyl.
R6, R7, and R8 can include trifluoromethyl, halogen, substituted phenyl, and branched alkyl groups.
The patent expressly covers pharmaceutically acceptable solvates.

The claim is not limited to dutasteride, a particular dose, a particular indication, a specific formulation, or a specific manufacturing route.

A compound would fall within claim 1 if its structure satisfies the steroid framework and all listed substituent limitations. A generic compound with the same active ingredient as dutasteride would be within the claim regardless of capsule color, excipient system, strength, or manufacturer.

What do claims 2 through 10 add?

Claims 2 through 10 narrow the genus by selecting particular substituent combinations.

Claims	Principal limitation
2	X is hydrogen
3	R2 is hydrogen
4	Narrows the permitted R6, R7, and R8 groups
5	C1-C2 is a double bond
6	Limits the structure to formula IB
7	Limits certain branched alkyl combinations
8	Further narrows R6 and R7/R8 substituents
9	Selects trifluoromethyl, hydrogen, and X-hydrogen combinations
10	R6 and R8 are independently trifluoromethyl or tert-butyl; R7 and X are hydrogen

Claim 10 is particularly relevant to dutasteride because the commercial compound has the 2,5-bis-trifluoromethyl phenyl substitution pattern and an unsaturated 4-aza steroid nucleus.

Claim 19 identifies ten specific compounds, including:

The 2,5-bis-trifluoromethyl compound corresponding to dutasteride.
The 2-tert-butyl-5-trifluoromethyl analogues.
The 2,5-di-tert-butyl analogues.
Saturated and unsaturated steroid variants.
4-methyl-4-aza variants.
7-beta-methyl variants.

Claim 19 functions as an express species list within the broader genus of claim 1. It reduces the need to determine whether a particular named compound falls within the abstract Markush definitions.

Does U.S. Patent 5,998,427 cover dutasteride specifically?

Yes. Dutasteride is expressly identified in claim 19 and is also encompassed by the broader structural definitions in claims 1, 6, 8, 9, and 10.

The relevant dutasteride features are:

Dutasteride feature	Corresponding claim limitation
4-aza steroid nucleus	Formula I and formula IB
Androst-1-en-3-one structure	C1-C2 double bond
17-beta phenylcarbamoyl group	R3 definition
2,5-bis-trifluoromethyl phenyl group	R6/R7/R8 substituent pattern
No 4-methyl group	R1/R2 selection corresponding to the named species
No 7-beta methyl group	Base steroid structure

The patent therefore provided direct compound protection for dutasteride, not merely indirect protection through a method of treatment.

What formulation protection does the patent provide?

Claim 11 covers a pharmaceutical formulation containing:

An effective amount of a compound within claim 1; and
A pharmaceutically acceptable carrier.

The formulation claim is broad. It does not require a particular capsule shell, excipient, dissolution profile, particle size, dosage strength, or release mechanism.

A conventional oral capsule containing dutasteride and standard pharmaceutical excipients would generally be the type of product addressed by claim 11, subject to the claim’s legal construction and the patent’s expired status.

The claim does not create a separate, active formulation monopoly today. Its practical value was greatest before expiration, when it could be asserted against products containing a covered compound even if the manufacturer used a different excipient formulation.

Does claim 11 cover Avodart?

Historically, yes. Avodart is an oral dutasteride capsule. A dutasteride capsule with a pharmaceutically acceptable carrier fits the basic architecture of claim 11.

The claim is not limited to the precise Avodart formulation. It reaches other dosage forms and excipient combinations if they contain an effective amount of a claim 1 compound.

What manufacturing methods are protected?

Claims 12 through 14 cover processes for preparing the claimed compounds.

Hydrogenation route

Claim 12(A) covers hydrogenation of formula IVa compounds to produce compounds in which carbons 1 and 2 are joined by a single bond.

This route is relevant to saturated 4-aza steroid analogues, including androstan-3-one compounds.

Condensation route

Claim 12(B) covers reaction of formula V with an amine of formula IIa:

H2N-R3

The process creates the 17-beta carbamoyl substituent. The claim also covers downstream operations such as:

Interconversion between compounds of formula I.
Removal of protecting groups.
Conversion to pharmaceutically acceptable solvates.

Claim 13 narrows the process by requiring treatment of formula V with a halogenating agent in the presence of a base before reaction with the amine.

Claim 14 covers dehydrogenation of a saturated precursor to produce an unsaturated compound with a C1-C2 double bond.

How strong are the process claims?

The process claims were narrower than the compound claims because they require particular starting materials and reaction sequences. A manufacturer using a materially different synthetic route could potentially avoid literal infringement of the process claims while still producing a compound covered by claim 1.

For commercial enforcement, the compound claims were more important than the process claims. Process claims could still have created discovery and evidentiary issues where the manufacturing route was confidential.

What method-of-use patents does U.S. Patent 5,998,427 contain?

Claims 15 through 17 cover pharmacological and therapeutic use.

Claim	Scope
15	Contacting 5-alpha-testosterone reductase with an effective inhibitory amount
16	Treating an androgen-responsive or androgen-mediated disease in a mammal
17	BPH, prostate cancer, acne, male pattern baldness, and hirsutism

The method claims are broader than the FDA-approved BPH indication because claim 17 lists several androgen-mediated conditions. The patent is not limited to human treatment, and claim 16 refers generally to a mammal.

The method claims also cover both enzyme inhibition and therapeutic administration. A product label directed to BPH would have been commercially relevant to the claims, while off-label use and induced-infringement questions would have depended on product labeling, marketing conduct, and evidence of intent.

What intermediate compounds are protected?

Claim 18 separately protects formula IVa intermediates.

These intermediates have:

R1 and R2 independently selected from hydrogen or methyl; and
R3 within the same substituted phenylcarbamoyl definition used in claim 1.

Claim 18 is important because it protects a precursor class rather than only the final 5-alpha-reductase inhibitor. It could have applied to intermediates used to manufacture saturated compounds through hydrogenation.

The intermediate claim is narrower in commercial relevance than the final compound claim but could have increased manufacturing and supply-chain exposure for a competing producer.

When did U.S. Patent 5,998,427 expire?

Event	Date
U.S. filing	June 17, 1996
Patent issuance	December 7, 1999
Patent number	US 5,998,427
U.S. patent term end	June 17, 2016
Current status	Expired

The patent’s expiration date follows the 20-year term measured from the U.S. nonprovisional filing date, subject to any applicable patent-term adjustment or disclaimer. Public patent records identify the patent as expired.[1]

Because the patent expired in 2016:

A new dutasteride product does not require a license from the patent owner based solely on this patent.
Paragraph IV certification against this patent is no longer an effective current challenge.
A generic manufacturer cannot be blocked today by an infringement action based on an expired claim.
Historical litigation and settlement analysis remains relevant to the timing of generic entry.

What was the Orange Book status of U.S. Patent 5,998,427?

U.S. Patent 5,998,427 was historically associated with the Avodart regulatory patent estate. The FDA Orange Book records patents and exclusivity information submitted for approved drug products. Orange Book listings do not extend patent duration; they identify patents that may affect an ANDA applicant’s certification obligations.[3]

For a live patent, an ANDA applicant could have been required to submit a Paragraph III certification, a Paragraph IV certification, or a statement that the patent was not applicable, depending on the listing and product application.

After expiration, the patent no longer creates a current Orange Book barrier to approval or launch. Regulatory exclusivity and patent term must be analyzed separately. FDA approval does not revive an expired patent, and patent expiration does not itself guarantee immediate approval of a generic product.

Were there Paragraph IV challenges to dutasteride patents?

Dutasteride generic applicants faced the historical patent estate associated with Avodart, including compound and related patent protection. Paragraph IV certifications were commercially relevant before the principal patents expired.

A Paragraph IV certification asserts that a listed patent is invalid, unenforceable, or will not be infringed. Filing notice can trigger patent litigation under the Hatch-Waxman framework and may create a 30-month stay of FDA approval under specified conditions.[4]

The commercially important result was eventual generic entry after the core patent barriers expired or were otherwise resolved. The expired status of U.S. Patent 5,998,427 means that any historical Paragraph IV dispute involving this patent no longer presents a current U.S. launch barrier.

Which companies challenged the dutasteride patent estate?

Publicly documented generic competition involved companies pursuing ANDA approval for dutasteride capsules after the Avodart patent estate approached expiration. Generic dutasteride products were subsequently approved and marketed by multiple manufacturers.

The relevant competitive group included:

GlaxoSmithKline, as Avodart sponsor and historical patent-holder affiliate.
Actavis and other generic applicants pursuing dutasteride capsules.
Additional generic manufacturers entering after patent expiry.

A company-by-company litigation conclusion requires docket-level review for each defendant, patent, jurisdiction, and settlement instrument. The available claim and patent data establish the expiry of U.S. Patent 5,998,427, but do not by themselves establish the terms of every historical settlement.

How does the dutasteride patent estate compare with finasteride?

Issue	Dutasteride	Finasteride
Primary commercial product	Avodart	Proscar and Propecia
Enzyme profile	Type 1 and type 2 5-alpha-reductase	Primarily type 2 5-alpha-reductase
Key use	BPH	BPH and male pattern hair loss, depending on product
Core patent discussed	US 5,998,427	Multiple earlier finasteride patents
Compound scope	Broad substituted 4-aza steroid genus	Distinct 4-aza steroid compound class
U.S. patent status	Expired June 17, 2016	Core patents also expired
Current generic risk	No patent barrier from US 5,998,427	No barrier from expired core patents

Dutasteride had a broader pharmacological target profile, while finasteride had an earlier market position and separate product-specific regulatory history. The patents should not be treated as interchangeable because their chemical structures and claim architectures differ.

What generic launch risks existed before expiration?

Before June 17, 2016, a generic dutasteride applicant faced several risks:

Compound infringement risk. A product containing dutasteride could fall directly within claims 1 and 19.
Formulation risk. A conventional dutasteride capsule could implicate claim 11.
Method-of-use risk. Labeling for BPH or other androgen-mediated conditions could implicate claims 16 and 17.
Process risk. Use of the patented synthetic sequence could implicate claims 12 through 14.
Intermediate risk. Use or supply of formula IVa intermediates could implicate claim 18.
Regulatory delay. A listed patent could affect ANDA certification and approval timing.
Settlement risk. A Paragraph IV case could result in a launch date controlled by settlement terms rather than patent expiry.

After expiration, the main barriers shifted from patent exclusivity to FDA approval, manufacturing capacity, bioequivalence, product quality, supply, and commercial pricing.

How strong was the patent estate?

The patent estate was strongest in the following order:

Express species coverage for dutasteride in claim 19.
Broad compound genus coverage in claim 1.
Narrower species and subgenus claims in claims 6 through 10.
Pharmaceutical formulation coverage in claim 11.
Method-of-treatment claims in claims 15 through 17.
Manufacturing and intermediate claims in claims 12 through 14 and 18.

The compound claims provided the most direct enforcement route. The formulation, use, process, and intermediate claims added layers of protection but were more dependent on product composition, labeling, manufacturing evidence, or clinical use.

The estate had geographic value only in jurisdictions where corresponding national patents issued. U.S. Patent 5,998,427 had no continuing U.S. force after June 17, 2016. Foreign family members required separate term and validity analysis.

Key Takeaways

U.S. Patent 5,998,427 covers dutasteride and a broad family of substituted 4-aza steroid 5-alpha-reductase inhibitors.
Claim 1 is the principal genus claim; claim 19 expressly identifies dutasteride and related species.
Claim 11 covers pharmaceutical formulations containing a claim 1 compound.
Claims 12 through 14 cover selected synthesis routes and interconversion steps.
Claims 15 through 17 cover enzyme inhibition and treatment of BPH, prostate cancer, acne, male pattern baldness, and hirsutism.
Claim 18 covers formula IVa intermediates.
The patent expired on June 17, 2016.
It no longer blocks U.S. generic dutasteride entry.
Historical Paragraph IV and Orange Book issues were relevant before expiration but do not restore exclusivity today.
The commercial patent risk has shifted from this patent to FDA approval, manufacturing, formulation, supply, and any separate unexpired patents.

FAQs

Is dutasteride explicitly named in U.S. Patent 5,998,427?

Yes. Claim 19 expressly lists the 17-beta-N-(2,5-bis-trifluoromethyl)phenylcarbamoyl 4-aza-androst-1-en-3-one compound corresponding to dutasteride.

Can a company now manufacture generic dutasteride in the United States?

U.S. Patent 5,998,427 no longer prevents manufacture or sale because it expired in 2016. The manufacturer still needs FDA approval and must satisfy applicable drug-quality, labeling, manufacturing, and bioequivalence requirements.

Does the patent cover dutasteride salts or solvates?

The claims expressly include pharmaceutically acceptable solvates. The exact scope for a salt or other solid form depends on whether it satisfies the claimed compound structure and the applicable claim construction.

Did the patent protect the Avodart brand name?

No. The patent protected chemical compounds, formulations, methods, processes, and intermediates. The Avodart name was protected through trademark and regulatory mechanisms, not through this patent.

Is a new dutasteride formulation automatically free of patent risk?

No. U.S. Patent 5,998,427 has expired, but separate patents covering a particular formulation, delivery system, polymorph, combination, manufacturing process, or method of use must be assessed independently.

References

United States Patent and Trademark Office. (1999). U.S. Patent No. 5,998,427, 4-aza-5-alpha-androst-1-ene-3-one derivatives as 5-alpha-reductase inhibitors. https://patents.google.com/patent/US5998427
U.S. Food and Drug Administration. (2001). Avodart (dutasteride) prescribing information. https://www.accessdata.fda.gov
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book
United States Code. (2024). 21 U.S.C. § 355(j): Abbreviated applications for new drugs. https://uscode.house.gov/

Details for Patent: 5,998,427

Summary for Patent: 5,998,427