Details for Patent: 4,329,364

Summary for Patent: 4,329,364

Title:	Antiandrogenic agents and methods for the treatment of androgen dependent disease states
Abstract:	This application relates to treatment of prostatic carcinoma with 4'-nitro-3'-trifluoromethylisobutyranilide.
Inventor(s):	Rudolph O. Neri, John G. Topliss
Assignee:	Merck Sharp and Dohme LLC
Application Number:	US05/725,821
Patent Claim Types: see list of patent claims	Use;

United States Drug Patent 4,329,364: Flutamide Claims, Patent Scope, Expiration, and Competitive Landscape

US Patent No. 4,329,364 covers a treatment method using flutamide, the nonsteroidal antiandrogen formerly marketed as Eulexin. The supplied claim is narrow: it requires administration of flutamide to a mammal suffering from prostatic carcinoma in a therapeutically effective quantity. The patent did not create a broad, currently enforceable monopoly over all antiandrogens, all prostate-cancer treatments, or all flutamide formulations.

The patent was granted on Jan. 11, 1983, and, under the pre-Uruguay Round patent-term regime, its 17-year term expired on Jan. 11, 2000. The patent therefore presents no current US patent barrier to generic flutamide or to a competing prostate-cancer product.[1][2]

What drug does US Patent 4,329,364 protect?

The claimed compound is flutamide.

Attribute	Data
Generic name	Flutamide
Chemical name	2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide
Alternative name in patent claim	4'-nitro-3'-trifluoromethylisobutyranilide
CAS number	13311-84-7
Drug class	Nonsteroidal androgen-receptor antagonist
Original US brand	Eulexin
Original sponsor	Schering-Plough
Original indication	Advanced or metastatic prostatic carcinoma
US patent	US 4,329,364
Patent grant date	Jan. 11, 1983
Patent expiration	Jan. 11, 2000

Flutamide blocks androgen-receptor signaling after conversion to its active metabolite, hydroxyflutamide. It was used in prostate cancer, often with a luteinizing hormone-releasing hormone agonist or antagonist. The FDA-approved label warned of hepatotoxicity and required liver-function monitoring.[3]

What does claim 1 of US 4,329,364 cover?

Claim 1 recites:

“A method for the treatment of prostatic carcinoma which comprises administering to a mammal suffering from prostatic carcinoma a therapeutically effective quantity of 4'-nitro-3'-trifluoromethylisobutyranilide.”

The claim contains four material limitations:

1. A method of treatment.
2. Treatment of prostatic carcinoma.
3. Administration to a mammal suffering from that disease.
4. Administration of a therapeutically effective quantity of flutamide.

A direct infringement theory would require proof that each element is met. The claim does not cover a product merely because it contains flutamide. It covers the claimed therapeutic use.

Claim construction and chemical identity

The chemical name identifies flutamide rather than a broad genus of substituted anilides. A product containing another antiandrogen, such as bicalutamide or enzalutamide, would not literally satisfy the active-ingredient limitation.

The claim does not expressly limit:

• Tablet, capsule, suspension, or other dosage form
• Oral or parenteral administration
• Specific dose or dosing schedule
• Combination treatment with an LHRH agonist
• Stage of prostate cancer
• Hormone-sensitive or castration-resistant disease
• Salt, solvate, polymorph, or particle-size form
• Manufacturing process
• Specific formulation excipients

The absence of a dosage-form limitation gives the claim broad coverage across administration formats, but only for the claimed use of flutamide in prostatic carcinoma.

What does US Patent 4,329,364 not cover?

The claim does not expressly cover flutamide as a composition of matter. It therefore differs materially from a compound patent that would prohibit making, using, selling, offering for sale, or importing the active ingredient for any purpose.

The claim also does not cover:

Subject matter	Coverage under supplied claim
Flutamide as a chemical compound	No express composition claim
Manufacturing flutamide	No
Flutamide for breast cancer	No express coverage
Flutamide for hirsutism or androgen-related disorders	No express coverage
Flutamide for benign prostatic hyperplasia	No express coverage
A formulation without a prostate-cancer use	No
A different antiandrogen	No
Prostate-cancer treatment without flutamide	No
Veterinary androgen-blocking treatment	Potentially, if the animal has prostatic carcinoma and the other limitations are met
Combination therapy containing flutamide	Potentially, because the claim does not exclude combination treatment

The word “mammal” includes humans and potentially nonhuman mammals. The disease limitation remains controlling. Use in an animal for a non-prostatic condition would fall outside the literal claim.

When did US Patent 4,329,364 lose exclusivity?

The patent lost enforceable patent exclusivity on Jan. 11, 2000.

Event	Date
Patent grant	Jan. 11, 1983
Applicable term	17 years from grant
Expiration	Jan. 11, 2000
Current status	Expired
Patent-term extension or adjustment	None relevant to the expired patent term

US Patent 4,329,364 predates the effective date of the 20-year patent term measured from the earliest effective nonprovisional filing date. Its term was governed by the prior 17-years-from-grant rule.[1][4]

Because the patent expired before the modern wave of US generic litigation involving flutamide, a present-day Paragraph IV challenge to this patent would have no commercial value. The relevant patent term had already ended.

What was the FDA and Orange Book status of flutamide?

Flutamide was approved by the FDA in 1989 under NDA 018858 for use in combination with an LHRH agonist for metastatic prostate cancer. The reference product was Eulexin capsules.[3][5]

Flutamide subsequently became available through abbreviated new drug applications. Generic approval did not depend on preserving an unexpired patent right under US 4,329,364. Any historical Orange Book listing associated with that patent ceased to block approval once the patent expired.[2]

FDA regulatory position

Flutamide is a small-molecule drug, so biosimilar regulation does not apply. A competing manufacturer uses the ANDA pathway, not the 351(k) biosimilar pathway.

The main regulatory issues are:

• Demonstration of pharmaceutical equivalence
• Bioequivalence
• Compliance with labeling requirements
• Manufacturing controls
• Liver-safety warnings and monitoring information
• Appropriate handling of the product’s discontinued or limited commercial status

The FDA has continued to identify serious hepatic injury as a key safety risk for flutamide. That safety profile limits commercial attractiveness even though the patent barrier has disappeared.[3]

How many patents cover flutamide and prostate-cancer use?

The supplied claim identifies one enforceable historical use claim. The broader flutamide patent landscape included related patent-family filings and regulatory exclusivities, but US Patent 4,329,364 is no longer live.

The patent landscape can be divided into four categories:

Category	Relevance to flutamide	Current US risk
Compound patents	Potentially cover flutamide itself	None from US 4,329,364; historical rights expired
Therapeutic-use patents	Cover prostate-cancer treatment with flutamide	US 4,329,364 expired
Formulation patents	Could cover dosage forms or release systems	No current barrier identified from the supplied claim
Manufacturing patents	Could cover synthesis or purification	Not covered by claim 1

A full freedom-to-operate opinion would require a family-level search of all US continuation, divisional, reissue, and related formulation filings. The supplied claim itself, however, contains no formulation or manufacturing limitation and cannot be used to assert those categories independently.

What formulations are protected by US Patent 4,329,364?

No formulation is specifically protected.

The claim uses the functional phrase “administering” and does not identify:

• A capsule shell
• An excipient
• A dissolution profile
• A particle-size distribution
• A sustained-release matrix
• A particular flutamide concentration
• A specific oral dosage regimen

An oral generic capsule containing flutamide could have satisfied the expired method claim when used to treat prostatic carcinoma during the patent term. That historical exposure did not convert the capsule into a patented formulation.

A new formulation developed today would require separate patent protection based on formulation-specific technical features. The expired claim would not provide current exclusivity.

Did the patent create method-of-use or induced-infringement risk?

Yes, during its term. The claim was a method-of-use claim, so the principal enforcement theory would have involved treatment of prostate-cancer patients with flutamide.

Potentially relevant actors included:

• Physicians administering or directing treatment
• Hospitals and clinics
• Manufacturers promoting flutamide for the claimed indication
• Distributors supplying the product with knowledge of the claimed use
• Label sponsors whose prescribing information encouraged the claimed therapy

The practical strength of an induced-infringement case would have depended on the product label, promotional conduct, physician instructions, and evidence of the intended use. A generic manufacturer selling a drug with substantial noninfringing uses could have faced a different analysis from a manufacturer whose label and marketing specifically promoted prostate-cancer treatment.

These issues are historical because the patent expired in 2000. No current infringement claim can be based on conduct occurring after expiration.

Which companies challenged or competed with flutamide?

Flutamide competed first with other androgen-deprivation strategies and later with newer androgen-receptor pathway inhibitors.

Product	Active ingredient	Company or originator	Competitive position
Eulexin	Flutamide	Schering-Plough	Original flutamide brand
Casodex	Bicalutamide	AstraZeneca	More widely adopted nonsteroidal antiandrogen
Xtandi	Enzalutamide	Medivation, later Astellas and Pfizer	Later-generation androgen-receptor inhibitor
Erleada	Apalutamide	Janssen	Earlier-stage and nonmetastatic castration-resistant settings
Nubeqa	Darolutamide	Bayer and Orion	Nonmetastatic castration-resistant and metastatic hormone-sensitive settings
Zytiga	Abiraterone acetate	Janssen	Androgen biosynthesis inhibition rather than direct receptor antagonism

Bicalutamide reduced flutamide’s commercial importance because it offered convenient once-daily dosing and became a widely used antiandrogen. Enzalutamide, apalutamide, darolutamide, abiraterone, and modern androgen-deprivation combinations further displaced flutamide in many treatment settings.

What generic entry risks exist for flutamide?

The patent risk is low because US 4,329,364 expired more than two decades ago. The principal barriers are regulatory, clinical, and commercial rather than patent-based.

Generic launch scenarios

A generic manufacturer could pursue:

1. An ANDA referencing the approved flutamide product.
2. A conventional immediate-release capsule or equivalent oral dosage form.
3. Labeling that preserves required hepatic-safety warnings.
4. Commercial distribution to limited clinical segments where flutamide remains medically appropriate.

A Paragraph IV certification against US 4,329,364 would no longer be necessary as a strategy to accelerate entry because the patent is expired. Any present application would focus on bioequivalence, manufacturing compliance, labeling, and market viability.

Commercial exposure

The original branded product’s historical revenue depended on prostate-cancer use and combination androgen-deprivation therapy. Current revenue exposure from the expired patent is zero in patent terms. No branded manufacturer can claim a continuing US patent premium based on this patent.

Generic commercial opportunity is constrained by:

• Declining use relative to newer agents
• Hepatotoxicity
• Availability of competing antiandrogens
• Limited guideline preference
• Physician willingness to monitor liver function
• Potential discontinuation or restricted marketing of some presentations

How strong is the patent estate for flutamide?

The historical patent position was meaningful during the term but narrow in claim type. Its strengths were:

• Specific identification of flutamide
• Direct linkage to prostate-cancer treatment
• No limitation to a particular dose or dosage form
• Coverage potentially extending to human and veterinary mammalian use

Its weaknesses were:

• No composition-of-matter claim in the supplied claim
• No formulation claim
• No manufacturing claim
• No express dosing regimen
• No protection for other antiandrogens
• Complete expiration in 2000

From a current diligence perspective, the estate has no blocking strength in the United States. A company evaluating flutamide today should treat the patent as historical prior art and freedom-to-operate context, not as an active exclusion right.

What patent litigation and settlements affect US Patent 4,329,364?

No current US litigation or settlement can preserve the expired patent’s exclusionary effect. Any historical Paragraph IV litigation associated with generic flutamide would have ended no later than patent expiration, absent unusual issues involving damages for pre-expiration conduct.

The patent’s expiration also prevents a settlement from extending exclusivity beyond the statutory patent term. A private agreement could allocate commercial conduct between parties, but it could not recreate the expired patent right against unrelated manufacturers.

How does flutamide’s patent position compare with newer prostate-cancer drugs?

Drug	Patent position today	Regulatory pathway	Commercial risk profile
Flutamide	Core US patent expired	ANDA generics	Low patent risk; high clinical and commercial substitution risk
Bicalutamide	Mature patent estate; primary rights expired or largely expired	ANDA generics	Low patent risk
Enzalutamide	Historically strong composition and method-of-use estate; later patents may remain relevant by jurisdiction and product	NDA and authorized generics	Higher patent complexity
Apalutamide	Active or recently active product-specific estate may include composition, formulation, and use claims	NDA	Higher patent complexity
Darolutamide	Product-specific composition and use rights may remain relevant	NDA	Higher patent complexity
Abiraterone acetate	Core rights expired, but formulation and use history is complex	ANDA and 505(b)(2) activity	Medium historical litigation complexity

Flutamide is therefore a low-risk generic molecule from a US patent perspective. Its weaker position is clinical demand, not intellectual-property exclusion.

Key Takeaways

• US Patent 4,329,364 covers a method of treating prostatic carcinoma with flutamide.
• The claimed compound is 4'-nitro-3'-trifluoromethylisobutyranilide, also known as flutamide.
• Claim 1 is a method claim, not an express compound, formulation, or manufacturing claim.
• The claim potentially covered human and veterinary mammalian treatment if the disease and therapeutic-dose limitations were satisfied.
• The patent was granted Jan. 11, 1983, and expired Jan. 11, 2000.
• No current US patent exclusivity or Paragraph IV barrier arises from US 4,329,364.
• Flutamide is regulated as a small molecule through the ANDA pathway; biosimilar rules do not apply.
• Current commercial constraints are flutamide’s hepatotoxicity and displacement by bicalutamide, enzalutamide, apalutamide, darolutamide, and abiraterone.
• The patent has historical importance but no present US blocking value.

FAQs

Is flutamide still protected by a US patent?

No. US Patent 4,329,364 expired Jan. 11, 2000. It does not block current US manufacture, sale, or use of flutamide.

Does US Patent 4,329,364 cover bicalutamide?

No. The claim identifies flutamide by its specific chemical name. Bicalutamide is a different active ingredient.

Can a generic company sell flutamide for prostate cancer?

Yes, subject to FDA approval, applicable labeling, manufacturing controls, and safety requirements. The expired patent does not prevent generic entry.

Does flutamide have biosimilar competition?

No. Flutamide is a chemically synthesized small molecule. Competitors use generic-drug pathways rather than the FDA biosimilar pathway.

Could a new flutamide formulation receive patent protection?

Potentially. A new formulation would need claims directed to a patentable technical feature, such as a defined release profile, composition, stability improvement, or manufacturing process. US Patent 4,329,364 does not provide that protection.

References

1. United States Patent and Trademark Office. (1983). US Patent No. 4,329,364, method for the treatment of prostatic carcinoma.
2. U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book.
3. U.S. Food and Drug Administration. (n.d.). Eulexin (flutamide) prescribing information.
4. 35 U.S.C. §§ 154, 156, 271, 282.
5. U.S. Food and Drug Administration. (1989). Drugs@FDA: Eulexin NDA 018858.

Drugs Protected by US Patent 4,329,364

Applicant	Tradename	Generic Name	Dosage	NDA	Approval Date	TE	Type	RLD	RS	Patent No.	Patent Expiration	Product	Substance	Delist Req.	Patented / Exclusive Use	Submissiondate