United States Patent 4,282,251: Scope, Claims, Expiration, and Naftifine Patent Landscape

U.S. Patent No. 4,282,251 covers a broad class of substituted N-(1-naphthylmethyl)amines with antifungal activity, including trans-N-methyl-N-(1-naphthylmethyl)-3-phenyl-2-propen-1-amine, commonly known as naftifine. The patent issued August 4, 1981, and its original 17-year term would have expired August 4, 1998, assuming no earlier terminal disclaimer or unusual adjustment. The patent is therefore expired and cannot currently block generic manufacture, sale, or use in the United States.

The patent remains important as the foundational compound patent for naftifine, but its present commercial significance is historical and freedom-to-operate related rather than exclusionary.

What drug and chemical class does U.S. Patent 4,282,251 cover?

The patent covers substituted allylic tertiary amines containing:

A 1-naphthylmethyl group attached to nitrogen.
A second nitrogen substituent, including hydrogen or alkyl.
An alkenyl or related side chain.
Optional substitution on the aromatic ring.
Cis or trans stereochemistry for specifically claimed compounds.
Chemotherapeutically acceptable acid-addition salts.

The principal commercial compound is naftifine, generally administered as naftifine hydrochloride in topical antifungal products. Naftifine belongs to the allylamine class of antifungal agents, although its precise side-chain structure differs from terbinafine.

What is the structure of the core claimed compound?

Claim 1 defines a Markush genus. In functional terms, the claimed compounds contain a substituted tertiary or secondary amine connecting a 1-naphthylmethyl moiety to a substituted unsaturated side chain.

The variables have the following effect:

Variable	Permitted substituents	Claim significance
R1	Hydrogen or alkyl	Controls substitution at the nitrogen-containing portion
R2	Alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkylalkyl	Defines the principal nitrogen-side-chain substituent
R3	Hydrogen or lower alkyl	Adds substitution to the unsaturated side chain
R4-R7	Hydrogen, halogen, trifluoromethyl, hydroxy, nitro, lower alkyl or lower alkoxy	Defines optional aromatic-ring substitution
Salt form	Chemotherapeutically acceptable acid-addition salts	Includes hydrochloride and other pharmaceutically acceptable salts

The claim language is broad because it covers multiple substituent classes rather than only naftifine. Claims 4 through 27 progressively narrow that genus.

What does claim 1 of U.S. Patent 4,282,251 protect?

Claim 1 is the principal composition-of-matter claim. It covers compounds falling within the defined formula and their acceptable acid-addition salts.

Its scope has four major dimensions:

Nitrogen substitution.
Side-chain variation.
Aromatic-ring substitution.
Salt form.

The claim is not limited to naftifine. It potentially reaches numerous chemical analogs, including compounds with alkyl, alkenyl, alkynyl, cycloalkyl, or cycloalkylalkyl substituents.

How broad is the Markush genus?

The genus is materially broader than the commercial compound because:

R2 is not limited to methyl.
R1 may be hydrogen or alkyl.
R3 may be hydrogen or lower alkyl.
The aromatic ring may carry multiple classes of substituents.
Claim 1 does not expressly limit the compound to a single alkene geometry.
Acceptable acid-addition salts are included.

The practical scope would depend on construction of the chemical formula, definitions in the specification, and whether particular compounds were enabled and supported across the full genus. A broad chemical claim is not automatically enforceable against every theoretical member if written-description, enablement, anticipation, obviousness, or indefiniteness issues apply.

Which claims specifically cover naftifine?

Claim 6 is the clearest direct claim to naftifine:

Trans-N-(cinnamyl)-N-methyl-(1-naphthylmethyl)amine.

Naftifine is generally identified chemically as trans-N-methyl-N-(1-naphthylmethyl)-3-phenyl-2-propen-1-amine. The patent claims the free-base compound in claim 6, while claim 1 separately covers acceptable acid-addition salts.

Claims 28 and 29 provide narrow commercial-use fallbacks:

Claim 28 covers a pharmaceutical composition containing trans-N-cinnamyl-N-methyl-(1-naphthylmethyl)amine.
Claim 29 covers treatment of mycotic disorders using that compound.

The commercially used hydrochloride salt is best analyzed through claim 1's acid-addition-salt language and the specific compound limitations in claim 6, together with the specification's salt examples.

Which claims cover close naftifine analogs?

Claim	Covered subject matter
7	Trans fluorophenyl cinnamyl analog
8	Cis 4-chlorophenyl analog
9	Trans p-tolyl analog
10	Trans 4-chloro analog
11	Trans dichloro analog
12	Trans 4-methoxy analog
13	Trans hydroxy-substituted analog
14	Trans isopropyl nitrogen substituent
15	Trans methyl-substituted analog
16	N-methyl-substituted analog with methyl at R1
17	Trans 2-fluoro analog
18	Trans 2-chloro analog
19	Trans 4-hydroxy analog
20	Trans ethyl analog
21	Trans 4-chloro positional analog
22	Trans 4-methyl analog
23	Trans 2-methoxy analog
24	Trans 4-methoxy analog
25	Cis unsubstituted phenyl analog
26	Cis 4-fluoro analog
27	Trans allyl analog

Some listed compounds appear duplicative or structurally overlapping at the level of the supplied text. Exact scope requires comparison with the patent's chemical drawing and nomenclature because the variable positions in the OCR-style claim text may not map cleanly to conventional ring numbering.

What do claims 2 and 3 protect?

Claim 2 is a pharmaceutical-composition claim. It covers a chemotherapeutically effective amount of a claim 1 compound combined with an acceptable carrier or diluent.

Claim 3 is a method-of-treatment claim covering administration of a claim 1 compound to an animal with a mycotic disorder.

These claims are narrower in litigation than the compound claim because infringement requires proof of additional elements:

For claim 2, a qualifying composition and claim 1 compound.
For claim 3, administration for treatment of a mycotic disorder.
For claim 29, the specifically identified trans-cinnamyl compound.

Claim 3 would not necessarily reach every use of naftifine. Its language is directed to treatment of mycotic disorders, which generally includes fungal infections but may require analysis of the accused indication and conduct.

When did U.S. Patent 4,282,251 expire?

U.S. Patent 4,282,251 issued on August 4, 1981. For a U.S. patent filed before June 8, 1995, the governing term was generally 17 years from issuance. On that basis, the patent expired on August 4, 1998.

Event	Date
U.S. patent issuance	August 4, 1981
Calculated 17-year expiration	August 4, 1998
Current enforceability	Expired
Current generic-blocking effect	None

The patent predates the Uruguay Round Agreement Act transition to a 20-year term from the earliest effective nonprovisional filing date. Patent-term adjustment did not generally apply to patents of this vintage in the modern form used for post-1995 applications.

Does the patent have current Orange Book value?

No current exclusionary value should be attributed to U.S. Patent 4,282,251 because the patent expired in 1998. Even if historical Orange Book listings existed for an approved naftifine product, an expired patent cannot support a current patent-based bar to ANDA approval or commercial launch.

The relevant regulatory question for a modern applicant is whether any later, unexpired patents cover:

A particular naftifine concentration.
A cream, gel, or other topical formulation.
A manufacturing process.
A crystalline or salt form.
A specific dosing regimen or indication.
A device or delivery system.

The 1981 compound patent itself does not provide those current barriers.

What is the FDA and Orange Book status of naftifine?

Naftifine hydrochloride is an FDA-approved topical antifungal active ingredient used for dermatophyte and related superficial fungal infections. Commercial products have included cream and gel dosage forms, including products marketed under the Naftin name and later generic versions.

Naftifine is a small-molecule drug, not a biologic. Biosimilar provisions therefore do not apply. Generic competition proceeds through the ANDA pathway rather than the abbreviated pathway used for biosimilars.

Regulatory issue	Assessment
Active ingredient	Naftifine hydrochloride
Drug class	Topical allylamine antifungal
Dosage forms	Cream and gel products have been marketed
FDA pathway for generics	ANDA
Biosimilar pathway	Not applicable
Compound patent	Expired
Current patent barrier from U.S. 4,282,251	None
Likely regulatory focus	Product sameness, topical formulation, bioequivalence, labeling

FDA approval of a generic topical product does not require infringement of the expired patent to be resolved through a current Paragraph IV dispute. Any Paragraph IV certification directed solely to U.S. Patent 4,282,251 would be legally immaterial because the patent is no longer enforceable.

Were there Paragraph IV challenges to U.S. Patent 4,282,251?

A current Paragraph IV challenge to this patent is not commercially relevant because the patent expired more than two decades ago.

Paragraph IV certifications are used when an ANDA applicant asserts that a listed patent is invalid, unenforceable, or will not be infringed. A patent that has already expired cannot delay approval through the Hatch-Waxman 30-month stay mechanism. The ordinary generic-entry analysis for naftifine therefore shifts from the 1981 composition patent to any later-listed patents associated with a specific reference product.

No litigation conclusion should be drawn from the existence of generic naftifine products alone. Generic availability confirms that the original compound patent is no longer a practical barrier, but it does not resolve the status of later formulation or product-specific patents.

What formulation patents protect naftifine products?

The supplied patent claims do not contain detailed formulation limitations. Claim 2 requires only a compound and a pharmaceutically acceptable diluent or carrier. It does not specify:

Cream viscosity.
Emulsion phase structure.
Preservative system.
Particle size.
Gel polymer.
Solvent ratio.
Skin penetration enhancer.
Packaging configuration.
Concentration range.

As a result, claim 2 is a basic composition claim rather than a modern product-by-process or formulation-optimization claim. It would not be expected to provide meaningful protection for a later-developed cream or gel architecture once the compound patent expired.

Potential later patent categories include:

Later patent category	Potential commercial relevance
Topical cream formulation	Could restrict a particular excipient or emulsion system
Gel formulation	Could cover polymer, solvent, or delivery characteristics
Enhanced penetration	Could protect a skin-delivery method or excipient combination
Salt or solid-state form	Could matter for manufacturing and stability
Packaging	Could protect a metered applicator or container
Method of treatment	Could cover a particular dosing frequency or patient population

The original patent does not, on the supplied claims, establish protection for these later categories.

How strong is the patent estate for naftifine?

The original naftifine estate was strong at launch because claim 1 covered a broad chemical genus and claim 6 directly claimed the principal compound. Its present strength is zero as an exclusionary asset because the patent expired.

Estate component	Historical strength	Current position
Broad compound genus	High, subject to validity limits	Expired
Naftifine compound claim	High for the named compound	Expired
Acid-addition salts	Material historical coverage	Expired
Pharmaceutical composition	Moderate; carrier language is broad but generic	Expired
Mycotic-treatment method	Moderate, subject to use and proof issues	Expired
Formulation specificity	Low in this patent	No current barrier
Manufacturing protection	Not established by supplied claims	Requires separate patent review
Biosimilar protection	Not applicable	Not applicable

The main weakness of the patent from a modern portfolio perspective is the absence of a live term. The main historical strength was the combination of a broad genus claim and a direct claim to naftifine.

Which companies are challenging naftifine exclusivity?

The competitive field consists primarily of generic manufacturers and topical antifungal marketers. Because U.S. Patent 4,282,251 expired in 1998, current competition is not a challenge to that patent. It is competition against branded and authorized generic products through FDA-approved topical formulations.

Relevant competitor classes include:

Generic naftifine hydrochloride manufacturers.
Brand or branded-generic topical antifungal suppliers.
Manufacturers of terbinafine, butenafine, and other topical antifungals.
Contract manufacturers supplying cream and gel products.

Public information associated with this patent does not establish a current patent litigation campaign, settlement agreement, or license that preserves exclusivity under U.S. Patent 4,282,251. Any commercial agreement involving naftifine would need to be tied to a later patent, trademark, supply arrangement, or formulation right.

How does naftifine compare with terbinafine patent protection?

Naftifine and terbinafine are both allylamine-class antifungals, but their patent estates are distinct.

Issue	Naftifine	Terbinafine
Core structure	Naphthylmethyl-substituted allylic amine	Tert-butyl-substituted naphthalenic allylamine
Foundational patent	U.S. 4,282,251	Separate terbinafine patent family
Original compound patent status	Expired	Original U.S. patents also expired
Current competition	Generic topical products	Generic topical and oral products
Biosimilar relevance	None	None
Main residual IP risk	Later topical formulation or product patents	Later formulation, dosage, or product patents

The expiration of the original compound patent does not create freedom to copy a competitor's later formulation, label, trade dress, or manufacturing process.

What generic-entry risks exist for naftifine?

Generic entry risk is high because the core patent expired long ago and the active ingredient is a conventional small molecule. The remaining risks are product-specific rather than molecule-wide.

Generic launch scenarios

Scenario	Risk level	Reason
Generic naftifine hydrochloride using a non-protected formulation	High launch feasibility	No barrier from U.S. 4,282,251
Copy of a branded cream formulation	Moderate	Potential formulation or trade-secret issues
Copy of a branded gel formulation	Moderate	Potential excipient, process, or product patents
New concentration or indication	Variable	May implicate later method or regulatory exclusivity
Manufacturing by an established API supplier	High feasibility	Original compound patent is expired
Biosimilar-style launch	Not applicable	Naftifine is not a biologic

Revenue exposure for the original patent holder is therefore limited to any continuing commercial rights outside the expired patent, such as trademarks, supply agreements, formulation licenses, or later patent rights.

What geographic coverage did the patent provide?

U.S. Patent 4,282,251 provided rights only in the United States. Patent protection in Europe, Japan, Canada, or other jurisdictions would have required separate national or regional patents derived from related priority filings.

The U.S. expiration date does not determine foreign expiration dates. Foreign family members could have expired earlier or later depending on:

Priority date.
National filing date.
Local patent-term rules.
Patent-term extensions.
Validation requirements.
Maintenance-fee status.
Opposition or limitation proceedings.

For U.S. freedom-to-operate analysis, the relevant conclusion is direct: the U.S. patent is expired and does not block current activity.

What manufacturing and intellectual-property barriers remain?

U.S. Patent 4,282,251 does not appear, from the supplied claims, to create a live manufacturing barrier. A manufacturer may still need to address:

API quality and impurity specifications.
Stereochemical control of the trans isomer.
Salt formation and conversion.
Residual solvents.
Topical formulation reproducibility.
Container-closure compatibility.
FDA current good manufacturing practice requirements.
Potential later process patents.
Trade secrets relating to scale-up or crystallization.

The trans configuration may have commercial and pharmacological importance, but a process that produces trans-naftifine is not blocked by an expired compound patent. Process risk must be assessed against later patents and publicly available manufacturing disclosures.

Key Takeaways

U.S. Patent 4,282,251 is the foundational U.S. patent for naftifine-related substituted N-(1-naphthylmethyl)amines.
Claim 1 is a broad Markush compound claim covering multiple nitrogen substituents, side chains, aromatic substituents, and acid-addition salts.
Claim 6 directly claims trans-N-methyl-N-(1-naphthylmethyl)-3-phenyl-2-propen-1-amine, the compound commonly identified as naftifine.
Claims 2 and 3 cover pharmaceutical compositions and treatment of mycotic disorders.
The patent issued August 4, 1981, and its calculated 17-year term expired August 4, 1998.
The patent has no current blocking effect on generic naftifine manufacture, FDA approval, or commercial launch.
Naftifine is a small-molecule drug, so biosimilar rules do not apply.
Current competitive risk depends on later formulation, manufacturing, method-of-use, trademark, and regulatory rights.
Any present Paragraph IV or Orange Book analysis must focus on later patents, not U.S. Patent 4,282,251.

FAQs About U.S. Patent 4,282,251 and Naftifine

Is naftifine hydrochloride still protected by U.S. Patent 4,282,251?

No. The underlying U.S. patent expired in 1998. Later patents could cover specific products or formulations, but they would be separate rights.

Does the patent cover both cis-naftifine and trans-naftifine?

Claim 1 is written broadly and does not appear, from the supplied text, to impose a single alkene geometry. Claims 6 through 27 expressly identify cis or trans compounds. Exact coverage depends on the patent's structural formula and claim construction.

Can a generic manufacturer use a different acid-addition salt?

The genus claim includes chemotherapeutically acceptable acid-addition salts. Because the patent expired, that salt limitation no longer creates a current U.S. patent barrier. Separate later patents or regulatory requirements could still apply.

Does claim 2 cover every naftifine cream or gel?

Historically, claim 2 was broad enough to reach a composition containing a claim 1 compound and an acceptable carrier. It does not, however, provide a live patent right today and does not necessarily cover later formulation features under separate patents.

Is a new naftifine indication protected by claim 3?

Claim 3 is directed to treating mycotic disorders. It expired with the patent. A later patent could protect a specific indication, dosing schedule, patient group, or formulation, but that protection would not come from claim 3.

References

U.S. Patent No. 4,282,251. (1981). Substituted N-(1-naphthylmethyl)-amines. United States Patent and Trademark Office.
United States Food and Drug Administration. (n.d.). Naftifine hydrochloride: FDA-approved drug labeling and product information. FDA.
United States Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA.
United States Patent and Trademark Office. (n.d.). Patent term calculator and patent term examination guidance. USPTO.
U.S. Food and Drug Administration. (2024). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Switzerland	5335/76	Apr 28, 1976
Switzerland	16182/76	Dec 22, 1976
Switzerland	920/77	Jan 26, 1977
Switzerland	921/77	Jan 26, 1977

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	362348	⤷ Start Trial
Austria	370406	⤷ Start Trial
Austria	A293677	⤷ Start Trial
Austria	A8079	⤷ Start Trial
Australia	2459177	⤷ Start Trial
Australia	513249	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,282,251

Summary for Patent: 4,282,251