United States Patent 4,713,394: Claim Scope, Expiration, and Azelaic Acid Patent Landscape

United States Patent 4,713,394 protected topical treatment methods using azelaic acid and related straight-chain dicarboxylic acids. Its broadest claims covered nonacne inflammatory dermatoses, infectious skin diseases, and inflammatory or hormone-related hair loss. The patent was granted on December 15, 1987, and its 17-year term expired on December 15, 2004. It no longer creates an exclusionary barrier to generic azelaic acid products or competing dermatological formulations. [1]

The patent remains commercially relevant as prior art and as an example of method-of-use protection, but it has no current blocking force in the United States.

What does U.S. Patent 4,713,394 protect?

The patent claims methods of applying azelaic acid or related compounds to affected skin. The claims do not primarily protect a new chemical compound, a specific cream base, a manufacturing process, or a particular product brand. They protect therapeutic use.

Claim	Protected subject matter	Active ingredient scope	Concentration	Indications
1	Treatment method using azelaic acid	Azelaic acid only	Not specified	Nonacne inflammatory dermatoses, infectious cutaneous disease, inflammatory hair loss, hormone-related hair loss
2	Treatment method for nonacne inflammation	Straight-chain C7-C13 dicarboxylic acids, mercapto derivatives, and salts	About 2%-40% by weight	Nonacne inflammation
3	Treatment method for infectious skin disease	Same genus as claim 2	About 2%-40% by weight	Infectious cutaneous disease
4	Treatment method using azelaic acid	Azelaic acid only	About 15%-20% by weight	Nonacne inflammation or infection of dermis, epidermis, or adnexa
5	Treatment method using azelaic acid	Azelaic acid only	About 15%-20% by weight	Hair loss caused by inflammatory or hormonal anomalies

The patent therefore combines a broad azelaic-acid method claim with broader chemical-genus claims and narrower concentration-specific azelaic-acid claims.

How broad is claim 1 of U.S. Patent 4,713,394?

Claim 1 is the patent's principal broad species claim. It requires:

Skin suffering from one of the listed conditions;
Application to the affected area; and
A therapeutically effective amount of azelaic acid.

The claim does not impose a concentration limitation. A topical product containing azelaic acid could theoretically fall within the claim regardless of whether it contained 10%, 15%, 20%, or another concentration, provided the product was used for one of the recited conditions.

The indication language is the principal limiting element. Claim 1 does not cover every use of azelaic acid. It is directed to:

Nonacne inflammatory dermatoses;
Infectious cutaneous disease;
Inflammatory hair loss; and
Hormone-related hair loss.

A product marketed solely for acne would not fall within claim 1 based on the claim language alone. A product used for rosacea, folliculitis, dermatitis, or other nonacne inflammatory conditions could present a closer historical claim question, depending on the specific diagnosis and labeling.

The phrase "therapeutically effective amount" is functional. It requires an amount that produces the claimed treatment effect but does not specify a numerical dose. This type of limitation can broaden practical coverage but may create proof issues in litigation involving off-label use or an allegedly nontherapeutic concentration.

What chemical compounds are covered by claims 2 and 3?

Claims 2 and 3 extend beyond azelaic acid. They cover a genus consisting of:

Straight-chain dicarboxylic acids having 7 to 13 carbon atoms;
Mercapto derivatives of those acids; and
Salts of those compounds.

Azelaic acid is a straight-chain nine-carbon dicarboxylic acid, chemically known as nonanedioic acid. It falls within the C7-C13 genus.

The claims require a dermatological formulation containing approximately 2% to 40% by weight of the relevant compound. The claims are therefore broader than claims 4 and 5 in chemical identity but less specific in the treatment method.

Claim 2 covers nonacne inflammation. Claim 3 covers infectious cutaneous disease. Their potential reach includes compounds other than azelaic acid, assuming the compound satisfies the structural and concentration requirements.

The phrase "about 2% to about 40%" creates a measurement tolerance around the stated endpoints. It does not automatically cover every concentration below 2% or above 40%. The scope would historically have depended on claim construction, specification support, analytical measurement, and whether the accused formulation fell within a reasonable interpretation of the approximate ranges.

What do claims 4 and 5 cover at 15% to 20% azelaic acid?

Claims 4 and 5 are narrower concentration-specific claims directed exclusively to azelaic acid formulations containing approximately 15% to 20% by weight.

Claim 4 covers treatment of:

Nonacne inflammation; or
Infection involving the dermis, epidermis, or adnexa.

"Adnexa" generally refers to skin-associated structures such as hair follicles, sebaceous glands, and related appendages.

Claim 5 covers hair loss resulting from:

Inflammatory anomalies; or
Hormonal anomalies.

These claims are commercially relevant because 15% and 20% azelaic acid concentrations correspond to concentrations used in prescription dermatology products and historically marketed formulations. Their concentration limitation, however, does not preserve enforceability after patent expiration.

Before expiration, a 15%-20% azelaic acid topical product marketed for a covered nonacne, infectious, or hair-loss indication would have faced a stronger literal-coverage argument than a product outside the claimed concentration range.

When did U.S. Patent 4,713,394 lose exclusivity?

U.S. Patent 4,713,394 was granted on December 15, 1987. Because it was granted before the modern 20-year term regime became applicable, its ordinary U.S. term was 17 years from grant. The patent expired on December 15, 2004. [1]

Event	Date
U.S. patent grant	December 15, 1987
Ordinary patent term	17 years from grant
Expiration	December 15, 2004
Current status	Expired
Current enforcement risk	None as an enforceable U.S. patent right

The patent cannot support a new infringement action for conduct occurring after expiration. It also cannot be revived through an Orange Book listing, a regulatory exclusivity period, or a later azelaic acid product approval.

The patent's disclosure and claims remain relevant as prior art. Expiration removes the exclusionary right, not the document's evidentiary value in later novelty, obviousness, written-description, enablement, or claim-construction disputes.

What is the Orange Book status of U.S. Patent 4,713,394?

U.S. Patent 4,713,394 should not be treated as a current Orange Book barrier. The Orange Book lists patents submitted by applicants for approved drug products and identifies patent information relevant to abbreviated new drug applications. A patent that expired in 2004 cannot create a current patent-based delay to an ANDA launch. [2]

The patent also is not a substitute for the patents historically associated with later azelaic acid products, including 15% gel and other topical formulations. Those products may have had separate composition, formulation, manufacturing, or method-of-use patents.

FDA regulatory exclusivity and patent term are separate concepts:

Protection type	Effect on azelaic acid products
U.S. Patent 4,713,394	Expired in 2004
New chemical entity exclusivity	Not created by this patent
Orphan-drug exclusivity	Not established by this patent
Pediatric exclusivity	Not established by this patent
Orange Book patent stay	No current stay can arise from this expired patent
ANDA approval	Governed by FDA requirements and any currently listed unexpired patents

Azelaic acid is a small-molecule active ingredient. Biosimilar regulation does not apply. Competitive entry occurs through generic-drug pathways, including ANDAs where the reference product and FDA requirements support that route.

What patent landscape surrounded azelaic acid products?

The azelaic acid landscape has historically included four principal patent categories.

Early therapeutic-use patents

Early patents addressed azelaic acid treatment for acne and other dermatological conditions. U.S. Patent 4,713,394 expanded the use-case profile beyond acne by covering nonacne inflammation, infectious skin disease, and certain hair-loss conditions. [1]

These early method patents have expired. They may still appear in patent citations and validity analyses but do not restrict current commercialization.

Formulation patents

Later patents focused on topical delivery systems, including:

Creams;
Gels;
Aqueous or hydroalcoholic vehicles;
Carbomer-based systems;
pH-controlled formulations;
Suspension and solubilization approaches; and
Enhanced skin penetration or stability.

A current product may therefore have historically depended more on formulation patents than on U.S. Patent 4,713,394. Formulation claims can protect excipient combinations, viscosity ranges, particle size, pH, delivery performance, or physical stability. The existence and status of those patents must be assessed product by product in the FDA Orange Book and USPTO records.

Method-of-use patents

Method-of-use patents may claim treatment of specific conditions such as:

Rosacea;
Acne;
Hyperpigmentation;
Inflammatory dermatoses;
Follicular disorders; or
Other skin conditions.

The relevant distinction is between the approved label and actual use. A generic applicant can use a section viii statement to carve out a patented method of use from its labeling when FDA rules permit. A carve-out does not necessarily eliminate all infringement theories based on physician prescribing, pharmacy substitution, promotional conduct, or induced infringement.

Manufacturing and process patents

Manufacturing patents can cover:

Purification of azelaic acid;
Crystal form or particle characteristics;
Milling and micronization;
Cream or gel manufacture;
Preservation systems; and
Batch-control or processing conditions.

For a simple commodity molecule such as azelaic acid, manufacturing patents generally present a narrower barrier than formulation or method-of-use patents. They can still affect a particular supplier if the commercial process practices a claimed step.

Which companies are challenging U.S. Patent 4,713,394?

No Paragraph IV challenge to U.S. Patent 4,713,394 can currently create litigation or a statutory ANDA stay because the patent expired in 2004.

A Paragraph IV certification is relevant only when an ANDA applicant challenges an unexpired patent listed for the reference product. The certification can trigger patent litigation and, subject to statutory conditions, a 30-month FDA approval stay. [3] That framework does not restore rights under an expired patent.

Any historical ANDA dispute involving azelaic acid products would more likely have concerned later unexpired patents covering a specific reference product, formulation, or labeled indication. The expired 1987 patent would have been available as prior art in such litigation but would not independently support a current injunction.

What generic launch risks exist for azelaic acid products?

The direct patent risk from U.S. Patent 4,713,394 is zero because the patent expired. Current launch risk depends on other factors.

Risk category	Relevance to current azelaic acid launch
Expired method patent	No blocking effect
Unexpired formulation patent	Potentially significant
Unexpired method-of-use patent	Depends on label and carve-out availability
Orange Book-listed patent	Requires product-specific review
Non-Orange Book patent	May still support litigation, but does not create an automatic ANDA stay
Regulatory equivalence	Can affect approval timing and substitution
Trade secret manufacturing process	May affect supply but does not block independent manufacture
Trademark and trade dress	Commercial risk separate from patent risk
Biosimilar competition	Not applicable

For a 15% or 20% topical product, the main historical commercial question would have been whether the formulation or label infringed later patents. The concentration alone does not create a current barrier under the expired patent.

How strong was the patent estate for azelaic acid?

The estate reflected in U.S. Patent 4,713,394 was strong in breadth but weak in durability.

Historical strengths

Claim 1 covered azelaic acid without a numerical concentration limit.
Claims 2 and 3 covered a broader chemical genus.
Claims 4 and 5 targeted 15%-20% azelaic acid formulations.
The claims reached multiple therapeutic categories.
The claims covered topical treatment methods rather than only a narrow product configuration.

Structural weaknesses

The claims were use-limited.
The broad genus claims depended on structural and concentration requirements.
The patent did not establish exclusive ownership of azelaic acid as a compound.
The patent did not independently protect every formulation or manufacturing process.
The patent term ended in 2004.

Its practical value was therefore highest during the patent term and lowest for present-day launch analysis. The patent is now a historical foundational right rather than an active asset.

What licensing deals are associated with this patent?

The patent document itself does not establish a current licensing arrangement. No license, assignment, settlement, or royalty agreement can be inferred solely from the claim language or patent number.

Commercial rights may historically have moved through assignments, corporate acquisitions, product licenses, or regional distribution agreements. Those transactions do not extend the patent beyond its statutory expiration. Any surviving license would concern commercial know-how, trademarks, regulatory materials, or other rights rather than an enforceable patent monopoly under U.S. Patent 4,713,394.

What litigation and settlement issues affect the patent?

U.S. Patent 4,713,394 cannot support present-day patent litigation because it is expired. Historical disputes may still matter for:

Claim construction;
Prosecution-history estoppel;
Prior-art analysis;
Inventorship or ownership history;
Settlement interpretation; and
Product-development strategy.

A settlement agreement involving the patent could have restricted conduct during its term, but contractual restrictions and patent rights are distinct. Contractual obligations may survive according to their terms, while the patent itself cannot be enforced as an unexpired exclusionary right.

How does U.S. Patent 4,713,394 compare with later azelaic acid protection?

Issue	U.S. Patent 4,713,394	Later azelaic acid patents
Primary protection	Therapeutic use	Formulation, delivery, product, or specific use
Active ingredient	Azelaic acid and related dicarboxylic acids	Often azelaic acid in defined compositions
Key concentrations	2%-40% for genus claims; 15%-20% for claims 4-5	Product-specific ranges or formulation parameters
Covered indications	Broad nonacne, infectious, and hair-loss uses	Often narrower approved indications
Current status	Expired December 15, 2004	Must be checked individually
Orange Book significance	No current blocking effect	Potentially relevant if unexpired and listed
Biosimilar relevance	None	None, because azelaic acid is a small molecule
Generic risk	No patent risk from this patent	Depends on current formulation and use patents

Key Takeaways

U.S. Patent 4,713,394 is a method-of-treatment patent centered on topical azelaic acid.
Claim 1 covers nonacne inflammatory dermatoses, infectious cutaneous disease, and inflammatory or hormonal hair loss.
Claims 2 and 3 broaden the chemical scope to C7-C13 straight-chain dicarboxylic acids, mercapto derivatives, and salts at about 2%-40%.
Claims 4 and 5 specifically cover 15%-20% azelaic acid formulations for nonacne, infectious, and hair-loss conditions.
The patent expired on December 15, 2004.
It cannot support a current injunction, Paragraph IV stay, or Orange Book-based launch delay.
Current azelaic acid patent risk must be assessed against later formulation, delivery, manufacturing, and method-of-use patents.
Biosimilar analysis is not applicable.
The patent remains relevant as prior art but has no current U.S. exclusionary value.

FAQs

Does U.S. Patent 4,713,394 cover azelaic acid acne products?

Not directly based on the supplied claims. The claims target nonacne inflammation, infectious skin disease, and inflammatory or hormonal hair loss. The patent does not expressly claim acne treatment.

Can a company sell a 15% azelaic acid gel today?

The expired patent does not prevent sale of a 15% azelaic acid gel. The product must still satisfy FDA approval requirements and avoid infringement of any separate unexpired patents.

Does the patent cover oral azelaic acid treatment?

The claims require applying the formulation to the affected area and are directed to topical dermatological treatment. They do not cover oral administration based on the supplied language.

Are azelaic acid salts covered by the patent?

Claims 2 and 3 expressly include salts of the covered straight-chain dicarboxylic acids and their mercapto derivatives, subject to the structural, concentration, formulation, and treatment limitations.

Can the patent be used to challenge a later azelaic acid patent?

Yes. Its disclosure and claims may be prior art in a validity challenge, depending on the later patent's priority date, claim scope, disclosure, and applicable prior-art rules. It cannot itself be enforced as an active patent.

References

United States Patent No. 4,713,394. (1987, December 15). Methods for treating dermatological disorders with azelaic acid and related compounds. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2025). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book
United States Code, 21 U.S.C. § 355(j). (2024). Abbreviated applications for new drugs and patent certifications.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Germany	229654	⤷ Start Trial
Germany	3750934	⤷ Start Trial
Germany	3751780	⤷ Start Trial
European Patent Office	0229654	⤷ Start Trial
European Patent Office	0593093	⤷ Start Trial
Japan	2505983	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,713,394

Summary for Patent: 4,713,394