US Drug Patent 4,942,162: Ketoconazole Seborrheic Dermatitis Claims, Expiration, and Patent Landscape

US Patent No. 4,942,162 protects a treatment method using topical ketoconazole for seborrheic dermatitis. Its broadest claim covers topical application of an effective, lesion-reducing amount of ketoconazole to affected human skin. Dependent claims narrow the method to a water-based cream containing 1% to 5% ketoconazole and twice-daily application.

The patent issued on July 17, 1990. Under the pre-1995 patent-term rules applicable to the patent, its ordinary term ended on July 17, 2007, absent a recorded term adjustment or extension. The patent is therefore expired and does not create a current US barrier to generic ketoconazole products or competing topical treatments. [1][4]

What does US Patent 4,942,162 protect?

The patent protects a therapeutic use of ketoconazole rather than ketoconazole as a chemical compound or a particular commercial product.

Claim	Protected subject matter	Principal limitations
1	Treatment of seborrheic dermatitis	Human patient; topical application; ketoconazole; affected areas; effective lesion-reducing amount
2	Cream formulation method	All limitations of claim 1; water-based cream; 1%-5% ketoconazole
3	Dosing regimen	All limitations of claims 1 and 2; application twice daily

The claim set is short, but claim 1 is materially broader than claims 2 and 3. A treatment could infringe claim 1 without using a cream, without using a 2% concentration, and without applying the product twice daily.

How broad is claim 1 of US 4,942,162?

Claim 1 has five core elements:

Treatment of a human.
The patient has seborrheic dermatitis.
Ketoconazole is applied topically.
The application is made to affected areas.
The amount is effective and lesion reducing.

The claim does not expressly limit:

Ketoconazole concentration.
Cream, shampoo, foam, gel, lotion, solution, or another vehicle.
Application frequency.
Duration of treatment.
Use of a particular salt, particle size, or excipient.
A specific severity of seborrheic dermatitis.
Use of ketoconazole alone or with another active ingredient.

The claim therefore reaches topical ketoconazole treatment methods across multiple dosage forms, provided the product is applied to affected areas and the treatment produces the claimed therapeutic result.

What does “effective, lesion reducing, amount” mean?

The phrase is functional. It requires an amount that reduces lesions associated with seborrheic dermatitis, rather than a fixed mass or concentration.

This language generally operates as a treatment-result limitation. A product is not automatically outside the claim merely because its label does not specify a precise amount. The relevant issue would be whether the accused method uses ketoconazole in an amount capable of producing the claimed lesion-reducing effect.

The limitation also creates potential proof issues. An infringement case would likely examine:

Label instructions.
Clinical data.
Product concentration.
Dosing instructions.
Physician or patient use.
Whether the treated condition is seborrheic dermatitis rather than another dermatosis.

What formulations are protected by claims 2 and 3?

Claim 2 narrows the patent to a water-based cream containing 1%-5% ketoconazole.

A conventional 2% ketoconazole cream is within the numerical range. The claim does not require the commercial product to be called “Nizoral,” and it does not identify a proprietary excipient system. The formulation limitation is functional from a patent-scope perspective: the product must be a cream, water based, and contain ketoconazole within the stated concentration range.

Does claim 2 require a 2% cream?

No. Claim 2 covers the full stated range:

1%.
Concentrations between 1% and 5%.
5%.

A 0.5% product would fall outside the literal concentration range. A product above 5% would also fall outside the literal range, although a patent dispute could raise doctrine-of-equivalents issues depending on the facts.

The patent does not state the concentration unit in the claim text supplied. In pharmaceutical formulation practice, the concentration would ordinarily be interpreted using the specification and surrounding technical context, most likely as a percentage of the formulation by weight. The specification would control the final construction.

What does “water based cream” exclude?

The phrase likely excludes dosage forms that are not creams or that are substantially nonaqueous. Potentially relevant distinctions include:

Ointment versus cream.
Gel versus cream.
Foam versus cream.
Shampoo versus cream.
Anhydrous vehicle versus aqueous emulsion.
Lotion or solution versus cream.

A competing product could avoid claim 2 by using a noncream dosage form while remaining potentially within claim 1.

What does claim 3 add?

Claim 3 requires twice-daily application of the claim 2 cream.

It therefore covers a specific regimen:

Seborrheic dermatitis.
Topical ketoconazole.
Water-based cream.
1%-5% concentration.
Application to affected areas.
Twice-daily dosing.

Claim 3 does not necessarily require exactly 12-hour intervals. “Twice daily” would ordinarily mean two applications per day, subject to the specification, prosecution history, labeling, and ordinary clinical meaning.

A once-daily product would not literally satisfy claim 3, although it could remain relevant to claim 1 if the product is used in an effective topical regimen.

When did US Patent 4,942,162 lose exclusivity?

The patent’s ordinary expiration date was July 17, 2007.

Event	Date or status
Patent issued	July 17, 1990
Governing term	17 years from grant under the pre-1995 regime
Ordinary expiration	July 17, 2007
Current enforceability	Expired
Current patent-based generic blocking right	None

The 2007 expiration date is separate from FDA marketing exclusivity. Patent expiration does not itself establish FDA approval status, and FDA approval does not revive an expired patent.

No modern patent-term restoration or pediatric extension is ordinarily associated with this type of method patent. A patent-term extension under 35 U.S.C. § 156 generally applies to qualifying regulatory review delays for eligible products, not as a general extension for an expired topical-use patent. [4]

What is the Orange Book status of ketoconazole products?

Ketoconazole is a small-molecule drug, not a biologic. The relevant FDA pathway is an NDA or ANDA, not a biosimilar application.

The principal regulatory distinction is between:

Ketoconazole cream, generally marketed as a topical antifungal product.
Ketoconazole shampoo, used for dandruff and seborrheic dermatitis.
Other topical or systemic dosage forms.

The FDA Orange Book lists approved drug products and, where applicable, patent and exclusivity information associated with approved applications. Patent 4,942,162 could have been relevant to historical listing and generic certifications, but its expiration means it cannot support a current Paragraph IV litigation strategy. [2]

FDA labeling for ketoconazole products must be reviewed by dosage form and indication. A patent claim can cover treatment of seborrheic dermatitis even when a particular approved label uses different wording or does not include the same indication. Patent scope and FDA labeling are separate legal questions. [3]

Were Paragraph IV challenges relevant to this patent?

Historically, an ANDA applicant seeking approval for a product that implicated an unexpired listed patent could have used a Paragraph IV certification under the Hatch-Waxman framework. That certification would assert that the patent was invalid, unenforceable, or not infringed.

For Patent 4,942,162, the practical timeline was limited:

The patent issued in 1990.
The patent expired in 2007.
Any Paragraph IV dispute would have needed to arise before expiration.
After expiration, an ANDA applicant no longer needed to defeat this patent to launch on patent grounds.

A current applicant can rely on patent expiration rather than challenge the validity of the claims. Any historical Paragraph IV litigation would have been product-specific and would depend on whether the patent was listed against the relevant FDA application.

What patent landscape surrounded ketoconazole?

The ketoconazole estate historically included several distinct patent categories.

Ketoconazole compound patents

Early Janssen patents covered imidazole derivatives and related antifungal compounds, including ketoconazole. Those rights were separate from Patent 4,942,162, which is a method-of-treatment patent.

The compound and original pharmaceutical-chemistry patents expired decades ago. They cannot now prevent manufacture or sale of ketoconazole as an active pharmaceutical ingredient.

Topical formulation patents

Formulation rights could cover:

Cream emulsions.
Solubilization systems.
Particle-size control.
Preservatives.
Surfactant systems.
Vehicle composition.
Stability improvements.
Shampoo or foam delivery systems.

A formulation patent would require separate analysis. Patent 4,942,162 does not claim a detailed excipient composition. It claims use of a water-based cream at a concentration range in dependent claim 2.

Method-of-use patents

Patent 4,942,162 is primarily a method-of-use patent directed to seborrheic dermatitis. Method claims may remain relevant even when the active ingredient and formulation are off-patent. Here, the method claims have also expired.

Later patents could have addressed:

Specific dosing schedules.
Combination therapy.
Treatment of scalp or facial seborrheic dermatitis.
Shampoo or foam dosage forms.
Reduced-irritation formulations.
New indications or patient populations.

A later patent would need a valid priority date and claim scope that does not merely duplicate the expired method.

Manufacturing and supply-chain rights

Manufacturing barriers for ketoconazole are more likely to arise from:

API quality requirements.
Impurity control.
Crystallinity and particle-size specifications.
Scale-up consistency.
Topical formulation stability.
FDA current good manufacturing practice requirements.
Supplier qualification.

Patent 4,942,162 does not create a current manufacturing barrier. It does not claim a ketoconazole synthesis process or a specific manufacturing method.

How strong was the patent estate for ketoconazole seborrheic dermatitis treatment?

Claim 1

Claim 1 was commercially important because it covered the therapeutic concept directly. Its weaknesses were its functional wording and the breadth of prior-art risk surrounding topical antifungal treatment.

Potential validity challenges could have included:

Anticipation by earlier disclosures of topical ketoconazole for seborrheic dermatitis.
Obviousness based on known ketoconazole antifungal activity and known seborrheic dermatitis treatments.
Insufficient disclosure of the claimed therapeutic result.
Claim-construction disputes over “lesion reducing.”
Questions concerning the boundaries of seborrheic dermatitis as a diagnosed condition.

Claim 2

Claim 2 was narrower and more concrete. A 1%-5% water-based ketoconazole cream would likely be easier to identify in a product comparison. Its validity would depend on the disclosure and prior art concerning topical cream vehicles and concentration selection.

Claim 3

Claim 3 was the narrowest claim. The twice-daily regimen creates a clear additional limitation but may be vulnerable if twice-daily topical dosing was already conventional or disclosed in the prior art.

Because every claim expired in 2007, these historical strength questions have no current blocking effect.

Which companies are challenging ketoconazole patent rights?

There is no current patent challenge required for commercial entry against Patent 4,942,162. Generic and branded-generic manufacturers can market approved ketoconazole products without overcoming this expired patent.

The competitive field includes:

Generic manufacturers of ketoconazole cream.
Manufacturers of ketoconazole shampoo.
Suppliers of alternative topical antifungals.
Products containing ciclopirox, selenium sulfide, zinc pyrithione, clotrimazole, or other antifungal agents.
Nonprescription dandruff and seborrheic dermatitis products.

A company’s ability to market a product still depends on FDA approval, labeling, manufacturing compliance, trademark clearance, and any later unexpired patents. Patent 4,942,162 alone does not restrict competition.

What generic launch risks remain?

The patent-specific launch risk is zero because the patent expired. Remaining risks are regulatory and commercial rather than based on this patent.

Risk category	Relevance
Patent 4,942,162	No current blocking risk
Active-ingredient patent	Expired for historic ketoconazole chemistry
Formulation patents	Must be checked separately by dosage form
Method-of-use patents	Must be checked for later, unexpired patents
FDA approval	Required
Label carve-out	May matter if indications differ
Trademark risk	Separate from patent rights
API and formulation supply	Commercial and quality risk
Biosimilar risk	Not applicable

How does Patent 4,942,162 compare with competing ketoconazole rights?

Patent 4,942,162 is narrower than a compound patent but broader than a formulation-specific patent.

Right type	Typical scope	Status relative to 4,942,162
Compound patent	Ketoconazole molecule and related compounds	Earlier, expired
Formulation patent	Cream, shampoo, foam, or excipient system	Product-specific
Method patent	Use of ketoconazole for a disease	4,942,162 falls in this category
Dosing patent	Frequency, duration, or treatment sequence	Claim 3 is a limited dosing claim
Trademark	Product name and branding	Separate legal right
Regulatory exclusivity	FDA approval-related exclusivity	Separate from patent term

Key Takeaways

US Patent 4,942,162 claims topical ketoconazole treatment of seborrheic dermatitis.
Claim 1 is the broadest claim and does not require a cream, a fixed concentration, or twice-daily dosing.
Claim 2 covers a water-based cream containing 1%-5% ketoconazole.
Claim 3 adds twice-daily application.
The patent issued July 17, 1990 and ordinarily expired July 17, 2007.
It is not a current barrier to generic ketoconazole products.
Paragraph IV certification may have been relevant historically, but no current challenge is needed against this expired patent.
The patent does not claim ketoconazole itself, a synthesis process, or a proprietary excipient system.
Current diligence should focus on later formulation, delivery-system, dosing, regulatory, trademark, and manufacturing rights.
Biosimilar analysis is not relevant because ketoconazole is a small-molecule drug.

FAQs About US Patent 4,942,162 and Ketoconazole

Can a generic manufacturer market a ketoconazole cream for seborrheic dermatitis today?

Patent 4,942,162 does not prevent market entry because its term ended in 2007. The manufacturer must still satisfy FDA approval and labeling requirements.

Does the patent cover ketoconazole shampoo?

Claim 1 is not limited to a cream and could historically have reached a shampoo if used topically to treat seborrheic dermatitis. Claims 2 and 3 are limited to a water-based cream and twice-daily use.

Is a 2% ketoconazole cream within the patent claims?

Historically, a 2% water-based ketoconazole cream would fall within the concentration range in claim 2, assuming the other claim limitations were met. The expired status eliminates current infringement exposure under this patent.

Does the patent cover treatment of dandruff?

The claim language identifies seborrheic dermatitis. Dandruff may overlap clinically with seborrheic dermatitis, but the patent scope would depend on diagnosis, claim construction, labeling, and the facts of use.

Can a newer foam or gel formulation avoid claims 2 and 3?

A foam or gel would not literally satisfy the “water based cream” limitation in claim 2. It could still have been analyzed against claim 1 historically, but Patent 4,942,162 no longer creates current US infringement risk.

References

United States Patent and Trademark Office. (1990). U.S. Patent No. 4,942,162, treatment of seborrheic dermatitis with ketoconazole.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations: Orange Book. https://www.accessdata.fda.gov/scripts/cder/ob/
U.S. Food and Drug Administration. (n.d.). Ketoconazole topical product labeling. Drugs@FDA. https://www.accessdata.fda.gov/scripts/cder/daf/
United States Code. (2024). 35 U.S.C. § 154: Contents and terms of patents; provisional rights. https://uscode.house.gov/ geschniegelt

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Belgium	896321	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,942,162

Summary for Patent: 4,942,162