United States Patent 6,387,383: Scope, Claims, Expiration, and Competitive Patent Landscape

US Patent 6,387,383 protects selected low-viscosity, aqueous topical gels that use a lightly cross-linked polyacrylic acid polymer, pH adjustment, water, and an active dermatological compound. The broadest claims cover compositions, treatment methods, and manufacturing methods. The most commercially relevant embodiments are clindamycin phosphate gels, including formulations with propylene glycol, polyethylene glycol 400, methylparaben, and purified water.

The patent issued May 14, 2002, and its listed patent term expired on January 28, 2020. It no longer presents a live U.S. patent barrier to generic topical products, although its claim structure remains relevant to historical infringement analysis and to the design of related formulation patents. The patent covers a formulation platform rather than clindamycin phosphate as an active pharmaceutical ingredient.

What does US Patent 6,387,383 protect?

The patent protects topical aqueous gels with five central technical limitations:

A therapeutic dermatological active.
A hydrophilic, pharmaceutically acceptable, lightly cross-linked polyacrylic acid polymer.
A pharmaceutically acceptable base for pH adjustment.
Water.
A pH of approximately 3 to 9 and viscosity below approximately 15,000 cP.

Water-miscible solvents and preservatives are optional under the independent claims. The patent therefore targets a formulation architecture rather than a single commercial ingredient.

The independent claims are:

Claim	Claim category	Principal subject matter
1	Composition	Aqueous topical gel for a skin disorder
18	Method of treatment	Topical administration to affected skin
37	Manufacturing method	Preparing the aqueous gel
16	Combination	Composition with an accurate-dose container
17	Combination	Composition, container, and treatment labeling

Claims 16 and 17 depend on the composition claims. Claims 52 and 53 add corresponding container and labeling limitations to the manufacturing-method branch.

The patent’s claim architecture creates three distinct infringement routes: sale or use of the composition, performance of the dermatological treatment method, and performance of the claimed preparation method.

How broad are the independent claims?

Claim 1: composition protection

Claim 1 is broad because it does not restrict the active ingredient to clindamycin phosphate. Dependent claims extend coverage to:

Antibiotics
Imidazoles
Retinoids
Corticosteroids
Non-steroidal anti-inflammatory drugs
Combinations of antibiotics with corticosteroids
Combinations of antibiotics with retinoids

The claim is limited by the polymer and physical-property requirements. A topical product would not fall within claim 1 merely because it is an aqueous gel containing a dermatological active. It would also need to contain the claimed type of lightly cross-linked polyacrylic acid polymer, have a pH within the stated range, and have viscosity below approximately 15,000 cP.

Claim 18: treatment-method protection

Claim 18 covers topically administering the claimed composition to affected skin in an amount and for a period sufficient to improve the disorder. Claim 19 narrows the disorders to inflammatory skin disorders, acne, and rosacea.

Claims 20 through 36 add dosing, active-ingredient, and disease limitations. Claim 20 specifically covers once-daily administration. Claims 21 through 27 concentrate on acne and clindamycin phosphate.

Claim 37: manufacturing-method protection

Claim 37 covers a method of preparing the gel by:

Combining water, the active, and the lightly cross-linked polyacrylic acid polymer.
Adjusting the pH to approximately 3 to 9.
Optionally adding a water-miscible solvent and preservative.

This claim does not require the product to contain clindamycin phosphate. The dependent claims create species for clindamycin phosphate, clindamycin-tretinoin combinations, corticosteroids, NSAIDs, and other listed actives.

Which claims are most commercially important?

The clindamycin phosphate claims are the most commercially significant because they correspond to topical acne products and to the historical Clindagel product configuration.

Claim group	Active ingredient	Key formulation limitations
5, 25, 41	Clindamycin phosphate	Antibiotic alone
6, 26, 42	Clindamycin phosphate	0.5%-2.0%; polymer 0.1%-0.4%; solvent 15%-25%; pH 4-7
7, 27, 43	Clindamycin phosphate	1.0%-1.5%; polymer about 0.2%; propylene glycol about 15%; PEG 400 about 5%; methylparaben 0.1%-0.15%; pH 5-6
9, 30, 45	Clindamycin phosphate plus tretinoin	Combination product
10, 31, 46	Clindamycin phosphate plus tretinoin	Clindamycin 0.5%-2.0%; tretinoin 0.01%-0.05%; polymer 0.1%-0.5%; pH 4-7
54-59	Desonide	Desonide 0.01%-1.0% as sole active

Claims 6, 7, 26, 27, 42, and 43 are narrower than claim 1 but are more readily mapped to a specific commercial formula. Claim 7 is particularly formulation-specific because it recites approximate concentrations for the active, polymer, solvents, and preservative.

What formulations are protected by the patent?

The patent protects several formulation families.

Clindamycin phosphate gel

The central formulation range is:

Clindamycin phosphate: approximately 0.5% to 2.0% w/w
Lightly cross-linked polyacrylic acid polymer: approximately 0.1% to 0.4% w/w
Water-miscible solvent: approximately 15% to 25% w/w
Preservative: less than approximately 0.2% w/w
pH: approximately 4.0 to 7.0
Purified water: quantity sufficient to 100%

The preferred formulation in claim 7 narrows the product to:

Clindamycin phosphate: approximately 1.0% to 1.5%
Polymer: approximately 0.2%
Propylene glycol: approximately 15%
Polyethylene glycol 400: approximately 5%
Methylparaben: approximately 0.1% to 0.15%
pH: approximately 5.0 to 6.0

Clindamycin phosphate and tretinoin gel

Claims 10, 31, and 46 cover a combination gel with:

Clindamycin phosphate: approximately 0.5% to 2.0%
Tretinoin: approximately 0.01% to 0.05%
Polyacrylic acid polymer: approximately 0.1% to 0.5%
Water-miscible solvent: approximately 10% to 30%
Preservative: less than approximately 0.2%
pH: approximately 4 to 7

These limitations overlap conceptually with acne products combining an antibiotic and retinoid, but a product must also satisfy the polymer, pH, viscosity, and composition limitations.

Corticosteroid formulations

The patent lists several corticosteroids:

Desonide
Hydrocortisone valerate
Fluocinolone acetonide
Hydrocortisone butyrate
Triamcinolone acetonide
Diflorasone diacetate
Fluticasone propionate
Halobetasol propionate
Budesonide

Claims 54 through 59 specifically add desonide at approximately 0.01% to 1.0% w/w. The claims do not require clindamycin when the corticosteroid is the sole active agent.

NSAID and imidazole formulations

The patent also covers topical gels containing naproxen, diclofenac, pharmaceutically acceptable salts of those compounds, and imidazole compounds. These claims are technically broad but commercially less important than the clindamycin claims because the patent’s most visible product relationship was topical acne therapy.

How should “consists essentially of” be interpreted?

The claims use “consists essentially of,” which is narrower than “comprising” but broader than “consisting of.”

The phrase generally permits additional ingredients that do not materially alter the basic and novel characteristics of the claimed gel. In this patent, the basic characteristics appear to include the low-viscosity aqueous gel structure, the lightly cross-linked polyacrylic acid polymer, the selected pH range, and compatibility with the active compound.

An accused product could face a claim issue even if it contains additional excipients, provided those excipients do not materially change the claimed formulation characteristics. Conversely, a product with an additional gelling system, materially different polymer network, or different physical behavior may have a stronger non-infringement position. The analysis would depend on the claim language, specification, prosecution history, and product composition.

When did US Patent 6,387,383 expire?

Event	Date
Earliest priority date used for term analysis	January 28, 1999
Patent issued	May 14, 2002
Listed expiration date	January 28, 2020
Current status	Expired

The patent’s term was governed by the modern 20-year term measured from the applicable nonprovisional filing date, subject to any patent-term adjustment or extension. Public patent records list the patent as expired on January 28, 2020.[1]

The expiration removed the patent-based barrier to launch for products that otherwise satisfy FDA requirements. It did not eliminate regulatory requirements, trade-secret protection, trademark rights, product-liability exposure, or potential rights under later patents.

What was the FDA and Orange Book status?

US Patent 6,387,383 was associated with the topical clindamycin product Clindagel. The relevant regulatory framework was an abbreviated new drug application pathway for generic versions of an approved small-molecule topical product, rather than a biologic or biosimilar pathway.

The Orange Book relevance was tied to the approved drug product and its listed patent information. A patent listing does not itself establish infringement, validity, or enforceability. It identifies patent information submitted by the NDA holder and can support a Paragraph IV certification by an ANDA applicant.[2]

The patent is now expired. No current Orange Book listing can create a new exclusivity period after expiration. FDA approval of a generic product remains dependent on product-specific requirements, including pharmaceutical equivalence, bioequivalence or applicable topical-product standards, chemistry and manufacturing controls, labeling, and facility compliance.

Were Paragraph IV challenges likely?

A Paragraph IV certification would have been the principal route for an ANDA applicant seeking approval before patent expiration while asserting that the patent was invalid, unenforceable, or not infringed. Under the Hatch-Waxman framework, a Paragraph IV notice could trigger patent litigation and a potential 30-month stay of approval, subject to statutory conditions.[3]

The practical risk profile depended on whether the generic product:

Used a different polymer system;
Fell outside the claimed pH or viscosity range;
Used a different solvent or preservative system;
Omitted the claimed polymer;
Used a different active concentration;
Avoided the claimed combination of clindamycin and tretinoin;
Challenged validity based on anticipation or obviousness.

The strongest design-around path would generally have been to avoid the claimed lightly cross-linked polyacrylic acid polymer or to develop a formulation outside the concentration and physical-property ranges. A product using the same polymer system and the claim 7 composition would have presented a materially higher historical Paragraph IV risk.

Which companies challenged or competed with the protected products?

The relevant competitive field included branded and generic topical acne manufacturers.

Product or platform	Active ingredients	Relationship to the patent landscape
Clindagel	Clindamycin phosphate	Product most closely associated with the patented formulation platform
Generic clindamycin phosphate gel products	Clindamycin phosphate	Generic competition after patent and regulatory barriers
Ziana	Clindamycin phosphate and tretinoin	Competing combination acne product with separate product and patent history
Veltin	Clindamycin phosphate and tretinoin	Combination acne product
Duac	Clindamycin phosphate and benzoyl peroxide	Different active combination and distinct formulation estate
Evoclin	Clindamycin phosphate foam	Different dosage form and formulation technology

A competing product does not necessarily infringe because it uses the same active ingredient. Product-by-product comparison must address the polymer, pH, viscosity, solvent, preservative, concentration, and “consists essentially of” limitations.

How strong was the patent estate?

The estate was broad in subject matter but limited in duration and vulnerable to design-around strategies.

Strengths

Coverage extended beyond clindamycin to multiple dermatological drug classes.
The claims covered compositions, treatment methods, and manufacturing methods.
The patent included specific claims directed to commercially recognizable concentrations and excipients.
The low-viscosity and aqueous-gel limitations could distinguish the claimed products from creams, ointments, foams, lotions, and high-viscosity gels.
The claims addressed both single-active and combination therapy.

Weaknesses

The independent claims used functional and approximate terms, including “compatible,” “therapeutically effective,” “about,” and “lightly cross-linked.”
The active ingredient genus was broad relative to the narrower commercial embodiments.
Prior art involving aqueous polyacrylic acid gels, topical antibiotics, retinoids, corticosteroids, and NSAIDs could support obviousness arguments.
Formulation modifications could avoid literal infringement.
The patent has expired, eliminating present enforcement value.

The estate had its greatest historical value against a product that copied the clindamycin phosphate formulation, polymer type, solvent system, pH range, and viscosity profile. Its value was lower against products using a different polymer technology or dosage form.

What generic launch risks existed?

Before January 28, 2020, a generic entrant faced four primary risks:

Patent litigation following a Paragraph IV certification.
A 30-month regulatory stay if statutory requirements were met.
Difficulty proving pharmaceutical equivalence for a topical gel.
Potential infringement of later patents covering specific formulations, delivery systems, or combination products.

After expiration, the 6,387,383 patent ceased to be a launch blocker. The remaining risks were regulatory and commercial:

FDA approval timing;
Formulation performance;
Product availability and manufacturing scale;
Substitution and reimbursement;
Competing generic prices;
Separate, later-expiring patents;
Trademark and labeling restrictions.

Because clindamycin phosphate is a small molecule, biosimilar risk is not applicable. The relevant competitive mechanism is ANDA-based generic entry, not a 351(k) biosimilar application.

What geographic coverage did the patent have?

US Patent 6,387,383 provided rights only in the United States. It did not automatically protect the formulation in Canada, Europe, Japan, China, or other markets.

Foreign protection would require separate national or regional patents. The scope, expiration, and enforceability of foreign counterparts would depend on the relevant priority claims, national-phase filings, prosecution history, patent-term rules, and maintenance-fee status. A U.S. freedom-to-operate conclusion cannot be extended to foreign markets.

What manufacturing and intellectual-property barriers remain?

The expired patent no longer blocks manufacture of a matching formulation in the United States. Manufacturing barriers may still include:

Valid later patents covering a specific gel, container, or combination product;
Trade secrets involving polymer hydration, mixing order, pH adjustment, or preservative control;
Know-how required to maintain active stability;
Microbial-control requirements for aqueous products;
Viscosity and content-uniformity controls;
Packaging compatibility;
FDA facility and quality-system requirements;
Product-specific bioequivalence or comparative-performance testing.

The claimed manufacturing method is simple at a high level, but commercial execution may require controlled addition order, hydration conditions, neutralization, mixing speed, and filling parameters. Those process details are not necessarily coextensive with claim 37.

Key Takeaways

US Patent 6,387,383 is a formulation and method patent, not a basic clindamycin patent.
Its core technology is a low-viscosity aqueous topical gel using a lightly cross-linked polyacrylic acid polymer.
Claims 1, 18, and 37 cover compositions, treatment methods, and manufacturing methods.
Claims 6, 7, 26, 27, 42, and 43 are the most relevant to clindamycin phosphate gel products.
Claims 10, 31, and 46 cover clindamycin phosphate and tretinoin combinations.
Claims 54 through 59 cover desonide formulations.
The patent’s listed U.S. expiration date was January 28, 2020.
No biosimilar pathway applies; the relevant route was ANDA-based generic entry.
A product using a different polymer, dosage form, or materially different formulation could have avoided literal infringement.
The patent is no longer an active U.S. barrier, but later patents, trade secrets, and FDA requirements remain relevant.

Frequently Asked Questions

Does US Patent 6,387,383 cover all clindamycin phosphate gels?

No. It covers clindamycin phosphate gels only when the product also satisfies the specified polymer, pH, viscosity, solvent, preservative, and water limitations of the relevant claim.

Does the patent cover clindamycin phosphate foam products?

Generally, the claims are directed to aqueous gels. A foam product would require separate analysis and would not automatically fall within the claims merely because it contains clindamycin phosphate.

Can a generic use propylene glycol and avoid the patent?

Not necessarily. Propylene glycol is expressly included in the preferred clindamycin formulation. Avoidance would require analysis of the full composition, including polymer, concentration ranges, pH, viscosity, preservative, and the applicable claim.

Is the patent relevant to clindamycin-tretinoin products such as Ziana?

Historically, potentially. Claims 9, 10, 30, 31, 45, and 46 specifically address clindamycin phosphate and tretinoin gels. Any current analysis must also consider the expiration of this patent and separate patents associated with the commercial product.

Does patent expiration eliminate FDA requirements for a generic topical gel?

No. Expiration removes the patent barrier but does not eliminate the need for FDA approval, chemistry and manufacturing controls, product-performance data, compliant labeling, and manufacturing-facility qualification.

References

United States Patent and Trademark Office. (2002). U.S. Patent No. 6,387,383: Aqueous gel compositions and methods of use thereof. https://patents.google.com/patent/US6387383
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. https://www.fda.gov/drugs/drug-approvals-and-databases/orange-book-data-files
U.S. Food and Drug Administration. (2024). Abbreviated new drug application submissions and patent certifications. https://www.fda.gov/drugs/abbreviated-new-drug-application-anda/abbreviated-new-drug-application-anda
U.S. Food and Drug Administration. (2023). Approved labeling for clindamycin phosphate topical gel products. DailyMed. https://dailymed.nlm.nih.gov/
35 U.S.C. §§ 154, 156, 271, 355. (2024). Patent term, patent infringement, and abbreviated new drug applications. https://uscode.house.gov/

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	1304992	⤷ Start Trial	C300617	Netherlands	⤷ Start Trial
European Patent Office	1304992	⤷ Start Trial	PA2013025	Lithuania	⤷ Start Trial
European Patent Office	1304992	⤷ Start Trial	1390049-3	Sweden	⤷ Start Trial
European Patent Office	1304992	⤷ Start Trial	92401	Luxembourg	⤷ Start Trial
European Patent Office	1304992	⤷ Start Trial	CR 2013 00053	Denmark	⤷ Start Trial
European Patent Office	1304992	⤷ Start Trial	PA2013025,C1304992	Lithuania	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,387,383

Summary for Patent: 6,387,383