US Patent 6,117,843: Claim Scope, Legal Status, and Clindamycin-Benzoyl Peroxide Patent Landscape

US Patent 6,117,843 covers stable topical compositions combining benzoyl peroxide with clindamycin phosphate or clindamycin hydrochloride. Its central limitation is not the mere presence of both active ingredients. The claims require a specific formulation architecture: benzoyl peroxide must remain suspended, clindamycin must initially be in solution at a pH of about 5.9 to 6.9 before combination, and the final composition must have a pH from about 4.0 to less than 7.0 and remain stable at room temperature.

The patent was directed to the formulation technology used in clindamycin/benzoyl peroxide acne products, including BenzaClin-type products. The patent term has expired, so the claims no longer create a current US blocking right. They remain relevant for historical freedom-to-operate analysis, generic launch analysis, patent validity review, and evaluation of later formulation patents.

What does US Patent 6,117,843 protect?

The patent protects a topical pharmaceutical composition containing two chemically different phases:

A suspension of benzoyl peroxide.
A solution containing pharmaceutical-grade clindamycin phosphate or clindamycin hydrochloride.

The key process-related limitation is the pH of the clindamycin solution before it is mixed with benzoyl peroxide. That solution must have an adjusted pH of approximately 5.9 to 6.9. After mixing, the finished product must have a pH from approximately 4.0 to below 7.0 and must be stable at room temperature. (U.S. Patent No. 6,117,843, 2000).

The patent therefore targets compatibility and stability problems caused by combining an oxidizing acne active, benzoyl peroxide, with an antibiotic, clindamycin.

What is the inventive concept?

The practical inventive concept is the controlled preparation of a low-pH, room-temperature-stable clindamycin/benzoyl peroxide composition. The claims focus on:

Maintaining benzoyl peroxide as a suspension rather than dissolving it.
Maintaining clindamycin in a solution phase.
Adjusting the clindamycin solution before combination.
Keeping the final formulation below pH 7.
Achieving room-temperature stability.
In several claims, excluding dioctyl sodium sulfosuccinate, also known as DSS.

The patent does not claim benzoyl peroxide alone, clindamycin alone, or every possible acne formulation containing the two actives.

How are the claims structured?

Claims 1, 12, and 14 are the three principal independent claims. They overlap substantially but use different drafting approaches.

Claim	Claim type	Principal scope
1	Composition claim	BPO suspension plus clindamycin solution, pre-combination pH 5.9-6.9, final pH about 4.0 to below 7.0, room-temperature stability
12	Composition claim	Similar to claim 1, without the gelling-agent limitation
14	Product-by-process claim	Composition made by combining the specified BPO suspension and adjusted clindamycin solution
2	Dependent composition claim	Adds a gelling agent
3	Dependent composition claim	Requires a gel
4	Dependent composition claim	Gelling agent is a carboxylated polymer
5	Dependent composition claim	Carboxylated polymer is a carboxy vinyl polymer
6	Dependent composition claim	Carboxy vinyl polymer is carboxypolymethylene
7	Dependent composition claim	Clindamycin is clindamycin phosphate
8	Dependent composition claim	Composition is free of DSS
9	Dependent composition claim	BPO is an aqueous slurry of BPO powder
10	Dependent composition claim	BPO is present at 1% to 20% by weight
11	Dependent composition claim	Clindamycin concentration is 2% to 15% by weight
13	Dependent composition claim	Claim 12 composition is free of DSS
15	Dependent composition claim	Claim 14 composition is free of DSS

Claims 2 through 11 depend from claim 1. Claim 13 depends from claim 12. Claim 15 depends from claim 14.

What limitations must a product satisfy to infringe claim 1?

A product accused under claim 1 would generally need to satisfy all of the following limitations:

Limitation	Required feature
Dosage form	Topical therapeutic composition
pH of final product	About 4.0 to less than 7.0
Stability	Stable at room temperature
BPO phase	Suspension
Clindamycin phase	Solution
Clindamycin identity	Pharmaceutical-grade clindamycin phosphate or clindamycin hydrochloride
Pre-mixing condition	Clindamycin solution adjusted to about pH 5.9 to 6.9 before combination

A product containing both actives would not necessarily fall within the claim if, for example:

The final pH is 7.0 or higher.
The clindamycin is not present in a solution before mixing.
Benzoyl peroxide is dissolved rather than suspended.
The composition uses a different antibacterial active.
The clindamycin solution was not adjusted to the claimed pre-combination pH.
The product is not stable at room temperature.

The terms "about" and "stable at room temperature" create potential claim-construction and proof issues. The patent does not convert every formulation near the numerical boundaries into an infringement case automatically. The relevant question would be how a court construes the ranges and what stability evidence establishes the claimed result.

What do claims 2 through 11 add?

How do the gel claims narrow the patent?

Claims 2 and 3 limit the formulation by requiring a gelling agent and then a gel composition. Claims 4 through 6 narrow the gelling system further:

Claim 4: carboxylated polymer.
Claim 5: carboxy vinyl polymer.
Claim 6: carboxypolymethylene.

Carboxypolymethylene is associated with carbomer-type polymeric gelling systems commonly used in topical gels. A cream, lotion, liquid, or emulsion without the claimed gel structure would not meet these dependent limitations, although it could still implicate an independent claim if all independent-claim elements were present.

What does the DSS limitation do?

Claims 8, 13, and 15 require the composition to be free of dioctyl sodium sulfosuccinate. The limitation creates narrower, formulation-specific claim positions. It does not broaden the patent to cover all surfactant-free compositions because the claims still require the other independent limitations.

A product containing DSS could avoid these dependent claims while potentially remaining within claim 1 or claim 12.

What are the concentration limitations?

Claim 10 requires benzoyl peroxide at 1% to 20% by weight. Claim 11 requires clindamycin at 2% to 15% by weight.

These ranges are broad compared with commercial acne products. A typical clindamycin phosphate/benzoyl peroxide product has approximately 1.2% clindamycin phosphate and 5% benzoyl peroxide, depending on how the product labels the active concentration. A product at 5% BPO could fall within claim 10. The claim 11 concentration range requires careful analysis of whether the claimed percentage refers to clindamycin active, clindamycin phosphate, or the formulation’s labeled salt concentration.

Does US Patent 6,117,843 cover BenzaClin?

The patent is historically associated with the clindamycin phosphate/benzoyl peroxide gel technology used in BenzaClin products. BenzaClin was approved by the FDA as a topical acne treatment containing clindamycin phosphate and benzoyl peroxide. The approved product used a combination of clindamycin phosphate and benzoyl peroxide in a topical gel vehicle. (U.S. Food and Drug Administration, 2000).

The relationship between a patent and an FDA-approved product depends on the exact product formulation and the patent listings made in the Orange Book. A patent may cover an approved product’s formulation, method of manufacture, or method of use. Orange Book listing does not establish that every claim is valid or infringed, but it provides the principal regulatory patent notice for an approved drug product. (FDA, 2024).

What was the Orange Book status of US Patent 6,117,843?

US Patent 6,117,843 was listed in connection with the relevant clindamycin/benzoyl peroxide product franchise. Its regulatory significance was highest during the period when the patent remained unexpired and an ANDA applicant had to address the listed patent.

The typical ANDA options under the Hatch-Waxman Act were:

Paragraph I: no patent information had been submitted.
Paragraph II: the patent had expired.
Paragraph III: the applicant would wait until patent expiration.
Paragraph IV: the patent was invalid, unenforceable, or would not be infringed.

After expiration, the practical Orange Book function of the patent shifted from a barrier to an historical record. An expired patent cannot support a new injunction against a generic product based solely on future commercial launch.

When did US Patent 6,117,843 lose exclusivity?

The patent is expired as of 2025. Its enforceable US patent term ended before the current generic market period for clindamycin/benzoyl peroxide products.

The exact terminal date should be taken from the USPTO patent record and the applicable Orange Book entry because patent term can be affected by:

The effective US filing date.
Patent-term adjustment.
Patent-term extension, if any.
Terminal disclaimers.
Continuity or priority relationships.

No current patent-term extension appears to create an active blocking right for this patent. The expiration means that the patent cannot presently prevent a competing formulation that meets the old claim language.

Were Paragraph IV challenges relevant to this patent?

Yes. A generic applicant seeking approval before the listed patent’s expiration could use a Paragraph IV certification. The applicant would typically argue one or more of the following:

The proposed product does not contain a clindamycin solution adjusted to the claimed pre-combination pH.
The product does not have a final pH below 7.
The product lacks the claimed room-temperature stability.
Benzoyl peroxide is not present as the claimed suspension.
The claims are invalid for anticipation or obviousness.
The claim terms are indefinite or not adequately supported.

A Paragraph IV certification would expose the applicant to patent litigation if the patent owner filed suit within the statutory period. Once the patent expired, the Paragraph IV risk became historical rather than a current launch barrier. The public records for any individual ANDA challenge, notice letter, settlement, or court disposition must be checked in FDA ANDA records, federal district court dockets, and the Orange Book litigation listing.

What prior art and validity issues affect the patent?

The strongest validity questions concern whether the patent’s specific combination of features was nonobvious over earlier acne formulations.

Potential prior-art categories

Prior-art category	Relevance
Benzoyl peroxide topical preparations	Establishes the BPO suspension and acne-treatment background
Topical clindamycin products	Establishes the antibiotic component and conventional vehicles
Separate clindamycin/BPO formulations	Could challenge the combination itself
pH-adjusted antibiotic solutions	Could challenge the pre-combination pH limitation
Carbomer gels	Could challenge claims 2-6
DSS-containing or DSS-free vehicles	Relevant to claims 8, 13, and 15
Stability studies	Relevant to enablement, written description, and obviousness

The patent’s better validity position historically came from the interaction between the limitations. A reference disclosing clindamycin and benzoyl peroxide separately would not necessarily anticipate the claimed composition. A stronger challenge would require a reference disclosing the two active phases, the pre-mixing pH adjustment, the final pH range, and the required stability.

The claims also contain functional limitations. "Stable at room temperature" may require objective testing and an agreed definition of acceptable potency, degradation, appearance, and physical stability. That term could become central in both infringement and validity disputes.

What formulations are protected by the patent?

The claim set is broad enough to reach multiple formulation types, but the dependent claims concentrate on gel products.

Formulation type	Potential relevance
Clindamycin phosphate/BPO gel	Core commercial embodiment
Clindamycin hydrochloride/BPO gel	Expressly included in independent claims
Carbomer gel	Covered by claims 4-6 when other limitations are met
Aqueous BPO slurry gel	Specifically addressed by claim 9
DSS-free gel	Addressed by claims 8, 13, and 15
BPO concentration of 1%-20%	Covered by claim 10 if other limitations are met
Clindamycin concentration of 2%-15%	Covered by claim 11 if other limitations are met
Product with pH 7 or above	Outside the express final-pH limitation
Product without a clindamycin solution phase	Potentially outside the independent claims
Product using clindamycin free base or another salt	Potentially outside the expressly listed clindamycin species

A formulation engineer attempting to design around the expired patent could change the active form, phase behavior, manufacturing sequence, pH profile, vehicle, or concentration. Those design-around concepts have no practical current value against this expired patent, but they may matter when evaluating whether a later patent is independent of the 6,117,843 disclosure.

How does this patent compare with competing acne-drug patent estates?

US Patent 6,117,843 belongs to the small-molecule topical acne patent field. It is distinct from later patents directed to alternative active combinations, delivery vehicles, preservation systems, or improved stability platforms.

Product or technology	Active ingredients	Principal patent risk
BenzaClin-type product	Clindamycin phosphate plus BPO	Historical combination and stability patents, including US 6,117,843
Duac-type product	Clindamycin phosphate plus BPO	Separate formulation, vehicle, and product-specific patent estate
Acanya-type product	Clindamycin phosphate plus BPO	Different BPO concentration and vehicle technology
Ziana-type product	Clindamycin phosphate plus tretinoin	Separate antibiotic/retinoid formulation patents
Generic clindamycin/BPO gel	Clindamycin phosphate plus BPO	Expired legacy patents plus any later formulation patents
Novel topical antibiotic delivery system	Varies	Potentially active platform, manufacturing, or use patents

The key comparison is that 6,117,843 is formulation-specific rather than a broad patent on treating acne with clindamycin and benzoyl peroxide. A competitor with a materially different vehicle or manufacturing sequence could have faced a narrower infringement theory even before expiration.

Are biosimilar risks relevant to this patent?

No. Clindamycin and benzoyl peroxide are small-molecule active ingredients. Products referencing a clindamycin/benzoyl peroxide drug product use the ANDA pathway under section 505(j) of the Federal Food, Drug, and Cosmetic Act, not the biosimilar pathway under section 351(k) of the Public Health Service Act.

The relevant competitive risks are:

ANDA generic entry.
Authorized-generic competition.
Formulation-specific 505(b)(2) products.
OTC or prescription acne products using different active combinations.
Private-label and contract-manufactured topical products.

No biosimilar interchangeability analysis applies.

What manufacturing and IP barriers existed?

The manufacturing issue was the need to combine an oxidizing peroxide suspension with a clindamycin-containing solution without unacceptable degradation or physical instability.

Relevant manufacturing controls include:

Preparation and pH adjustment of the clindamycin solution.
Control of the BPO slurry or suspension.
Order of addition.
Mixing energy and shear.
Polymer hydration and gel formation.
Control of oxygen exposure and temperature.
Uniformity of BPO distribution.
Packaging compatibility.
Stability testing at room temperature.

The patent’s process language gives the pre-combination pH adjustment particular importance. A manufacturer could potentially avoid a literal claim theory by using a different preparation sequence, although the doctrine of equivalents would have been a possible issue while the patent was enforceable.

Because the patent has expired, these manufacturing considerations now primarily affect product quality, regulatory comparability, and later patent analysis rather than current infringement risk under 6,117,843.

What patent litigation and settlement risks remain?

No current injunction or enforceable exclusionary right arises from US Patent 6,117,843 after expiration. Historical litigation risk could have involved:

ANDA litigation following a Paragraph IV notice.
Claims for formulation infringement.
Invalidity challenges based on obviousness or anticipation.
Disputes over whether the generic product was stable at room temperature.
Disputes over whether the clindamycin component was a solution before mixing.
Settlement agreements governing an earlier generic launch date.

Any settlement would have commercial relevance only as historical evidence unless it included continuing contractual restrictions independent of the expired patent. Patent settlements can contain provisions that survive patent expiration, but those terms must be reviewed in the actual agreement.

How strong is the patent estate today?

The current estate strength is low because the principal patent has expired.

Factor	Assessment
Core patent validity relevance	Historical
Current enforceability	None after expiration
Composition coverage	Broad within the defined pH and phase structure
Gel coverage	Narrower but commercially relevant
Process coverage	Potentially significant before expiration
Orange Book value	Historical regulatory notice
Generic entry barrier	No current barrier from this patent
Biosimilar exposure	Not applicable
Later continuation risk	Must be checked separately by family and continuation records
Commercial relevance	Product history, formulation know-how, and prior-art significance

The main residual risk is not enforcement of 6,117,843. It is the possibility that a later patent family covers a particular vehicle, concentration, delivery system, preservative system, manufacturing process, or method of use. A freedom-to-operate conclusion for a current clindamycin/benzoyl peroxide product therefore cannot rely on this patent alone.

What is the likely generic launch position?

For a conventional clindamycin phosphate/benzoyl peroxide topical gel, the patent-specific launch position is favorable because US 6,117,843 has expired. A generic applicant no longer needs to defer launch based on this patent.

Commercial launch still depends on:

FDA approval of the ANDA or other regulatory application.
Product quality and stability data.
Bioequivalence or product-equivalence requirements.
Current Orange Book listings for the reference product.
Later patents covering the specific formulation.
Market exclusivity unrelated to this patent.
Manufacturing capacity and supply-chain reliability.

The expired patent does not remove regulatory requirements. It removes one historical patent barrier.

Key Takeaways

US Patent 6,117,843 covers stable topical compositions combining a benzoyl peroxide suspension with a solution of clindamycin phosphate or clindamycin hydrochloride.
The critical limitations are pre-combination clindamycin-solution pH of about 5.9 to 6.9, final pH of about 4.0 to below 7.0, and room-temperature stability.
Claims 2-11 narrow the invention to gels, carbomer-type polymers, DSS-free formulations, aqueous BPO slurries, and specified concentration ranges.
Claims 12 and 14 provide alternative independent claim formats with overlapping composition and product-by-process coverage.
The patent was historically relevant to BenzaClin-type products and their generic equivalents.
The patent has expired and does not create a current US launch injunction or Paragraph IV barrier.
No biosimilar pathway applies because the products contain small-molecule actives.
Current freedom-to-operate analysis must examine later patents covering formulation vehicles, delivery systems, manufacturing methods, preservatives, packaging, and product-specific improvements.

FAQs

Does US Patent 6,117,843 cover all clindamycin and benzoyl peroxide products?

No. It requires specific phase characteristics, pH conditions, clindamycin forms, and room-temperature stability. Products outside those limitations may not fall within the claims.

Does a product with clindamycin phosphate and 5% benzoyl peroxide automatically infringe?

No. The 5% benzoyl peroxide concentration may fall within claim 10, but infringement would still require the other limitations, including the pre-combination clindamycin-solution pH and final pH below 7.

Can a generic launch now be blocked by US Patent 6,117,843?

No. The patent has expired. A generic launch could still face regulatory or later-patent issues, but this patent no longer provides a current exclusionary right.

Is clindamycin hydrochloride commercially important under this patent?

It is legally important because the independent claims expressly cover clindamycin hydrochloride as an alternative to clindamycin phosphate. Commercial products have more commonly relied on clindamycin phosphate.

What should be checked before launching a new clindamycin/benzoyl peroxide gel?

The relevant review should include current Orange Book listings, later US continuation and divisional patents, formulation patents, manufacturing patents, method-of-use patents, FDA product requirements, and any active patent litigation involving the selected reference product.

References

U.S. Patent No. 6,117,843. (2000). Stable pharmaceutical compositions containing benzoyl peroxide and clindamycin. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (2000). BenzaClin clindamycin phosphate and benzoyl peroxide topical gel: FDA approval materials and prescribing information. FDA.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA.
United States Code. (2024). 35 U.S.C. §§ 154 and 156: Patent term and patent term extension. Office of the Law Revision Counsel.
United States Code. (2024). 21 U.S.C. § 355: New drug applications and abbreviated new drug applications. Office of the Law Revision Counsel.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	197248	⤷ Start Trial
Australia	3478893	⤷ Start Trial
Australia	666169	⤷ Start Trial
Brazil	9305884	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,117,843

Summary for Patent: 6,117,843