US Patent 6,469,015: Penciclovir Topical Formulation Claims, Expiration, and Patent Landscape

US Patent 6,469,015 protects topical penciclovir formulations containing at least 30% propylene glycol, with dependent claims covering defined water, oil, penciclovir, and emulsifier ranges. It also protects topical treatment of herpes infections, including herpes simplex virus types 1 and 2 and varicella-zoster virus. The patent is associated with the penciclovir 1% cream marketed in the United States as Denavir.

The patent’s commercial importance was concentrated in the formulation and topical-delivery limitations, rather than in penciclovir as a molecule. Based on the patent’s priority framework and ordinary US patent-term rules, the patent term ended in 2016. The claims are therefore expired and cannot presently block a generic or other third party on a patent-enforcement basis.

What does US Patent 6,469,015 cover?

The patent covers two principal subject-matter categories:

A topical pharmaceutical composition containing:
- At least 30% propylene glycol;
- 0.5% to 10% solubilized penciclovir; and
- An oil-in-water or aqueous formulation environment.
A method of treating herpes viral infections by administering that formulation topically.

The claims do not broadly cover every penciclovir formulation. They require a combination of penciclovir concentration, propylene glycol concentration, and topical formulation characteristics.

Claim structure

Claim group	Subject matter	Principal limitation
1	Independent formulation claim	At least 30% propylene glycol and 0.5%-10% solubilized penciclovir
2-5	Narrower formulation ranges	Water, propylene glycol, oil phase, and 1% penciclovir
6	Formulation with emulsifier	Emulsifier required
7	Independent treatment method	Topical treatment using the claimed formulation
8	Method for varicella-zoster virus	Depends from claim 7
9-18	Specific emulsifiers	Includes polysorbate 60, sorbitan esters, fatty alcohols, sodium lauryl sulfate, Cetomacrogol 1000, and Carbomer 940
19	Method for HSV-1 or HSV-2	Depends from claim 7
20-29	Treatment methods with specified emulsifiers	Narrows claim 7 by emulsifier identity

How broad is claim 1 of US 6,469,015?

Claim 1 is the principal composition claim. A formulation generally falls within its literal scope if it contains all of the following:

Penciclovir in solubilized form;
Penciclovir at 0.5% to 10%;
Propylene glycol at 30% or more; and
An oil-in-water or aqueous topical pharmaceutical formulation.

The claim does not require a particular emulsifier, a particular oil, a particular dosage regimen, or a particular herpes virus. Those limitations appear in dependent claims or method claims.

Key claim limitations

"At least 30% propylene glycol"

This is a quantitative limitation. A product containing 29% propylene glycol would not literally satisfy the limitation, assuming the percentage is measured on the same basis used in the patent. A product containing 30% or more would satisfy the numerical threshold if the remaining limitations are present.

The claim language does not limit propylene glycol to a narrow range in claim 1. Claims 2 through 5 introduce narrower ranges:

Claim 2: 30%-60% propylene glycol and at least 15% water.
Claim 3: 30%-50% propylene glycol and at least 20% water.
Claim 4: 35%-45% propylene glycol, 25%-40% water, 0.75%-5% penciclovir, and an oil phase.
Claim 5: Claim 4 with 1% penciclovir.

"0.5 to 10% solubilized penciclovir"

The claim requires a concentration range and a solubilized state. A conventional suspension containing undissolved penciclovir could present a non-infringement position if the active ingredient is not solubilized, although claim construction would depend on the patent specification and product testing.

The 1% penciclovir concentration used in Denavir falls within both the broad range in claim 1 and the narrower concentration limitation in claim 5.

"Oil in water or aqueous topical pharmaceutical formulation"

The formulation limitation places the claim in the topical semisolid or emulsion field. An oil-in-water cream is within the express language. A purely nonaqueous ointment would raise a stronger non-infringement argument, depending on whether it qualifies as an "aqueous topical pharmaceutical formulation" under the patent’s specification.

The claim is not limited to a cream by name. A gel, lotion, emulsion, or other topical dosage form could potentially fall within the claim if it satisfies the required composition and formulation characteristics.

What formulations are protected by claims 2 through 5?

Claims 2 through 5 progressively narrow the formulation space.

Claim	Penciclovir	Propylene glycol	Water	Other requirement
1	0.5%-10%	At least 30%	Not expressly quantified	Oil-in-water or aqueous topical formulation
2	Within claim 1	30%-60%	At least 15%	Depends on claim 1
3	Within claim 2	30%-50%	At least 20%	Depends on claim 2
4	0.75%-5%	35%-45%	25%-40%	Oil phase required
5	1%	35%-45%	25%-40%	Oil phase; depends on claim 4

Claim 5 is commercially significant because it captures a 1% penciclovir oil-in-water cream with the specified vehicle ranges. It is substantially narrower than claim 1 but more closely aligned with the marketed product profile.

A formulation containing 1% penciclovir, 40% propylene glycol, 30% water, and an oil phase would fall squarely within the numerical limitations of claim 5, assuming the formulation otherwise satisfies the claim language.

What emulsifiers are protected by US 6,469,015?

Claim 6 adds an emulsifier to the broad formulation of claim 1. Claim 9 identifies a closed list of emulsifiers, and claims 10 through 18 separately claim each listed emulsifier.

The listed substances are:

Claim	Emulsifier
10	Polyoxyethylene sorbitan monostearate, also known as polysorbate 60
11	Sorbitan monostearate
12	Sorbitan monooleate
13	Cetostearyl alcohol
14	Myristyl alcohol
15	Glyceryl monostearate
16	Sodium lauryl sulfate
17	Cetomacrogol 1000
18	Carbomer 940

The method claims repeat much of this structure. Claims 20 through 27 and 29 apply the emulsifier limitations to the treatment method. Claim 28 specifically requires Cetomacrogol 1000 but depends from claim 4 rather than claim 20, creating a narrower formulation-method combination.

Claim-drafting implications

The emulsifier claims are composition-specific. A product using an emulsifier outside the listed group may avoid literal infringement of claims 9 through 18, but it could remain exposed under claim 6 if the product still contains an emulsifier and satisfies claim 1.

The presence of an emulsifier is not required by claim 1. A formulation that satisfies claim 1 without an emulsifier could still fall within the broad composition claim.

What methods of use are protected?

Claim 7 protects topical administration of the claimed penciclovir formulation to a mammal with a herpes viral infection.

The method claims cover:

Herpes viral infections generally under claim 7;
Varicella-zoster virus under claim 8;
Herpes simplex virus type 1 under claim 19; and
Herpes simplex virus type 2 under claim 19.

Claims 20 through 29 add specified emulsifiers to the treatment method.

The method claims require more than administering penciclovir in any form. The administered formulation must contain at least 30% propylene glycol and 0.5%-10% solubilized penciclovir. A systemic penciclovir product, oral famciclovir product, or topical formulation that does not meet those composition limitations would not literally satisfy claim 7.

When did US Patent 6,469,015 lose exclusivity?

US Patent 6,469,015 expired in 2016 under the standard US patent-term framework. The patent is no longer an enforceable barrier to commercial entry.

Event	Status
Patent type	US utility patent
Patent number	US 6,469,015
Issued	October 22, 2002
Technology	Topical penciclovir formulations
Patent term	Ended in 2016
Current enforceability	Expired
Patent-based generic launch barrier	None from this patent

The exact expiration calculation depends on the patent’s earliest effective nonprovisional filing date, any applicable patent-term adjustment, and any terminal disclaimer. Those factors do not alter the commercial conclusion: the patent term has ended.

What is the Orange Book status of the penciclovir product?

Denavir, a 1% penciclovir cream, was approved by the FDA through NDA 020604. Penciclovir is a small-molecule antiviral, and the product is not subject to the biologic-license and biosimilar framework.

The Orange Book historically identified patents associated with approved drug products, but listing status must be distinguished from enforceability. An expired patent may remain visible in historical or current FDA patent records while providing no continuing exclusionary right.

FDA and Orange Book considerations

Issue	Assessment
Reference product	Denavir cream, 1% penciclovir
FDA pathway	New Drug Application
NDA	020604
Dosage form	Topical cream
Active ingredient	Penciclovir
Biosimilar pathway	Not applicable
Generic pathway	Abbreviated New Drug Application, subject to FDA requirements
Patent 6,469,015	Expired
Current patent block	None from this patent

FDA approval and patent expiry are separate events. FDA approval does not establish patent infringement, and patent expiry does not by itself establish that a proposed generic satisfies all regulatory requirements.

Were there Paragraph IV challenges to this patent?

A Paragraph IV certification is used when an ANDA applicant asserts that a listed patent is invalid, unenforceable, or will not be infringed. Public patent records and FDA regulatory records should be evaluated separately for each listed patent and each ANDA.

For US 6,469,015, the commercially relevant point is that any Paragraph IV dispute tied to the patent no longer creates a present launch barrier because the patent has expired. A historical Paragraph IV certification, litigation filing, or settlement would not revive the expired patent.

The patent should also be distinguished from other penciclovir and Denavir-related patents. A generic applicant may have faced multiple listed patents, including formulation or active-ingredient patents, even where one patent did not independently prevent launch.

What patent litigation affected Denavir or penciclovir?

The principal litigation risk historically would have involved:

Whether a proposed topical product contained solubilized penciclovir;
Whether propylene glycol was present at 30% or more;
Whether the product was an oil-in-water or aqueous formulation;
Whether the product contained a listed emulsifier;
Whether the claimed formulation was invalid for anticipation or obviousness; and
Whether a listed patent was enforceable after prosecution-history review.

No current litigation exposure can arise from enforcing US 6,469,015 itself because the patent has expired. Any later dispute would need to rely on a different unexpired patent, trade-secret claim, regulatory theory, or commercial agreement.

Likely validity issues

The claim set presents several potential validity pressure points:

Prior-art formulation technology.
Propylene glycol, emulsions, aqueous creams, and surfactants were established pharmaceutical excipients. The patentable distinction would therefore center on the particular combination and its effect on penciclovir solubilization and topical delivery.
Obviousness.
A challenger could argue that combining known penciclovir with a high propylene glycol concentration and conventional emulsifiers was predictable. The patent owner would rely on formulation performance, stability, solubility, skin delivery, or other evidence of unexpected results.
Claim construction.
The meanings of "solubilized," "aqueous," "oil in water," and the percentage calculations could affect infringement and validity.
Enablement and written description.
Broad claims covering 0.5%-10% penciclovir and at least 30% propylene glycol would be tested against the working examples and the full scope of the claims.

How strong is the patent estate for topical penciclovir?

The patent estate was strongest before expiration because it combined broad and narrow claims around the commercial product.

Estate element	Commercial value
Broad formulation claim	Covered a wide range of high-propylene-glycol topical products
Narrow formulation claims	Mapped more closely to a 1% penciclovir cream
Emulsifier claims	Added product-specific fallback positions
Method-of-use claims	Covered treatment of HSV and varicella-zoster infections
Active ingredient	Penciclovir itself was a separate technology category
Manufacturing claims	The patent does not principally claim a manufacturing process
Remaining strength	None against current products after expiration

The estate was not a biologic patent estate and did not depend on cell lines, antibodies, biosimilar interchangeability, or complex manufacturing controls. Its value came from formulation know-how and market exclusivity for a topical cream.

What manufacturing and formulation barriers remain?

Patent expiration removes the legal barrier created by US 6,469,015, but development barriers can remain.

A competing manufacturer would need to demonstrate:

Adequate penciclovir solubilization;
Physical and chemical stability;
Consistent particle or droplet characteristics;
Acceptable skin feel and spreadability;
Microbiological quality;
Preservative effectiveness where applicable;
Container-closure compatibility;
Uniformity of the active ingredient; and
Comparable topical performance under the applicable FDA pathway.

The listed emulsifiers are conventional pharmaceutical excipients. They do not create a continuing exclusivity barrier by themselves. A manufacturer can also investigate alternative emulsifiers, nonemulsion vehicles, different propylene glycol concentrations, or different topical delivery systems.

How does penciclovir compare with competing antiviral products?

Product or ingredient	Primary use	Delivery	Patent relevance
Penciclovir	Herpes labialis and herpesvirus infections	Topical cream	US 6,469,015 focused on formulation and use
Acyclovir	HSV and varicella-zoster infections	Oral, topical, injectable	Separate active-ingredient and formulation estates
Famciclovir	Systemic HSV and varicella-zoster infections	Oral	Prodrug technology; separate patents
Valacyclovir	Systemic HSV and varicella-zoster infections	Oral	Prodrug and formulation technology
Docosanol	Cold sores	Topical cream	Different mechanism and formulation estate

Penciclovir cream competes mainly with topical acyclovir and docosanol for herpes labialis. Oral antivirals compete in patients requiring systemic treatment or treatment of broader herpesvirus disease.

Which companies are challenging the commercial position?

The commercial position for Denavir is exposed to generic topical penciclovir manufacturers because US 6,469,015 has expired. A company need not overcome this patent through a Paragraph IV challenge now. It can rely on patent expiry, subject to any other unexpired listed patents and FDA requirements.

The relevant competitive groups are:

Generic dermatology manufacturers;
Contract manufacturers developing topical semisolids;
Companies with established ANDA portfolios;
Branded manufacturers selling acyclovir or docosanol; and
Manufacturers with expertise in emulsion and cream scale-up.

No biosimilar competition is relevant. Penciclovir is a small molecule, so the competitive pathway is generic drug approval rather than biosimilar approval.

What generic launch scenarios exist?

Scenario 1: Direct formulation match

A manufacturer develops a 1% penciclovir cream with high propylene glycol and an oil-in-water structure that resembles the historical product. The expired patent does not block launch. Regulatory approval remains the principal hurdle.

Scenario 2: Formulation design-around

A manufacturer uses a different vehicle, a different emulsifier, or less than 30% propylene glycol. This can reduce claim-overlap risk, but it may create additional development work involving stability, performance, and product sameness.

Scenario 3: Alternative topical dosage form

A gel, lotion, or other topical dosage form could avoid some narrow cream claims. It would still require analysis under claim 1 and any other relevant patent.

Scenario 4: Alternative antiviral

A manufacturer launches topical acyclovir or another antiviral rather than penciclovir. This avoids penciclovir-specific claims but competes in the same therapeutic market.

What is the revenue exposure from patent expiry?

The patent’s expiration removes formulation exclusivity for the commercial 1% penciclovir cream. Revenue exposure depends on:

The size of the US herpes labialis market;
Denavir prescription volume;
Pricing relative to acyclovir and docosanol;
Insurance coverage;
Generic substitution;
Prescriber loyalty;
OTC competition; and
The existence of any separate unexpired patents or regulatory exclusivities.

Because this patent expired years ago, its current revenue exposure is historical rather than prospective. Any remaining brand value would arise from trademarks, distribution, physician familiarity, or formulation and manufacturing execution, not from enforceable rights under US 6,469,015.

What licensing deals are relevant?

The patent’s commercial history is linked to the penciclovir and Denavir product programs developed by the GlaxoSmithKline predecessor organizations. Public patent ownership and product commercialization should be distinguished from private licensing arrangements. A patent assignment, corporate merger, or product divestiture does not necessarily disclose all contractual rights involving formulation technology.

No continuing license can preserve exclusionary rights after the patent’s expiration. A private license could still allocate royalties, know-how, trademarks, or confidential manufacturing information, but it would not extend the patent term against third parties.

What is the geographic coverage?

US 6,469,015 provides rights only in the United States. Parallel protection would require separate foreign patents or applications.

Jurisdiction	Effect of US 6,469,015
United States	Patent expired
European Union	Requires separate national or European patent analysis
United Kingdom	Requires separate UK or European patent analysis
Canada	Requires separate Canadian patent analysis
Japan	Requires separate Japanese patent analysis
Australia	Requires separate Australian patent analysis
Other countries	No effect without local rights

A US patent cannot block manufacture, sale, or use outside the United States. Foreign patent terms may have differed, particularly where applications claimed different priority dates or received supplementary protection or other national adjustments.

Key Takeaways

US 6,469,015 covers topical penciclovir formulations with at least 30% propylene glycol and 0.5%-10% solubilized penciclovir.
Claims 2 through 5 narrow the formulation using water, oil-phase, propylene glycol, and penciclovir ranges.
Claims 6 and 9 through 18 cover formulations containing specified emulsifiers.
Claims 7 through 8 and 19 through 29 cover topical treatment of herpes infections, including HSV-1, HSV-2, and varicella-zoster virus.
The patent’s claims were relevant to a 1% penciclovir cream such as Denavir.
The patent expired in 2016 and is no longer a current US patent barrier.
Penciclovir is a small molecule, so biosimilar analysis is not applicable.
Generic manufacturers can pursue topical penciclovir products without overcoming this expired patent, subject to other listed patents and FDA requirements.
Any continuing commercial protection would have to come from other patents, trademarks, regulatory rights, know-how, or market position.

FAQs

Does US Patent 6,469,015 cover all penciclovir creams?

No. It covers creams and other topical formulations only when they satisfy the claim limitations, including at least 30% propylene glycol and 0.5%-10% solubilized penciclovir for the broad composition claim.

Is a penciclovir gel potentially outside the patent?

Yes. A gel may avoid some claims directed to oil-in-water formulations or narrower oil-phase formulations. It could still fall within claim 1 if it is an aqueous topical pharmaceutical formulation containing the required penciclovir and propylene glycol concentrations.

Does using a different emulsifier avoid infringement?

Not necessarily. A different emulsifier may avoid the closed-list claims in claims 9 through 18, but claim 6 is broader and requires only an emulsifier in addition to the claim 1 formulation.

Can an expired patent be used to block an ANDA?

No. An expired patent cannot provide a current injunction or statutory exclusivity barrier. It may remain relevant to historical litigation or patent-record analysis, but not as an enforceable US patent right.

Are topical penciclovir products subject to biosimilar approval?

No. Penciclovir is a small-molecule active ingredient. A competing product would generally proceed through the generic drug framework, not the biosimilar pathway.

References

U.S. Patent and Trademark Office. (2002). U.S. Patent No. 6,469,015: Pharmaceutical formulations containing penciclovir. U.S. Department of Commerce.
U.S. Food and Drug Administration. (n.d.). Drugs@FDA: Denavir (penciclovir) cream, NDA 020604. U.S. Department of Health and Human Services.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.
U.S. Food and Drug Administration. (n.d.). Orange Book: Approved drug products with therapeutic equivalence evaluations. U.S. Department of Health and Human Services.
U.S. Patent and Trademark Office. (2024). Manual of Patent Examining Procedure, Chapter 2700: Patent terms and adjustments. U.S. Department of Commerce.
U.S. Food and Drug Administration. (2017). Approved drug products with therapeutic equivalence evaluations, 37th edition. U.S. Department of Health and Human Services.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
African Regional IP Organization (ARIPO)	197	⤷ Start Trial
African Regional IP Organization (ARIPO)	9000236	⤷ Start Trial
Austria	142880	⤷ Start Trial
Australia	643975	⤷ Start Trial
Australia	7155891	⤷ Start Trial
Canada	2074503	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 6,469,015