US Patent 6,923,983: Scope, Claims, Expiration, Orange Book Status, and Transdermal Hormone Patent Landscape

US Patent 6,923,983 protects transdermal hormone formulations that combine a hormone, a skin-tolerant ester sunscreen used as a penetration enhancer, and a volatile liquid. The broadest practical embodiment is a hormone formulation containing octyl salicylate and ethanol or isopropanol. The patent also covers estradiol formulations, systemic hormone administration, large-area application, and fixed or variable metered-dose applicators.

The patent issued on August 2, 2005, from an application filed December 20, 2001. Its 20-year statutory term expired on December 20, 2021, absent a term adjustment or extension that would materially change the expiration date. The patent therefore no longer creates an enforceable US blocking right for new commercial products. Its historical importance is greatest for transdermal testosterone and estradiol products using octyl salicylate.

What does US Patent 6,923,983 protect?

The patent protects a transdermal drug delivery system with three required components:

A therapeutically effective amount of a hormone.
At least one specified ester sunscreen functioning as a dermal penetration enhancer.
At least one volatile liquid.

Claim 1 is the principal composition claim. It covers the formulation architecture rather than a particular commercial product, dosage, indication, or application site.

The core claim can be expressed as follows:

Required element	Scope
Active ingredient	A therapeutically effective hormone
Penetration enhancer	A safe, skin-tolerant ester sunscreen within the claimed formula
Enhancer concentration	About 10 to about 10,000 wt% based on hormone weight
Volatile liquid	Required, but not limited in claim 1 to ethanol or isopropanol
Formulation type	Transdermal drug delivery system
Claim format	“Comprising,” which generally leaves room for additional ingredients

Claim 2 identifies octyl salicylate as a specific claimed enhancer. Octyl salicylate is also known as octisalate. This limitation is commercially important because octisalate was used in transdermal hormone products, including products associated with Acrux technology.

How broad is independent claim 1?

Claim 1 is broad in formulation structure but narrower than a generic claim to any hormone gel or spray.

Hormone requirement

The claim requires a hormone but does not limit the invention to testosterone or estradiol. Dependent claims identify a broad group of steroidal hormones, including:

Levonorgestrel
Gestodene
Oestriol
Oestrone
Mestranol
Progesterone-related compounds
Norethisterone and norethisterone acetate
Medroxyprogesterone
Megestrol
Nestorone
MENT
Ethinylestradiol
Estradiol
Testosterone

The use of “a hormone” in claim 1 means the claim is not restricted to the listed hormones in claims 5 through 8. Those dependent claims narrow the invention to specific hormone classes or individual actives.

Penetration-enhancer requirement

The claimed enhancer must be a “safe skin-tolerant ester sunscreen” falling within the formula identified in the patent. The structural definition includes substituents such as hydrogen, lower alkyl, lower alkoxy, halide, hydroxy, or amino groups, together with a C8-C18 alkyl group.

The claim is not directed to every ester, every sunscreen, or every penetration enhancer. A formulation using oleic acid, isopropyl myristate, propylene glycol, or a terpene would not fall within claim 1 merely because those substances enhance skin penetration. The enhancer must meet the formula and functional characterization stated in the claim.

Volatile-liquid requirement

A volatile liquid is mandatory. Claim 3 specifies ethanol, isopropanol, or a mixture of the two. Claims 9 and 10 further define ethanol-based and hydroalcoholic embodiments.

A nonvolatile cream, ointment, adhesive patch matrix, or anhydrous lipid vehicle may fall outside claim 1 if it does not contain a qualifying volatile liquid. The presence of a volatile solvent is therefore a meaningful design-around axis.

What formulations are protected by US Patent 6,923,983?

The most commercially relevant formulations are the estradiol and testosterone embodiments containing octyl salicylate and alcohol.

Claim	Formulation or use	Principal limitations
1	Broad transdermal hormone system	Hormone, claimed ester sunscreen, volatile liquid
2	Octyl salicylate formulation	Claim 1 plus octyl salicylate
3	Alcohol-based system	Claim 1 plus ethanol, isopropanol, or both
4	Concentration-defined system	0.1%-10% hormone, 0.1%-12% enhancer, 78%-99.8% volatile liquid
5	Listed hormone group	Multiple steroid hormones
6	Levonorgestrel	Claim 1 plus levonorgestrel
7	Nestorone or MENT	Claim 1 plus one of those hormones
8	Estradiol, testosterone, and other hormones	Narrower hormone group
9	Estradiol alcoholic system	0.1%-10% estradiol, 1%-12% octyl salicylate, 78%-99.8% USP alcohol
10	Estradiol hydroalcoholic gel	Estradiol, octyl salicylate, alcohol, water, thickener
11	Administration method	Applying the claimed system to an animal
16	Estradiol administration	Claim 11 plus estradiol
17-19	Application area	About 10-800, 10-400, or 10-200 cm²
20	Metered application	Fixed or variable metered-dose applicator

Claim 9: ethanol-based estradiol formulation

Claim 9 is directed to a relatively simple estradiol formulation:

0.1% to 10% estradiol
1% to 12% octyl salicylate
78% to 99.8% Alcohol USP, identified as 95% ethanol

The claim does not require water, a thickener, a pump, or a specific dosing regimen. A formulation meeting these compositional ranges could potentially satisfy claim 9 even if it used a different container or application method.

Claim 10: hydroalcoholic estradiol gel

Claim 10 is narrower and requires:

0.1% to 10% estradiol
1% to 12% octyl salicylate
45% to 90% ethanol, isopropanol, or a mixture
5% to 45% water
0.5% to 5% thickening agent

This claim targets a gel or semisolid system rather than a simple alcoholic spray. The thickener is not specified by chemical identity, leaving the claim open to different carbomers, cellulose derivatives, or other rheology modifiers if they fall within the claim’s scope.

What do the method claims cover?

Claims 11 through 20 cover administration of the formulation to an animal. In patent-claim terminology, “animal” ordinarily includes humans unless the specification or prosecution history indicates otherwise.

The method claims require:

An effective amount of at least one systemic hormone.
Delivery in the formulation of claim 1.
Application to the skin.

Claims 17 through 19 impose application-area ranges. Claim 20 adds a fixed or variable metered-dose applicator.

The method claims are commercially relevant because they reach use of a qualifying formulation even where a product claim might be challenged. They also create potential method-of-use exposure for a manufacturer, distributor, or healthcare provider depending on the conduct and applicable indirect-infringement theory.

The claims do not require:

A particular therapeutic indication
A particular dose per actuation
A specific body site
A particular treatment duration
A particular package or pump
A specific pharmacokinetic profile

When did US Patent 6,923,983 lose exclusivity?

The patent’s statutory term expired on December 20, 2021, based on the December 20, 2001 US nonprovisional filing date and the 20-year term under 35 U.S.C. § 154. The patent issued well before the end of that term, so the issue date did not control expiration.

Event	Date
Priority date	December 20, 2000
US filing date	December 20, 2001
Publication	2003
Patent grant	August 2, 2005
Statutory expiration	December 20, 2021
Current enforceable patent term	Expired

The provisional or priority filing date does not ordinarily start the US patent term. The relevant term generally runs from the earliest effective nonprovisional application in the application chain.

There is no biologic exclusivity issue. The patent covers a small-molecule transdermal drug-delivery system, not a biologic subject to the FDA Purple Book framework.

What is the Orange Book status of US Patent 6,923,983?

The patent was relevant to FDA-listed transdermal hormone products, particularly products using Acrux-style alcohol and octisalate delivery technology. Orange Book relevance is product-specific. A patent is not automatically listed for every drug that uses a similar formulation.

An Orange Book listing can identify:

The reference listed drug
The patent number
The patent expiration date
Whether the patent is a drug-substance, drug-product, or method-of-use patent
Whether an approved generic applicant must address the patent through a Paragraph IV certification

After patent expiration, the listing can remain historically visible, but it no longer creates a live patent barrier. Regulatory exclusivity and patent exclusivity must be analyzed separately. A product may retain FDA marketing exclusivity after a patent expires, but the time periods for these hormone products are generally distinct from the patent term.

The relevant FDA pathway for a generic transdermal product would generally be an abbreviated new drug application, subject to dosage-form equivalence, pharmaceutical equivalence, bioequivalence, labeling, and any remaining listed patents or exclusivities. See FDA, Approved Drug Products with Therapeutic Equivalence Evaluations.

Were Paragraph IV challenges relevant?

Paragraph IV certifications would have been relevant while the patent was listed with an unexpired term for a reference product. A generic applicant could assert that:

The patent is invalid.
The patent is unenforceable.
The proposed product does not infringe.

A Paragraph IV notice could trigger litigation under the Hatch-Waxman framework and a potential 30-month stay of approval under 21 U.S.C. § 355(j)(5)(B)(iii).

Because the patent expired in 2021, a new Paragraph IV challenge directed solely to this patent would generally have limited commercial value. A generic applicant would not need to overcome an enforceable patent term that has already ended. Historical Paragraph IV activity could still matter for understanding market entry timing, litigation settlements, or damages, but it would not restore exclusivity.

Which companies are associated with the commercial technology?

The claimed combination is closely associated with Acrux’s transdermal delivery platform. Acrux developed alcohol-based transdermal products using penetration-enhancing excipients, applicator systems, and controlled dosing concepts. The platform was commercialized through licensing and collaboration arrangements involving hormone products.

Acrux’s commercial relationships included:

Eli Lilly and Company for Axiron testosterone topical solution.
Other product-specific partners for transdermal hormone products in different markets.

The patent itself should not be equated automatically with every product developed by Acrux. A product may use related technology while relying on different patents, later continuations, formulation patents, device patents, or regulatory exclusivities.

How strong was the patent estate?

The patent was commercially useful but technically vulnerable along several claim-construction and validity dimensions.

Strengths

Feature	Commercial effect
Broad claim 1	Captures multiple hormones and alcohol-based systems
Octyl salicylate limitation	Reads on a commercially important enhancer
Wide enhancer-to-hormone ratio	Covers dilute and highly concentrated enhancer systems
“Comprising” language	Permits additional excipients
Method claims	Extends coverage to use of the formulation
Metered-dose claim	Connects formulation protection with delivery hardware

Vulnerabilities

Issue	Potential challenge
Broad hormone genus	Written-description and enablement challenges
“Safe skin-tolerant” language	Claim-construction and definiteness disputes
“Volatile liquid”	Scope may depend on intrinsic disclosure and prosecution history
“About” ranges	Boundary disputes
Known octyl salicylate use	Obviousness arguments based on sunscreen and penetration-enhancer prior art
Broad application method	Anticipation or obviousness based on known transdermal hormone administration
Formula limitations	Design-around using nonqualifying enhancers

The strongest practical claim was likely a formulation claim directed to estradiol or testosterone, octyl salicylate, and an alcohol vehicle within specified concentration ranges. The broad genus claim was more exposed to prior-art and enablement arguments than the narrower product claims.

What generic launch risks existed?

Before expiration, a generic entrant faced several potential barriers:

Patent litigation following a Paragraph IV certification.
Difficulty developing a formulation with equivalent delivery performance.
FDA requirements for transdermal bioequivalence or other product-specific evidence.
Device or applicator differences.
Additional patents in continuations or related families.
Commercial complexity in demonstrating equivalent dose delivery and pharmacokinetics.

After December 20, 2021, the primary risk shifted from this patent to:

Later-expiring formulation patents
Applicator and device patents
Manufacturing-process patents
Labeling or method-of-use patents
Regulatory exclusivity
Product-specific bioequivalence requirements
Trade secrets involving manufacturing or dose uniformity

Expiration of US 6,923,983 does not establish freedom to operate for every transdermal estradiol or testosterone product. It removes one patent right only.

What manufacturing and IP barriers remain?

The patent does not claim a particular manufacturing process. Its claims focus on the composition, administration, application area, and metered applicator. Manufacturing barriers may nevertheless remain in other patent families or in confidential know-how concerning:

Dissolution of the hormone and octyl salicylate
Control of evaporation
Uniformity of dose per actuation
Pump calibration
Container compatibility
Microbial control
Scale-up of hydroalcoholic gels
Stability and crystallization control
Skin permeation performance

A competing manufacturer can avoid the expired claims through a different penetration enhancer, a nonvolatile vehicle, a different hormone, or a formulation outside the claimed concentration ranges. Regulatory equivalence remains a separate requirement.

How does this patent compare with competing transdermal hormone patent strategies?

Strategy	Primary protection	Typical design-around
US 6,923,983	Hormone plus octyl salicylate and volatile liquid	Replace enhancer or vehicle
Adhesive patch	Polymer matrix, reservoir, adhesive, backing	Change matrix or delivery architecture
Hydroalcoholic gel	Hormone, alcohol, water, thickener	Alter excipient system or concentration
Metered spray	Dose-metering device and spray composition	Use a different pump or applicator
Cream or emulsion	Emulsion structure and excipient system	Use gel, spray, or patch
Manufacturing patent	Process controls and production method	Change process sequence or equipment

The patent was strongest against products that copied both the chemical delivery system and the metered-dose approach. It was less effective against materially different transdermal architectures.

Key Takeaways

US Patent 6,923,983 covers transdermal hormone systems containing a claimed ester sunscreen penetration enhancer and a volatile liquid.
Octyl salicylate is the central commercial enhancer identified in the dependent claims.
Estradiol and testosterone formulations are among the most commercially relevant embodiments.
Claims 9 and 10 specifically target alcoholic and hydroalcoholic estradiol formulations.
Claims 11 through 20 cover systemic administration, skin-area ranges, and metered-dose application.
The patent expired on December 20, 2021, based on the December 20, 2001 US filing date.
The patent no longer provides a live US blocking right, although related patents, regulatory exclusivities, device rights, and manufacturing IP may remain relevant.
Historical Orange Book and Paragraph IV significance was product-specific and depended on the reference listed drug.
The principal technical design-around options are changing the enhancer, vehicle, delivery architecture, concentration ranges, or applicator.

FAQs

Does US Patent 6,923,983 cover all octyl salicylate hormone products?

No. The product must also contain a qualifying hormone and volatile liquid and must satisfy the remaining limitations of the applicable claim. The patent’s expiration removes the current enforcement risk, but the historical claim scope was not unlimited.

Does the patent cover testosterone gel without octyl salicylate?

Not necessarily. Octyl salicylate is required only by dependent claims such as claims 2, 9, and 10. Claim 1 covers a broader class of claimed ester sunscreen enhancers, but the formulation must still satisfy the formula and volatile-liquid limitations.

Can a transdermal estradiol spray launch after patent expiration?

Patent expiration removes the blocking effect of US 6,923,983. FDA approval still requires compliance with the applicable regulatory pathway, including product-specific bioequivalence, labeling, quality, and manufacturing requirements.

Are claims 17 through 19 overlapping?

Yes. The ranges are nested. A system applied over 10 to 200 cm² also falls within the broader 10 to 400 cm² and 10 to 800 cm² ranges, assuming the other method limitations are met.

Does claim 20 require a particular pump?

No. Claim 20 covers a fixed or variable metered-dose applicator without specifying a particular pump design. Separate device patents may still protect the structure or operation of a particular applicator.

References

United States Patent No. 6,923,983. (2005). Transdermal drug delivery system. United States Patent and Trademark Office.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. FDA.
U.S. Food and Drug Administration. (n.d.). Orange Book: Approved drug products with therapeutic equivalence evaluations. FDA.
21 U.S.C. § 355. (2024). New drugs.
35 U.S.C. § 154. (2024). Contents and term of patent; provisional rights.
U.S. Patent and Trademark Office. (n.d.). Patent term adjustment and patent term calculation. USPTO.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Australia	PN8144	Feb 19, 1996

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
European Patent Office	0901368	⤷ Start Trial	C300523	Netherlands	⤷ Start Trial
European Patent Office	0901368	⤷ Start Trial	CA 2012 00010	Denmark	⤷ Start Trial
European Patent Office	0901368	⤷ Start Trial	91973	Luxembourg	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,923,983

Summary for Patent: 6,923,983