United States Patent 5,266,329: Scope, Claims, Expiration, and Vaginal Drug-Delivery Patent Landscape

U.S. Patent No. 5,266,329 covers bioadherent vaginal liquid or semi-solid delivery systems using a high-internal-phase emulsion. Its central technical requirement is a continuous external lipoidal phase containing an internal nonlipoidal phase that occupies at least 70% of the system by volume. The claims target controlled vaginal delivery of imidazole antifungals and other antimicrobial agents while reducing treatment duration or drug quantity by at least 25%.

The patent was issued in 1993 and is no longer enforceable under the ordinary pre-Uruguay Round patent-term rule. Its principal commercial significance is historical: it describes a formulation platform that could have covered certain mucoadhesive vaginal creams, gels, emulsions, and related antimicrobial products before expiration.

What does U.S. Patent 5,266,329 protect?

The patent protects a formulation architecture, not a particular named antifungal product.

Its core elements are:

Claim element	Required limitation
Route	Vaginal delivery
Physical form	Liquid or semi-solid
Adhesion	Bioadherent to vaginal surfaces
Phase structure	At least two phases
External phase	Continuous lipoidal phase
Internal phase	Nonlipoidal phase
Internal-phase volume	At least 70% by volume
Active ingredient	Imidazole, antifungal, antibacterial, or other antimicrobial, depending on claim
Release	Controlled release to a receptor site, site of action, absorption site, or use site
Clinical or dosing result	At least 25% reduction in treatment period or active-agent quantity

The strongest unifying limitation is the high-internal-phase emulsion structure. A conventional oil-in-water cream would not automatically fall within the claims. The accused product would need to satisfy the specified phase arrangement, volume ratio, delivery characteristics, and therapeutic reduction requirement.

How do the individual claims differ?

Claim 1: Imidazole vaginal delivery system

Claim 1 requires a vaginal delivery system for fungal infections that:

Is bioadherent to vaginal surfaces.
Contains an active antimicrobial agent comprising an imidazole.
Releases the agent in a controlled manner.
Has a continuous lipoidal external phase.
Has a nonlipoidal internal phase occupying at least 70% of the system by volume.
Reduces treatment duration or imidazole quantity by at least 25%.

This is the principal platform claim for imidazole antifungal formulations. It is limited by both formulation structure and performance.

The phrase "comprising an imidazole" is open-ended. A formulation containing miconazole, clotrimazole, econazole, ketoconazole, or another imidazole-class compound could potentially satisfy the active-agent limitation, provided the remaining limitations are met.

Claim 2: Specific phase arrangements

Claim 2 depends on claim 1 and identifies permitted phase configurations, including:

Emulsions.
Emulsion/dispersions.
Double emulsions.
Suspensions within emulsions.
Mixtures.

Because claim 2 depends on claim 1, it retains all limitations of claim 1. It does not independently cover every vaginal emulsion containing an imidazole. The system must still be bioadherent, contain the specified phase structure, use controlled release, and produce the claimed 25% reduction.

Claim 3: Broader antimicrobial delivery-system claim

Claim 3 removes the express imidazole limitation and covers a vaginal drug-delivery system for treating microorganisms. It requires:

At least two phases.
A continuous external lipoidal phase.
A nonlipoidal internal phase occupying at least 70% by volume.
A liquid or semi-solid high-internal-phase emulsion.
An antimicrobial agent.
A 25% reduction in treatment period or antimicrobial quantity.

This is potentially broader than claim 1 as to the active agent. It may reach antibacterial and antifungal formulations that do not contain an imidazole.

Claim 4: Method of treating vaginal fungal infection

Claim 4 is a method claim requiring administration to a female human of:

A therapeutically effective amount.
A bioadherent liquid or semi-solid system.
A high-internal-phase emulsion.
A continuous lipoidal phase.
A nonlipoidal phase occupying at least 70% by volume.
An antifungal agent.
The claimed 25% reduction in treatment period or drug quantity.

The method claim introduces an infringement question absent from the product claims: whether the formulation was actually administered for the claimed treatment and achieved the specified reduction.

Claims 5 and 6: Antifungal and antibacterial agents

Claims 5 and 6 specify that the active antimicrobial agent may be an antifungal or antibacterial agent.

Claim 5 depends on claim 1, so its interpretation must account for claim 1's imidazole limitation. Claim 6 depends on claim 3 and therefore is potentially broader because claim 3 does not expressly require an imidazole.

Claim 7: Imidazole treatment method

Claim 7 narrows claim 4 by requiring that the antifungal agent be an imidazole agent. It is the most specific method claim directed to imidazole-based vaginal antifungal treatment.

What formulation technology is protected?

The patent's technical center is a high-internal-phase emulsion, often abbreviated HIPE. In the claimed arrangement:

The lipoidal phase is continuous.
The nonlipoidal phase is dispersed internally.
The internal nonlipoidal phase occupies at least 70% by volume.
The system remains suitable for vaginal administration as a liquid or semi-solid.
The formulation is bioadherent and capable of controlled antimicrobial delivery.

The 70% threshold is material. A formulation with 69% internal nonlipoidal phase would not satisfy that numerical limitation under a literal infringement theory, although the doctrine of equivalents could become relevant in litigation.

The claims also require a therapeutic or dosing benefit of at least 25%. That limitation creates a major enforcement issue. The patent owner would need to establish how the baseline treatment period or drug quantity is measured and what comparator is used. Relevant questions would include:

Is the comparison against a conventional cream?
Is the comparator the same active ingredient at a different concentration?
Is treatment duration measured by symptom resolution, mycological cure, or label-directed dosing?
Must the 25% reduction be demonstrated in clinical trials?
Does the result apply to every formulation or only tested embodiments?

When did U.S. Patent 5,266,329 lose exclusivity?

Patent-term timeline

Event	Date or period
Patent issued	November 30, 1993
Governing ordinary term	17 years from grant for a pre-URAA patent
Ordinary expiration	November 30, 2010
Current enforceability	Expired under the ordinary term calculation

U.S. Patent 5,266,329 was issued before the change to the modern 20-year-from-effective-filing-date term. Under the pre-URAA rule, the ordinary term ran for 17 years from issuance. The patent therefore expired in 2010 absent an unusual extension, terminal-disclaimer issue, or other prosecution-specific adjustment. Patent term adjustment generally does not apply in the same manner to patents issued under this historical regime. The statutory framework is reflected in 35 U.S.C. § 154 and the transition rules implemented after the Uruguay Round Agreements Act.[2]

The patent's expiration means its claims cannot ordinarily support a current U.S. infringement action. The technical disclosure may remain relevant as prior art against later patent applications.

What is the Orange Book status of U.S. Patent 5,266,329?

U.S. Patent 5,266,329 should not be treated as a current Orange Book barrier.

The FDA Orange Book lists patents submitted by applicants for approved drug products when the patents meet the applicable listing criteria. A formulation patent does not enter the Orange Book merely because it concerns a drug-delivery technology. The patent must be associated with an approved drug product and submitted in the context of that product's regulatory application.[3]

The patent claims do not identify:

A specific FDA-approved product.
A New Drug Application.
A commercial sponsor.
A dosage strength.
A proprietary product name.
A current listed patent number.

Even if the patent had once been submitted for an approved product, its 2010 expiration would remove it as a current patent-based obstacle to an ANDA applicant. It would not create a present Paragraph IV risk.

What Paragraph IV challenges affect this patent?

No current Paragraph IV challenge should be expected against U.S. Patent 5,266,329 because the patent expired years ago.

A Paragraph IV certification is relevant when an ANDA applicant asserts that a listed patent is invalid, unenforceable, or will not be infringed. The statutory mechanism under the Hatch-Waxman Act applies to patents listed for an approved reference drug and still relevant to the ANDA certification process.[4]

For this patent:

A new ANDA applicant would not ordinarily need to challenge the expired patent.
The patent could not support a 30-month stay.
The patent could not delay FDA approval as an unexpired listed patent.
Any historical Paragraph IV dispute would be a matter of litigation history, not current market exclusivity.

How strong was the patent estate?

The patent was technically distinctive but legally vulnerable in several respects.

Strengths

The claims combine several limitations that can distinguish the platform from ordinary vaginal creams:

Bioadhesion.
Controlled release.
A continuous lipoidal phase.
A nonlipoidal internal phase of at least 70% by volume.
Liquid or semi-solid administration.
A claimed 25% treatment or dose reduction.

A competitor using a conventional formulation might avoid literal infringement even if it used the same antifungal ingredient.

The claims also cover multiple phase configurations. Claim 2's references to double emulsions, suspensions within emulsions, and emulsion mixtures broaden the disclosed formulation space.

Weaknesses

The principal weaknesses are claim clarity, proof of performance, and prior-art exposure.

The 25% reduction limitation is functional and outcome-based. A patent challenger could argue that the claims do not provide an objective test for determining when the requirement is met. The term "bioadherent" may also require a defined testing methodology. The same issue applies to "controlled manner" and "site of action."

The patent also combines composition, delivery, and clinical-performance requirements in a way that may complicate infringement proof. A formulation could satisfy the physical architecture but fail the claimed therapeutic reduction. Conversely, a product could produce a shorter treatment course through a mechanism unrelated to the claimed emulsion structure.

Potential prior-art categories include:

Vaginal creams and suppositories containing imidazole antifungals.
Oil-in-water and water-in-oil vaginal emulsions.
Mucoadhesive drug-delivery systems.
High-internal-phase emulsions.
Controlled-release antimicrobial formulations.
Vaginal dosage forms designed to reduce dosing frequency.

The patent's value would have depended more on formulation know-how and manufacturing control than on the imidazole molecule itself, many of which were known before the patent's filing.

What manufacturing and formulation barriers would a competitor face?

A competitor seeking to design around the patent would have several technical options:

Design-around approach	Potential effect
Use a solid tablet or ovule	Avoids liquid/semi-solid limitation
Use a conventional gel without the claimed phase structure	Avoids high-internal-phase emulsion limitations
Use an aqueous continuous phase	May avoid the continuous lipoidal-phase requirement
Keep the internal nonlipoidal phase below 70%	Avoids the express volume threshold
Use a non-imidazole agent	May avoid claims limited to imidazoles, but not necessarily claim 3
Use a nonbioadhesive dosage form	Avoids bioadhesion limitations
Use a formulation without documented 25% reduction	Creates a performance limitation issue

These design-around strategies do not eliminate regulatory requirements. A new vaginal antifungal product would still require an appropriate FDA pathway, including an ANDA for a therapeutically equivalent generic product where an approved reference exists, or an NDA or other applicable pathway for a new formulation or indication.

How does this patent compare with competing vaginal antifungal patent estates?

U.S. Patent 5,266,329 is different from a molecule patent and from a conventional dosage-form patent.

Patent category	Typical protected subject matter	Relationship to 5,266,329
Active-ingredient patent	Chemical compound or salt	5,266,329 does not claim a specific imidazole molecule
Formulation patent	Cream, gel, tablet, suppository, emulsion	5,266,329 is a specialized formulation patent
Method-of-use patent	Treatment of a defined infection or population	Claims 4 and 7 contain method-of-treatment elements
Manufacturing patent	Mixing, emulsification, filling, or process parameters	The supplied claims do not expressly claim a manufacturing process
Device or applicator patent	Vaginal applicator or delivery device	The supplied claims do not require an applicator
Regulatory exclusivity	FDA exclusivity period	Patent protection and FDA exclusivity are separate rights

The patent therefore would not necessarily block a competitor selling the same imidazole in a different vaginal dosage form. It also would not by itself prevent a competitor from developing a new active ingredient or a conventional non-HIPE formulation.

What litigation and licensing issues matter?

The supplied claims identify no litigation, assignment, license, settlement, or consent judgment. The claims also do not identify the original assignee or a current patent owner. Those matters cannot be inferred from claim language.

For a historical freedom-to-operate review, the relevant issues would have been:

Whether the accused product used a continuous lipoidal phase.
Whether the internal nonlipoidal phase was at least 70% by volume.
Whether the dosage form was bioadherent.
Whether the agent was an imidazole or another antimicrobial.
Whether the formulation provided controlled release.
Whether the 25% reduction could be demonstrated under a legally defensible comparator.

Because the patent expired in 2010, current licensing value would generally arise from know-how, trade secrets, manufacturing methods, or related unexpired continuation patents, not from the expired claims themselves.

Key Takeaways

U.S. Patent 5,266,329 covers bioadherent vaginal liquid or semi-solid high-internal-phase emulsions.
The central structural limitation is a continuous lipoidal phase with a nonlipoidal internal phase occupying at least 70% by volume.
Claims 1 and 7 focus on imidazole antifungals.
Claims 3 and 6 are broader as to antimicrobial agents.
Claims 4 and 7 are method claims requiring treatment of a vaginal fungal infection.
The claims require at least a 25% reduction in treatment duration or active-agent quantity.
The patent issued on November 30, 1993 and ordinarily expired on November 30, 2010.
It is not a current Paragraph IV or Orange Book barrier.
The primary historic validity risks were functional claim language, objective measurement of the 25% reduction, bioadhesion testing, and prior art involving vaginal emulsions and controlled-release systems.
Current commercial value would depend on related unexpired patents, proprietary formulation know-how, or manufacturing trade secrets rather than this patent's expired claims.

FAQs About U.S. Patent 5,266,329

Does U.S. Patent 5,266,329 cover miconazole vaginal products?

Only if the product satisfies all applicable claim limitations, including the claimed phase structure, bioadhesion, controlled release, and 25% reduction requirement. Use of miconazole alone is insufficient.

Can an expired patent still affect a generic vaginal antifungal launch?

It cannot ordinarily support an infringement action after expiration. Its disclosure may still be prior art against later patent applications and may affect validity analysis for related patents.

Does the patent cover vaginal suppositories?

Not automatically. The claims focus on liquid or semi-solid systems and high-internal-phase emulsions. A solid suppository would generally require a separate analysis.

Is the 70% internal-phase requirement likely to be tested analytically?

Yes. Particle-size analysis, microscopy, formulation composition, density calculations, and manufacturing records could be relevant to determining whether the nonlipoidal phase occupies at least 70% by volume.

Could a later patent cover the same delivery concept?

Yes. A later patent could claim a specific active ingredient, excipient combination, manufacturing process, release profile, applicator, patient population, or treatment regimen, subject to novelty, nonobviousness, enablement, and patent-term requirements.

References

U.S. Patent No. 5,266,329, claims 1-7 (issued Nov. 30, 1993).
35 U.S.C. § 154. Patent term.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
21 U.S.C. § 355(j). Abbreviated applications for new drugs.
U.S. Patent and Trademark Office. (2024). Manual of Patent Examining Procedure, §§ 2701-2710. Patent term and expiration.

PCT Information
PCT Filed	October 31, 1985	PCT Application Number:	PCT/US85/02145
PCT Publication Date:	May 07, 1987	PCT Publication Number:	WO87/02576

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	68686	⤷ Start Trial
Canada	1338977	⤷ Start Trial
Germany	3584523	⤷ Start Trial
European Patent Office	0244405	⤷ Start Trial
Japan	2519029	⤷ Start Trial
Japan	S63501563	⤷ Start Trial
World Intellectual Property Organization (WIPO)	8702576	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,266,329

Summary for Patent: 5,266,329