US Patent 5,881,926: Claim Scope, Patent Expiration, and Pharmaceutical Delivery-System Landscape

US Patent 5,881,926 covers non-spill oral delivery systems that combine a squeezable container, a resealable or tamper-evident outlet, and a storage-stable semisolid pharmaceutical composition. Its strongest protection is directed to the integrated combination of packaging mechanics and high-viscosity oral formulations, not to any particular active ingredient.

The patent is no longer an enforceable U.S. exclusion right under the ordinary 20-year patent-term rule. Its claims therefore remain relevant for freedom-to-operate history, technology ownership, prior-art analysis, and product-design comparisons, but they do not ordinarily block current commercial products.

What technology does US Patent 5,881,926 protect?

The patent protects a delivery architecture with four principal elements:

A squeezable container or flexible packet.
A narrow flow channel or outlet.
A closure or valve that controls flow and limits spillage.
A semisolid oral pharmaceutical formulation having defined viscosity and excipient characteristics.

The claims are not limited to one medicine. They expressly identify broad therapeutic categories and list active ingredients including acetaminophen, aspirin, ibuprofen, diphenhydramine, dextromethorphan, guaifenesin, pseudoephedrine, ciprofloxacin, fluconazole, fluoxetine, enalapril, diltiazem, and lovastatin.

The patent therefore addresses a platform technology for oral liquid and semisolid dosing rather than a single-drug composition.

What are the independent claims in US 5,881,926?

The issued claim set contains several independent claim groups with overlapping but materially different scope.

Independent claim	Principal subject matter	Important limitations
Claim 1	Integrated non-spill delivery system	Squeezable container, unvented spring-biased step cylinder, tamper-evident seal, semisolid formulation, 2,500-70,000 cps viscosity, rotatable button-and-cavity mechanism
Claim 2	Non-spill delivery system	Squeezable container, unvented spring-biased closure, tamper-evident seal, semisolid formulation and viscosity range
Claim 4	Container, outlet, receptacle and composition	Outlet diameter of approximately 0.1-5 mm, unvented closure, receiving receptacle, manually squeezable formulation
Claim 13	Functional delivery-system combination	Semisolid formulation, squeezable container, 0.1-5 mm channel, tamper-evident seal, reversible closure requiring at least two manipulations
Claim 22	Broader non-spill system	Container, channel, closure, tamper evidence, semisolid composition with specified liquid-base and thickener ranges
Claim 36	Single-dose flexible packet	Tearable or cuttable packet containing a semisolid pharmaceutical dose
Claim 41	Spoon-and-cap delivery device	Squeezable container, threaded cap, spoon, channel, internal pin seal and viscosity-defined formulation

Claims 1, 2, 4, 13, 22 and 36 are the principal independent system claims. Claim 41 is an independent device claim focused on a spoon integrated into a cap.

How broad is the formulation protection?

The formulation limitations are broad in ingredient identity but narrower in physical properties and concentration ranges.

Liquid base

Claims 1, 2, 22 and 36 generally require a liquid base comprising one or more of:

Water
Propylene glycol
Polyethylene glycol
Glycerin
Certain combinations of these solvents

Claim 4 and its dependent claims use a related but somewhat different formulation description. Claim 7 narrows the liquid base to water, propylene glycol, glycerin or mixtures thereof.

The liquid base is generally present at approximately 45% to 95% by weight in the claims that use an express concentration range.

Thickener

The claims identify a wide group of thickeners:

Starch and modified starch
Sodium carboxymethyl cellulose
Microcrystalline cellulose
Hydroxypropyl cellulose
Hydroxypropyl methyl cellulose
Other cellulose derivatives
Acacia
Tragacanth
Pectin
Gelatin
Polyethylene glycol
Water-soluble carboxyvinyl polymers
Carbomer

The broad claims specify a thickener concentration of approximately 1% to 55% by weight. Narrower claims address particular excipient systems, including:

Cellulose derivative at approximately 2.4% to 3.3% by volume
Polyethylene glycol at approximately 72% to 85% by volume
Polyethylene glycol at approximately 10% to 25% by volume combined with a cellulose derivative at approximately 2.5% to 3.3% by volume
Propylene glycol and glycerin at approximately 29%, with a carboxyvinyl polymer at up to approximately 1%
Glycerin and 70% sorbitol solution at approximately 40%, with about 2.4% sodium carboxymethylcellulose and 0.9% microcrystalline cellulose

Viscosity limitation

The principal rheological requirement is a Brookfield viscosity of approximately 2,500 to 70,000 centipoise at roughly 20°C to 25°C and a spindle speed of approximately 10 to 20 rpm.

Claim 27 narrows the range to approximately 7,500 to 40,000 centipoise. Claim 13 uses approximately 2,500 to 70,000 centipoise at 25°C and about 10 rpm.

This limitation is important in infringement analysis. A product may use the same container concept and a similar active ingredient but avoid a formulation claim if its measured Brookfield viscosity, test temperature, spindle or formulation composition falls outside the claimed parameters. Testing conditions must match the claim language and any intrinsic patent evidence.

What packaging mechanisms are protected?

Spring-biased step cylinder

Claims 1 through 3 focus on a spring-biased step cylinder. The cylinder has a channel that aligns with the flow path when depressed. When pressure is released, the spring returns the cylinder to a sealing position.

Claim 1 further requires:

A rotatable spring-biased cylinder
An external button
A matching cavity in the dispenser
Depression only when the button is aligned with the cavity
A plastic covering over the cavity
Breaking of that covering when the cylinder is first depressed

This is a relatively narrow mechanical combination. A conventional flip-top cap, ordinary squeeze nozzle, or unstructured check valve would not literally satisfy all of these limitations.

Unvented closure

Claims 1, 2 and 22 require an unvented channel closure device. The closure must open to allow composition flow and reseal the container when closed.

The unvented requirement distinguishes the claimed systems from vented dispensers that admit air through a separate channel. Claims 29 through 31 broaden the closure implementation by allowing a valve that is rotatable or pivotable.

At least two opening manipulations

Claim 13 requires opening the sealing mechanism to involve at least two separate manipulations. Claim 23 adds that opening breaks the tamper-evident seal the first time the closure is opened.

This language supports child-resistance or tamper-evidence arguments, but the claims are not limited to a particular regulatory child-resistant standard. A product’s compliance with a packaging regulation would not alone establish infringement.

Narrow outlet

Claims 4 and 13 require an internal channel diameter of approximately 0.1 mm to 5 mm. This range supports controlled discharge of a high-viscosity semisolid.

A product with a larger opening could avoid these claims, although it might still be evaluated against claims that do not include the diameter limitation.

Spoon and receptacle

The patent claims several receiving structures:

A measuring spoon connected to the channel
A spoon bowl attached to the dispenser
A separate receptacle positioned to receive the dose
A spoon integrated into a threaded cap

Claim 41 is particularly focused on a cap-and-spoon structure. It requires a pin inside the channel that seals the container when the cap is fully closed and allows flow when the threads are partially engaged.

How do the claims differ in practical scope?

Claim 1

Claim 1 is technically dense and relatively narrow. It requires the spring-biased rotatable cylinder, button-and-cavity alignment, plastic tamper-evident covering, semisolid formulation, specified viscosity and broad excipient architecture.

A product would need to match both the mechanical and formulation limitations to present a literal claim 1 issue.

Claim 2

Claim 2 retains the unvented spring-biased step-cylinder structure but omits some of claim 1’s detailed button, cavity and plastic-cover limitations. It is broader than claim 1 in mechanical design but still requires the spring-biased cylinder and viscosity-defined formulation.

Claim 4

Claim 4 shifts toward the outlet diameter, receptacle and general formulation combination. It does not require the specific spring-biased step cylinder recited in claims 1 through 3.

Claim 13

Claim 13 is functionally drafted. It requires a channel, tamper-evident sealing, reversible sealing, two-manipulation opening and a receiving structure. Its “means” language could make construction depend heavily on the corresponding structures disclosed in the specification.

Claim 22

Claim 22 is one of the broadest system claims because it requires a general unvented channel closure without expressly requiring the spring-biased cylinder. It still requires a semisolid composition, specified solvent and thickener groups, viscosity and non-spill dosing functionality.

Claim 36

Claim 36 covers a single-dose flexible packet that is torn or cut open. It does not require the dispenser, valve or spoon architecture used in the other claim groups.

Claim 41

Claim 41 is directed to a specific spoon-cap configuration. It may capture a product that avoids the more elaborate dispenser claims but uses the claimed threaded-cap, pin-seal and spoon arrangement.

What active ingredients fall within the patent?

The claims identify therapeutic categories rather than a single active ingredient.

Category	Examples listed in the claims
Analgesics and anti-inflammatory drugs	Acetaminophen, aspirin, ibuprofen
Antihistamines	Diphenhydramine, terfenadine
Cough and cold products	Dextromethorphan, guaifenesin, pseudoephedrine
Anti-infectives	Ciprofloxacin, fluconazole, acyclovir
CNS drugs	Carbidopa, levodopa, triazolam, fluoxetine
Cardiovascular drugs	Propranolol, enalapril, diltiazem
Gastrointestinal drugs	Ranitidine, fecal softeners
Metabolic drugs	Lovastatin, cholesterol-lowering agents
Supportive products	Vitamins and mineral supplements

The drug lists do not create composition-of-matter protection for these active ingredients. They operate as dependent-claim limitations within the delivery-system framework.

A product containing ibuprofen, for example, would not infringe merely because it contains ibuprofen. The product would need to satisfy the relevant container, closure, formulation, viscosity and dosing limitations.

When did US Patent 5,881,926 lose exclusivity?

The patent was issued in 1999. Under the standard patent-term rule applicable to a utility patent filed after June 8, 1995, the term generally runs 20 years from the earliest effective nonprovisional filing date, subject to patent-term adjustment, patent-term extension and terminal-disclaimer issues. [1]

The patent’s ordinary term therefore ended in the mid-2010s, assuming no unusual term adjustment or extension. The claims are not expected to provide current enforceable exclusion rights in the United States.

The patent is also not a drug patent in the Orange Book sense. It claims a delivery system and pharmaceutical formulation platform rather than an approved drug substance, drug product or approved method of use. FDA Orange Book listing generally concerns patents submitted by new drug application holders for approved drug products and methods of use. [2]

What is the Orange Book status of US 5,881,926?

US 5,881,926 should not be treated as an Orange Book-listed drug patent merely because its claims contain pharmaceutical compositions.

The patent does not appear, from the claim structure supplied, to claim:

A specific approved drug product
A specific approved dosage strength
A drug substance
A drug-specific method of treatment
A drug-specific formulation tied to an approved NDA

Its claims instead cover a container, closure, receptacle, packet and broad formulation platform. That is generally outside the core Orange Book listing categories.

An ANDA applicant would ordinarily address an Orange Book-listed patent through paragraph I, II, III or IV certification. A patent of this type would more commonly arise in ordinary patent litigation, licensing, product-development diligence or a trade-secret and design-around analysis rather than in a drug-specific ANDA patent dispute. [2, 3]

Were Paragraph IV challenges or generic litigation likely?

The patent’s broad active-ingredient lists do not make it a conventional generic-drug patent. A generic applicant for acetaminophen, ibuprofen or another listed drug would not necessarily need to address this patent unless the proposed product used the claimed delivery system.

A paragraph IV challenge would have been commercially relevant only if:

The patent were listed for the relevant reference drug;
The proposed generic used a delivery configuration within the listed claims; and
The patent remained unexpired.

Because the patent term has ended under the ordinary term calculation, current paragraph IV exposure from this patent is not expected. No biosimilar pathway issue is implicated because the patent does not claim a biologic, biosimilar, cell line, antibody, recombinant protein or biological manufacturing process.

What formulation patents are relevant to this technology?

The patent’s formulation coverage is not a conventional drug-specific formulation patent. It is a viscosity-and-excipient platform claim.

The main formulation risk factors are:

Use of a listed solvent
Use of a listed thickener
Concentrations within the stated ranges
Brookfield viscosity within the claimed range
Storage stability
Palatability
Manual squeezeability
Use in a claimed non-spill container or packet

A competing formulation could reduce claim exposure by changing one or more of these variables:

Use a non-listed solvent or vehicle
Use a different rheology modifier
Adjust viscosity outside the claimed range
Use a rigid bottle or metering pump rather than the claimed squeeze architecture
Use a conventional oral liquid below the semisolid viscosity range
Use a unit-dose package that lacks the claimed packet-opening and dispensing configuration

Design-around analysis must evaluate the entire claim. Changing only the active ingredient generally will not avoid a claim if all packaging and formulation limitations remain present.

How strong is the patent estate?

The current patent estate is weak as an enforcement asset because the patent term has expired or ended under the ordinary statutory term framework. Its historical claim breadth was more significant than its current legal value.

Strength factor	Assessment
Active patent term	No current ordinary enforcement value
Drug-specific protection	Low; claims are not tied to one approved drug
Formulation breadth	Broad excipient lists, but constrained by viscosity and concentration
Mechanical breadth	Mixed; claims range from specific step cylinders to general closure systems
Design-around difficulty	Moderate to low for sophisticated packaging developers
Orange Book relevance	Low
Biosimilar relevance	None apparent
Prior-art value	High for non-spill semisolid oral delivery systems
Licensing value today	Primarily historical know-how, expired technology or product documentation

The estate’s strongest historical position was the combination of semisolid rheology with a controlled squeeze dispenser. Either element standing alone is less distinctive than the integrated system.

What manufacturing and intellectual-property barriers remain?

Expiration of the patent does not eliminate other development barriers. A commercial product based on the same general concept may still face:

Current patents covering newer valves or dispensing assemblies
Design patents for dispenser appearance
Trademark rights in product names and packaging
Regulatory requirements for dosing accuracy
Child-resistant and tamper-evident packaging requirements
Stability and preservative requirements
Container-closure compatibility testing
Manufacturing tolerances for small flow channels
Device quality-system obligations
Drug labeling and dosage-measurement requirements

For a high-viscosity oral product, manufacturing control is important. Small changes in cellulose grade, hydration, polymer neutralization, particle size, temperature and shear can materially affect viscosity and squeeze force.

A freedom-to-operate review should therefore separate the expired US 5,881,926 claims from later patents covering:

Specific valve geometries
One-way dispensing systems
Metering closures
Unit-dose pouches
Integrated oral syringes or spoons
Child-resistant squeeze packages
High-viscosity pediatric formulations
Specific commercial drug products

How does this patent compare with a conventional oral-liquid patent?

Issue	US 5,881,926	Conventional oral-liquid patent
Primary focus	Integrated package, closure and semisolid formulation	Formula, active ingredient or therapeutic use
Drug specificity	Broad drug categories and examples	Often tied to one active ingredient
Physical property	Brookfield viscosity is central	May focus on pH, particle size, dissolution or stability
Packaging	Core claim element	Often absent or secondary
Orange Book relevance	Usually low	Potentially significant if tied to an approved NDA
Generic litigation	Product-specific and limited	More common
Design-around route	Change package, valve, viscosity or excipients	Change formula, salt, process or dosage form
Current enforceability	Expired or otherwise no ordinary term value	Depends on each patent’s term

What generic launch risks exist?

For current products, this patent does not create a material generic launch barrier because its ordinary patent term has ended.

Historical launch risk would have depended on the proposed product’s architecture:

A flexible tube with a valve and high-viscosity semisolid could have implicated claims 2, 4, 13 or 22.
A rotatable button-operated step cylinder could have implicated claims 1 through 3.
A single-dose tearable packet could have implicated claim 36.
A spoon integrated into a threaded cap could have implicated claim 41.
A conventional bottle with a standard measuring cup would have faced materially lower literal-claim risk.

The presence of one listed active ingredient would not have been enough by itself to create infringement.

What is the geographic coverage?

US Patent 5,881,926 provides territorial rights only in the United States. Any corresponding foreign applications or patents would need separate review.

A U.S. patent does not automatically establish protection in:

Canada
Mexico
The European Union
The United Kingdom
Japan
China
Australia
Brazil
India

Foreign coverage would depend on the patent family, national-phase filings, prosecution outcomes, maintenance payments and individual expiration dates. The supplied claims do not establish foreign rights.

Key Takeaways

US 5,881,926 is a platform patent for non-spill oral delivery of semisolid pharmaceutical compositions.
Its claims combine squeezable containers, narrow outlets, unvented or resealable closures, tamper evidence, receptacles and viscosity-defined formulations.
Claim 1 is the narrowest major mechanical combination because it requires a rotatable spring-biased step cylinder, button alignment and a breakable plastic covering.
Claims 4, 13 and 22 provide broader alternatives based on outlet diameter, functional closure requirements and general non-spill delivery.
Claim 36 covers single-dose flexible packets, while claim 41 covers a spoon integrated with a threaded cap.
The patent is not a conventional active-ingredient or drug-specific patent.
It is not ordinarily an Orange Book patent merely because its claims include pharmaceutical compositions.
Paragraph IV and biosimilar risks are not expected to be material for current products because the patent’s ordinary term has ended and the claims do not target biologics.
Current commercial risk should focus on later patents covering valves, metering closures, unit-dose packages and high-viscosity formulations.
The patent remains relevant as prior art, historical technology and a design-basis reference, but not as a current ordinary U.S. exclusion right.

FAQs About US Patent 5,881,926

Does US 5,881,926 cover ibuprofen products?

Only conditionally. Ibuprofen is listed as an example, but a product would need to satisfy the applicable container, closure, formulation, viscosity and dosing limitations.

Does the patent cover a standard oral syringe?

Not necessarily. A standard oral syringe lacks the claimed combination unless its structure and semisolid formulation meet the relevant claim limitations.

Can a company sell a semisolid oral drug in a squeeze tube today?

The expired patent does not ordinarily prevent sale. The company must still review later patents, regulatory packaging rules, stability requirements and any applicable device or design rights.

Does patent expiration eliminate all rights in the dispenser design?

No. Patent expiration removes the expired utility-patent exclusion right. Separate design patents, trademarks, trade dress, confidential manufacturing information or later utility patents may remain relevant.

Is the viscosity range the main infringement test?

It is a significant test element, but not the only one. Infringement requires the accused product to satisfy every limitation of at least one asserted claim, including the specified packaging and closure elements where present.

References

United States Patent and Trademark Office. (n.d.). Patent term adjustment and patent term provisions under 35 U.S.C. § 154. https://www.uspto.gov
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/orange-book
United States Code. (2024). 35 U.S.C. § 355: New drugs. Legal Information Institute, Cornell Law School. https://www.law.cornell.edu/uscode/text/21/355
United States Patent and Trademark Office. (1999). U.S. Patent No. 5,881,926, Non-spill delivery system for oral administration of a pharmaceutical agent. https://patents.google.com/patent/US5881926A en

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	296089	⤷ Start Trial
Australia	5762894	⤷ Start Trial
Australia	679956	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 5,881,926