United States Drug Patent 4,305,502: Claim Scope, Expiration, and Patent Landscape

U.S. Patent No. 4,305,502 protects an integrated freeze-dried oral dosage and blister-packaging system associated with early rapidly disintegrating dosage-form technology. Its core combination is a porous, water-soluble or water-dispersible pharmaceutical matrix formed by solvent sublimation directly in a depression of a thermoplastic film, then sealed with a peelable foil or foil laminate. The patent issued on December 15, 1981, and its enforceable term expired no later than December 15, 1998 under the pre-Uruguay Round patent-term regime.[1][2]

The patent has no current blocking effect in the United States. Its historical importance remains relevant when analyzing later orally disintegrating tablet, lyophilized dosage-form, blister-packaging, and Zydis-type patent estates.

What does U.S. Patent 4,305,502 protect?

The patent protects both a packaged pharmaceutical product and a manufacturing process.

Claim group	Subject matter	Principal limitations
Claims 1-6	Packaged dosage form	A film sheet with depressions, a dosage form molded in the depression, an open matrix carrying a unit dose, and a peelable covering sheet
Claims 2-3	Carrier-material alternatives	Partially hydrolyzed gelatin, dextrin, hydrolyzed dextran, or alginate
Claim 4	Film limitation	Thermoplastic film
Claim 5	Cover limitation	Aluminum foil or aluminum foil laminate
Claim 6	Narrow combination	Thermoplastic film; specified carrier materials; aluminum foil or laminate
Claims 7-10	Manufacturing process	Sublimation from a solid composition in a mold formed by film depressions, followed by application of a peelable cover

The independent product claims are combination claims. A product generally must contain every required element to fall within the literal scope of claims 1 or 6. The patent does not broadly claim every fast-disintegrating tablet, every lyophilized dosage form, or every pharmaceutical blister.

How does claim 1 define the protected packaged dosage form?

Claim 1 contains six material limitations:

A sheet of filmy material.
One or more depressions in that sheet.
A shaped pharmaceutical article molded within the depression.
A solid oral dosage form that rapidly disintegrates in water.
An open matrix network carrying a unit dose of pharmaceutical substance.
A peelable covering sheet adhering to the film sheet and enclosing the dosage form.

The claim is directed to a relationship between the dosage form and the package. The dosage form is not merely placed into a conventional cavity after manufacture. The claim states that the shaped article is molded within the depression. That limitation is significant when comparing the patent with later products in which freeze-dried tablets are manufactured separately and subsequently inserted into blister cavities.

The claim also requires an open matrix network. A conventional compressed orally disintegrating tablet may disintegrate rapidly but ordinarily would not satisfy this limitation unless its structure and manufacturing process produce the claimed open matrix.

The claim does not require:

A particular active pharmaceutical ingredient.
A particular dose.
A particular tablet shape.
A specified solvent.
Aluminum foil.
Thermoplastic film.
A specific drying temperature or pressure.
A particular marketed drug.

Those limitations appear in dependent claims or the process claims.

What formulations are protected by claims 2, 3, and 6?

Claims 2, 3, and 6 narrow the carrier-material scope.

Claim	Carrier limitation	Commercial significance
Claim 2	Partially hydrolyzed gelatin	Covers a protein-based porous matrix commonly associated with freeze-dried dosage forms
Claim 3	Dextrin, hydrolyzed dextran, or alginate	Covers selected carbohydrate and polysaccharide carriers
Claim 6	Partially hydrolyzed gelatin, dextrin, hydrolyzed dextrin, or alginate	Combines specified carrier materials with thermoplastic film and aluminum foil or laminate

Claim 1 is broader as to the carrier because it covers any pharmacologically acceptable water-soluble or water-dispersible carrier material. Claims 2 and 3 provide narrower species claims that may have been easier to defend against prior art directed to other matrix materials.

Claim 6 is narrower than claim 1 in three separate ways:

The film must be thermoplastic.
The carrier must be one of the listed materials.
The cover must be aluminum foil or an aluminum foil laminate.

A product using a different carrier, a non-thermoplastic mold, or a non-aluminum peelable cover may fall outside claim 6 while still raising a claim 1 issue.

How does the patent protect the manufacturing process?

Claim 7 covers a process for preparing a rapidly disintegrating solid oral dosage form by subliming solvent from a pharmaceutical composition in the solid state. The process must include:

A composition containing the pharmaceutical substance and a soluble or dispersible carrier.
Solidification in a mold corresponding to the dosage-form size and shape.
Sublimation of solvent to create an open matrix.
A mold formed by one or more depressions in a sheet of film.
Application of a peelable covering sheet after sublimation.

The process claim is narrower than a general lyophilization claim. It requires the film sheet itself to provide the mold depression. A process in which a dosage form is lyophilized in a metal tray, removed, and later packaged in a blister is materially different from the process recited in claim 7.

Claim 7 also requires the covering step after sublimation. The sequence matters. A manufacturer that applies a cover before the claimed sublimation stage could raise separate claim-construction and process-order issues.

What additional process limitations appear in claims 8-10?

Claim 8 requires thermoplastic film.
Claim 9 identifies PVC, PVC/polyvinylidene chloride, PVC/polytetrafluoroethylene, and PVC/polyvinylidene chloride/polyethylene laminates.
Claim 10 requires aluminum foil or an aluminum foil laminate as the covering sheet.

The film choices in claim 9 indicate that the patent addressed both forming performance and barrier properties. PVC-based films can be thermoformed into cavities, while polyvinylidene chloride and foil laminates can improve moisture and oxygen protection.

When did U.S. Patent 4,305,502 lose exclusivity?

The patent issued on December 15, 1981.[1] For a U.S. application governed by the pre-1995 patent-term rules, the ordinary term was 17 years from issuance. That produces an expiration date of December 15, 1998, subject to any term adjustment, disclaimer, or other record-specific modification.[2]

Event	Date
Patent issued	December 15, 1981
Ordinary 17-year term from issuance	December 15, 1998
Current enforceable patent rights	None

The patent therefore cannot support a current U.S. infringement action. Later patents in the same technical field could have extended protection for improvements, specific active ingredients, formulations, manufacturing parameters, or commercial delivery systems. Those later rights must be analyzed independently and cannot revive the expired claims of U.S. Patent 4,305,502.

What is the Orange Book status of U.S. Patent 4,305,502?

U.S. Patent 4,305,502 is not a current Orange Book barrier to generic approval.

The Orange Book lists patents submitted by an NDA holder for a specific approved drug product. A patent directed primarily to a general dosage-form package and manufacturing platform is not automatically eligible for listing merely because it concerns pharmaceutical delivery technology.[3] Even if the patent had historically been associated with an approved product, its expiration would eliminate any current period of patent-based FDA approval delay.

The patent does not create:

Current Hatch-Waxman exclusivity.
A current 30-month stay.
A live Paragraph IV litigation risk.
A current regulatory block on an ANDA.
A current product-specific formulation monopoly.

FDA exclusivity and patent term are separate rights. Any five-year, three-year, orphan-drug, pediatric, or other regulatory exclusivity would have depended on the relevant drug and approval history, not on this patent alone.

What generic entry risks did the patent create historically?

Before expiration, the main risk applied to products combining three characteristics:

A rapidly disintegrating oral dosage form based on an open matrix.
Direct formation of the dosage form in a blister cavity or film depression.
A peelable foil or foil-laminate cover.

A generic or competing product could have avoided literal infringement by changing one or more structural elements:

Manufacturing the dosage form outside the blister cavity.
Using a compressed porous tablet rather than a sublimation-derived matrix.
Using a non-film mold.
Applying the dosage form to a carrier after lyophilization.
Replacing the specified packaging arrangement.
Using a different matrix architecture.

Design-around analysis would still need to consider the doctrine of equivalents, prosecution-history estoppel, and the scope of later patents. A change in packaging alone would not avoid a separate patent directed to the underlying lyophilized matrix or a particular formulation.

Which companies and technologies are associated with this patent landscape?

The patent is associated with the early development of freeze-dried, rapidly disintegrating dosage forms packaged in unit-dose blister systems. Later commercial development of related technology included R.P. Scherer and its successor organizations, including Catalent, as well as pharmaceutical companies using orally disintegrating products under licensing, supply, or technology-transfer arrangements.

The relevant competitive landscape had several layers:

Technology category	Representative design	Relationship to U.S. 4,305,502
Freeze-dried oral dosage forms	Porous matrix produced by sublimation	Closest technical field
Molded blister dosage forms	Dosage form formed in film cavity	Core claimed package
Compressed ODTs	Direct compression with superdisintegrants	Often outside the core matrix limitation
Thin films	Polymer film carrying drug	Different dosage architecture
Conventional blisters	Tablet manufactured separately and inserted into cavity	May avoid the molded-in-cavity limitation
Orally disintegrating capsules or granules	Non-tablet solid dosage forms	Usually outside the claimed shaped article unless claim elements are met

The most important commercial distinction is between a platform patent and a drug-specific patent. U.S. 4,305,502 is principally a platform and packaging patent. It does not identify a single active ingredient or establish exclusivity for a particular branded medicine.

How strong was the patent estate?

The issued claims had meaningful historical scope but limited present value.

Historical strengths

Claims 1 and 7 covered the package and process, creating two infringement theories.
Claim 1 was not limited to the listed carrier materials.
The claims linked dosage-form structure with packaging, making simple substitution of a conventional blister less relevant.
Claims 2-6 supplied narrower fallback positions.
The process claims targeted direct sublimation in the film depression.

Historical vulnerabilities

The claims combined several known technical areas: lyophilization, porous pharmaceutical matrices, thermoformed packaging, and peelable foil sealing.
The open-matrix requirement could create factual disputes over microstructure and manufacturing history.
The phrase "rapidly disintegrated by water" could require testing or objective evidence.
"Molded within" could distinguish direct cavity formation from later placement.
Prior art involving freeze-dried dosage forms and blister packaging could affect novelty or obviousness.
The patent did not provide current protection after 1998.

The strongest historical enforcement position would have involved a product manufactured by filling a liquid drug-carrier composition into PVC cavities, freezing it, subliming the solvent in place, and sealing the cavities with peelable aluminum foil. The weakest position would have involved a conventionally compressed tablet manufactured separately from a standard blister package.

What patent litigation or Paragraph IV activity affects the patent today?

No current Paragraph IV or infringement exposure can arise from the expired claims of U.S. Patent 4,305,502. Any historical litigation involving a product using related technology would have turned on the asserted patent family, the specific NDA product, and later continuation or improvement patents rather than on the expired patent alone.

A historical litigation review should distinguish:

The original patent.
Continuations and divisionals.
Foreign counterparts.
Later patents directed to specific actives.
Formulation patents.
Packaging improvements.
Manufacturing-process patents.
Settlement agreements involving later patents.

A settlement concerning a later patent would not extend the term of U.S. 4,305,502 or independently establish that its claims were valid or infringed.

How does U.S. Patent 4,305,502 compare with later ODT and lyophilized dosage-form patents?

Issue	U.S. 4,305,502	Later ODT patent strategies
Dosage form	Open matrix carrying a unit dose	May claim compression, granulation, films, beads, or specialized excipients
Manufacturing	Sublimation from solid composition	May claim compression force, particle engineering, spray drying, or lyophilization parameters
Package	Film depression with peelable cover	May claim moisture-barrier laminates, child-resistant systems, or unit-dose dispensers
Active ingredient	Not specified	Often active-specific
Term	Expired in 1998	Depends on each later patent
Orange Book relevance	No current barrier	Potentially relevant if tied to an approved NDA and properly listed

Later patent estates often separated the technology into multiple claim categories. This enabled applicants to pursue independent protection for the active ingredient, dosage strength, excipient system, tablet architecture, manufacturing process, and packaging configuration.

What are the geographic coverage and manufacturing barriers?

The patent provided U.S. protection only. Foreign counterparts, if granted, would have had separate terms and enforceability analyses in each jurisdiction. A U.S. expiration did not automatically terminate corresponding European, Canadian, Japanese, or other national rights, although comparable foreign patents would now generally also be expired given the age of the technology.

The principal manufacturing barriers were technical rather than legal:

Uniform filling of low-viscosity pharmaceutical solutions into small cavities.
Controlled freezing without damaging the film.
Complete solvent sublimation.
Maintenance of dosage uniformity across cavities.
Prevention of collapse or shrinkage of the open matrix.
Moisture protection after drying.
Reliable peel performance of the foil seal.
Mechanical handling of fragile dosage forms.

Those process controls can remain commercially relevant after patent expiration as know-how, trade secrets, equipment capability, and quality-system requirements. They do not create patent exclusivity by themselves.

Key Takeaways

U.S. Patent 4,305,502 is a foundational package-and-process patent for rapidly disintegrating, open-matrix oral dosage forms.
Claims 1-6 require a dosage form molded in a film depression and enclosed by a peelable cover.
Claims 7-10 require sublimation from a solid composition in the film depression, followed by covering.
The broadest carrier language appears in claim 1; claims 2, 3, and 6 narrow the carrier to specified materials.
Claim 6 is limited to thermoplastic film, listed matrix materials, and aluminum foil or foil laminate.
The patent issued December 15, 1981, and its ordinary term expired December 15, 1998.
It has no current Orange Book, Paragraph IV, generic-entry, or infringement significance.
Later patents may still matter for specific products, active ingredients, formulation systems, manufacturing parameters, or packaging improvements.
The principal historical design-around was to manufacture the dosage form separately rather than form it directly in the blister cavity.

FAQs

Did U.S. Patent 4,305,502 cover all orally disintegrating tablets?

No. It covered a specific combination involving an open matrix, rapid water disintegration, direct formation in a film depression, and a peelable covering sheet.

Could a conventionally compressed ODT infringe claim 1?

Usually not on the supplied claim language unless the product also has the claimed open matrix and molded-in-depression structure. A compressed ODT must be evaluated against every limitation, including the package relationship.

Does the patent cover aluminum blister packaging by itself?

No. Aluminum foil or an aluminum foil laminate is a limitation in claim 5, claim 6, and claim 10. The patent does not broadly claim every aluminum pharmaceutical blister.

Does expiration of the patent eliminate trade-secret risk?

No. Manufacturing parameters, equipment configuration, filling controls, freeze-drying cycles, and quality-control methods may remain protected by trade-secret law or confidential contractual obligations.

Can a later continuation extend the term of U.S. Patent 4,305,502?

A later continuation could have produced a separate patent with its own claims, but it could not extend the expired term of the original patent. Any surviving rights must be assessed from the separate patent’s filing history, claims, and expiration date.

References

United States Patent and Trademark Office. (1981). U.S. Patent No. 4,305,502, Pharmaceutical dosage forms.
United States Code, 35 U.S.C. §§ 154, 156, 271.
U.S. Food and Drug Administration. (2023). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book. FDA.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
United Kingdom	30399/77	Jul 20, 1977

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	2882577	⤷ Start Trial
Australia	513845	⤷ Start Trial
Belgium	859291	⤷ Start Trial
Canada	1083042	⤷ Start Trial
Canada	1097233	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 4,305,502

Summary for Patent: 4,305,502