United States Patent 4,968,509: Scope, Claims, Expiration, and Acetaminophen Sustained-Release Patent Landscape

U.S. Patent No. 4,968,509 covers acetaminophen sustained-release tablets made with a hydroxyethyl cellulose and povidone matrix, together with wicking and erosion-promoting excipients. The patent issued November 6, 1990, and its ordinary 17-year patent term expired November 6, 2007. The claims are no longer enforceable against generic manufacturers or other products.[1][2]

The patent remains relevant as an historical formulation reference. It does not create a current U.S. blocking right, Orange Book exclusivity period, Paragraph IV litigation risk, or biosimilar barrier.

What does U.S. Patent 4,968,509 protect?

The patent protects two related subject matter categories:

A manufacturing process for producing acetaminophen sustained-release tablets.
The resulting tablet composition, including defined quantities of povidone, hydroxyethyl cellulose, wicking agents, erosion promoters, lubricants, and glidants.

The central technical concept is a hydrophilic matrix in which:

Acetaminophen is the principal drug substance.
Hydroxyethyl cellulose contributes matrix formation and controlled release.
Povidone functions as a granulating binder.
Microcrystalline cellulose or powdered cellulose promotes liquid penetration.
Starch, sodium starch glycolate, croscarmellose sodium, or crospovidone promotes matrix erosion or disintegration.
Magnesium stearate, stearic acid, silicon dioxide, or related excipients support tablet manufacture.

The patent does not claim acetaminophen generally. It claims a particular sustained-release formulation architecture and, in several claims, a defined wet-granulation process.

Patent identification and term

Item	Information
Patent	U.S. Patent No. 4,968,509
Title	Sustained release acetaminophen compositions
Patent type	Utility patent
Technology	Oral sustained-release acetaminophen tablet
Applicant or assignee identified in patent records	McNeilab, Inc.
Issue date	November 6, 1990
Ordinary term	17 years from issue for the pre-Uruguay Round filing regime
Expected expiration	November 6, 2007
Current enforceability	Expired
Current U.S. blocking effect	None

For applications filed before June 8, 1995, the applicable transition rules generally provided a 17-year term from issuance rather than the modern 20-year term measured from the earliest effective nonprovisional filing date.[2] No term extension could preserve this patent into the current period based solely on the information in the patent claims.

How broad is independent process claim 1?

Claim 1 is the principal process claim. It requires all seven process steps:

Dissolving 5 to 25 parts by weight of povidone in water or an alcohol-water mixture.
Dry blending acetaminophen, hydroxyethyl cellulose, and a wicking agent.
Adding the povidone solution or suspension to the dry blend to produce wet granulation.
Drying the granulation.
Milling the dried granulation.
Blending the milled granulation with an erosion promoter and optional lubricant and glidant.
Compressing the final material into a tablet or tablet layer.

Required process elements

Element	Claimed requirement
Active ingredient	Acetaminophen
Acetaminophen concentration	Approximately 68% to 94% by weight
Binder solution	Povidone, 5 to 25 parts by weight
Initial matrix excipient	Hydroxyethyl cellulose, 5 to 25 parts
Initial wicking agent	5 to 25 parts
Wet granulation	Required
Drying	Required
Milling	Required
Post-milling blend	Erosion promoter, additional wicking agent, optional lubricant and glidant
Final dosage form	Compressed tablet or tablet layer
Release profile	Slow release after administration

A product can avoid literal infringement of claim 1 by omitting one required step, changing the order of operations, using a dry-granulation or direct-compression process, or replacing the claimed excipient system. The process claim is therefore narrower than a composition claim that covers the same formulation independent of manufacturing method.

The most important limitation is the required sequence. The claim does not merely require wet granulation. It requires wet granulation before drying and milling, followed by the addition of the Part III excipients and compression.

What is the scope of composition claim 6?

Claim 6 is the broadest composition claim in the supplied set. It covers a shaped and compressed sustained-release acetaminophen composition in which:

Acetaminophen is present.
The tablet contains povidone and hydroxyethyl cellulose.
The ingredients form a sustained-release solid matrix.
The combined amount of granulating agent and excipients is greater than about 6% and less than about 32% of the tablet weight.

Claim 6 does not expressly require:

A particular wet-granulation process.
Microcrystalline cellulose.
Pregelatinized starch.
Magnesium stearate.
Colloidal silicon dioxide.
A specific acetaminophen percentage.
A particular dissolution profile or release specification.

Its breadth is constrained by the functional requirement that the matrix bind acetaminophen and produce slow release. A tablet containing povidone and hydroxyethyl cellulose would not automatically fall within the claim. The composition would also need to satisfy the claimed percentage range and sustained-release matrix limitation.

Quantitative limitation in claim 6

The combined povidone and excipient content must be:

More than approximately 6% of the total tablet weight; and
Less than approximately 32% of the total tablet weight.

The phrase "about" introduces ordinary claim-construction flexibility, but it does not eliminate the quantitative limitation. A formulation with a combined binder and excipient load materially below 6% or at or above 32% would present a stronger noninfringement position, subject to the precise composition and claim construction.

How do dependent claims 7 through 14 narrow the patent?

The dependent claims add increasingly specific excipient and dosage-form limitations.

Claim 7

Claim 7 requires:

Povidone at 5 to 25 parts.
Hydroxyethyl cellulose at 5 to 25 parts.
Wicking agent at 10 to 70 parts.
Erosion promoter at 1 to 15 parts.
Lubricant at 0 to 10 parts.
Glidant at 0 to 5 parts.

This claim is broader in its wicking-agent range than process claim 1 because it allows a total wicking-agent amount of 10 to 70 parts in the composition.

Claim 8

Claim 8 narrows claim 7 to a specific excipient family:

Povidone: 5 to 25 parts.
Hydroxyethyl cellulose: 5 to 25 parts.
Microcrystalline cellulose: 10 to 70 parts.
Pregelatinized starch: 2 to 15 parts.
Magnesium stearate: 0 to 10 parts.
Colloidal silicon dioxide: 0 to 5 parts.

This is the principal formulation-defined claim for a conventional acetaminophen extended-release tablet using microcrystalline cellulose, pregelatinized starch, magnesium stearate, and colloidal silicon dioxide.

Claims 9 through 11

Claim 9 clarifies that the parts by weight can refer to milligrams per tablet or to proportional amounts.

Claims 10 and 11 narrow the total granulating-agent and excipient content to more than approximately 6% and less than 15% of the tablet weight. These claims are materially narrower than claim 6, which extends to less than approximately 32%.

Claims 12 and 13

Claim 12 identifies a specific formulation:

Ingredient	Parts by weight
Acetaminophen	325.0
Povidone	10.7
Hydroxyethyl cellulose	10.7
Pregelatinized starch	5.0
Microcrystalline cellulose	15.0
Magnesium stearate	5.0
Water	Quantity sufficient

Claim 13 specifies that the amounts may be expressed as milligrams per tablet.

The listed dry ingredients total 371.4 mg. Acetaminophen represents approximately 87.5% of the listed dry mass. Povidone and the excipients total 47.4 mg, or approximately 12.8% of the listed dry mass. If the calculation is limited to the matrix-forming and excipient components identified in claim 6, povidone plus hydroxyethyl cellulose equals 21.4 mg, or approximately 5.8% of the listed dry mass. The patent’s use of "about," water removal during drying, and proportional scaling affects the precise calculation.

Claim 14

Claim 14 covers a tablet made by wet granulating:

68% to 94% acetaminophen;
Hydroxyethyl cellulose;
Microcrystalline cellulose;
Povidone in water or an alcohol-water mixture;

followed by drying, milling, blending with additional excipients, and compression.

The Part III excipients are:

Pregelatinized starch: 1 to 15 parts.
Microcrystalline cellulose: 5 to 45 parts.
Magnesium stearate: 0 to 10 parts.
Colloidal silicon dioxide: 0 to 5 parts.

Claim 14 is a product claim defined partly by the manufacturing history. It is narrower than a pure composition claim because the product must be made using the specified wet-granulation sequence.

What formulation patents are covered by the claim language?

The patent’s formulation coverage falls into four technical groups.

Hydrophilic matrix patents

Hydroxyethyl cellulose is the principal release-controlling polymer. It hydrates after administration and contributes to a gel-like matrix that slows acetaminophen diffusion and supports controlled erosion.

Povidone has a different primary function. It is introduced as a granulating agent rather than as the principal sustained-release polymer. The claims require both components in the core embodiments.

Wicking-agent combinations

The claims identify microcrystalline cellulose and powdered cellulose as wicking agents. These materials promote water penetration into the tablet. Their inclusion balances the release-retarding effect of hydroxyethyl cellulose.

A formulation with hydroxyethyl cellulose and povidone but no wicking agent may avoid the process claims that require a wicking agent. It could still require analysis under the broader composition claims if the remaining elements are present.

Erosion-promoter combinations

The claimed erosion promoters include:

Pregelatinized starch.
Starch NF.
Rice starch.
Sodium starch glycolate.
Croscarmellose sodium.
Crospovidone.

The patent separates these materials from the initial wet granulation in the principal process claim. They are added after drying and milling. That sequencing is a meaningful limitation for process-based enforcement.

Manufacturing excipients

The claims identify magnesium stearate and stearic acid as lubricants, and colloidal or fumed silicon dioxide as glidants. These excipients are conventional tablet-processing materials. Their presence alone would not create infringement. Infringement would depend on the full combination and the applicable claim.

Are there drafting or dependency problems in the claims?

Yes. The supplied claim text contains a material dependency defect.

Claim 5 states: "The process of claim 11." Claim 11 is a composition claim, not a process claim. Claim 5 appears technically intended to depend on claim 1 or claim 2, with the high-shear-granulator limitation added to the wet-granulation step.

That error affects how claim 5 should be analyzed. It does not automatically invalidate the entire patent, but it creates a claim-construction and validity issue. The issued patent, prosecution history, claim-correction records, reexamination history, and any certificate of correction would control the operative text.

The claims also use "parts by weight of the total composition" in ways that can produce apparent arithmetic tension. Several independent ranges, if all taken simultaneously as percentages, exceed 100%. Courts generally interpret such language in light of the specification, formulation examples, and prosecution history rather than treating every listed range as a mandatory percentage that must independently sum to 100%.

When did U.S. Patent 4,968,509 lose exclusivity?

The patent lost enforceable exclusivity on November 6, 2007, based on its November 6, 1990 issue date and the pre-1995 17-year patent-term regime.[1][2]

Exclusivity timeline

Date	Event
May 1988	Patent application filed, based on available patent bibliographic records
November 6, 1990	Patent issued
November 6, 2007	Ordinary patent expiration
November 7, 2007 onward	No enforceable patent exclusion based on this patent

The patent’s expiration is separate from FDA regulatory exclusivity. Patent rights arise under the Patent Act. FDA marketing exclusivity arises under the Food, Drug, and Cosmetic Act and related regulations. The supplied patent does not establish any FDA exclusivity period.

What is the Orange Book status of U.S. Patent 4,968,509?

U.S. Patent 4,968,509 is not a current Orange Book barrier because it expired in 2007. An expired patent cannot support a current Paragraph IV challenge with commercially meaningful patent exposure.

Acetaminophen immediate-release and extended-release consumer products are often marketed through OTC pathways rather than through the abbreviated new drug application system used for prescription generics. Orange Book listing therefore depends on the relevant approved application and product category, not merely on the existence of an old formulation patent.[3]

The practical regulatory conclusions are:

The patent does not currently block FDA approval.
A generic or private-label manufacturer would not need to wait for the patent’s expiration.
A Paragraph IV certification directed only to this patent would have no current enforceability consequence.
The patent cannot support a 30-month stay under the Hatch-Waxman framework because it is expired.[4]

Which companies are challenging U.S. Patent 4,968,509?

No current Paragraph IV challenge is commercially relevant because the patent expired in 2007. The claim set alone does not establish a historical ANDA filing, patent-litigation docket, settlement agreement, or license transaction.

The likely commercial context was McNeil’s acetaminophen extended-release product portfolio, including products associated with the Tylenol brand. The patent’s expired status means that current competitors can use the claimed formulation concepts without obtaining a license from the former patent owner, subject to separate patents, trade secrets, trademarks, regulatory requirements, and product liability obligations.

What patent litigation affects U.S. Patent 4,968,509?

The patent has no current litigation effect because its claims are expired. Historical litigation or settlement activity cannot extend the patent term or revive its exclusionary force.

Any current dispute involving acetaminophen extended-release tablets would more likely concern:

A later formulation patent.
A process patent with a later expiration date.
Trade dress or trademark rights.
Product labeling.
Manufacturing know-how.
Quality, dissolution, or bioequivalence requirements.
Product liability or consumer-protection claims.

The expired patent could still appear in invalidity, obviousness, written-description, or prior-art analysis. It may also be cited as prior art against later patents claiming similar use of hydroxyethyl cellulose, povidone, microcrystalline cellulose, and starch-based erosion systems.

How strong is the patent estate for acetaminophen sustained-release tablets?

The estate represented by Patent 4,968,509 was technically focused but legally narrow in several respects.

Strengths

It combined process and composition claims.
It covered a commercially practical 325 mg acetaminophen tablet embodiment.
It claimed both broad excipient classes and narrower preferred combinations.
It addressed wet granulation, an important manufacturing route.
It claimed product-by-process alternatives through claims 14 through 17.

Weaknesses

The patent has expired.
Several excipients are conventional pharmaceutical ingredients.
The claim ranges are broad and may create enablement or obviousness questions at their outer boundaries.
The required excipient combinations can be designed around.
The claim set contains an apparent dependency error in claim 5.
Functional language such as "slow release" and "effective to bind" may require specification-based construction.
The listed formulation percentages can create interpretation issues when combined.

For historical validity analysis, the most vulnerable subject matter would likely be a broad claim covering conventional hydrophilic-matrix excipients without a narrow dissolution limitation. The most defensible historical claim would likely have been the specific wet-granulated formulation represented by claims 12 through 14, assuming the specification supported the full claimed ranges.

What generic launch risks existed, and what risks exist now?

Historical generic launch risks

Before November 6, 2007, a competitor using the claimed formulation and process could have faced:

Infringement allegations under claims 1 through 5.
Composition infringement allegations under claims 6 through 14.
Product-by-process allegations under claims 15 through 17.
A potential Hatch-Waxman dispute if the patent was listed for an applicable approved product.
Injunctive relief and damages exposure.

Design-around options included:

Using direct compression instead of wet granulation.
Eliminating povidone.
Replacing hydroxyethyl cellulose with another release-controlling polymer.
Changing the wicking-agent and erosion-promoter system.
Altering the sequence by incorporating all excipients before granulation.
Using a different manufacturing process and a composition outside the quantitative ranges.

Current generic launch risks

The patent itself creates no current launch risk. Current risk must be assessed against later patents and regulatory requirements.

A generic manufacturer still must address:

Acetaminophen content uniformity.
Dissolution and release profile.
Impurity control.
Tablet hardness and friability.
Labeling and maximum daily dose.
FDA OTC or prescription regulatory pathway.
Manufacturing controls for high-dose acetaminophen products.

These are regulatory and technical barriers, not surviving rights under Patent 4,968,509.

Does biosimilar risk apply to this patent?

No. Biosimilar law does not apply to acetaminophen, which is a chemically synthesized small-molecule drug. The relevant competitive pathway is a generic or OTC pathway, not a biosimilar application under the Biologics Price Competition and Innovation Act.

The patent has no relevance to biologic exclusivity, interchangeable biosimilars, reference-product exclusivity, or the FDA Purple Book.[5]

What geographic coverage did the patent have?

The patent provided protection only in the United States. Any foreign counterparts would have required separate national or regional rights and separate expiration analyses.

The U.S. patent did not automatically protect:

Canada.
Europe.
Japan.
China.
Latin America.
Other markets.

For international commercialization, the relevant patent families, national-stage applications, continuations, divisionals, and local term adjustments would need separate review. U.S. expiration did not necessarily coincide with foreign expiration.

How does Patent 4,968,509 compare with later acetaminophen formulation patents?

Patent 4,968,509 is an early hydrophilic-matrix formulation patent. Its claims focus on:

Excipients.
Relative quantities.
Wet granulation.
Tablet compression.
Sustained-release behavior.

Later patent strategies in oral controlled-release products commonly move toward narrower technical features, such as:

Specific dissolution windows.
Multilayer tablets.
Coated particles or multiparticulates.
Osmotic delivery.
Abuse-deterrent or tamper-resistant formats.
Combination products.
Manufacturing controls.
Specific particle-size distributions.
Pharmacokinetic performance.

The older patent is therefore most useful as prior art and as a disclosure of a conventional formulation platform. It is not a current substitute for a live freedom-to-operate review covering later patents.

Key Takeaways

U.S. Patent 4,968,509 claims acetaminophen sustained-release tablets using povidone, hydroxyethyl cellulose, wicking agents, and erosion promoters.
Claims 1 through 5 focus on wet granulation, drying, milling, post-milling blending, and compression.
Claims 6 through 14 cover the resulting sustained-release matrix and specified excipient ranges.
Claim 12 discloses a 325 mg acetaminophen formulation with povidone, hydroxyethyl cellulose, pregelatinized starch, microcrystalline cellulose, and magnesium stearate.
Claim 5 contains an apparent dependency error because it refers to claim 11 while claiming a process limitation.
The patent issued November 6, 1990, and expired November 6, 2007.
It has no current enforceable patent, Orange Book, Paragraph IV, settlement, generic-launch, or biosimilar effect.
The patent remains relevant as historical prior art and as a technical reference for hydrophilic-matrix acetaminophen tablets.
Current freedom-to-operate risk depends on later patents, trademarks, regulatory requirements, manufacturing know-how, and product-specific approval status.

Frequently Asked Questions

Can a company manufacture the exact claim 12 formulation today?

Yes, U.S. Patent 4,968,509 no longer prevents manufacture of the disclosed formulation. Separate later patents, trademarks, regulatory requirements, and contractual restrictions must be assessed independently.

Does expiration of the patent eliminate FDA dissolution testing?

No. FDA requirements remain. A manufacturer must still demonstrate that the product meets applicable quality, labeling, dissolution, stability, and manufacturing standards.

Is hydroxyethyl cellulose alone patented for acetaminophen sustained release?

No. This patent does not claim hydroxyethyl cellulose alone. The claims require combinations involving acetaminophen and, in the composition claims, povidone plus defined excipient or functional limitations.

Could a later patent cover the same ingredients?

Yes. A later patent could claim a different dissolution profile, manufacturing sequence, dosage form, particle structure, coating, tablet geometry, or clinical use even if it uses the same excipients.

Does the patent cover liquid acetaminophen products?

No. The supplied claims are directed to a shaped and compressed tablet, tablet layer, or product made through the claimed tablet process. They do not cover ordinary liquid dosage forms.

References

United States Patent and Trademark Office. (1990). Sustained release acetaminophen compositions (U.S. Patent No. 4,968,509).
United States Code. (2023). 35 U.S.C. § 154: Contents and term of patent; provisional rights.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. FDA, Center for Drug Evaluation and Research.
United States Code. (2023). 21 U.S.C. § 355: New drugs.
U.S. Food and Drug Administration. (2024). Purple Book: Database of licensed biological products. FDA.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Australia	2001288	⤷ Start Trial
Australia	611704	⤷ Start Trial
Canada	1315202	⤷ Start Trial
Germany	3880762	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Summary for Patent: 4,968,509