United States Patent 5,948,438: Claim Scope, Expiration, and Pharmaceutical Patent Landscape

U.S. Patent No. 5,948,438 covers compressed oral tablets containing microcrystalline cellulose (MCC) combined with a “compressibility augmenting agent” in agglomerated, intimate association. The claims focus on excipient architecture rather than a particular active pharmaceutical ingredient. The principal embodiments use colloidal silicon dioxide, sodium lauryl sulfate, or polysorbate 40.

The patent issued on September 7, 1999. Based on its late-1990s filing date, its ordinary 20-year patent term has expired. The patent therefore presents historical freedom-to-operate relevance but does not presently create an enforceable U.S. exclusion right, absent an unusual term adjustment or other surviving rights not apparent from the claim set. It is not a conventional Orange Book drug patent and does not independently delay generic approval.

What does U.S. Patent 5,948,438 protect?

The patent protects a formulation platform for making MCC-containing tablets more compressible and, in certain claims, more absorbable or rapidly disintegrating.

The core elements of claim 1 are:

An oral solid dosage form.
A compressed tablet.
An excipient containing:
- microcrystalline cellulose; and
- a compressibility augmenting agent.
The augmenting agent must physically restrict the proximity of adjacent cellulose surfaces, inhibit interactions between those surfaces, or do both.
MCC and the augmenting agent must exist as agglomerated particles in intimate association.
The tablet must contain a therapeutically active agent.

The claim does not require a specific drug, dose, tablet weight, release profile, compression force, MCC grade, or percentage of the augmenting agent.

What is the central inventive concept?

The technical concept is that MCC particles can become less effective as a tablet binder when cellulose surfaces interact too closely or form structures that impede compression and disintegration. A second material is associated with the MCC during agglomeration. That material changes the surface environment and improves tablet manufacture or performance.

The claim uses functional language rather than a narrowly defined chemical formula. The augmenting agent is defined by what it does:

limits contact between cellulose surfaces;
inhibits cellulose-cellulose interactions; or
performs both functions.

This structure makes claim 1 potentially broad on composition but more dependent on factual proof concerning particle structure, manufacturing history, and performance.

How do the dependent claims narrow the patent?

Claim	Additional limitation	Practical scope
1	MCC, compressibility augmenting agent, agglomerated intimate association, active agent, compressed tablet	Broad platform claim
2	Agent provides a hydrophobic boundary and improves absorptivity	Requires both structural and performance characteristics
3	Silicon dioxide, average primary particle size about 1 nm to 100 μm, improves disintegration	Broad silica particle-size limitation plus performance result
4	Colloidal silicon dioxide	Narrower silica embodiment
5	Surfactant with HLB of at least 10	Broad hydrophilic-surfactant category
6	Surfactant with HLB from about 15 to about 50	More specific HLB range
7	Sodium lauryl sulfate	Specific surfactant
8	Polysorbate 40	Specific surfactant

Claim 6 is substantively narrower than claim 5 because its lower HLB threshold is 15 rather than 10. A formulation with an HLB value of 15 or higher may fall within both claims, assuming the other limitations are met. A formulation with an HLB value between 10 and below 15 could fall within claim 5 but not claim 6.

What formulations are covered by U.S. Patent 5,948,438?

MCC and colloidal silicon dioxide tablets

Claims 3 and 4 target MCC combined with silicon dioxide, particularly colloidal silicon dioxide. The relevant formulation must involve more than simply placing both ingredients somewhere in the same tablet. The claim language requires agglomerated particles in intimate association.

Potentially relevant products include:

directly compressed tablets containing MCC and colloidal silicon dioxide;
pre-agglomerated MCC-silica excipients;
co-processed MCC-silica excipients;
tablets using such an excipient with an active drug.

The claim does not require the silicon dioxide to be the only glidant, binder, or disintegrant. Other excipients can be present because the claims use “comprising” language.

The particle-size range in claim 3 is very broad, extending from approximately 1 nanometer to 100 micrometers. A particle-size dispute would likely concern the meaning of “average primary particle size,” the measurement method, aggregation, and whether the tested material is the same material used in the tablet.

MCC and surfactant tablets

Claims 5 through 8 cover MCC associated with a surfactant. The specifically identified materials are:

sodium lauryl sulfate;
polysorbate 40.

These claims require a surfactant that inhibits interactions between adjacent cellulose surfaces. A simple dry blend may not satisfy the “agglomerated particles” and “intimate association” requirements inherited from claim 1.

A formulation containing sodium lauryl sulfate as a separate external tablet excipient may present a weaker literal infringement case than a co-processed MCC-sodium lauryl sulfate excipient. The factual result would depend on particle morphology, manufacturing sequence, and the interpretation of “intimate association.”

What the patent does not expressly cover

The claims do not expressly cover:

ordinary MCC products without an augmenting agent;
a capsule containing the claimed excipient but no compressed tablet;
a liquid, injectable, transdermal, or buccal formulation;
a tablet in which MCC and the agent are merely present without agglomeration;
an active pharmaceutical ingredient by itself;
a drug-specific method of treatment;
a specific dosage strength;
a specific release profile;
a specific manufacturing apparatus.

A tablet containing a protected excipient may still require separate analysis under later patents covering the drug substance, polymorph, formulation, delivery system, or therapeutic use.

How strong are the claims technically and legally?

The claim set has meaningful breadth but several potential validity and infringement pressure points.

Strengths

Claim 1 has no API limitation and applies across therapeutic categories. It also uses “comprising” language, allowing additional excipients and formulation components.

The claims capture both silica-based and surfactant-based embodiments. Claims 4, 7, and 8 provide clear commercial targets for products using colloidal silicon dioxide, sodium lauryl sulfate, or polysorbate 40.

The agglomerated-particle requirement can distinguish a co-processed excipient from a conventional formulation in which ingredients are blended separately before compression.

Vulnerabilities

The functional language creates claim-construction questions. Terms such as “compressibility augmenting agent,” “physically restricts,” “inhibits interactions,” and “intimate association” may require technical evidence.

The patent also appears vulnerable to prior-art challenges based on:

MCC as a direct-compression binder;
colloidal silicon dioxide as a glidant or disintegration aid;
surfactants as wetting or processing aids;
co-processed excipients;
agglomerated pharmaceutical particles;
conventional tablet formulations containing MCC and silica or surfactants.

A validity analysis would need to distinguish between the presence of ingredients and the claimed co-agglomerated particle structure. Ingredient overlap alone would not establish anticipation of the full claim.

When did U.S. Patent 5,948,438 expire?

The patent issued on September 7, 1999. For a U.S. patent filed in the late 1990s, the ordinary term is generally 20 years from the earliest effective nonprovisional U.S. filing date, subject to patent-term adjustment and other statutory provisions [1].

The ordinary expiration date is therefore in the late 2010s, most likely around 2017 based on the patent’s filing period. The patent is no longer an active U.S. exclusion right under its ordinary term.

Event	Date or period
U.S. patent application	Late 1990s
Patent grant	September 7, 1999
Ordinary statutory term	Approximately 20 years from effective nonprovisional filing
Expected ordinary expiration	Late 2010s
Current enforcement posture	Expired based on ordinary term analysis

Patent expiration eliminates prospective infringement liability for post-expiration conduct. It does not erase liability for infringement occurring during the enforceable term, and it does not eliminate the historical relevance of the patent as prior art.

A certified term calculation should be based on the USPTO Patent Center record, including any patent-term adjustment, terminal disclaimer, disclaimer filing, reexamination certificate, or post-grant status [2].

Is U.S. Patent 5,948,438 listed in the FDA Orange Book?

The patent is not, based on the claim subject matter, a conventional Orange Book-listed drug patent. The FDA Orange Book generally identifies patents submitted by an NDA holder that claim an approved drug substance, drug product, or method of use [3].

U.S. Patent 5,948,438 claims:

an excipient composition;
particle association;
tablet compression characteristics;
silica or surfactant components.

It does not claim a named active ingredient, a particular approved drug product, or a drug-specific method of treatment. It therefore would not normally support an Orange Book listing for a branded medicine.

Does the patent create a Paragraph IV risk?

No current Paragraph IV risk ordinarily arises from an expired excipient patent. Paragraph IV certifications address patents listed for an approved reference drug under the Hatch-Waxman framework [4]. An excipient patent that is not listed in the Orange Book does not independently block an Abbreviated New Drug Application.

During the patent’s active period, a branded company could have attempted to assert the patent outside the Orange Book context, but the patent would not automatically have generated a 30-month stay. The patent’s commercial impact would have depended on litigation, licensing, or the use of a non-infringing excipient process.

What patent litigation affects U.S. Patent 5,948,438?

The supplied claim set identifies no drug-specific litigation, ANDA case, settlement, or licensing dispute. Because the patent is an excipient-platform patent rather than a drug patent, litigation would likely have focused on:

whether the accused excipient was agglomerated;
whether MCC and the second component were in intimate association;
whether the second component performed the claimed cellulose-surface function;
whether a tablet incorporated the excipient as manufactured;
whether the patent remained enforceable at the time of the accused conduct.

There is no basis in the claim text alone to attribute a Paragraph IV case, generic settlement, or branded-drug injunction to this patent. Any historical case assessment must be made from PACER, USPTO records, and commercial patent-litigation databases.

Which companies and products are relevant to the patent landscape?

The patent sits within the broader market for directly compressible and co-processed excipients. Relevant commercial categories include:

Category	Typical materials or products	Relevance
MCC	Standard and high-functionality MCC grades	Baseline direct-compression excipient
Silicified MCC	MCC co-processed with colloidal silicon dioxide	Closest technical category to claims 3 and 4
Surfactant-modified MCC	MCC associated with sodium lauryl sulfate or other surfactants	Relevant to claims 5 through 8
Coprocessed excipients	MCC combined with starches, sugars, silica, or binders	Potential design-around and prior-art field
Conventional blends	MCC and silica added separately during tableting	May avoid the agglomerated-particle limitation

Commercial suppliers in this field have included FMC Corporation and successor excipient businesses, JRS Pharma, DuPont-related excipient operations, DFE Pharma, BASF, and other specialty excipient manufacturers. Product-by-product patent ownership cannot be inferred solely from the presence of MCC, silica, or surfactant.

A key distinction is between:

a physically co-processed excipient manufactured as an agglomerated particle; and
a formulation blend in which MCC and a second excipient are separately added.

The first category is more directly aligned with the claim language.

How does this patent compare with drug-substance and formulation patents?

Patent type	What it protects	Commercial effect
Drug-substance patent	Active ingredient, salt, polymorph, stereoisomer	Can block manufacture and sale of the drug
Drug-product patent	Composition, release profile, dosage form	Can restrict specific formulations
Method-of-use patent	Treatment method or patient population	Can affect labeling and induced-infringement risk
Excipient-platform patent	Tablet architecture or co-processed excipient	Usually affects formulation manufacture rather than the API itself
Manufacturing patent	Process, equipment, granulation, coating, or particle production	Can require a process change or license

U.S. Patent 5,948,438 is closest to an excipient-platform and formulation-manufacturing patent. It does not confer exclusivity over any named therapeutic agent.

A product may therefore have been exposed to several independent patent layers during the patent’s term. For example, a tablet could use an excipient covered by this patent while also being covered by an active-ingredient patent, a controlled-release patent, and a method-of-use patent. Expiration of 5,948,438 would remove only the excipient-related layer.

What generic launch risks existed during the patent term?

During the enforceable period, generic manufacturers could have pursued several strategies:

Use a non-agglomerated blend

A manufacturer could add MCC, colloidal silicon dioxide, or sodium lauryl sulfate separately during blending rather than using a co-agglomerated excipient. The principal risk would be whether the final processing nevertheless produced agglomerated particles in intimate association.

Use an alternative excipient

Potential alternatives could include:

starch;
pregelatinized starch;
lactose;
mannitol;
dibasic calcium phosphate;
crospovidone;
croscarmellose sodium;
low-substituted hydroxypropyl cellulose;
alternative co-processed MCC systems.

The substitute would need to satisfy the target drug’s manufacturability, dissolution, stability, and regulatory specifications.

Use a different surfactant

Claims 7 and 8 identify sodium lauryl sulfate and polysorbate 40. A manufacturer could evaluate another surfactant with a different HLB value or a different processing route. Claim 5, however, is broader and could still be relevant to surfactants with HLB values of at least 10.

Challenge validity

A challenger could argue that the claimed combination was anticipated or obvious based on known MCC direct compression systems, silica glidants, surfactant-assisted formulations, and co-processing methods. The strongest challenge would likely require technical prior art addressing the agglomerated structure and functional relationship between MCC and the augmenting agent.

Are biosimilars relevant to this patent?

No. Biosimilar litigation concerns biological products and typically involves patents covering the biologic molecule, formulation, manufacturing process, or therapeutic use. U.S. Patent 5,948,438 concerns an oral compressed tablet excipient system and does not claim a biologic, biosimilar, injectable product, or biological manufacturing process.

It could theoretically be relevant to an oral small-molecule product, but it would not be a biosimilar patent.

What geographic coverage did the patent have?

U.S. Patent 5,948,438 provided rights only in the United States. Equivalent protection in Europe, Canada, Japan, or other jurisdictions would require separate national or regional patent rights.

The international landscape for silicified MCC, co-processed excipients, and direct-compression systems may include related applications with different:

claim scope;
priority dates;
prosecution histories;
expiration dates;
maintenance status;
national validation;
terminal disclaimers.

A U.S. expiration does not establish expiration of corresponding foreign patents.

What licensing and revenue exposure did the patent create?

The patent’s commercial value was concentrated in excipient suppliers and manufacturers of high-volume oral solid dosage forms. Potential licensees could have included:

excipient manufacturers;
contract development and manufacturing organizations;
generic drug companies;
branded drug companies using directly compressed tablets;
suppliers of co-processed MCC-silica systems.

Revenue exposure was unlikely to be attributable to one active drug because the claims are API-neutral. The relevant exposure would instead have depended on sales of excipient products, licensing royalties, or formulation services.

No royalty rate, settlement amount, license agreement, or product-specific revenue can be established from the claim language alone.

Key Takeaways

U.S. Patent 5,948,438 covers compressed oral tablets containing MCC and an augmenting agent in agglomerated, intimate association.
The principal embodiments involve colloidal silicon dioxide, sodium lauryl sulfate, and polysorbate 40.
Claim 1 is broad because it does not identify a particular active ingredient, dose, or therapeutic indication.
The main limiting feature is the required agglomerated-particle structure and intimate association between MCC and the augmenting agent.
The patent is an excipient and tablet-manufacturing patent, not a conventional drug-substance or drug-use patent.
Its ordinary U.S. patent term expired in the late 2010s.
It would not ordinarily be listed in the FDA Orange Book or create a current Paragraph IV barrier.
Biosimilar risk is not relevant.
Historical infringement disputes would likely have focused on particle structure, co-processing, and the meaning of “intimate association.”
A current generic launch analysis should focus on later patents covering the active ingredient, drug product, release profile, manufacturing process, and method of use.

FAQs

Does U.S. Patent 5,948,438 cover all tablets containing microcrystalline cellulose?

No. It requires a compressed oral tablet containing MCC and a qualifying compressibility augmenting agent in agglomerated particles that are in intimate association.

Is colloidal silicon dioxide alone covered by the patent?

No. The claimed combination requires MCC, colloidal silicon dioxide or another qualifying agent, the claimed particle relationship, and a therapeutically active agent in a compressed tablet.

Can a generic manufacturer use sodium lauryl sulfate after the patent expired?

Yes, the patent’s expiration removes its prospective U.S. exclusion right. Other active patents, regulatory requirements, or contractual restrictions could still affect the product.

Does a simple physical blend avoid the patent?

Not automatically. A simple blend may avoid the claim if it lacks the required agglomerated particles and intimate association, but processing can alter particle structure. The answer depends on the actual excipient and manufacturing process.

Does the patent protect a product such as acetaminophen, ibuprofen, or a prescription drug?

No. The claims are active-ingredient-neutral. They may cover a tablet containing such a drug only if the tablet satisfies every limitation of an enforceable claim.

References

United States Code, 35 U.S.C. §§ 154, 156, 271, 282. (2024). Patent term and infringement provisions.
United States Patent and Trademark Office. (n.d.). Patent Center and patent term adjustment resources. https://patentcenter.uspto.gov/
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations, commonly known as the Orange Book. https://www.fda.gov/drugs/drug-approvals-and-databases/approved-drug-products-therapeutic-equivalence-evaluations-orange-book
United States Code, 21 U.S.C. § 355(j). Abbreviated new drug applications and patent certifications.
U.S. Patent No. 5,948,438. (1999). Claims directed to oral solid dosage forms containing microcrystalline cellulose and a compressibility augmenting agent. United States Patent and Trademark Office.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	239450	⤷ Start Trial
Austria	441403	⤷ Start Trial
Austria	445391	⤷ Start Trial
Australia	4759896	⤷ Start Trial
Australia	5019996	⤷ Start Trial
Australia	5830399	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,948,438

Summary for Patent: 5,948,438