US Patent 6,217,909: Scope, Claims, Expiration, and Patent Landscape for Silicified Microcrystalline Cellulose

US Patent 6,217,909 covers a co-processed excipient made from microcrystalline cellulose and silicon dioxide, particularly colloidal silicon dioxide. The patent claims a particulate agglomerate with specified silicon-dioxide content, particle size, bulk density, moisture content, and surface area. The patent issued on April 17, 2001, and its ordinary 20-year patent term has expired. It does not provide current US exclusivity for silicified microcrystalline cellulose or prevent manufacture and sale of products falling within the claims.

The patent is an excipient patent, not a drug patent. It has no Orange Book listing, no FDA drug exclusivity, and no Paragraph IV pathway directed specifically to the patent. The principal commercial relevance is historical: it helped protect the technical architecture used in products such as silicified microcrystalline cellulose, including Prosolv-type excipients.

What does US Patent 6,217,909 protect?

The patent protects a composition rather than a pharmaceutical formulation containing a particular active ingredient. Independent claims 1 and 15 require a particulate agglomerate formed from:

Microcrystalline cellulose;
Silicon dioxide present at approximately 0.1% to 20% by weight;
An intimate association between the cellulose and silicon dioxide;
Silicon dioxide derived from particles having an average primary particle size of approximately 1 nm to 100 micrometers; and
A defined bulk-density range.

Claim 1 requires a bulk density of approximately 0.35 g/mL to 0.6 g/mL. Claim 15 is broader in one respect because it permits a bulk density of approximately 0.2 g/mL to 0.6 g/mL, but it expressly requires an average excipient particle size of approximately 10 to 1,000 micrometers.

The patent therefore targets a physical excipient architecture rather than merely a mixture of two ingredients. A product containing microcrystalline cellulose and silicon dioxide would not necessarily infringe solely because both ingredients are present. The claimed composition must satisfy the agglomeration, co-processing, intimate-association, particle-size, composition, and density limitations.

Claim structure

Claim group	Principal limitations	Commercial significance
Claim 1	Agglomerated, co-processed microcrystalline cellulose and silicon dioxide; 0.1%-20% silicon dioxide; 0.35-0.6 g/mL bulk density	Primary composition claim
Claims 2-6	Narrower silicon-dioxide particle size and concentration ranges	Preferred embodiments
Claims 7-9	Average excipient particle size of 10-1,000, 10-500, or 30-250 micrometers	Granulation and tableting specifications
Claim 10	Moisture content of 0.5%-15%	Product-quality limitation
Claim 11	Additional excipients, including metal oxides, starches, surfactants, polyalkylene oxides, celluloses, cellulose ethers, and cellulose esters	Broadens possible composition variants
Claims 12-13	Silicon-dioxide surface area of 10-500 or 175-350 m²/g	Captures high-surface-area colloidal silica
Claim 14	Bulk density of 0.35-0.55 g/mL	Narrower density limitation
Claim 15	Similar agglomerate with 0.2-0.6 g/mL density and 10-1,000 micrometer particle size	Separate independent composition claim
Claims 16-20	Narrower particle-size and silicon-dioxide parameters	Preferred embodiments under claim 15

What technical features are required for infringement?

A potential product would generally need to satisfy all limitations of at least one asserted claim. The most important limitations are the following.

Co-processing and intimate association

The claims require more than physical blending. “Coprocessed” and “intimate association” indicate that the cellulose and silicon dioxide must be integrated into the same particulate agglomerate. The specification and prosecution history would be relevant to determining whether simple dry blending, ordered mixing, spray processing, wet granulation, or other production methods meet this requirement.

A manufacturer seeking to design around the patent could consider:

Selling the ingredients separately for blending by the customer;
Using a conventional physical blend rather than a co-processed agglomerate;
Using a different carrier instead of microcrystalline cellulose;
Selecting a silicon-dioxide level or density outside the claimed ranges; or
Producing a product in which silicon dioxide is not intimately associated with the cellulose particles.

Because the patent has expired, these design-around strategies are no longer required to avoid US infringement of this patent. They remain relevant when evaluating later patents or proprietary know-how.

Silicon-dioxide concentration

Claims 1 and 15 recite approximately 0.1% to 20% silicon dioxide. Claims 5 and 6 narrow the preferred range to approximately 0.5%-10% and 1.25%-5%, respectively.

Claim 4 states that the silicon dioxide is measured based on the weight of microcrystalline cellulose. This creates a potential measurement issue because claim 1 describes the amount in terms of the composition, while claim 4 uses the cellulose weight as the denominator. Product specifications and analytical methods would matter in any historical infringement analysis.

Colloidal silicon dioxide

Claim 3 and claim 19 specifically identify colloidal silicon dioxide. Claims 12 and 13 add surface-area limitations, including 175-350 m²/g. These limitations are consistent with the use of high-surface-area colloidal silica as a glidant and flow-modifying component.

The claims are not limited to a single commercial grade or supplier. A product using a different brand of colloidal silicon dioxide could still have fallen within the claims if the relevant physical parameters were met.

Bulk density

Bulk density is a central claim limitation:

Claim 1: approximately 0.35-0.6 g/mL;
Claim 14: approximately 0.35-0.55 g/mL;
Claim 15: approximately 0.2-0.6 g/mL.

Bulk density can vary with test method, tapping, moisture, particle-size distribution, and handling. A technical assessment would need to identify whether the patent refers to loose bulk density, tapped density, or another standardized measurement. The wording supplied for the claims does not itself resolve that issue.

Particle size and moisture

Claims 7-9 and 15-17 cover average excipient particle sizes ranging from approximately 10 to 1,000 micrometers, with narrower ranges of 10-500 and 30-250 micrometers.

Claim 10 covers moisture content of approximately 0.5%-15%. Moisture is a relatively broad limitation and may be affected by storage conditions and test protocol. It is unlikely to differentiate many commercial silicified cellulose products unless the product is deliberately dried or conditioned outside the claimed range.

When did US Patent 6,217,909 expire?

US Patent 6,217,909 issued on April 17, 2001. Based on the standard 20-year term measured from the relevant nonprovisional filing date, the patent expired in 2019. Public USPTO records identify the patent as expired or expired for the statutory term.[1]

Event	Date
US patent application filing	February 11, 1999, based on publicly available patent bibliographic records
Patent issue	April 17, 2001
Standard patent-term endpoint	February 11, 2019, subject to any applicable adjustment
Current status	Expired
Current US exclusivity	None

Any patent-term adjustment would need to be confirmed from the USPTO patent-term calculation. It would not change the commercial conclusion that the patent is no longer an enforceable US barrier.

What is the Orange Book status of US Patent 6,217,909?

US Patent 6,217,909 is not an Orange Book patent. The Orange Book lists patents associated with approved drug products, including patents claiming a drug substance, drug product, or approved method of use. An excipient composition patent does not ordinarily qualify for listing merely because the excipient is used in tablets or capsules.[2]

The patent therefore has:

No Orange Book listing;
No associated FDA patent expiry date for a drug product;
No drug-substance exclusivity;
No drug-product exclusivity; and
No Paragraph IV challenge directed to the patent as an Orange Book-listed patent.

A generic drug applicant could use an excipient covered by the patent without filing a Paragraph IV certification to this patent, although other active patents or regulatory requirements could affect the product.

Does the patent create a Paragraph IV or generic-entry risk?

No current Paragraph IV risk arises from US Patent 6,217,909 because the patent is expired and is not an Orange Book-listed drug patent.

The patent could have created historical commercial risk for a company selling a co-processed silicified microcrystalline cellulose excipient. That risk would have been based on direct patent infringement, contributory infringement, or induced infringement theories, not on the Hatch-Waxman certification process.

For drug manufacturers, the patent was also unlikely to block generic entry directly. A generic company could have faced supply-chain or excipient procurement issues if its selected supplier sold a product covered by the patent. The drug applicant itself would not necessarily have infringed merely by purchasing and using the excipient, depending on the relevant claim, supplier conduct, license rights, and jurisdiction.

Which commercial products and companies are relevant?

The claimed technology corresponds to the commercial category generally known as silicified microcrystalline cellulose, or SMCC. The best-known commercial example is Prosolv, associated with JRS Pharma. Other excipient manufacturers and distributors have marketed microcrystalline cellulose products, colloidal silicon dioxide products, and alternative co-processed excipients.

Company or product category	Relevance to the patent landscape
JRS Pharma / Prosolv	Major commercial association with silicified microcrystalline cellulose
FMC Corporation / Avicel	Major historical microcrystalline cellulose supplier; conventional Avicel products are not necessarily silicified or co-processed
DFE Pharma	Competing pharmaceutical excipient supplier with cellulose and co-processed excipient products
Roquette	Supplier of pharmaceutical excipients, including multifunctional and directly compressible excipient systems
MEGGLE	Supplier of cellulose-, lactose-, and co-processed tableting excipients
Evonik, Cabot, and other silica suppliers	Potential sources of colloidal or fumed silicon dioxide used in excipient manufacture

The existence of a competing product does not establish infringement. Product-specific testing would be needed to compare composition, agglomeration, density, surface area, moisture, and particle-size data against the claims.

How strong was the patent estate?

The patent was technically meaningful but legally narrow in several respects.

Strengths

The independent claims covered the composition itself, not only a manufacturing process.
The claims combined ingredient identity with measurable physical properties.
The ranges were broad enough to encompass many practical silicified cellulose products.
Claim 11 allowed additional excipients, reducing the effectiveness of some formulation changes as a design-around.
The claims covered colloidal silicon dioxide and high-surface-area silica, important commercial materials.

Weaknesses

The claims required a particulate agglomerate and intimate association, creating factual proof issues.
Multiple physical parameters could vary with test methodology.
The claims did not cover all microcrystalline cellulose and silicon dioxide blends.
The patent did not claim a specific active pharmaceutical ingredient, dosage form, indication, or finished drug.
The patent term ended in 2019.
A competitor could potentially avoid the claims through non-co-processed blends, different carriers, or parameters outside the claimed ranges.

The patent was stronger as a product-supply barrier against a directly competing excipient than as a barrier to pharmaceutical products generally.

What formulations and dosage forms were affected?

The claimed excipient is suited to solid oral dosage forms, especially:

Direct-compression tablets;
Immediate-release tablets;
Nutraceutical tablets;
Hard capsules filled with powders or granules;
Multiparticulate systems;
Granulated tablet formulations; and
Low-dose formulations requiring improved powder flow and content uniformity.

The patent does not claim a particular tablet, capsule, active ingredient, dissolution profile, therapeutic use, or release mechanism. Its commercial value derived from excipient performance, including flow, compressibility, dilution potential, and handling.

A finished tablet containing an expired-patent excipient is not subject to a current patent barrier from this patent. Later patents could still cover specific drug-excipient combinations, modified-release systems, manufacturing processes, or commercial formulations.

What manufacturing and intellectual-property barriers remain?

Although US Patent 6,217,909 has expired, commercial barriers may remain outside its legal claims.

Manufacturing know-how

Production of consistent silicified microcrystalline cellulose can depend on:

Mixing sequence;
Silicon-dioxide dispersion;
Moisture control;
Agglomeration conditions;
Drying parameters;
Milling and classification;
Bulk-density control; and
Batch-to-batch particle-size management.

These factors may be protected by trade secrets, quality specifications, regulatory files, supplier qualification, or later patents.

Later patent families

A freedom-to-operate review should separate the expired 2001 patent from later patent families directed to:

New grades of silicified cellulose;
Modified-density or engineered-particle excipients;
Co-processed excipients containing additional binders;
Continuous manufacturing;
Spray-dried or granulated excipient systems;
Specific pharmaceutical formulations; and
Manufacturing methods or equipment.

The expired patent should not be treated as a proxy for the entire current SMCC patent landscape.

What litigation and settlement activity affects the patent?

The supplied record does not establish an active US infringement action, settlement, or license dispute involving US Patent 6,217,909. Because the patent is expired, a new US enforcement action based solely on unlicensed conduct occurring after expiration would not present a conventional current infringement threat.

Historical ownership and licensing should be reviewed through the USPTO assignment database. Commercial product licenses may also have existed independently of recorded assignments, particularly where an excipient business or product line changed ownership.

How does US Patent 6,217,909 compare with alternative excipient strategies?

Strategy	Likely relationship to the claims	Commercial tradeoff
Conventional microcrystalline cellulose	May avoid silicon-dioxide limitations	Lower flow improvement and different compression behavior
Physical blend of MCC and colloidal silica	May avoid co-processed agglomerate limitations	Greater segregation risk and less consistent functionality
Silicified cellulose from a different supplier	Could have historically fallen within the claims if parameters matched	Supplier brand alone is not a design-around
Lactose-cellulose co-processed excipient	Generally outside the claimed MCC/silicon-dioxide combination	Different compatibility and compaction profile
Starch- or polyol-based co-processed excipient	Usually outside the core combination	May require reformulation and process development
MCC with non-silicon glidant	Avoids silicon-dioxide limitations	May provide different flow and tablet-strength performance

Key Takeaways

US Patent 6,217,909 covers co-processed microcrystalline cellulose and silicon dioxide in a particulate agglomerate.
The core limitations are silicon-dioxide concentration, intimate association, particle size, bulk density, and, in several claims, moisture and surface area.
The patent issued on April 17, 2001 and expired in 2019 under the ordinary 20-year term.
It is not an Orange Book patent and does not create a current Paragraph IV obstacle.
The patent protected an excipient platform, not a drug, active ingredient, indication, tablet, or capsule.
Historical infringement analysis would depend heavily on whether a product was truly co-processed and whether its physical parameters fell within the claimed ranges.
Current freedom-to-operate work must focus on later patents, trade secrets, supplier agreements, and product-specific formulation claims.

FAQs

Is Prosolv covered by US Patent 6,217,909?

Prosolv-type silicified microcrystalline cellulose products are technically relevant to the patent because the claims cover co-processed microcrystalline cellulose and silicon dioxide. Product-specific coverage would depend on the formulation and measured physical characteristics. The patent is now expired.

Can a company manufacture silicified microcrystalline cellulose in the United States?

Yes, US Patent 6,217,909 no longer prevents manufacture. A company must still assess later patents, manufacturing know-how, trademarks, regulatory specifications, and contractual restrictions.

Does using colloidal silicon dioxide with microcrystalline cellulose infringe the patent?

Not automatically. The patent requires a co-processed particulate agglomerate with specified composition and physical characteristics. A simple physical blend may not satisfy all limitations, although the patent is expired in any event.

Is US Patent 6,217,909 relevant to an ANDA filing?

It is not relevant as an Orange Book-listed patent or Paragraph IV patent. It may be relevant to excipient sourcing and historical freedom-to-operate analysis, but it does not create current Hatch-Waxman exclusivity.

Are later patents likely to matter more than US Patent 6,217,909?

Yes. Current risk is more likely to arise from later patents covering specific co-processed excipients, manufacturing methods, modified-release formulations, drug-excipient combinations, or proprietary commercial grades.

References

United States Patent and Trademark Office. (2001). Silicon dioxide-containing excipient composition, U.S. Patent No. 6,217,909. https://patents.google.com/patent/US6217909B1/en
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. https://www.fda.gov/drugs/drug-approvals-and-databases/orange-book-data-files
United States Patent and Trademark Office. (n.d.). Patent Center. https://patentcenter.uspto.gov/
U.S. Food and Drug Administration. (n.d.). Generic drug user fee amendments and abbreviated new drug applications. https://www.fda.gov/drugs/abbreviated-new-drug-application-anda/generic-drug-facts-labeling-and-approval-process

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
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 6,217,909

Summary for Patent: 6,217,909