United States Patent 5,618,845: Modafinil Particle-Size Claims, Scope, Validity, and Patent Landscape

U.S. Patent No. 5,618,845 protected modafinil pharmaceutical compositions in which at least about 95% of particles were smaller than about 200 microns. Dependent claims narrowed the particle distribution, dose, and therapeutic use. The patent was directed to particle-size control rather than a new chemical entity, salt, polymorph, formulation excipient, or manufacturing process.

The patent issued on April 8, 1997, and its 20-year term from the relevant U.S. filing date ended in October 2014. Any pediatric exclusivity associated with the product would not revive the patent after expiration. The patent therefore presents no current U.S. blocking right against ordinary modafinil products, although its claims remain relevant to historical Paragraph IV litigation, generic-entry settlements, and freedom-to-operate analysis for products marketed before expiration.

What does U.S. Patent 5,618,845 protect?

The patent protects a pharmaceutical composition containing a substantially homogeneous population of modafinil particles meeting a particle-size threshold.

Claim	Protected subject matter	Practical limitation
1	Pharmaceutical composition containing modafinil particles	At least approximately 95% of cumulative particles must have a diameter below approximately 200 μm
2	Composition of claim 1	Median particle diameter must be approximately 2-60 μm
3	Composition of claim 1	Contains approximately 50-700 mg of modafinil
4	Method of altering a mammal's somnolent state	Administration of an effective amount of the claim 1 composition
5	Method of claim 4	Somnolent state is narcolepsy
6	Method of claim 4	Effective amount is approximately 50-700 mg per day

The independent composition claim is the commercial center of the patent. Claims 2 and 3 are narrower composition claims. Claims 4-6 are method-of-use claims that depend on the composition requirement rather than claiming administration of any modafinil product.

How should claim 1 of patent 5,618,845 be construed?

Claim 1 has four principal limitations:

A pharmaceutical composition must exist.
The composition must contain modafinil particles.
The particles must form a substantially homogeneous mixture.
At least about 95% of the cumulative total of particles must have a diameter below about 200 μm.

Particle-size limitation

The claim uses a cumulative particle-size distribution. It does not require every particle to be below 200 μm. Up to approximately 5% of the particles may be at or above that size, subject to the interpretation of "about" and the relevant measurement method.

The claim is materially different from a median-size limitation. A composition could have a median diameter below 60 μm yet fail claim 1 if a sufficient tail of large particles causes more than approximately 5% of the particles to reach 200 μm or greater. Conversely, a composition could satisfy the 95% threshold without satisfying claim 2's median range.

Particle-size evidence would normally require:

The analytical method used.
The sample-preparation procedure.
Whether the result is number-weighted, volume-weighted, or mass-weighted.
The definition of particle diameter.
Sampling and batch-representativeness data.
Treatment of agglomerates and aggregates.
The meaning assigned to "about 95%" and "about 200 μm."

Those variables can materially affect infringement and validity analyses. Laser diffraction, microscopy, sieving, and other methods can produce different distributions for the same material.

"Substantially homogeneous mixture"

This language is broader than a requirement that every tablet or batch contain identical particles. It indicates a sufficiently uniform distribution of modafinil particles within the pharmaceutical composition. The claim does not expressly require:

A particular excipient.
A tablet.
A capsule.
A suspension.
A particular compression process.
A particular milling process.
A specific crystal form.
A particular particle-shape distribution.

The composition must still be a pharmaceutical composition, not merely bulk micronized modafinil. Whether a commercial product satisfies that requirement would depend on its dosage form and product specifications.

What formulations are covered by patent 5,618,845?

The patent is formulation-platform protection based on particle size, not conventional excipient-based formulation protection.

Potentially covered products

Subject to meeting the particle-size and homogeneity limitations, the claims can reach:

Immediate-release tablets.
Capsules.
Powder-filled dosage forms.
Oral solid dosage forms containing micronized modafinil.
Formulations containing approximately 50-700 mg of modafinil.
Products used to treat narcolepsy or other somnolent states.

Claim 1 does not expressly limit the composition to the Provigil brand formulation. A product using different excipients could still fall within the claim if its modafinil particle distribution and mixture characteristics satisfy the limitations.

Products not necessarily covered

The claims do not automatically cover:

Modafinil API without a pharmaceutical composition.
A formulation in which fewer than approximately 95% of particles are below 200 μm.
A product with a different active pharmaceutical ingredient.
Armodafinil solely because it is the R-enantiomer of modafinil.
A process for manufacturing modafinil.
A formulation defined only by dissolution, bioavailability, hardness, or excipient identity.
A composition that lacks the required particle-size distribution.

The patent could be relevant to a formulation containing a different physical form of modafinil only if the resulting particles satisfy the claimed limitations. The claim does not expressly require a particular polymorph or crystal structure.

How do claims 1, 2, and 3 compare?

Claim 1 establishes the broadest composition scope. Claim 2 adds a median particle-size restriction. Claim 3 adds a quantity restriction.

Feature	Claim 1	Claim 2	Claim 3
Pharmaceutical composition	Yes	Yes	Yes
Modafinil particles	Yes	Yes	Yes
At least about 95% below about 200 μm	Yes	Yes	Yes
Median diameter of about 2-60 μm	No	Yes	No
Modafinil quantity of about 50-700 mg	No	Not expressly added	Yes
Potential dosage-form limitation	None stated	None stated	None stated

Claim 2 is narrower in particle distribution but does not add a dose limitation. Claim 3 is narrower by modafinil content but does not require the 2-60 μm median range.

The use of "about" creates an evidentiary boundary rather than eliminating the limitation. A competitor with a median diameter of 61 μm, for example, would not automatically avoid claim 2 because the court would need to interpret the term in the technical and prosecution context.

Do the method claims cover all modafinil treatment?

No. Claims 4-6 require use of the composition described in claim 1.

Claim 4

Claim 4 covers administering an effective amount of the claim 1 composition to alter a mammal's somnolent state. It is not a generic claim to administering any modafinil product.

Claim 5

Claim 5 narrows the method to treatment of narcolepsy. It does not expressly require a particular dose, dosage form, treatment duration, or administration schedule beyond the inherited limitations.

Claim 6

Claim 6 specifies approximately 50-700 mg per day. Its wording refers to the amount of "said composition," although the commercially meaningful interpretation would generally focus on the amount of modafinil administered per day. The drafting creates potential claim-construction issues, particularly if "composition" is read as the total mass of the dosage form rather than active ingredient.

The method claims could have supported an infringement theory against a generic product labeled for narcolepsy if the underlying composition met claim 1. They would not necessarily reach an off-label use of a product that did not satisfy the claimed particle distribution.

When did patent 5,618,845 lose exclusivity?

The patent's U.S. term ended in October 2014, based on the patent's post-Uruguay Round patent-term framework and the relevant U.S. filing date. The patent was listed in the FDA Orange Book for Provigil, the modafinil product marketed by Cephalon. The principal commercial exclusivity timeline was:

Event	Date or period
U.S. patent issued	April 8, 1997
Provigil NDA approval	1998
Paragraph IV litigation and settlements	Early-to-mid 2000s
Agreed generic-entry period	Primarily 2011-2012, depending on challenger
Patent term expiration	October 2014
Current enforceability	Expired

The commercial entry date preceded the patent's nominal expiration because Cephalon entered settlement agreements with generic challengers allowing launches before the end of the patent term. The settlements did not extend the patent term.

FDA approval of Provigil did not itself create a continuing patent right. FDA marketing exclusivity and patent exclusivity are separate mechanisms. The product's early regulatory exclusivity expired well before the patent term.

What was the Orange Book status of patent 5,618,845?

U.S. Patent 5,618,845 was listed in the Orange Book for Provigil, NDA 020717. The listing identified a formulation and use-related patent covering modafinil products marketed for somnolence-related indications. Generic applicants challenging the listing could submit Paragraph IV certifications alleging that the patent was invalid, unenforceable, or not infringed.

The Orange Book listing had four commercial effects:

It required generic applicants to address the patent in abbreviated new drug applications.
A Paragraph IV notice exposed the applicant to patent litigation.
A timely infringement action could trigger a 30-month stay of FDA approval under the Hatch-Waxman statute.
Settlement terms determined whether generic launch occurred before patent expiry.

The listing did not establish that every modafinil product infringed. It identified the patent as potentially relevant to the approved product.

Which companies challenged the modafinil patent estate?

Generic companies associated with the Provigil patent disputes included Teva, Ranbaxy, Mylan, Barr Laboratories, and Apotex. The litigation and settlement structure involved challenges to Cephalon's listed modafinil patents, including U.S. Patent 5,618,845.

The principal business result was early generic-entry permission rather than immediate invalidation of the patent. The Federal Trade Commission later challenged Cephalon's agreements as reverse-payment settlements. The FTC alleged that Cephalon made payments and other concessions to delay generic entry, while the settling companies agreed to launch at dates materially earlier than the patent's nominal expiration. The Supreme Court's later decision in FTC v. Actavis established that large unexplained reverse payments can violate antitrust law even when the underlying patent case is not resolved on the merits (Federal Trade Commission v. Actavis, Inc., 2013).

What patent litigation affected patent 5,618,845?

The litigation centered on whether generic modafinil products infringed Cephalon's listed patents and whether the patents were valid and enforceable. The relevant disputes involved:

Paragraph IV certifications.
Infringement allegations based on particle-size specifications.
Obviousness and validity arguments.
Claim construction concerning particle-size measurements.
Settlement agreements restricting generic launch.
Antitrust scrutiny of settlement consideration.

The legal significance of the particle-size patent was unusual because a generic applicant could potentially challenge the patent without reproducing the brand's formulation in every respect. The applicant's product-development data, ANDA specifications, manufacturing controls, and proposed labeling would determine the exposure.

Public records concerning the Provigil settlements are more important to the historical commercial landscape than to current freedom to operate. Because the patent has expired, new U.S. products are no longer exposed to an infringement claim under the expired patent.

How strong was the patent estate for modafinil?

The estate was commercially strong during the period before generic launch because the compound patent had already expired or was no longer the principal barrier, while the particle-size patent supplied a later-forming product and formulation right.

Estate element	Strategic role	Current position
Original modafinil compound protection	Protected the active ingredient	Expired
U.S. Patent 5,618,845	Covered particle-size-controlled pharmaceutical compositions	Expired
Method-of-use claims in '845	Covered use of the claimed composition for somnolence and narcolepsy	Expired
Provigil Orange Book listing	Created Hatch-Waxman litigation exposure	Historical
Armodafinil patents	Covered a related enantiomer and products such as Nuvigil	Separate estate, largely expired in the U.S.
Manufacturing or process patents	Could create product-specific barriers	Must be assessed patent by patent

During its enforceable period, the patent had practical leverage because commercial immediate-release modafinil products commonly used controlled particle-size API to support consistent dissolution and dosage performance. That commercial overlap increased infringement risk even though the claims did not recite a particular excipient or brand formulation.

Its weaknesses included:

Functional dependence on particle-size testing.
Ambiguity in "substantially homogeneous."
Ambiguity in "about."
Potential measurement-method disputes.
Lack of an express limitation to a specific formulation.
Method claims dependent on proving the composition limitation.
A relatively narrow technical concept compared with a compound patent.

What generic launch risks existed before expiration?

Before October 2014, a generic applicant faced several possible outcomes:

Launch scenario	Patent consequence	Commercial result
Paragraph III certification	Applicant accepted patent validity through expiry	Launch after expiry
Paragraph IV certification with settlement	Early launch on agreed date	Launch before expiry
Paragraph IV certification with litigation victory	Immediate launch after approval, subject to other barriers	Potential at-risk entry
Non-infringing formulation	Possible launch if FDA requirements were met	Reduced patent exposure
Successful invalidity challenge	Patent barrier removed	Earlier launch
Product outside claim 1 particle distribution	Avoided the central composition claim	Technical and regulatory development burden

A non-infringing design would have required more than changing tablet excipients. A developer would need to demonstrate that its product did not meet the claimed particle-size distribution, or that another claim element was absent. That could conflict with dissolution, uniformity, bioavailability, or manufacturing objectives.

Are there biosimilar risks for modafinil?

No conventional biosimilar pathway applies. Modafinil is a small-molecule drug, not a biologic subject to the Public Health Service Act's biosimilar framework. Competitive products proceed through the ANDA pathway or, depending on the product and regulatory circumstances, a 505(b)(2) application.

The relevant competition is generic substitution, not biosimilar interchangeability. FDA approval depends on pharmaceutical equivalence, bioequivalence, quality, labeling, and other ANDA requirements. Patent risk historically arose through Orange Book certifications rather than a biosimilar patent dance.

How does patent 5,618,845 compare with competing modafinil estates?

Modafinil versus armodafinil

Modafinil is a racemic mixture of the two enantiomers. Armodafinil contains the R-enantiomer and was commercialized as Nuvigil. Armodafinil patents were separate from the '845 patent and could not be assumed to cover ordinary modafinil.

Issue	Modafinil	Armodafinil
Active ingredient	Racemic modafinil	R-modafinil
Main U.S. brand	Provigil	Nuvigil
Regulatory pathway	Small-molecule NDA and ANDA generics	Separate NDA and generic pathway
'845 applicability	Directly directed to modafinil particles	Not automatically applicable
Key patent issue	Particle-size composition and use	Separate compound, formulation, and use claims

A modafinil product does not avoid every possible patent concern merely because the '845 patent has expired. Separate patents covering formulations, combinations, delivery technologies, or manufacturing processes must be reviewed independently. Those rights cannot be inferred from the claims provided.

What manufacturing and IP barriers did the patent create?

The patent made particle engineering a legal as well as technical issue. A product developer would need to control:

Milling or micronization conditions.
Feed material and crystal characteristics.
Agglomeration.
Blend uniformity.
Batch-to-batch particle-size variation.
Storage-related particle growth or aggregation.
Sampling and analytical reproducibility.

The patent did not claim a specific milling machine or micronization process. A manufacturer could therefore potentially design around it by using a different particle distribution, but a design-around might create a less favorable dissolution profile or require additional formulation development.

The main evidentiary barrier was proving the distribution in the commercial product. A single certificate of analysis would not necessarily resolve infringement if the claim required a representative batch population and the product's particle-size distribution varied materially across lots.

What is the current commercial impact of patent 5,618,845?

The direct current impact is negligible because the patent is expired. The commercial value of the patent was realized through delayed generic entry and settlement-based launch timing before expiration.

Provigil generated approximately $1 billion in annual sales around its peak commercial period, making the patent estate commercially significant to Cephalon and generic challengers. Generic entry materially changed the revenue profile after launch, and Teva's acquisition of Cephalon in 2011 transferred the relevant commercial and litigation position to Teva (Teva Pharmaceutical Industries Ltd., 2011).

Current investment and licensing analysis should focus on:

Product-level formulation patents that remain unexpired.
ANDA status and approved generic suppliers.
Manufacturing specifications.
Armodafinil and other wakefulness-promoting products.
Contracting and substitution dynamics.
Any later patents covering delivery systems or combinations.

Key Takeaways

U.S. Patent 5,618,845 covered modafinil compositions with at least about 95% of particles below about 200 μm.
Claim 2 added a median particle-size range of about 2-60 μm.
Claim 3 added a modafinil quantity of about 50-700 mg.
Claims 4-6 covered treatment of somnolent states, including narcolepsy, only when the administered composition satisfied claim 1.
The patent was listed for Provigil and triggered Paragraph IV litigation against generic applicants.
Cephalon settled with multiple generic challengers, permitting entry before the patent's nominal expiration.
The patent term ended in October 2014.
No biosimilar pathway applies because modafinil is a small molecule.
The patent is no longer a current U.S. blocking right, but its claim structure remains relevant to historical generic-entry analysis and technical freedom-to-operate studies.

FAQs about U.S. Patent 5,618,845

Could a modafinil API supplier infringe claim 1 without selling tablets?

Not ordinarily. Claim 1 requires a pharmaceutical composition, not merely bulk modafinil API. Liability would depend on the supplier's role, product characteristics, and any induced or contributory infringement theory applicable during the patent term.

Does a median particle size below 60 μm automatically satisfy claim 1?

No. Median size alone does not establish that at least about 95% of particles are below about 200 μm. The full cumulative particle-size distribution must be evaluated.

Did patent 5,618,845 cover armodafinil?

No automatic coverage follows. The claims recite modafinil particles. Armodafinil is a distinct enantiomeric drug substance and required separate patent analysis.

Could a generic company avoid the patent by changing only the excipients?

Not necessarily. The central limitation is particle size and particle distribution. A different excipient system could still contain modafinil particles meeting claim 1.

Is patent 5,618,845 relevant to a new U.S. modafinil launch today?

Not as an enforceable patent right. A current launch still requires analysis of FDA requirements, Orange Book patents listed for the relevant reference product, later formulation or process patents, regulatory exclusivity, and manufacturing rights.

References

Cephalon, Inc. (1997). Pharmaceutical compositions comprising modafinil particles of a defined size (U.S. Patent No. 5,618,845). U.S. Patent and Trademark Office.
Federal Trade Commission. (2015). In the matter of Cephalon, Inc., et al. Administrative proceedings concerning agreements delaying generic entry for Provigil.
Federal Trade Commission v. Actavis, Inc., 570 U.S. 136 (2013).
U.S. Food and Drug Administration. (1998). Provigil (modafinil) prescribing information. NDA 020717.
U.S. Food and Drug Administration. (2024). Approved drug products with therapeutic equivalence evaluations. Center for Drug Evaluation and Research.
Teva Pharmaceutical Industries Ltd. (2011). Annual report and acquisition disclosures concerning Cephalon, Inc.

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	188607	⤷ Start Trial
Austria	199216	⤷ Start Trial
Austria	400260	⤷ Start Trial
Australia	3509099	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,618,845

Summary for Patent: 5,618,845