United States Drug Patent 5,985,864: Donepezil Hydrochloride Polymorph Claims and Patent Landscape

U.S. Patent No. 5,985,864 protected selected crystalline forms of donepezil hydrochloride, principally polymorphs II, IV and V, together with manufacturing processes, therapeutic uses and pharmaceutical compositions containing those forms. The patent was assigned to Eisai Co., Ltd. and has expired. Its core commercial relevance was the potential to restrict manufacture of specific donepezil hydrochloride solid forms after expiration of the basic donepezil compound patent.

The patent term ran through December 10, 2017, based on the underlying filing chronology. It therefore presents no current U.S. blocking right against generic donepezil hydrochloride products. Historical Paragraph IV disputes involving donepezil were primarily directed to the basic compound and listed Aricept patents, rather than creating a continuing obstacle under this expired polymorph patent. [1][2]

What does U.S. Patent 5,985,864 protect?

The patent has four substantive protection categories:

Protection category	Claims	Subject matter
Polymorph product claims	1, 30-33	Donepezil hydrochloride polymorphs II, IV and V, identified by XRPD and infrared peaks
Manufacturing-process claims	2-25	Solvent, acidification, humidity, crystallization and drying processes producing polymorphs II, IV or V
Method-of-treatment claims	26-28	Administration of the claimed polymorphs for acetylcholinesterase-related disease, including Alzheimer-type senile dementia
Composition claim	29	A pharmaceutical composition containing a claimed donepezil hydrochloride polymorph and an acceptable carrier

The patent does not claim donepezil generally. The basic molecule is 1-benzyl-4-[(5,6-dimethoxy-1-indanon)-2-yl]methylpiperidine, administered commercially as the hydrochloride salt. Patent 5,985,864 is directed to solid-state forms of that salt and processes that generate them.

What are the main elements of claim 1?

Claim 1 is the central product claim. It covers donepezil hydrochloride in polymorph II, IV or V form, with each form defined by a combination of:

Specified powder X-ray diffraction peaks and relative intensities; and
Specified infrared absorption peaks measured in potassium bromide.

The claim is therefore a product-by-characterization claim. A material does not fall within the literal scope merely because it is donepezil hydrochloride. It must also correspond to one of the claimed analytical profiles.

Polymorph II

Polymorph II is characterized by a dense XRPD pattern with its strongest listed peak at 16.20 degrees two-theta and additional high-intensity peaks at approximately 15.74, 15.82, 16.46 and 23.38 degrees.

The claimed infrared profile includes peaks at approximately 560.1, 698.9, 749.1, 846.2, 1,036.1, 1,222.7, 1,318.7, 1,458.3, 1,500.9, 1,592.0, 1,637.0, 1,689.5, 1,718.3, 1,734.7, 1,751.7, 1,793.8 and 3,448.1 cm-1.

Polymorph II is commercially important because most of the process claims are directed to producing it. The processes use ethanol, ethers, acidification, drying or solvent exchange.

Polymorph IV

Polymorph IV has its strongest listed XRPD peak at 17.36 degrees, with significant peaks at 12.46, 22.48 and 25.28 degrees.

The infrared pattern includes peaks at approximately 561.5, 709.0, 766.2, 857.0, 1,041.5, 1,318.7, 1,458.1, 1,499.2, 1,588.1, 1,636.6, 1,684.3, 1,718.2, 1,734.4, 1,751.4, 1,793.5 and 3,324.0 cm-1.

The patent treats polymorph IV as obtainable from polymorph II through humidification. It also claims direct preparation from water, alcohol, hydrochloric acid, tetrahydrofuran, toluene, n-hexane and related systems.

Polymorph V

Polymorph V has its strongest listed XRPD peak at 21.96 degrees and another high-intensity peak at 24.66 degrees. Other notable peaks occur at 13.64, 18.44, 22.24 and 24.22 degrees.

Its infrared pattern includes peaks at approximately 506.5, 559.7, 594.4, 698.0, 740.8, 861.9, 1,039.9, 1,120.8, 1,264.8, 1,314.6, 1,458.0, 1,499.5, 1,592.1, 1,692.9, 2,500.1, 2,924.2, 2,998.9 and 3,422.1 cm-1.

Polymorph V is claimed through a conversion process: drying polymorph IV.

How broad is the product coverage?

The product coverage is narrower than a conventional active-ingredient claim but broader than a claim limited to one manufacturing route.

Claim 1 reaches any sample of donepezil hydrochloride that satisfies the analytical definition of polymorph II, IV or V, regardless of who made it or which process was used. A noninfringing process could still produce an infringing product if the resulting material falls within the claimed analytical profile.

The claim has several limiting characteristics:

Limitation	Scope effect
Donepezil hydrochloride	Excludes free-base donepezil and other salts
Polymorph II, IV or V	Excludes other crystalline forms unless they are analytically the same form
XRPD peaks	Requires correspondence to the listed diffraction profile
Infrared peaks	Provides a second structural fingerprint
Listed intensity values	Creates potential disputes over acceptable analytical tolerance
No particle-size limitation	Does not distinguish particle size or morphology unless those affect the analytical profile
No purity threshold stated	Does not expressly require a particular chemical purity level

The lack of stated tolerances for peak position and intensity is significant. XRPD results can vary with instrument geometry, sample preparation, preferred orientation, crystallinity, humidity and calibration. Infrared peak positions can also vary with sample handling. In an infringement dispute, the analytical method, measurement tolerance and identity of the tested lot would be central.

How do claims 30-33 affect polymorph coverage?

Claims 30, 32 and 33 narrow claim 1 to polymorph II, IV and V, respectively.

Claim 31 purports to cover polymorph III. That presents an internal drafting inconsistency because claim 1, as supplied, selects only polymorphs II, IV and V. A dependent claim cannot ordinarily introduce a species excluded from the claim on which it depends. Claim 31 would therefore face a substantial construction problem and may be treated as indefinite, incorrect or legally ineffective unless the issued patent contains a correction, prosecution-history explanation or claim-text variation.

The practical coverage is:

Claim	Intended subject
30	Polymorph II
31	Polymorph III, despite the inconsistency with claim 1
32	Polymorph IV
33	Polymorph V

The supplied claim language should be compared with the certified issued patent before relying on claim 31 in litigation or freedom-to-operate analysis. [1]

What manufacturing processes are protected?

Claims 2-25 create route-specific protection. They do not cover every method of making donepezil hydrochloride. Each process claim requires the stated solvents, acid, humidity, temperature, sequence or isolation step.

Processes for polymorph II

Claims 2-7 and 9-15 cover variations involving:

Dissolution in ethanol;
Addition of diethyl ether, isopropyl ether, tert-butyl methyl ether or diisopropyl ether;
Addition of hydrochloric acid or hydrogen chloride;
Dissolution in isopropyl alcohol, methylene chloride or acetone;
Stirring for specified periods;
Filtration after precipitation;
Drying polymorph I or amorphous donepezil hydrochloride.

Claims 3 and 7 are narrower because they specify stirring and filtration periods. Claims 12 and 13 add particular solvent addition conditions. Claim 15 is especially process-oriented: it covers production of polymorph II by drying polymorph I or the amorphous form.

Processes for polymorph IV

Claims 8 and 16-24 cover:

Humidification of polymorph II;
Humidification of amorphous donepezil hydrochloride;
Crystallization from water;
Water and tetrahydrofuran systems;
Hydrochloric acid and tetrahydrofuran;
Toluene or n-hexane with hydrochloric acid;
Methanol and hydrochloric acid;
Direct crystallization of donepezil hydrochloride from water.

Claims 8 and 16 are duplicative on the supplied text. Claims 23 and 24 also substantially overlap. That redundancy does not expand the technical scope beyond the underlying humidification concept.

Processes for polymorph V

Claim 25 covers drying polymorph IV. It is a narrow conversion claim and would require proof that the starting material was polymorph IV and that the drying operation produced polymorph V as claimed.

What method-of-use claims are protected?

Claim 26 covers administering a pharmacologically effective amount of a claimed donepezil hydrochloride polymorph to a human patient for inhibiting acetylcholinesterase activity.

Claims 27 and 28 narrow the disease indication to:

Senile dementia; and
Senile dementia of the Alzheimer type.

The method claims require use of the specified polymorphic material. They do not claim every use of donepezil, every acetylcholinesterase inhibitor, or every Alzheimer treatment.

The supplied text states that claims 27 and 28 depend on claim 1 rather than claim 26. That is another apparent dependency error. If this wording appears in the issued patent, it creates a formal and construction issue. It does not convert the claims into broad claims covering all donepezil therapy.

What formulation protection does the patent provide?

Claim 29 covers a therapeutic composition containing:

A pharmacologically effective amount of donepezil hydrochloride in a claimed polymorphic form; and
A pharmacologically acceptable carrier.

This is a broad composition claim in formulation terms, but it remains limited by the polymorph requirement. It does not identify:

Tablet excipients;
Film coatings;
Orally disintegrating technology;
Liquid vehicles;
Specific release profiles;
Particle size;
Compression parameters; or
A particular dosage strength.

A generic tablet could theoretically implicate claim 29 if its active ingredient were a claimed polymorph. A formulation using an unclaimed polymorph, amorphous material, a different salt or a different analytical form would fall outside the literal product limitation, subject to equivalence analysis.

When did U.S. Patent 5,985,864 lose exclusivity?

The patent expired on December 10, 2017, based on the 20-year term measured from the relevant filing date. [1]

Event	Date
Priority basis	1996
Relevant international or U.S. filing chronology	December 10, 1997
U.S. patent issued	November 16, 1999
Expected patent expiration	December 10, 2017
Current status	Expired

The patent was not a current barrier to U.S. generic entry after that date. Any patent-term-adjustment or patent-term-extension issue should be checked against the USPTO patent-term record, but the public patent record identifies the patent as expired.

What was the FDA and Orange Book status?

Donepezil hydrochloride was approved by FDA as Aricept under NDA 020690. FDA-approved dosage forms include conventional tablets and orally disintegrating tablets. Generic donepezil hydrochloride products were subsequently approved through the ANDA pathway. [2][3]

The Orange Book is relevant because listed patents can trigger Paragraph IV notice, a 45-day infringement suit window and, in some cases, a 30-month stay of ANDA approval under the Hatch-Waxman framework. [4]

Patent 5,985,864 was associated with the solid-state patent landscape for Aricept, but its commercial effect was time-limited. The basic donepezil compound patent, U.S. Patent No. 4,895,841, expired earlier and was the principal composition-of-matter barrier. The polymorph patent extended the relevant patent estate into 2017, but did not create protection for the active ingredient after its expiration.

Which companies challenged donepezil exclusivity?

Multiple generic manufacturers entered the U.S. donepezil market through ANDAs. Publicly documented generic competition included companies such as Teva, Dr. Reddy's Laboratories, Ranbaxy, Mylan and other ANDA sponsors.

The principal legal disputes involved the Aricept product patents and generic approval timing. The existence of an ANDA or Paragraph IV notice does not by itself establish infringement of Patent 5,985,864. A product-specific analysis would require the ANDA formulation, drug-substance polymorph, manufacturing process and certification position.

After December 10, 2017, a Paragraph IV challenge to this patent had no prospective exclusionary value because the patent had already expired. Litigation could still have historical relevance for pre-expiration damages, but it could not support a new forward-looking injunction based solely on this patent.

How does this patent compare with the broader donepezil estate?

Patent layer	Representative protection	Commercial significance
Basic compound	U.S. 4,895,841	Core donepezil molecule; expired earlier
Polymorphs	U.S. 5,985,864	Selected crystalline forms and processes; expired December 10, 2017
Regulatory exclusivity	NDA 020690	Historical FDA exclusivity for Aricept
Formulations	Separate patents and applications may exist	Depends on dosage form and technology
Methods of use	Alzheimer and dementia treatment claims	Narrowed by claim language and expiration
Manufacturing	Solid-state conversion and crystallization processes	Relevant only if the accused route meets every limitation

The patent was commercially stronger than a route-only patent because claim 1 covered the product itself. Its weakness was analytical dependence. A generic manufacturer could pursue a nonclaimed polymorph, amorphous form or alternate salt, provided regulatory and performance requirements were satisfied.

What generic launch risks existed before expiration?

Before expiration, generic launch risk depended on four factors:

Whether the proposed active ingredient was polymorph II, IV or V;
Whether the ANDA manufacturing process practiced a claimed route;
Whether the product was listed or certified against the patent; and
Whether the patent holder filed an infringement action within the statutory period.

The highest-risk scenario was a generic using polymorph II produced through ethanol and ether crystallization, acidification in ethanol, or drying of polymorph I or amorphous material. A product using polymorph IV or V also required solid-state characterization because conversion and humidity conditions could implicate claims 8, 16-25.

The lowest-risk historical scenario was an ANDA using an unclaimed solid form and a manufacturing process outside claims 2-25. That strategy would still have required analysis of other Aricept patents and FDA requirements.

Are biosimilar risks relevant?

No. Donepezil hydrochloride is a synthetic small-molecule drug, not a biologic. The relevant competitors are ANDA-based generic manufacturers, not biosimilar applicants under the Public Health Service Act. Solid-state form, salt identity, bioequivalence, dissolution and manufacturing controls are the central technical issues.

Does the patent create current licensing or manufacturing barriers?

No current U.S. licensing barrier arises from Patent 5,985,864 because it is expired. Historical licenses or supply arrangements involving Eisai, Pfizer or generic manufacturers would be contract-specific and cannot be inferred from the patent claims.

The patent also does not currently block manufacture of donepezil hydrochloride in the United States. Manufacturing barriers may remain for reasons unrelated to this patent, including:

FDA current good manufacturing practice requirements;
Control of polymorphic conversion during processing;
Analytical method validation;
Impurity control;
Bioequivalence;
Stability;
Supply of qualified starting materials; and
Confidential know-how not disclosed in the patent.

Those are operational barriers, not enforceable patent rights under the expired patent.

What is the current competitive and revenue exposure?

Donepezil is a mature generic product with broad competition. Aricept revenue exposure to this patent ended when the patent expired. The patent no longer supports exclusivity-based pricing, a generic launch delay or an injunction against an ANDA applicant.

The economic value of the patent was concentrated in the period between expiry of the basic compound patent and December 2017. After that date, generic competition could target tablets, orally disintegrating tablets and other approved presentations subject to separate active patents, regulatory requirements and applicable product-specific obligations.

How strong was the patent estate?

The estate was moderate to strong before expiration and weak to nonexistent as a current U.S. exclusionary right.

Factor	Assessment
Product coverage	Strong before expiration because claim 1 covered the polymorph itself
Analytical certainty	Moderate; peak tolerances and test conditions could create disputes
Process coverage	Moderate; numerous routes were claimed, but each was limitation-heavy
Formulation coverage	Moderate to weak; claim 29 lacked specific formulation architecture
Method coverage	Moderate; limited to administration of claimed polymorphs
Geographic scope	U.S. only for this patent
Current enforceability	None after expiration
Design-around potential	Meaningful through alternative polymorphs and processes
Biosimilar relevance	None

Key Takeaways

U.S. Patent 5,985,864 covered donepezil hydrochloride polymorphs II, IV and V.
Claim 1 was the principal product claim and required matching XRPD and infrared characteristics.
Claims 2-25 covered specific crystallization, solvent, humidification and drying processes.
Claim 29 covered compositions containing a claimed polymorph but did not claim a detailed formulation technology.
Claims 26-28 covered therapeutic use for acetylcholinesterase-related disease and Alzheimer-type senile dementia.
The supplied text contains apparent dependency problems in claims 27, 28 and 31.
The patent expired on December 10, 2017.
It is not a current U.S. barrier to generic donepezil hydrochloride entry.
Donepezil is a small molecule; biosimilar analysis is not applicable.
Historical generic challenges had to be assessed against the full Aricept patent estate, not Patent 5,985,864 alone.

FAQs About U.S. Patent 5,985,864

Is donepezil polymorph II still patent-protected in the United States?

No. The polymorph II claims of U.S. Patent 5,985,864 expired with the patent term on December 10, 2017.

Can a generic manufacturer use a different donepezil polymorph?

Yes, subject to FDA requirements and other enforceable patents. Patent 5,985,864 does not claim every possible solid form of donepezil hydrochloride.

Did Patent 5,985,864 cover Aricept's active ingredient broadly?

No. It covered selected polymorphic forms of donepezil hydrochloride. The basic donepezil compound was protected by a separate patent.

Does an orally disintegrating donepezil tablet infringe claim 29 automatically?

No. Claim 29 requires the composition to contain donepezil hydrochloride in a claimed polymorphic form. The dosage form alone does not establish infringement.

Is a Paragraph IV certification still commercially relevant for this patent?

No, because the patent expired. A Paragraph IV certification could have had historical relevance before expiration, but it cannot now delay generic approval based on this expired patent.

References

United States Patent and Trademark Office. (1999). U.S. Patent No. 5,985,864: Crystalline forms of donepezil hydrochloride and processes for preparation thereof.
U.S. Food and Drug Administration. (n.d.). Drugs@FDA: Aricept (donepezil hydrochloride), NDA 020690.
U.S. Food and Drug Administration. (n.d.). Approved drug products with therapeutic equivalence evaluations. Orange Book.
21 U.S.C. § 355(j). Abbreviated new drug applications and patent certifications.

Foriegn Application Priority Data
Foreign Country	Foreign Patent Number	Foreign Patent Date
Japan	8-146293	Jun 07, 1996

Country	Patent Number	Estimated Expiration	Supplementary Protection Certificate	SPC Country	SPC Expiration
Austria	230396	⤷ Start Trial
Austria	445603	⤷ Start Trial
Australia	1153097	⤷ Start Trial
Australia	2979297	⤷ Start Trial
Australia	731282	⤷ Start Trial
Canada	2252806	⤷ Start Trial
Canada	2516108	⤷ Start Trial
>Country	>Patent Number	>Estimated Expiration	>Supplementary Protection Certificate	>SPC Country	>SPC Expiration

Details for Patent: 5,985,864

Summary for Patent: 5,985,864